EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-EP-2018-348 LHCb-PAPER-2018-047

Measurement of the mass and production rate of ${{\mathchar
28932\relax}^{-}_{b}}$ baryons

LHCb collaboration†††Authors are listed at the end of this paper.

The first measurement of the production rate of ${{\mathchar
28932\relax}^{-}_{b}}$ baryons in $pp$ collisions relative to that of
${{\mathchar 28931\relax}^{0}_{b}}$ baryons is reported, using data samples
collected by the LHCb experiment, and corresponding to integrated luminosities
of 1, 2 and 1.6$\text{\,fb}^{-1}$ at $\sqrt{s}=7,~{}8$ and 13 TeV,
respectively. In the kinematic region $2<\eta<6$ and
$p_{\mathrm{T}}<20$$\text{\,Ge\kern-1.00006ptV\\!/}c$, we measure

$\displaystyle\frac{f_{{{\mathchar 28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}\frac{{\mathcal{B}}({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{{\mathcal{B}}({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}$ $\displaystyle=(10.8\pm 0.9\pm 0.8)\times
10^{-2}~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$
$\displaystyle\frac{f_{{{\mathchar 28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}\frac{{\mathcal{B}}({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{{\mathcal{B}}({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}$ $\displaystyle=(13.1\pm 1.1\pm 1.0)\times
10^{-2}~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}],$

where $f_{{{\mathchar 28932\relax}^{-}_{b}}}$ and $f_{{{\mathchar
28931\relax}^{0}_{b}}}$ are the fragmentation fractions of $b$ quarks into
${{\mathchar 28932\relax}^{-}_{b}}$ and ${{\mathchar 28931\relax}^{0}_{b}}$
baryons, respectively, ${\mathcal{B}}$ represents branching fractions, and the
uncertainties are due to statistical and experimental systematic sources. The
values of $f_{{{\mathchar 28932\relax}^{-}_{b}}}/f_{{{\mathchar
28931\relax}^{0}_{b}}}$ are obtained by invoking SU(3) symmetry in the
${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}$ and ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}$ decays. Production asymmetries between
${{\mathchar 28932\relax}^{-}_{b}}$ and ${{\kern
1.79993pt\overline{\kern-1.79993pt{\mathchar 28932\relax}}}{}_{b}^{+}}$
baryons are also reported.

The mass of the ${{\mathchar 28932\relax}^{-}_{b}}$ baryon is also measured
relative to that of the ${{\mathchar 28931\relax}^{0}_{b}}$ baryon, from which
it is found that

$\displaystyle m({{\mathchar 28932\relax}^{-}_{b}})$ $\displaystyle=5796.70\pm
0.39\pm 0.15\pm 0.17\text{\,Me\kern-1.00006ptV\\!/}c^{2},$

where the last uncertainty is due to the precision on the known ${{\mathchar
28931\relax}^{0}_{b}}$ mass. This result represents the most precise
determination of the ${{\mathchar 28932\relax}^{-}_{b}}$ mass.

Published in Phys. Rev. D99 052006 (2019)

© 2024 CERN for the benefit of the LHCb collaboration. CC-BY-4.0 licence.

The decays of beauty ($b$) quarks provide a sensitive probe of physics within,
and beyond, the Standard Model. Due to the large ${{b}{\overline{b}}}$
production cross-section at the Large Hadron Collider, beauty hadrons of all
species are abundantly produced. Measurements of branching fractions in
specific decay channels are often needed in order to make quantitative
comparisons to theoretical predictions. However, absolute branching fraction
measurements at hadron colliders are difficult to perform without external
input. Instead, one generally resorts to measuring a particular branching
fraction relative to that of a topologically similar decay mode, frequently
one that involves either a ${{B}^{0}}$ or a ${{{B}^{-}}}$ meson, whose
absolute branching fractions are known from $B$-factory measurements. When
${{B}^{0}_{s}}$ or ${{\mathchar 28931\relax}^{0}_{b}}$ branching fractions are
measured relative to those of a ${{B}^{0}}$ decay, knowledge of the ratio of
fragmentation fractions, $f_{s}/f_{d}$ for ${{B}^{0}_{s}}$ decays, or
$f_{{{\mathchar 28931\relax}^{0}_{b}}}/f_{d}$ for ${{\mathchar
28931\relax}^{0}_{b}}$ decays, is required. Here, $f_{d}$, $f_{s}$ and
$f_{{{\mathchar 28931\relax}^{0}_{b}}}$ represents the rates at which a $b$
quark hadronizes into a ${{B}^{0}}$, ${{B}^{0}_{s}}$ or ${{\mathchar
28931\relax}^{0}_{b}}$ hadron, respectively.

Theoretically, the most robust way to measure the $b$-quark fragmentation
fractions is to exploit the well tested prediction from heavy quark effective
theory [1, 2, 3, 4, 5, 6, 7, 8] that, to first order, all $b$ hadrons
containing a single heavy quark have equal semileptonic decay widths. Such
analyses have been carried out by the LHCb experiment at
$\sqrt{s}=7\text{\,Te\kern-1.00006ptV}$ [9] and 13 TeV [10], where it is found
that $\langle f_{s}/f_{d}\rangle\simeq 0.26$ and $\langle f_{{{\mathchar
28931\relax}^{0}_{b}}}/f_{d}\rangle\simeq 0.6$, averaged over the
pseudorapidity ($\eta$) and transverse momentum ($p_{\mathrm{T}}$) region
$2<\eta<5$ and $3<p_{\mathrm{T}}<25$$\text{\,Ge\kern-1.00006ptV\\!/}c$. An
alternative technique, which relies on factorization and SU(3) flavor symmetry
in the ${{B}^{0}_{s}}\rightarrow{{D}^{-}_{s}}{{\pi}^{+}}$ and
${{B}^{0}}\rightarrow{{D}^{-}}{{K}^{+}}$ decays [11], has also been used to
measure $f_{s}/f_{d}$, yielding a value consistent with that obtained in
semileptonic decays.

With the large samples of $b$ hadrons collected by the LHCb experiment, a
number of new decay modes of ${{\mathchar 28932\relax}^{0}_{b}}$, ${{\mathchar
28932\relax}^{-}_{b}}$, and even ${{\mathchar 28938\relax}^{-}_{b}}$ baryons
have been searched for, and in many cases have led to first observations [12,
13, 14, 15, 16, 17, 18, 19, 20]. However, when new decay modes of these
baryons are observed, absolute branching fractions cannot be determined due to
a lack of knowledge of the fragmentation fractions $f_{{{\mathchar
28932\relax}^{0}_{b}}}$, $f_{{{\mathchar 28932\relax}^{-}_{b}}}$ and
$f_{{{\mathchar 28938\relax}^{-}_{b}}}$. For example, in one such measurement,
evidence of the strangeness-changing weak decay ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{\mathchar 28931\relax}^{0}_{b}}{{\pi}^{-}}$
is reported [16], with the result that $(f_{{{\mathchar
28932\relax}^{-}_{b}}}/f_{{{\mathchar
28931\relax}^{0}_{b}}}){\mathcal{B}}({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{\mathchar
28931\relax}^{0}_{b}}{{\pi}^{-}})=(5.7\pm 1.8^{+0.8}_{-0.9})\times 10^{-4}$.
To compute the decay width $\Gamma({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{\mathchar 28931\relax}^{0}_{b}}{{\pi}^{-}})$
and compare to theoretical predictions requires knowledge of the ratio
$f_{{{\mathchar 28932\relax}^{-}_{b}}}/f_{{{\mathchar 28931\relax}^{0}_{b}}}$.

In principle, the same procedure used to measure $f_{s}/f_{d}$ and
$f_{{{\mathchar 28931\relax}^{0}_{b}}}/f_{d}$ can be applied to semileptonic
${{\mathchar 28932\relax}^{0}_{b}}\rightarrow{{\mathchar
28932\relax}^{+}_{c}}{\mu^{-}}{{\overline{\nu}}_{\mu}}X$ and ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{\mathchar
28932\relax}^{0}_{c}}{\mu^{-}}{{\overline{\nu}}_{\mu}}X$ decays to measure
$f_{{{\mathchar 28932\relax}^{0}_{b}}}/f_{d}$ and $f_{{{\mathchar
28932\relax}^{-}_{b}}}/f_{d}$. However, an obstacle to such an analysis is the
limited knowledge of absolute branching fractions for the decays of the
${{\mathchar 28932\relax}^{+}_{c}}$ or ${{\mathchar 28932\relax}^{0}_{c}}$
baryon. Recently, the Belle experiment published a first measurement of the
absolute branching fractions for three ${{\mathchar 28932\relax}^{0}_{c}}$
decay modes, each with a relative precision of about 40% [21]. No such
measurements exist yet for the ${{\mathchar 28932\relax}^{+}_{c}}$ baryon.
Precise measurements of branching fractions for both ${{\mathchar
28932\relax}^{+}_{c}}$ and ${{\mathchar 28932\relax}^{0}_{c}}$ decays should
be feasible in the Belle II experiment [22].

Production ratio measurements of the hadronic ${{\mathchar
28932\relax}^{0}_{b}}\rightarrow{{\mathchar 28932\relax}^{+}_{c}}{{\pi}^{-}}$
and ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{\mathchar
28931\relax}^{+}_{c}}{{\pi}^{-}}$ decays [14], where both the ${{\mathchar
28932\relax}^{+}_{c}}$ and ${{\mathchar 28931\relax}^{+}_{c}}$ baryons are
reconstructed in the $p{{K}^{-}}{{\pi}^{+}}$ final state, have been used to
predict $f_{{{\mathchar 28932\relax}^{0}_{b}}}/f_{{{\mathchar
28931\relax}^{0}_{b}}}$. In this case, theoretical estimates of
${\mathcal{B}}({{\mathchar 28932\relax}^{+}_{c}}\rightarrow
p{{K}^{-}}{{\pi}^{+}})$ are used, resulting in predictions of $f_{{{\mathchar
28932\relax}^{0}_{b}}}/f_{{{\mathchar 28931\relax}^{0}_{b}}}=0.065\pm 0.020$
[23] and $f_{{{\mathchar 28932\relax}^{0}_{b}}}/f_{{{\mathchar
28931\relax}^{0}_{b}}}=0.054\pm 0.020$ [24].

An alternative approach to either of these two methods is to exploit the
decays ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}$ and ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}$, where the ${{\mathchar
28932\relax}^{-}}$ baryon is detected in its decay to ${\mathchar
28931\relax}{{\pi}^{-}}$. Charge-conjugate processes are implicitly included.
These decay rates are related through SU(3) flavor symmetry, where one finds
[25, 26, 27]

$\displaystyle\frac{\Gamma({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{\Gamma({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}=\frac{3}{2}.$ (1)

The ratio

$\displaystyle R\equiv\frac{f_{{{\mathchar
28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}\frac{{\mathcal{B}}({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{{\mathcal{B}}({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}=\frac{f_{{{\mathchar
28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}\frac{\Gamma({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{\Gamma({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}\frac{\tau_{{{\mathchar
28932\relax}^{-}_{b}}}}{\tau_{{{\mathchar 28931\relax}^{0}_{b}}}}$ (2)

depends on $f_{{{\mathchar 28932\relax}^{-}_{b}}}/f_{{{\mathchar
28931\relax}^{0}_{b}}}$, the partial decay widths, $\Gamma$, and the
lifetimes, $\tau$, of the indicated $b$ baryons. Experimentally, $R$ is
obtained from the ratio of efficiency-corrected yields

$\displaystyle R=\frac{N({{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}})}{N({{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax})}\frac{\epsilon_{{{\mathchar
28931\relax}^{0}_{b}}}}{\epsilon_{{{\mathchar 28932\relax}^{-}_{b}}}},$ (3)

where $\epsilon$ represents the detection efficiency and $N$ is the yield of
the indicated decays.

In this article, we report a first measurement of the ratio $R$ in $pp$
collision data collected by the LHCb experiment, corresponding to integrated
luminosities of 1.0$\text{\,fb}^{-1}$ at $\sqrt{s}=7$ TeV,
2.0$\text{\,fb}^{-1}$ at $\sqrt{s}=8$ TeV and 1.6$\text{\,fb}^{-1}$ at
$\sqrt{s}=13$ TeV. The measurement of $R$, along with the SU(3) assumption in
Eq. 1 and the known ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar
28932\relax}^{-}_{b}}$ baryon lifetimes [28], is used to infer the value of
$f_{{{\mathchar 28932\relax}^{-}_{b}}}/f_{{{\mathchar 28931\relax}^{0}_{b}}}$.
The same data samples are also used to measure the production asymmetry
between ${{\mathchar 28932\relax}^{-}_{b}}$ and ${{\kern
1.79993pt\overline{\kern-1.79993pt{\mathchar 28932\relax}}}{}_{b}^{+}}$
baryons, and make the most precise measurement of the ${{\mathchar
28932\relax}^{-}_{b}}$ mass.

The LHCb detector [29, 30] is a single-arm forward spectrometer designed for
the study of particles containing $b$ or $c$ quarks. The detector includes a
high-precision tracking system consisting of a silicon-strip vertex detector
surrounding the $pp$ interaction region, a large-area silicon-strip detector
located upstream of a dipole magnet with a bending power of about
$4{\mathrm{\,Tm}}$, and three stations of silicon-strip detectors and straw
drift tubes placed downstream of the magnet. The tracking system provides a
measurement of the momentum, $p$, of charged particles with a relative
uncertainty that varies from 0.5% at low momentum to 1.0% at
200$\text{\,Ge\kern-1.00006ptV\\!/}c$. The minimum distance of a track to a
primary vertex (PV), the impact parameter (IP), is measured with a resolution
of $(15+29/p_{\mathrm{T}})\,\upmu\text{m}$, where $p_{\mathrm{T}}$ is
expressed in $\text{\,Ge\kern-1.00006ptV\\!/}c$. Different types of charged
hadrons are distinguished using information from two ring-imaging Cherenkov
detectors. Photons, electrons and hadrons are identified by a calorimeter
system consisting of scintillating-pad and preshower detectors, an
electromagnetic and a hadronic calorimeter. Muons are identified by a system
composed of alternating layers of iron and multiwire proportional chambers.
The online event selection is performed by a trigger which consists of a
hardware stage, based on information from the calorimeter and muon systems,
followed by a software stage, which applies a full event reconstruction.

Simulation is required to model the effects of the detector acceptance and the
imposed selection requirements. In the simulation, $pp$ collisions are
generated using Pythia [31, *Sjostrand:2007gs] with a specific LHCb
configuration [33]. Decays of unstable particles are described by EvtGen [34],
in which final-state radiation is generated using Photos [35]. The interaction
of the generated particles with the detector, and its response, are
implemented using the Geant4 toolkit [36, *Agostinelli:2002hh] as described in
Ref. [38].

The ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}(\rightarrow{\mathchar
28931\relax}{{\pi}^{-}})$ and ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}$ decays both contain a
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ meson and a ${\mathchar
28931\relax}$ baryon in the decay chain, and are kinematically similar. To
reduce systematic uncertainties, selection requirements are tailored to
exploit the common particles in the final state of the ${{\mathchar
28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$ decays. At the
trigger level, both modes are required to satisfy requirements based solely on
the ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\rightarrow{\mu^{+}}{\mu^{-}}$ decay. Firstly, the hardware stage must
register either a single high-$p_{\mathrm{T}}$ muon or a ${\mu^{+}}{\mu^{-}}$
pair. The software stage [39] then requires a ${\mu^{+}}{\mu^{-}}$ pair whose
decay vertex is displaced from all PVs in the event, and that has an invariant
mass consistent with the known ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}$ mass [28].

Selected events may contain more than one PV. Each particle is associated to
the PV for which the corresponding value of $\chi^{2}_{\text{IP}}$ is
smallest, where $\chi^{2}_{\text{IP}}$ is defined as the difference in the
vertex-fit $\chi^{2}$ of a given PV reconstructed with and without the
particle under consideration.

In the offline analysis, each muon must have $p_{\mathrm{T}}$ in excess of
550$\text{\,Me\kern-1.00006ptV\\!/}c$ and have IP to all PVs in the event that
exceeds approximately three times the expected uncertainty. The
${\mu^{+}}{\mu^{-}}$ pair must form a good-quality vertex and have an
invariant mass within 40$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ of the known
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ mass, corresponding to about
three times the mass resolution.

Reconstructed charged particles are classified into two categories in this
analysis. The _long_ category refers to tracks that have reconstructed
segments in both the vertex detector and the tracking stations upstream and
downstream of the LHCb magnet. The _downstream_ category consists of those
tracks that are not reconstructed in the vertex detector, and thus only
include information from the tracking detectors just before and after the LHCb
magnet. While most of the reconstructed particles from the $pp$ interactions
are in the long category, the decay products of long-lived strange particles
tend to be mostly reconstructed as downstream tracks. Because of the presence
of vertex detector measurements, the trajectories, and hence the IP, of long
tracks are measured with better precision than those of downstream tracks.

Candidate ${\mathchar 28931\relax}\rightarrow p{{\pi}^{-}}$ decays are formed
by combining downstream $p$ and ${{\pi}^{-}}$ candidates with $p_{\mathrm{T}}$
in excess of 500$\text{\,Me\kern-1.00006ptV\\!/}c$ and
100$\text{\,Me\kern-1.00006ptV\\!/}c$, respectively. Both tracks are required
to be significantly detached from all PVs in the event, and together they must
form a good-quality vertex and must satisfy the requirement
$|M(p{{\pi}^{-}})-m_{{\mathchar
28931\relax}}|<8$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$, corresponding to
approximately three times the mass resolution. Here and throughout the text,
$M$ represents an invariant mass and $m$ represents the known mass of the
indicated particle [28].

The ${{\mathchar 28932\relax}^{-}}$ baryon is reconstructed through its decay
to ${\mathchar 28931\relax}{{\pi}^{-}}$. Due to the long ${{\mathchar
28932\relax}^{-}}$ and ${\mathchar 28931\relax}$ lifetimes, only ${\mathchar
28931\relax}$ candidates formed from downstream tracks are used, as they
contribute about 90% to the ${{\mathchar 28932\relax}^{-}}$ sample in
${{\mathchar 28932\relax}^{-}_{b}}$ decays. To maintain a uniform selection,
the same requirement is imposed on ${\mathchar 28931\relax}$ decays in the
${{\mathchar 28931\relax}^{0}_{b}}$ mode. The ${{\pi}^{-}}$ meson from the
${{\mathchar 28932\relax}^{-}}$ decay may be reconstructed as either a long or
a downstream track. For the ${{\mathchar 28932\relax}^{-}_{b}}$ mass and
production asymmetry measurements, both categories are used. However, for the
measurement of $R$, only the long-track sample is used, since the efficiency
for detecting the ${{\pi}^{-}}$ meson in the decay ${{\mathchar
28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}{{\pi}^{-}}$ enters
directly in Eq. 3, and long-track efficiencies have been precisely calibrated
using a tag-and-probe method [40]. No explicit momentum requirement is applied
to the ${{\pi}^{-}}$ meson, since it typically has low momentum. When
necessary, the notation $\pi^{-}_{\rm L}$ and $\pi^{-}_{\rm D}$ is used to
distinguish between long (L) and downstream (D) ${{\pi}^{-}}$ tracks. Tracks
in the $\pi^{-}_{\rm L}$ sample are required to be significantly detached from
all PVs in the event, corresponding to a requirement that the impact parameter
exceeds about four times the corresponding uncertainty; no such requirement is
necessary on the $\pi^{-}_{\rm D}$ sample. Exploiting the large ${{\mathchar
28932\relax}^{-}}$ baryon lifetime, ${{\mathchar 28932\relax}^{-}}$ candidates
must have $t_{\rm PV}>6$ ps, where $t_{\rm PV}$ is the decay time measured
relative to the associated PV. Lastly, ${{\mathchar 28932\relax}^{-}}$
candidates are required to satisfy the mass requirement $|M({\mathchar
28931\relax}\pi^{-}_{\rm L,D})-M(p{{\pi}^{-}})+m_{{\mathchar
28931\relax}}-m_{{{\mathchar
28932\relax}^{-}}}|<10$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$, corresponding
to about three times the mass resolution, and have positive decay time,
measured relative to the ${{\mathchar 28932\relax}^{-}_{b}}$ decay vertex.

The ${{\mathchar 28931\relax}^{0}_{b}}$ (${{\mathchar 28932\relax}^{-}_{b}}$)
candidates are formed by combining ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}$ and ${\mathchar 28931\relax}$ (${{\mathchar 28932\relax}^{-}}$)
candidates. A vertex fit of good quality is required. To suppress background
from prompt ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ production, the
$b$ hadron is required to have a reconstructed decay time larger than 0.2 ps,
which is about four times the resolution. Finally, to have a well-defined
fiducial region, the ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar
28932\relax}^{-}_{b}}$ candidates are required to be within the kinematic
region $2<\eta<6$ and $p_{\mathrm{T}}<20$$\text{\,Ge\kern-1.00006ptV\\!/}c$.
Multiple candidates in a single event occur in less than 1% of selected
events, and all candidates are kept. To improve the mass resolution, an
additional kinematic fit is performed on each candidate, employing both vertex
and mass constraints on the ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$,
${\mathchar 28931\relax}$ and ${{\mathchar 28932\relax}^{-}}$ candidates [41].
The resulting mass resolution is about 8$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$
for both modes.

The invariant-mass spectra of selected ${{\mathchar 28931\relax}^{0}_{b}}$ and
${{\mathchar 28932\relax}^{-}_{b}}$ candidates are shown in Fig. 1. The data
are partitioned into the combined 7, 8 TeV data samples and the 13 TeV data
sample, and show the distributions for ${{\mathchar 28931\relax}^{0}_{b}}$
candidates, and ${{\mathchar 28932\relax}^{-}_{b}}$ candidates formed from
either long or downstream pions. A simultaneous fit to all six distributions
is performed in order to determine the signal yields. Each of the signal
shapes is described by the sum of two Crystal Ball (CB) functions [42] with a
common peak position and a common width. The tail parameters, which describe
the non-Gaussian portion of the signal on either side of the signal peak, are
independent for the two CB components. The parameters of the signal shape are
determined from large samples of simulated signal decays. The background is
described by an exponential function, with the shape parameter left free in
the fit to data.

The signal-shape fit parameters are: (i) the peak positions, $\bar{m}$, of the
${{\mathchar 28931\relax}^{0}_{b}}$ mass in the 7, 8 TeV and 13 TeV data, (ii)
a single mass difference, $\delta m\equiv\bar{m}_{{{\mathchar
28932\relax}^{-}_{b}}}-\bar{m}_{{{\mathchar 28931\relax}^{0}_{b}}}$, and (iii)
a scale factor applied to the simulated width of the CB functions, which
allows the mass resolution in data to be slightly different than in
simulation. The values of $\bar{m}_{{{\mathchar 28931\relax}^{0}_{b}}}$ are
allowed to differ for the 7, 8 TeV data and the 13 TeV data, since the
statistical uncertainty on each is about four times smaller than the
systematic uncertainty from the momentum scale calibration [43]. However, that
same calibration renders the corresponding uncertainty on $\delta m$
negligible.

Figure 1: Invariant-mass distributions for (top) ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}$ candidates, (middle) ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}$, ${{\mathchar
28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}\pi^{-}_{\rm L}$, and
(bottom) ${{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}$, ${{\mathchar
28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}\pi^{-}_{\rm D}$. The
subscript on the ${{\pi}^{-}}$ refers to whether the corresponding track is
long or downstream. The left column shows the combined 7 and 8 TeV data and
the right one shows the 13 TeV data. The fitted probability distributions
functions (PDF) are overlaid.

The fitted signal yields and the values of $\bar{m}_{{{\mathchar
28931\relax}^{0}_{b}}}$ are shown in Table 1. From the fit, it is determined
that

$\displaystyle\delta m$ $\displaystyle=177.30\pm
0.39\text{\,Me\kern-1.00006ptV\\!/}c^{2},$ $\displaystyle m({{\mathchar
28932\relax}^{-}_{b}})$ $\displaystyle=5796.70\pm
0.39\text{\,Me\kern-1.00006ptV\\!/}c^{2},$

where the uncertainties are statistical only, and we have used $m({{\mathchar
28932\relax}^{-}_{b}})=\delta m+m_{{{\mathchar 28931\relax}^{0}_{b}}}$, with
$m_{{{\mathchar 28931\relax}^{0}_{b}}}=5619.60\pm
0.17$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ [28]. The value of $\delta m$ is
corrected by $+0.12\pm 0.06$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ to account
for a bias observed in the obtained value of $\delta m$, as seen in the fit to
large samples of simulated signal decays. The uncertainty on this value is due
to the size of the simulated samples.

Table 1: Fitted signal yields and peak position of the ${{\mathchar 28931\relax}^{0}_{b}}$ signal peak, as obtained from the fit described in the text. The subscript on the ${{\pi}^{-}}$ refers to whether the corresponding track is long or downstream. The uncertainties shown are statistical only. |  $7,\,8$ TeV | 13 TeV
---|---|---
$N({{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax})$ | $~{}\,13307\pm 137$ | $~{}\,14793\pm 150$
$N({{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}},~{}{{\mathchar 28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}\pi^{-}_{\rm L})$ | $~{}~{}~{}203\pm 16$ | $~{}~{}~{}258\pm 22$
$N({{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}},~{}{{\mathchar 28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}\pi^{-}_{\rm D})$ | $~{}~{}~{}266\pm 20$ | $~{}~{}~{}357\pm 26$
$\bar{m}_{{{\mathchar 28931\relax}^{0}_{b}}}$ (MeV/$\it{c}^{\rm 2}$) | $5619.52\pm 0.09$ | $5619.28\pm 0.09$

The ratio of efficiencies in Eq. 3 is determined from weighted simulations of
the signal decays. The ${{\mathchar 28931\relax}^{0}_{b}}$ simulation is
weighted in bins of ($\eta$, $p_{\mathrm{T}}$) of the $b$ baryon to reproduce
the 2D distribution observed in the data, after the background contribution is
subtracted using the sPlot method [44]. We assume that the ${{\mathchar
28932\relax}^{-}_{b}}$ spectrum is the same as that of the ${{\mathchar
28931\relax}^{0}_{b}}$, and variations are investigated when assessing
systematic uncertainties. By studying the distributions of the fraction of the
momentum carried by the decay products in each part of the decay chain, it is
found that the simulation differs from the corresponding spectra observed in
data. The simulation is weighted to match the distributions observed in data
for the momentum ratio $p_{{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}}/p_{{{\mathchar 28931\relax}^{0}_{b}}}$ and the momentum asymmetry
$(p_{p}-p_{{{\pi}^{-}}})/(p_{p}+p_{{{\pi}^{-}}})$ in the ${\mathchar
28931\relax}$ decay. After this weighting is applied, a large number of other
observables are compared, such as decay times, flight distances, $p$, and
$p_{\mathrm{T}}$, and good agreement is found between both ${{\mathchar
28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$ data and
simulation. For the ${{\mathchar 28932\relax}^{-}_{b}}$ sample, only the
$(\eta,p_{\mathrm{T}})$ and $(p_{p}-p_{{{\pi}^{-}}})/(p_{p}+p_{{{\pi}^{-}}})$
weights are needed to obtain good agreement with the data.

The resulting efficiencies are summarized in Table 2. The efficiencies
associated with the detector acceptance, the reconstruction and selection, and
the trigger requirements are given, along with the total selection
efficiencies. The relative efficiency is approximately 14% for both the 7, 8
TeV and 13 TeV data sets. For the 7, 8 TeV values, the efficiencies represent
the weighted average value. This small value is due to the combination of the
relatively low momentum and usage of only long tracks for the ${{\pi}^{-}}$
meson in the ${{\mathchar 28932\relax}^{-}}$ decay.

Table 2: Selection efficiencies as obtained from the simulation of ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}$ and ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}}$, ${{\mathchar 28932\relax}^{-}}\rightarrow{\mathchar 28931\relax}\pi^{-}_{\rm L}$ decays at $\sqrt{s}=7,\,8$ TeV and 13 TeV. The efficiencies ($\epsilon$) listed are those associated with the detector acceptance (acc), the reconstruction and selection (sel), the trigger (trig), their product, and the relative efficiency. | 7, 8 TeV | 13 TeV
---|---|---
Final state | ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}$ | ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}}$ | ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}$ | ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}}$
$\epsilon_{\rm acc}$ (%) | $18.9\pm 0.1$ | $\,17.3\pm 0.1$ | $19.8\pm 0.1$ | $18.0\pm 0.1$
$\epsilon_{\rm sel}$ (%) | $~{}\,2.86\pm 0.02$ | $~{}~{}0.42\pm 0.01$ | $~{}\,2.91\pm 0.01$ | $~{}\,0.42\pm 0.01$
$\epsilon_{\rm trig}$ (%) | $73.2\pm 0.3$ | $\,75.6\pm 0.7$ | $75.4\pm 0.2$ | $77.8\pm 0.5$
$\epsilon$ ($10^{-2}~{}\%$) | $39.5\pm 0.4$ | $~{}~{}5.56\pm 0.11$ | $43.5\pm 0.3$ | $~{}\,5.85\pm 0.06$
$\epsilon_{{{\mathchar 28932\relax}^{-}_{b}}}/\epsilon_{{{\mathchar 28931\relax}^{0}_{b}}}$ (%) | $14.1\pm 0.3$ | $13.4\pm 0.2$

From the signal yields and relative efficiencies, the ratios $R$ are computed
to be

$\displaystyle R$ $\displaystyle=(10.8\pm 0.9)\times
10^{-2}~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$ $\displaystyle R$
$\displaystyle=(13.1\pm 1.1)\times
10^{-2}~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}],$

where the uncertainties are statistical only.

The difference between the ${{\mathchar 28932\relax}^{-}_{b}}$ and
${{\mathchar 28931\relax}^{0}_{b}}$ baryon production asymmetries is
determined using the relation

$\displaystyle A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})-A_{\rm
prod}({{\mathchar 28931\relax}^{0}_{b}})=\alpha({{\mathchar
28932\relax}^{-}_{b}})-\alpha({{\mathchar 28931\relax}^{0}_{b}})-A_{\rm
det}({{\pi}^{-}}),$ (4)

where $\alpha({{\mathchar 28932\relax}^{-}_{b}})$ $[\alpha({{\mathchar
28931\relax}^{0}_{b}})]$ is the raw yield asymmetry between the ${{{\mathchar
28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\mathchar 28932\relax}^{-}}}$ and ${{{\kern
1.79993pt\overline{\kern-1.79993pt{\mathchar
28932\relax}}}{}_{b}^{+}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{{\kern 1.79993pt\overline{\kern-1.79993pt{\mathchar
28932\relax}}}^{+}}}$ $[{{{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}}$ and ${{{\kern
1.79993pt\overline{\kern-1.79993pt\mathchar
28931\relax}}{}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\kern 1.79993pt\overline{\kern-1.79993pt\mathchar 28931\relax}}}]$
decays. In the difference of the raw yield asymmetries, the ${\mathchar
28931\relax}$ detection asymmetry cancels since the kinematical properties are
similar. The ${{\pi}^{-}}$ detection asymmetry, $A_{\rm det}({{\pi}^{-}})$,
has been measured [45, 46], and, while it is consistent with zero, an
asymmetry of up to about 1% in this low momentum region cannot be discounted.
In the above expression, it is expected, and assumed, that there is no direct
$C\\!P$ violation in these decays.

The raw yield asymmetries are obtained by fitting for the signal yields
separately for the beauty baryon and antibaryon subsamples. The fit is similar
to that which was described previously, except that the CB width scale factors
are fixed to the values obtained from the fit to the full sample, since the
mass resolution can be assumed to be the same for the $b$ baryons and
antibaryons. The fitted signal yields are shown in Table 3, along with the
resulting raw asymmetries.

Table 3: Yields of ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$ decays, split by the charge of the final state, and their asymmetries, for the combined 7, 8 TeV data samples and the 13 TeV data sample. Uncertainties are statistical only. | ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}$ | ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{\mathchar 28932\relax}^{-}}$
---|---|---
| ${{\mathchar 28931\relax}^{0}_{b}}$ | ${{\kern 1.79993pt\overline{\kern-1.79993pt\mathchar 28931\relax}}{}^{0}_{b}}$ | ${{\mathchar 28932\relax}^{-}_{b}}$ | ${{\kern 1.79993pt\overline{\kern-1.79993pt{\mathchar 28932\relax}}}{}_{b}^{+}}$
$N_{\sqrt{s}=7,\,8\text{\,Te\kern-0.70004ptV}}$ | $6827\pm 94$ | $6480\pm 92$ | $236\pm 18$ | $230\pm 18$
$\alpha_{\sqrt{s}=7,\,8\text{\,Te\kern-0.70004ptV}}$ | $(2.6\pm 1.0)\%$ | $~{}~{}(1.3\pm 5.4)\%$
$N_{\sqrt{s}=13\text{\,Te\kern-0.70004ptV}}$ | $7602\pm 102$ | $7182\pm 99$ | $304\pm 21$ | $326\pm 22$
$\alpha_{\sqrt{s}=13\text{\,Te\kern-0.70004ptV}}$ | $(2.8\pm 1.0)\%$ | $(-3.5\pm 4.8)\%$

The difference in production asymmetries are readily found to be

$\displaystyle[A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})-A_{\rm
prod}({{\mathchar 28931\relax}^{0}_{b}})]$ $\displaystyle=(-1.3\pm
5.6)\%~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$ $\displaystyle[A_{\rm
prod}({{\mathchar 28932\relax}^{-}_{b}})-A_{\rm prod}({{\mathchar
28931\relax}^{0}_{b}})]$ $\displaystyle=(-6.3\pm
4.9)\%~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}],$

where the uncertainties are due to the signal yields obtained in this
analysis.

To obtain $A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})$, previous
measurements of $A_{\rm prod}({{\mathchar 28931\relax}^{0}_{b}})$ at
$\sqrt{s}=7$ and 8 TeV are used [47]. Since the value of $A_{\rm
prod}({{\mathchar 28931\relax}^{0}_{b}})$ averaged over the LHCb acceptance is
not expected to change significantly with center-of-mass energy [48], and the
measured values of $A_{\rm prod}({{\mathchar 28931\relax}^{0}_{b}})$ obtained
at $\sqrt{s}=7$ and 8 TeV are compatible [47], they are averaged, taking the
systematic uncertainties as fully correlated, to obtain ${A_{\rm
prod}({{\mathchar 28931\relax}^{0}_{b}})=(2.4\pm 1.4\pm 0.9)\%}$. An alternate
measurement of $A_{\rm prod}({{\mathchar 28931\relax}^{0}_{b}})$ yielded
results that are consistent with the above value [49]. The value at 7, 8 TeV
is also used for the ${{\mathchar 28932\relax}^{-}_{b}}$ asymmetry measurement
at 13 TeV, and a systematic uncertainty, which is discussed below, is
assigned. The ${{\mathchar 28932\relax}^{-}_{b}}$ asymmetries are found to be

$\displaystyle A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})$
$\displaystyle=(\phantom{-}1.1\pm
5.6)\%~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$ $\displaystyle A_{\rm
prod}({{\mathchar 28932\relax}^{-}_{b}})$ $\displaystyle=(-3.9\pm
4.9)\%~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}].$

In the mass measurement, most sources of systematic uncertainty cancel, since
it relies on the mass difference, $\delta m$. The modulus of the correction of
0.12$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ described previously is assigned as
a systematic uncertainty. The signal shape uncertainty is quantified by
performing an alternate fit using the sum of two Gaussian functions. Apart
from a common peak value, all shape parameters are left free in the fit. The
difference with respect to the nominal value,
0.06$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$, is assigned as a systematic
uncertainty. The background shape uncertainty is assessed by using a first-
order polynomial in place of the nominal exponential function, and is found to
change the result by 0.01$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$. The
systematic uncertainties due to the momentum scale and energy loss have been
evaluated previously [50] and are found to contribute
0.01$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ each. Knowledge of the ${{\mathchar
28932\relax}^{-}}$ mass contributes an uncertainty of
0.07$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$. Adding these uncertainties in
quadrature, the total systematic uncertainty on $\delta m$ is
0.15$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$.

For the measurement of $R$, several sources of uncertainty are considered,
which are summarized in Table 4. The efficiency for all decay products to be
within the LHCb acceptance is derived from the simulation, and could depend on
the polarization of the ${{\mathchar 28931\relax}^{0}_{b}}$ or ${{\mathchar
28932\relax}^{-}_{b}}$ baryon. To investigate this effect, variations in the
${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$
polarization are considered, including full polarization, zero polarization,
and using the helicity amplitudes presented in Ref. [51]. All three variations
are found to give statistically compatible acceptance corrections. The
assigned uncertainty of 3.0% reflects the statistical precision of the test.

The systematic uncertainty due to the signal and background functions is
estimated by using alternate choices for each, as described above for the
uncertainty on $\delta m$, leading to an uncertainty of 2.0%. The ${{\mathchar
28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$ simulations are
weighted as discussed previously and reproduce well the kinematical
distributions of the final-state particles seen in data. However, due to low
${{\mathchar 28932\relax}^{-}_{b}}$ signal yields, variations with respect to
the nominal weighting are considered. In particular, a 3% change in the
relative efficiency is seen when applying an additional weight to the
${{\mathchar 28932\relax}^{-}_{b}}$ pseudorapidity spectrum that is
permissible by the data. A significantly smaller difference is seen when
weighting the ${{\mathchar 28932\relax}^{-}_{b}}$ baryon’s $p_{\mathrm{T}}$
spectrum. A 3% uncertainty is therefore assigned to account for potential
differences in the $(\eta,p_{\mathrm{T}})$ spectrum of ${{\mathchar
28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{-}_{b}}$ baryons.

Uncertainties in the detection efficiency of the ${{\pi}^{-}}$ meson from the
${{\mathchar 28932\relax}^{-}}$ decay enters directly into the result for the
ratio $R$. The tracking efficiency in simulation has been calibrated using a
tag-and-probe method [40] using ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\rightarrow{\mu^{+}}{\mu^{-}}$ decays, however, the calibration only
covers the kinematic region $p>5$$\text{\,Ge\kern-1.00006ptV\\!/}c$ and
$1.9<\eta<4.9$. Outside this region, no correction to the tracking efficiency
in simulation is applied and an uncertainty of 5% is assigned to the tracking
efficiency. This value is justified based upon a comparison of the
reconstructed momentum spectrum of ${{\pi}^{-}}$ mesons from ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{\mathchar 28931\relax}$ decays in data and simulation, where the
${\mathchar 28931\relax}$ baryons are formed from long tracks. These tracks
serve as a good proxy for the ${{\pi}^{-}}$ meson from ${{\mathchar
28932\relax}^{-}}$ baryon decay, since they also have low momentum and large
impact parameter. Averaging over the tracks within and outside the range
covered by the tracking calibration, an uncertainty of 4.5% on the
${{\pi}^{-}}$ tracking efficiency is obtained. As a cross-check, the analysis
is repeated using only ${{\pi}^{-}}$ candidates in the range covered by the
calibration, and the $R$ values are consistent with the nominal results.

Potential uncertainties due to the ${{\mathchar 28932\relax}^{-}}$ mass
requirement may arise from differences in the ${{\mathchar 28932\relax}^{-}}$
mass resolution, or possibly a (Cabibbo-suppressed) nonresonant ${\mathchar
28931\relax}{{\pi}^{-}}$ contribution. To quantify the potential size of such
effects, the ${{\mathchar 28932\relax}^{-}_{b}}$ signal yield in the
${{\mathchar 28932\relax}^{-}}$ sideband region, $10<|M({\mathchar
28931\relax}\pi^{-}_{\rm L,D})-M(p{{\pi}^{-}})+m_{{\mathchar
28931\relax}}-m_{{{\mathchar
28932\relax}^{-}}}|<20$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ is measured. The
yield in that region, which is consistent with zero, is taken as a systematic
uncertainty. Other ${{\mathchar 28932\relax}^{-}}$ selections are very loose
and are studied by comparing background-subtracted distributions of relevant
variables in data with those in simulation. From the observed differences an
uncertainty of 1.4% is assigned. The uncertainty on $R$ due to the knowledge
of the ${{\mathchar 28932\relax}^{-}_{b}}$ lifetime, $\tau_{{{\mathchar
28932\relax}^{-}_{b}}}=1.571\pm 0.040$ ps [28], is estimated by weighting the
simulation to replicate 0.04 ps shorter and longer lifetimes. The effect on
$R$ of the ${{\mathchar 28931\relax}^{0}_{b}}$ lifetime uncertainty is
negligible. Lastly, the simulated sample sizes contribute 2.0% uncertainty to
the relative efficiency.

Table 4: Summary of relative systematic uncertainties on the production ratio $R$. Source | Value (%)
---|---
${{\mathchar 28931\relax}^{0}_{b}}$, ${{\mathchar 28932\relax}^{-}_{b}}$ polarization | 3.0
Signal and background shape | 2.0
${{\mathchar 28932\relax}^{-}_{b}}$ production spectra | 3.0
${{\pi}^{-}}$ tracking efficiency | 4.5
${{\mathchar 28932\relax}^{-}}$ mass resolution & non-resonant ${\mathchar 28931\relax}{{\pi}^{-}}$ | 3.0
${{\mathchar 28932\relax}^{-}}$ selections | 1.4
${{\mathchar 28932\relax}^{-}_{b}}$ lifetime | 0.5
Simulated sample sizes | 2.0
Total | 7.6

The uncertainty on the ${{\mathchar 28932\relax}^{-}_{b}}$ production
asymmetry receives contributions from the ${{\pi}^{-}}$ detection asymmetry
and the measurement of $A_{\rm prod}({{\mathchar 28931\relax}^{0}_{b}})$. The
pion detection asymmetry uncertainty is assigned to be 1%, as mentioned
previously. Taking the sum in quadrature of the statistical and systematic
uncertainties in the value of $A_{\rm prod}({{\mathchar
28931\relax}^{0}_{b}})=(2.4\pm 1.4\pm 0.9)\%$, a 1.7% systematic uncertainty
is assigned. Since the average value of $A_{\rm prod}({{\mathchar
28931\relax}^{0}_{b}})$ at $\sqrt{s}=7$ and 8 TeV [47] could differ from that
at 13 TeV [48], an additional systematic uncertainty of 1.5% is assigned to
the measured value of $A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})$ at 13
TeV. The total systematic uncertainty in $A_{\rm prod}({{\mathchar
28932\relax}^{-}_{b}})$ is therefore 1.9% and 2.5% for the 7, 8 TeV and 13 TeV
data samples, respectively.

In summary, data samples collected at $\sqrt{s}$ = 7, 8 and 13 TeV have been
used to measure the ratio of production rates of ${{\mathchar
28932\relax}^{-}_{b}}$ and ${{\mathchar 28931\relax}^{0}_{b}}$ baryons in the
pseudorapidity and $p_{\mathrm{T}}$ region, $2<\eta<6$ and
$p_{\mathrm{T}}<20$$\text{\,Ge\kern-1.00006ptV\\!/}c$, to be

$\displaystyle R$ $\displaystyle=(10.8\pm 0.9\pm 0.8)\times
10^{-2}~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$ $\displaystyle R$
$\displaystyle=(13.1\pm 1.1\pm 1.0)\times
10^{-2}~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}],$

where the uncertainties are statistical and systematic. From the values of
$R$, the ratios of fragmentation fractions are determined to be

$\displaystyle\frac{f_{{{\mathchar 28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}$ $\displaystyle=(6.7\pm 0.5\pm 0.5\pm 2.0)\times
10^{-2}~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$
$\displaystyle\frac{f_{{{\mathchar 28932\relax}^{-}_{b}}}}{f_{{{\mathchar
28931\relax}^{0}_{b}}}}$ $\displaystyle=(8.2\pm 0.7\pm 0.6\pm 2.5)\times
10^{-2}~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}].$

The last uncertainty, due to the assumed SU(3) flavor symmetry and taken to be
30%, is an estimate of the typical size of SU(3)-breaking effects between
decays related by this symmetry. The LHCb results show no significant
dependence on the center-of-mass energy in the 7 to 13 TeV range. These
results are consistent with the predictions in Refs. [23, 24], which used
production ratio measurements of ${{\mathchar
28932\relax}^{0}_{b}}\rightarrow{{\mathchar 28932\relax}^{+}_{c}}{{\pi}^{-}}$
and ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{\mathchar
28931\relax}^{+}_{c}}{{\pi}^{-}}$ decays at 7 and 8 TeV [14] and an estimated
value for ${\mathcal{B}}({{\mathchar 28932\relax}^{+}_{c}}\rightarrow
p{{K}^{-}}{{\pi}^{+}})$. Assuming that $f_{{{\mathchar
28932\relax}^{0}_{b}}}\approx f_{{{\mathchar 28932\relax}^{-}_{b}}}$, these
results indicate that in the forward region, $b$ quarks fragment into
${{\mathchar 28932\relax}_{b}}$ baryons at about 15% of the rate at which they
fragment into ${{\mathchar 28931\relax}^{0}_{b}}$ baryons. Previous
measurements of $R$ by the CDF [52] and D0 [53] collaborations are about two
standard deviations larger than the results reported here, however, those
measurements are performed in $p\bar{p}$ collisions at $\sqrt{s}=2$ TeV and in
the central rapidity region $|\eta|<2$.

The mass difference, $\delta m$, and the corresponding value of the
${{\mathchar 28932\relax}^{-}_{b}}$ mass, $m({{\mathchar
28932\relax}^{-}_{b}})$, are measured to be

$\displaystyle\delta m$ $\displaystyle=177.30\pm 0.39\pm
0.15\text{\,Me\kern-1.00006ptV\\!/}c^{2},$ $\displaystyle m({{\mathchar
28932\relax}^{-}_{b}})$ $\displaystyle=5796.70\pm 0.39\pm 0.15\pm
0.17\text{\,Me\kern-1.00006ptV\\!/}c^{2},$

where the last uncertainty is due to the ${{\mathchar 28931\relax}^{0}_{b}}$
mass. This ${{\mathchar 28932\relax}^{-}_{b}}$ mass measurement includes the
data used in Ref. [50], and therefore supersedes those results. This
measurement represents the most precise determination of the ${{\mathchar
28932\relax}^{-}_{b}}$ mass, and is consistent with the previous most precise
measurement of the mass difference of $178.36\pm 0.46\pm
0.16$$\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ [15].

The ${{\mathchar 28932\relax}^{-}_{b}}$ production asymmetry is also measured
for the first time. The values at the lower and higher center-of-mass
energies, are

$\displaystyle A_{\rm prod}({{\mathchar 28932\relax}^{-}_{b}})$
$\displaystyle=(\phantom{-}1.1\pm 5.6\pm
1.9)\%~{}~{}[\sqrt{s}=7,8\text{\,Te\kern-1.00006ptV}],$ $\displaystyle A_{\rm
prod}({{\mathchar 28932\relax}^{-}_{b}})$ $\displaystyle=(-3.9\pm 4.9\pm
2.5)\%~{}~{}[\sqrt{s}=13\text{\,Te\kern-1.00006ptV}].$

The asymmetries are consistent with zero at the level of a few percent.

## Acknowledgements

We thank M. Voloshin for interesting and helpful discussions on theoretical
aspects of this work. We express our gratitude to our colleagues in the CERN
accelerator departments for the excellent performance of the LHC. We thank the
technical and administrative staff at the LHCb institutes. We acknowledge
support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and
FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG
(Germany); INFN (Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA
(Romania); MSHE (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU
(Ukraine); STFC (United Kingdom); NSF (USA). We acknowledge the computing
resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany),
INFN (Italy), SURF (Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI
and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil),
PL-GRID (Poland) and OSC (USA). We are indebted to the communities behind the
multiple open-source software packages on which we depend. Individual groups
or members have received support from AvH Foundation (Germany); EPLANET, Marie
Skłodowska-Curie Actions and ERC (European Union); ANR, Labex P2IO and OCEVU,
and Région Auvergne-Rhône-Alpes (France); Key Research Program of Frontier
Sciences of CAS, CAS PIFI, and the Thousand Talents Program (China); RFBR, RSF
and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); the Royal Society
and the Leverhulme Trust (United Kingdom); Laboratory Directed Research and
Development program of LANL (USA).

## References

  * [1] V. A. Khoze and M. A. Shifman, _Heavy quarks_ , Sov. Phys. Usp. 26 (1983) 387
  * [2] I. I. Bigi and N. G. Uraltsev, _Gluonic enhancements in non-spectator beauty decays $-$ an inclusive mirage though an exclusive possibility_, Phys. Lett. B280 (1992) 271
  * [3] I. I. Bigi, N. G. Uraltsev, and A. I. Vainshtein, _Nonperturbative corrections to inclusive beauty and charm decays. QCD versus phenomenological models_ , Phys. Lett. B293 (1992) 430, Erratum ibid. B297 (1992) 477, arXiv:hep-ph/9207214
  * [4] B. Blok and M. Shifman, _The rule of discarding 1/ $N_{c}$ in inclusive weak decays (I)_, Nucl. Phys. B399 (1993) 441, arXiv:hep-ph/9207236
  * [5] B. Blok and M. Shifman, _The rule of discarding 1/ $N_{c}$ in inclusive weak decays (II)_, Nucl. Phys. B399 (1993) 459, arXiv:hep-ph/9209289
  * [6] M. Neubert, _B decays and the heavy quark expansion_ , Adv. Ser. Direct. High Energy Phys. 15 (1998) 239, arXiv:hep-ph/9702375
  * [7] N. Uraltsev, _Heavy quark expansion in beauty and its decays_ , arXiv:hep-ph/9804275, also published in proceedings, Heavy Flavour Physics: A Probe of Nature’s Grand Design, Proc. Intern. School of Physics “Enrico Fermi”, Course CXXXVII, Varenna, July 7-18 1997
  * [8] G. Bellini, I. I. Y. Bigi, and P. J. Dornan, _Lifetimes of charm and beauty hadrons_ , Phys. Rept. 289 (1997) 1
  * [9] LHCb collaboration, R. Aaij et al., _Measurement of ${b}$ hadron production fractions in 7 TeV ${p}{p}$ collisions_, Phys. Rev. D85 (2012) 032008, arXiv:1111.2357
  * [10] LHCb collaboration, R. Aaij et al., _Measurement of $b$-hadron fractions in 13 TeV $pp$ collisions_, LHCb-PAPER-2018-050, in preparation
  * [11] LHCb collaboration, R. Aaij et al., _Measurement of the fragmentation fraction ratio $f_{s}/f_{d}$ and its dependence on ${B}$ meson kinematics_, JHEP 04 (2013) 001, arXiv:1301.5286
  * [12] LHCb collaboration, R. Aaij et al., _Study of beauty baryon decays to ${{D}^{0}}{p}h^{-}$ and ${{\mathchar 28931\relax}^{+}_{c}}h^{-}$ final states_, Phys. Rev. D89 (2014) 032001, arXiv:1311.4823
  * [13] LHCb collaboration, R. Aaij et al., _Searches for ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{0}_{b}}$ decays to ${{K}^{0}_{\mathrm{S}}}{p}{{\pi}^{-}}$ and ${{K}^{0}_{\mathrm{S}}}{p}{{K}^{-}}$ final states with first observation of the ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{K}^{0}_{\mathrm{S}}}{p}{{\pi}^{-}}$ decay_, JHEP 04 (2014) 087, arXiv:1402.0770
  * [14] LHCb collaboration, R. Aaij et al., _Precision measurement of the mass and lifetime of the ${{\mathchar 28932\relax}^{0}_{b}}$ baryon_, Phys. Rev. Lett. 113 (2014) 032001, arXiv:1405.7223
  * [15] LHCb collaboration, R. Aaij et al., _Precision measurement of the mass and lifetime of the ${{\mathchar 28932\relax}^{-}_{b}}$ baryon_, Phys. Rev. Lett. 113 (2014) 242002, arXiv:1409.8568
  * [16] LHCb collaboration, R. Aaij et al., _Evidence for the strangeness-changing weak decay ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{\mathchar 28931\relax}^{0}_{b}}{{\pi}^{-}}$_, Phys. Rev. Lett. 115 (2015) 241801, arXiv:1510.03829
  * [17] LHCb collaboration, R. Aaij et al., _Observations of ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{\mathchar 28931\relax}{{K}^{+}}{{\pi}^{-}}$ and ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{\mathchar 28931\relax}{{K}^{+}}{{K}^{-}}$ decays and searches for other ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\mathchar 28932\relax}^{0}_{b}}$ decays to ${\mathchar 28931\relax}h^{+}h^{-}$ final states_, JHEP 05 (2016) 081, arXiv:1603.00413
  * [18] LHCb collaboration, R. Aaij et al., _Observation of the decay ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{p}{{K}^{-}}{{K}^{-}}$_, Phys. Rev. Lett. 118 (2017) 071801, arXiv:1612.02244
  * [19] LHCb collaboration, R. Aaij et al., _Observation of the ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}{{K}^{-}}$ decay_, Phys. Lett. B772 (2017) 265, arXiv:1701.05274
  * [20] LHCb collaboration, R. Aaij et al., _Measurement of branching fractions of charmless four-body ${{\mathchar 28931\relax}^{0}_{b}}$ and ${\mathchar 28932\relax}_{b}^{0}$ decays_, JHEP 02 (2018) 098, arXiv:1711.05490
  * [21] Belle collaboration, Y. B. Li et al., _First measurements of absolute branching fractions of ${{\mathchar 28932\relax}^{0}_{c}}$ at Belle_, arXiv:1811.09738
  * [22] Belle II collaboration, T. Abe et al., _Belle II Technical Design Report_ , arXiv:1011.0352
  * [23] D. Wang, _Sum rules for $C\\!P$ asymmetries of charmed baryon decays in the flavor $\mathrm{SU}(3)$ limit_, arXiv:1901.01776
  * [24] H.-Y. Jiang and F.-S. Yu, _Fragmentation-fraction ratio $f_{{{\mathchar 28932\relax}_{b}}}/f_{{{\mathchar 28931\relax}^{0}_{b}}}$ in $b$\- and $c$-baryon decays_, Eur. Phys. J. C78 (2018) 224, arXiv:1802.02948
  * [25] M. J. Savage and M. B. Wise, _SU(3) predictions for nonleptonic $B$ meson decays to charmed baryons_, Nucl. Phys. B326 (1989) 15
  * [26] M. Voloshin, _Remarks on measurement of the decay ${{\mathchar 28932\relax}^{-}_{b}}\rightarrow{{\mathchar 28931\relax}^{0}_{b}}{{\pi}^{-}}$_, arXiv:1510.05568
  * [27] Y. K. Hsiao, P. Y. Lin, L. W. Luo, and C. Q. Geng, _Fragmentation fractions of two-body b-baryon decays_ , Phys. Lett. B751 (2015) 127, arXiv:1510.01808
  * [28] Particle Data Group, M. Tanabashi et al., _Review of particle physics_ , Phys. Rev. D98 (2018) 030001
  * [29] LHCb collaboration, A. A. Alves Jr. et al., _The LHCb detector at the LHC_, JINST 3 (2008) S08005
  * [30] LHCb collaboration, R. Aaij et al., _LHCb detector performance_ , Int. J. Mod. Phys. A30 (2015) 1530022, arXiv:1412.6352
  * [31] T. Sjöstrand, S. Mrenna, and P. Skands, _PYTHIA 6.4 physics and manual_ , JHEP 05 (2006) 026, arXiv:hep-ph/0603175
  * [32] T. Sjöstrand, S. Mrenna, and P. Skands, _A brief introduction to PYTHIA 8.1_ , Comput. Phys. Commun. 178 (2008) 852, arXiv:0710.3820
  * [33] I. Belyaev et al., _Handling of the generation of primary events in Gauss, the LHCb simulation framework_ , J. Phys. Conf. Ser. 331 (2011) 032047
  * [34] D. J. Lange, _The EvtGen particle decay simulation package_ , Nucl. Instrum. Meth. A462 (2001) 152
  * [35] P. Golonka and Z. Was, _PHOTOS Monte Carlo: A precision tool for QED corrections in $Z$ and $W$ decays_, Eur. Phys. J. C45 (2006) 97, arXiv:hep-ph/0506026
  * [36] Geant4 collaboration, J. Allison et al., _Geant4 developments and applications_ , IEEE Trans. Nucl. Sci. 53 (2006) 270
  * [37] Geant4 collaboration, S. Agostinelli et al., _Geant4: A simulation toolkit_ , Nucl. Instrum. Meth. A506 (2003) 250
  * [38] M. Clemencic et al., _The LHCb simulation application, Gauss: Design, evolution and experience_, J. Phys. Conf. Ser. 331 (2011) 032023
  * [39] R. Aaij et al., _The LHCb trigger and its performance in 2011_, JINST 8 (2013) P04022, arXiv:1211.3055
  * [40] LHCb collaboration, R. Aaij et al., _Measurement of the track reconstruction efficiency at LHCb_ , JINST 10 (2015) P02007, arXiv:1408.1251
  * [41] W. D. Hulsbergen, _Decay chain fitting with a Kalman filter_ , Nucl. Instrum. Meth. A552 (2005) 566, arXiv:physics/0503191
  * [42] T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02
  * [43] LHCb collaboration, R. Aaij et al., _Precision measurement of ${D}$ meson mass differences_, JHEP 06 (2013) 065, arXiv:1304.6865
  * [44] M. Pivk and F. R. Le Diberder, _sPlot: A statistical tool to unfold data distributions_ , Nucl. Instrum. Meth. A555 (2005) 356, arXiv:physics/0402083
  * [45] LHCb collaboration, R. Aaij et al., _Measurement of the $C\\!P$ asymmetry in ${{B}^{0}_{s}}$–${{\kern 1.79993pt\overline{\kern-1.79993ptB}}{}^{0}_{s}}$ mixing_, Phys. Rev. Lett. 117 (2016) 061803, arXiv:1605.09768
  * [46] LHCb collaboration, R. Aaij et al., _Measurement of $D^{\pm}_{s}$ production asymmetry in $pp$ collisions at $\sqrt{s}=7$ and $8$ TeV_, JHEP 08 (2018) 008, arXiv:1805.09869
  * [47] LHCb collaboration, R. Aaij et al., _Measurement of ${B}^{0}$, ${B}^{0}_{s}$, ${{B}^{+}}$ and ${\mathchar 28931\relax}^{0}_{b}$ production asymmetries in $7$ and $8$ TeV $p$ $p$ collisions_, Phys. Lett. B774 (2017) 139, arXiv:1703.08464
  * [48] W. K. Lai and A. K. Leibovich, _${{\mathchar 28931\relax}^{+}_{c}}/{{\kern 1.79993pt\overline{\kern-1.79993pt\mathchar 28931\relax}}{}^{-}_{c}}$ and ${{\mathchar 28931\relax}^{0}_{b}}/{{\kern 1.79993pt\overline{\kern-1.79993pt\mathchar 28931\relax}}{}^{0}_{b}}$ production asymmetry at the LHC from heavy quark recombination_, Phys. Rev. D 91 (2015) 054022
  * [49] LHCb collaboration, R. Aaij et al., _Study of the productions of ${{\mathchar 28931\relax}^{0}_{b}}$ and ${{\kern 1.79993pt\overline{\kern-1.79993ptB}}{}^{0}}$ hadrons in ${p}{p}$ collisions and first measurement of the ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p}{{K}^{-}}$ branching fraction_, Chin. Phys. C 40 (2016) 011001, arXiv:1509.00292
  * [50] LHCb collaboration, R. Aaij et al., _Measurements of the ${{\mathchar 28931\relax}^{0}_{b}}$, ${{\mathchar 28932\relax}^{-}_{b}}$, and ${{\mathchar 28938\relax}^{-}_{b}}$ baryon masses_, Phys. Rev. Lett. 110 (2013) 182001, arXiv:1302.1072
  * [51] LHCb collaboration, R. Aaij et al., _Measurements of the ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{\mathchar 28931\relax}$ decay amplitudes and the ${{\mathchar 28931\relax}^{0}_{b}}$ polarisation in ${p}{p}$ collisions at $\sqrt{s}=7$ TeV_, Phys. Lett. B724 (2013) 27, arXiv:1302.5578
  * [52] CDF collaboration, T. Aaltonen et al., _Observation of the ${{\mathchar 28938\relax}^{-}_{b}}$ and measurement of the properties of the ${{\mathchar 28932\relax}^{-}_{b}}$ and ${{\mathchar 28938\relax}^{-}_{b}}$ baryons_, Phys. Rev. D80 (2009) 072003, arXiv:0905.3123
  * [53] D0 collaboration, V. M. Abazov et al., _Direct observation of the strange $b$ baryon ${{\mathchar 28932\relax}^{-}_{b}}$_, Phys. Rev. Lett. 99 (2007) 052001, arXiv:0706.1690

LHCb collaboration

R. Aaij28, C. Abellán Beteta46, B. Adeva43, M. Adinolfi50, C.A. Aidala77, Z.
Ajaltouni6, S. Akar61, P. Albicocco19, J. Albrecht11, F. Alessio44, M.
Alexander55, A. Alfonso Albero42, G. Alkhazov41, P. Alvarez Cartelle57, A.A.
Alves Jr43, S. Amato2, S. Amerio24, Y. Amhis8, L. An18, L. Anderlini18, G.
Andreassi45, M. Andreotti17, J.E. Andrews62, F. Archilli28, P. d’Argent13, J.
Arnau Romeu7, A. Artamonov40, M. Artuso63, K. Arzymatov37, E. Aslanides7, M.
Atzeni46, B. Audurier23, S. Bachmann13, J.J. Back52, S. Baker57, V.
Balagura8,b, W. Baldini17, A. Baranov37, R.J. Barlow58, G.C. Barrand8, S.
Barsuk8, W. Barter58, M. Bartolini20, F. Baryshnikov74, V. Batozskaya32, B.
Batsukh63, A. Battig11, V. Battista45, A. Bay45, J. Beddow55, F. Bedeschi25,
I. Bediaga1, A. Beiter63, L.J. Bel28, S. Belin23, N. Beliy66, V. Bellee45, N.
Belloli21,i, K. Belous40, I. Belyaev34, E. Ben-Haim9, G. Bencivenni19, S.
Benson28, S. Beranek10, A. Berezhnoy35, R. Bernet46, D. Berninghoff13, E.
Bertholet9, A. Bertolin24, C. Betancourt46, F. Betti16,44, M.O. Bettler51, M.
van Beuzekom28, Ia. Bezshyiko46, S. Bhasin50, J. Bhom30, M.S. Bieker11, S.
Bifani49, P. Billoir9, A. Birnkraut11, A. Bizzeti18,u, M. Bjørn59, M.P.
Blago44, T. Blake52, F. Blanc45, S. Blusk63, D. Bobulska55, V. Bocci27, O.
Boente Garcia43, T. Boettcher60, A. Bondar39,x, N. Bondar41, S. Borghi58,44,
M. Borisyak37, M. Borsato43, M. Boubdir10, T.J.V. Bowcock56, C. Bozzi17,44, S.
Braun13, M. Brodski44, J. Brodzicka30, A. Brossa Gonzalo52, D. Brundu23,44, E.
Buchanan50, A. Buonaura46, C. Burr58, A. Bursche23, J. Buytaert44, W.
Byczynski44, S. Cadeddu23, H. Cai68, R. Calabrese17,g, R. Calladine49, M.
Calvi21,i, M. Calvo Gomez42,m, A. Camboni42,m, P. Campana19, D.H. Campora
Perez44, L. Capriotti16,e, A. Carbone16,e, G. Carboni26, R. Cardinale20, A.
Cardini23, P. Carniti21,i, K. Carvalho Akiba2, G. Casse56, M. Cattaneo44, G.
Cavallero20, R. Cenci25,p, D. Chamont8, M.G. Chapman50, M. Charles9, Ph.
Charpentier44, G. Chatzikonstantinidis49, M. Chefdeville5, V. Chekalina37, C.
Chen3, S. Chen23, S.-G. Chitic44, V. Chobanova43, M. Chrzaszcz44, A.
Chubykin41, P. Ciambrone19, X. Cid Vidal43, G. Ciezarek44, F. Cindolo16,
P.E.L. Clarke54, M. Clemencic44, H.V. Cliff51, J. Closier44, V. Coco44, J.A.B.
Coelho8, J. Cogan7, E. Cogneras6, L. Cojocariu33, P. Collins44, T. Colombo44,
A. Comerma-Montells13, A. Contu23, G. Coombs44, S. Coquereau42, G. Corti44, M.
Corvo17,g, C.M. Costa Sobral52, B. Couturier44, G.A. Cowan54, D.C. Craik60, A.
Crocombe52, M. Cruz Torres1, R. Currie54, C. D’Ambrosio44, F. Da Cunha
Marinho2, C.L. Da Silva78, E. Dall’Occo28, J. Dalseno43,v, A. Danilina34, A.
Davis58, O. De Aguiar Francisco44, K. De Bruyn44, S. De Capua58, M. De Cian45,
J.M. De Miranda1, L. De Paula2, M. De Serio15,d, P. De Simone19, C.T. Dean55,
W. Dean77, D. Decamp5, L. Del Buono9, B. Delaney51, H.-P. Dembinski12, M.
Demmer11, A. Dendek31, D. Derkach38, O. Deschamps6, F. Desse8, F. Dettori56,
B. Dey69, A. Di Canto44, P. Di Nezza19, S. Didenko74, H. Dijkstra44, F.
Dordei23, M. Dorigo44,y, A. Dosil Suárez43, L. Douglas55, A. Dovbnya47, K.
Dreimanis56, L. Dufour44, G. Dujany9, P. Durante44, J.M. Durham78, D. Dutta58,
R. Dzhelyadin40,†, M. Dziewiecki13, A. Dziurda30, A. Dzyuba41, S. Easo53, U.
Egede57, V. Egorychev34, S. Eidelman39,x, S. Eisenhardt54, U. Eitschberger11,
R. Ekelhof11, L. Eklund55, S. Ely63, A. Ene33, S. Escher10, S. Esen28, T.
Evans61, A. Falabella16, N. Farley49, S. Farry56, D. Fazzini21,44,i, P.
Fernandez Declara44, A. Fernandez Prieto43, F. Ferrari16,e, L. Ferreira
Lopes45, F. Ferreira Rodrigues2, M. Ferro-Luzzi44, S. Filippov36, R.A. Fini15,
M. Fiorini17,g, M. Firlej31, C. Fitzpatrick45, T. Fiutowski31, F. Fleuret8,b,
M. Fontana44, F. Fontanelli20,h, R. Forty44, V. Franco Lima56, M. Frank44, C.
Frei44, J. Fu22,q, W. Funk44, C. Färber44, M. Féo44, E. Gabriel54, A. Gallas
Torreira43, D. Galli16,e, S. Gallorini24, S. Gambetta54, Y. Gan3, M.
Gandelman2, P. Gandini22, Y. Gao3, L.M. Garcia Martin76, B. Garcia Plana43, J.
García Pardiñas46, J. Garra Tico51, L. Garrido42, D. Gascon42, C. Gaspar44, L.
Gavardi11, G. Gazzoni6, D. Gerick13, E. Gersabeck58, M. Gersabeck58, T.
Gershon52, D. Gerstel7, Ph. Ghez5, V. Gibson51, O.G. Girard45, P. Gironella
Gironell42, L. Giubega33, K. Gizdov54, V.V. Gligorov9, D. Golubkov34, A.
Golutvin57,74, A. Gomes1,a, I.V. Gorelov35, C. Gotti21,i, E. Govorkova28, J.P.
Grabowski13, R. Graciani Diaz42, L.A. Granado Cardoso44, E. Graugés42, E.
Graverini46, G. Graziani18, A. Grecu33, R. Greim28, P. Griffith23, L.
Grillo58, L. Gruber44, B.R. Gruberg Cazon59, O. Grünberg71, C. Gu3, E.
Gushchin36, A. Guth10, Yu. Guz40,44, T. Gys44, C. Göbel65, T. Hadavizadeh59,
C. Hadjivasiliou6, G. Haefeli45, C. Haen44, S.C. Haines51, B. Hamilton62, X.
Han13, T.H. Hancock59, S. Hansmann-Menzemer13, N. Harnew59, T. Harrison56, C.
Hasse44, M. Hatch44, J. He66, M. Hecker57, K. Heinicke11, A. Heister11, K.
Hennessy56, L. Henry76, E. van Herwijnen44, J. Heuel10, M. Heß71, A.
Hicheur64, R. Hidalgo Charman58, D. Hill59, M. Hilton58, P.H. Hopchev45, J.
Hu13, W. Hu69, W. Huang66, Z.C. Huard61, W. Hulsbergen28, T. Humair57, M.
Hushchyn38, D. Hutchcroft56, D. Hynds28, P. Ibis11, M. Idzik31, P. Ilten49, A.
Inglessi41, A. Inyakin40, K. Ivshin41, R. Jacobsson44, J. Jalocha59, E.
Jans28, B.K. Jashal76, A. Jawahery62, F. Jiang3, M. John59, D. Johnson44, C.R.
Jones51, C. Joram44, B. Jost44, N. Jurik59, S. Kandybei47, M. Karacson44, J.M.
Kariuki50, S. Karodia55, N. Kazeev38, M. Kecke13, F. Keizer51, M. Kelsey63, M.
Kenzie51, T. Ketel29, E. Khairullin37, B. Khanji44, C. Khurewathanakul45, K.E.
Kim63, T. Kirn10, V.S. Kirsebom45, S. Klaver19, K. Klimaszewski32, T.
Klimkovich12, S. Koliiev48, M. Kolpin13, R. Kopecna13, P. Koppenburg28, I.
Kostiuk28,48, S. Kotriakhova41, M. Kozeiha6, L. Kravchuk36, M. Kreps52, F.
Kress57, P. Krokovny39,x, W. Krupa31, W. Krzemien32, W. Kucewicz30,l, M.
Kucharczyk30, V. Kudryavtsev39,x, A.K. Kuonen45, T. Kvaratskheliya34,44, D.
Lacarrere44, G. Lafferty58, A. Lai23, D. Lancierini46, G. Lanfranchi19, C.
Langenbruch10, T. Latham52, C. Lazzeroni49, R. Le Gac7, A. Leflat35, R.
Lefèvre6, F. Lemaitre44, O. Leroy7, T. Lesiak30, B. Leverington13, P.-R.
Li66,ab, Y. Li4, Z. Li63, X. Liang63, T. Likhomanenko73, R. Lindner44, F.
Lionetto46, V. Lisovskyi8, G. Liu67, X. Liu3, D. Loh52, A. Loi23, I.
Longstaff55, J.H. Lopes2, G.H. Lovell51, D. Lucchesi24,o, M. Lucio Martinez43,
Y. Luo3, A. Lupato24, E. Luppi17,g, O. Lupton44, A. Lusiani25, X. Lyu66, F.
Machefert8, F. Maciuc33, V. Macko45, P. Mackowiak11, S. Maddrell-Mander50, O.
Maev41,44, K. Maguire58, D. Maisuzenko41, M.W. Majewski31, S. Malde59, B.
Malecki44, A. Malinin73, T. Maltsev39,x, H. Malygina13, G. Manca23,f, G.
Mancinelli7, D. Marangotto22,q, J. Maratas6,w, J.F. Marchand5, U. Marconi16,
C. Marin Benito8, M. Marinangeli45, P. Marino45, J. Marks13, P.J. Marshall56,
G. Martellotti27, M. Martinelli44, D. Martinez Santos43, F. Martinez Vidal76,
A. Massafferri1, M. Materok10, R. Matev44, A. Mathad52, Z. Mathe44, C.
Matteuzzi21, A. Mauri46, E. Maurice8,b, B. Maurin45, M. McCann57,44, A.
McNab58, R. McNulty14, J.V. Mead56, B. Meadows61, C. Meaux7, N. Meinert71, D.
Melnychuk32, M. Merk28, A. Merli22,q, E. Michielin24, D.A. Milanes70, E.
Millard52, M.-N. Minard5, L. Minzoni17,g, D.S. Mitzel13, A. Mogini9, R.D.
Moise57, T. Mombächer11, I.A. Monroy70, S. Monteil6, M. Morandin24, G.
Morello19, M.J. Morello25,t, O. Morgunova73, J. Moron31, A.B. Morris7, R.
Mountain63, F. Muheim54, M. Mukherjee69, M. Mulder28, C.H. Murphy59, D.
Murray58, A. Mödden 11, D. Müller44, J. Müller11, K. Müller46, V. Müller11, P.
Naik50, T. Nakada45, R. Nandakumar53, A. Nandi59, T. Nanut45, I. Nasteva2, M.
Needham54, N. Neri22,q, S. Neubert13, N. Neufeld44, R. Newcombe57, T.D.
Nguyen45, C. Nguyen-Mau45,n, S. Nieswand10, R. Niet11, N. Nikitin35, A.
Nogay73, N.S. Nolte44, D.P. O’Hanlon16, A. Oblakowska-Mucha31, V. Obraztsov40,
S. Ogilvy55, R. Oldeman23,f, C.J.G. Onderwater72, A. Ossowska30, J.M. Otalora
Goicochea2, T. Ovsiannikova34, P. Owen46, A. Oyanguren76, P.R. Pais45, T.
Pajero25,t, A. Palano15, M. Palutan19, G. Panshin75, A. Papanestis53, M.
Pappagallo54, L.L. Pappalardo17,g, W. Parker62, C. Parkes58,44, G.
Passaleva18,44, A. Pastore15, M. Patel57, C. Patrignani16,e, A. Pearce44, A.
Pellegrino28, G. Penso27, M. Pepe Altarelli44, S. Perazzini44, D. Pereima34,
P. Perret6, L. Pescatore45, K. Petridis50, A. Petrolini20,h, A. Petrov73, S.
Petrucci54, M. Petruzzo22,q, B. Pietrzyk5, G. Pietrzyk45, M. Pikies30, M.
Pili59, D. Pinci27, J. Pinzino44, F. Pisani44, A. Piucci13, V. Placinta33, S.
Playfer54, J. Plews49, M. Plo Casasus43, F. Polci9, M. Poli Lener19, A.
Poluektov7, N. Polukhina74,c, I. Polyakov63, E. Polycarpo2, G.J. Pomery50, S.
Ponce44, A. Popov40, D. Popov49,12, S. Poslavskii40, E. Price50, J.
Prisciandaro43, C. Prouve43, V. Pugatch48, A. Puig Navarro46, H. Pullen59, G.
Punzi25,p, W. Qian66, J. Qin66, R. Quagliani9, B. Quintana6, N.V. Raab14, B.
Rachwal31, J.H. Rademacker50, M. Rama25, M. Ramos Pernas43, M.S. Rangel2, F.
Ratnikov37,38, G. Raven29, M. Ravonel Salzgeber44, M. Reboud5, F. Redi45, S.
Reichert11, A.C. dos Reis1, F. Reiss9, C. Remon Alepuz76, Z. Ren3, V.
Renaudin59, S. Ricciardi53, S. Richards50, K. Rinnert56, P. Robbe8, A.
Robert9, A.B. Rodrigues45, E. Rodrigues61, J.A. Rodriguez Lopez70, M.
Roehrken44, S. Roiser44, A. Rollings59, V. Romanovskiy40, A. Romero Vidal43,
J.D. Roth77, M. Rotondo19, M.S. Rudolph63, T. Ruf44, J. Ruiz Vidal76, J.J.
Saborido Silva43, N. Sagidova41, B. Saitta23,f, V. Salustino Guimaraes65, C.
Sanchez Gras28, C. Sanchez Mayordomo76, B. Sanmartin Sedes43, R.
Santacesaria27, C. Santamarina Rios43, M. Santimaria19,44, E. Santovetti26,j,
G. Sarpis58, A. Sarti19,k, C. Satriano27,s, A. Satta26, M. Saur66, D.
Savrina34,35, S. Schael10, M. Schellenberg11, M. Schiller55, H. Schindler44,
M. Schmelling12, T. Schmelzer11, B. Schmidt44, O. Schneider45, A. Schopper44,
H.F. Schreiner61, M. Schubiger45, S. Schulte45, M.H. Schune8, R. Schwemmer44,
B. Sciascia19, A. Sciubba27,k, A. Semennikov34, E.S. Sepulveda9, A. Sergi49,
N. Serra46, J. Serrano7, L. Sestini24, A. Seuthe11, P. Seyfert44, M.
Shapkin40, Y. Shcheglov41,†, T. Shears56, L. Shekhtman39,x, V. Shevchenko73,
E. Shmanin74, B.G. Siddi17, R. Silva Coutinho46, L. Silva de Oliveira2, G.
Simi24,o, S. Simone15,d, I. Skiba17, N. Skidmore13, T. Skwarnicki63, M.W.
Slater49, J.G. Smeaton51, E. Smith10, I.T. Smith54, M. Smith57, M. Soares16,
l. Soares Lavra1, M.D. Sokoloff61, F.J.P. Soler55, B. Souza De Paula2, B.
Spaan11, E. Spadaro Norella22,q, P. Spradlin55, F. Stagni44, M. Stahl13, S.
Stahl44, P. Stefko45, S. Stefkova57, O. Steinkamp46, S. Stemmle13, O.
Stenyakin40, M. Stepanova41, H. Stevens11, A. Stocchi8, S. Stone63, B.
Storaci46, S. Stracka25, M.E. Stramaglia45, M. Straticiuc33, U. Straumann46,
S. Strokov75, J. Sun3, L. Sun68, Y. Sun62, K. Swientek31, A. Szabelski32, T.
Szumlak31, M. Szymanski66, S. T’Jampens5, Z. Tang3, T. Tekampe11, G.
Tellarini17, F. Teubert44, E. Thomas44, J. van Tilburg28, M.J. Tilley57, V.
Tisserand6, M. Tobin31, S. Tolk44, L. Tomassetti17,g, D. Tonelli25, D.Y. Tou9,
R. Tourinho Jadallah Aoude1, E. Tournefier5, M. Traill55, M.T. Tran45, A.
Trisovic51, A. Tsaregorodtsev7, G. Tuci25,p, A. Tully51, N. Tuning28,44, A.
Ukleja32, A. Usachov8, A. Ustyuzhanin37,38, U. Uwer13, A. Vagner75, V.
Vagnoni16, A. Valassi44, S. Valat44, G. Valenti16, R. Vazquez Gomez44, P.
Vazquez Regueiro43, S. Vecchi17, M. van Veghel28, J.J. Velthuis50, M.
Veltri18,r, G. Veneziano59, A. Venkateswaran63, M. Vernet6, M. Veronesi28, M.
Vesterinen52, J.V. Viana Barbosa44, D. Vieira66, M. Vieites Diaz43, H.
Viemann71, X. Vilasis-Cardona42,m, A. Vitkovskiy28, M. Vitti51, V. Volkov35,
A. Vollhardt46, D. Vom Bruch9, B. Voneki44, A. Vorobyev41, V. Vorobyev39,x, N.
Voropaev41, J.A. de Vries28, C. Vázquez Sierra28, R. Waldi71, J. Walsh25, J.
Wang4, M. Wang3, Y. Wang69, Z. Wang46, D.R. Ward51, H.M. Wark56, N.K.
Watson49, D. Websdale57, A. Weiden46, C. Weisser60, M. Whitehead10, G.
Wilkinson59, M. Wilkinson63, I. Williams51, M.R.J. Williams58, M. Williams60,
T. Williams49, F.F. Wilson53, M. Winn8, W. Wislicki32, M. Witek30, G.
Wormser8, S.A. Wotton51, K. Wyllie44, D. Xiao69, Y. Xie69, A. Xu3, M. Xu69, Q.
Xu66, Z. Xu3, Z. Xu5, Z. Yang3, Z. Yang62, Y. Yao63, L.E. Yeomans56, H. Yin69,
J. Yu69,aa, X. Yuan63, O. Yushchenko40, K.A. Zarebski49, M. Zavertyaev12,c, D.
Zhang69, L. Zhang3, W.C. Zhang3,z, Y. Zhang44, A. Zhelezov13, Y. Zheng66, X.
Zhu3, V. Zhukov10,35, J.B. Zonneveld54, S. Zucchelli16,e.

1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3Center for High Energy Physics, Tsinghua University, Beijing, China
4Institute Of High Energy Physics (ihep), Beijing, China
5Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy,
France
6Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
7Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
8LAL, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France
9LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3,
Paris, France
10I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
11Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
12Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
13Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
14School of Physics, University College Dublin, Dublin, Ireland
15INFN Sezione di Bari, Bari, Italy
16INFN Sezione di Bologna, Bologna, Italy
17INFN Sezione di Ferrara, Ferrara, Italy
18INFN Sezione di Firenze, Firenze, Italy
19INFN Laboratori Nazionali di Frascati, Frascati, Italy
20INFN Sezione di Genova, Genova, Italy
21INFN Sezione di Milano-Bicocca, Milano, Italy
22INFN Sezione di Milano, Milano, Italy
23INFN Sezione di Cagliari, Monserrato, Italy
24INFN Sezione di Padova, Padova, Italy
25INFN Sezione di Pisa, Pisa, Italy
26INFN Sezione di Roma Tor Vergata, Roma, Italy
27INFN Sezione di Roma La Sapienza, Roma, Italy
28Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands
29Nikhef National Institute for Subatomic Physics and VU University Amsterdam,
Amsterdam, Netherlands
30Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of
Sciences, Kraków, Poland
31AGH - University of Science and Technology, Faculty of Physics and Applied
Computer Science, Kraków, Poland
32National Center for Nuclear Research (NCBJ), Warsaw, Poland
33Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest-Magurele, Romania
34Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
35Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow,
Russia
36Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS),
Moscow, Russia
37Yandex School of Data Analysis, Moscow, Russia
38National Research University Higher School of Economics, Moscow, Russia
39Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia
40Institute for High Energy Physics (IHEP), Protvino, Russia
41Konstantinov Nuclear Physics Institute of National Research Centre
”Kurchatov Institute”, PNPI, St.Petersburg, Russia
42ICCUB, Universitat de Barcelona, Barcelona, Spain
43Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de
Santiago de Compostela, Santiago de Compostela, Spain
44European Organization for Nuclear Research (CERN), Geneva, Switzerland
45Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL),
Lausanne, Switzerland
46Physik-Institut, Universität Zürich, Zürich, Switzerland
47NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
48Institute for Nuclear Research of the National Academy of Sciences (KINR),
Kyiv, Ukraine
49University of Birmingham, Birmingham, United Kingdom
50H.H. Wills Physics Laboratory, University of Bristol, Bristol, United
Kingdom
51Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
52Department of Physics, University of Warwick, Coventry, United Kingdom
53STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
54School of Physics and Astronomy, University of Edinburgh, Edinburgh, United
Kingdom
55School of Physics and Astronomy, University of Glasgow, Glasgow, United
Kingdom
56Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
57Imperial College London, London, United Kingdom
58School of Physics and Astronomy, University of Manchester, Manchester,
United Kingdom
59Department of Physics, University of Oxford, Oxford, United Kingdom
60Massachusetts Institute of Technology, Cambridge, MA, United States
61University of Cincinnati, Cincinnati, OH, United States
62University of Maryland, College Park, MD, United States
63Syracuse University, Syracuse, NY, United States
64Laboratory of Mathematical and Subatomic Physics , Constantine, Algeria,
associated to 2
65Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de
Janeiro, Brazil, associated to 2
66University of Chinese Academy of Sciences, Beijing, China, associated to 3
67South China Normal University, Guangzhou, China, associated to 3
68School of Physics and Technology, Wuhan University, Wuhan, China, associated
to 3
69Institute of Particle Physics, Central China Normal University, Wuhan,
Hubei, China, associated to 3
70Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia,
associated to 9
71Institut für Physik, Universität Rostock, Rostock, Germany, associated to 13
72Van Swinderen Institute, University of Groningen, Groningen, Netherlands,
associated to 28
73National Research Centre Kurchatov Institute, Moscow, Russia, associated to
34
74National University of Science and Technology “MISIS”, Moscow, Russia,
associated to 34
75National Research Tomsk Polytechnic University, Tomsk, Russia, associated to
34
76Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia -
CSIC, Valencia, Spain, associated to 42
77University of Michigan, Ann Arbor, United States, associated to 63
78Los Alamos National Laboratory (LANL), Los Alamos, United States, associated
to 63

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bLaboratoire Leprince-Ringuet, Palaiseau, France
cP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS),
Moscow, Russia
dUniversità di Bari, Bari, Italy
eUniversità di Bologna, Bologna, Italy
fUniversità di Cagliari, Cagliari, Italy
gUniversità di Ferrara, Ferrara, Italy
hUniversità di Genova, Genova, Italy
iUniversità di Milano Bicocca, Milano, Italy
jUniversità di Roma Tor Vergata, Roma, Italy
kUniversità di Roma La Sapienza, Roma, Italy
lAGH - University of Science and Technology, Faculty of Computer Science,
Electronics and Telecommunications, Kraków, Poland
mLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
nHanoi University of Science, Hanoi, Vietnam
oUniversità di Padova, Padova, Italy
pUniversità di Pisa, Pisa, Italy
qUniversità degli Studi di Milano, Milano, Italy
rUniversità di Urbino, Urbino, Italy
sUniversità della Basilicata, Potenza, Italy
tScuola Normale Superiore, Pisa, Italy
uUniversità di Modena e Reggio Emilia, Modena, Italy
vH.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom
wMSU - Iligan Institute of Technology (MSU-IIT), Iligan, Philippines
xNovosibirsk State University, Novosibirsk, Russia
ySezione INFN di Trieste, Trieste, Italy
zSchool of Physics and Information Technology, Shaanxi Normal University
(SNNU), Xi’an, China
aaPhysics and Micro Electronic College, Hunan University, Changsha City, China
abLanzhou University, Lanzhou, China
†Deceased