On behalf of the LHCb collaboration

# Review of recent LHCb results and expectations for Run II

A. Hicheur<EMAIL_ADDRESS>Instituto de Física, Universidade Federal do
Rio de Janeiro

###### Abstract

As first Run II data acquisition has begun, it is useful to expose the pending
questions by reviewing some of the most recent results obtained with Run I
data analyses. Early results of the current data taking and middle-term
prospects are also shown to illustrate the efficiency of the acquisition and
analysis chain.

##  I Introduction

The core of the LHCb research program lies in the use of heavy flavour decays
to probe the intervention of New Physics through the involvement of heavy new
particles in loop decays. For this purpose, rare $b$-hadron decays proceeding
through box or loop diagrams and in general any process in which a virtual
heavy particle could intervene, come as natural grounds to seek for any
deviation from Standard Model-based predictions. Although the spectroscopy of
heavy-flavoured hadrons and the study of new bound states might be considered
as side-products of the main research lines, recent studies show that
important results can emerge in this sector.

Beside low-energy hadron physics, the low transverse momentum threshold, the
excellent vertex reconstruction, and the peculiar forward geometry of the LHCb
detector is allowing for complementary studies to what is performed with ATLAS
or CMS detectors, on areas such as QCD, Electroweak and Higgs physics, as well
as searches for displaced vertices of heavy decaying particles.

The analyses exhibited in this paper are based on the full Run I (years 2011
and 2012) data sample, representing 1.0 and 2.0 $\mbox{\,fb}^{-1}$ of
integrated luminosity at $7$ and $8$ TeV center-of-mass energies in $pp$
collisions, respectively. The early results and measurements of the first run
II data at 13 TeV are based on samples of 4 to 6 $\mbox{\,pb}^{-1}$, from the
50 ns proton bunch spacing run which occurred in early summer 2015.

##  II LHCb detector and software

The LHCb detector Alves:2008td , Fig.1, is a single-arm forward spectrometer
covering the pseudorapidity range $2<\eta<5$, specially 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
$4{\rm\,Tm}$, and three stations of silicon-strip detectors and straw drift
tubes placed downstream. The combined tracking system has momentum resolution
$\Delta p/p$ that varies from 0.4% at 5${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$
to 0.6% at 100${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, and impact parameter
(IP) resolution of 20${\,\upmu\mathrm{m}}$ for tracks with high transverse
momentum. Charged hadrons are identified using two ring-imaging Cherenkov
detectors (RICH) RichPerf . Photon, electron and hadron candidates are
identified by a calorimeter system consisting of scintillating-pad and
preshower detectors, an electromagnetic calorimeter and a hadronic
calorimeter. Muons are identified by a system composed of alternating layers
of iron and multiwire proportional chambers.

The data acquisition chain is depicted in Fig.2. The trigger Aaij:2012me
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. Events triggered both on objects independent of the signal,
and associated with the signal, are used. In the latter case, the transverse
energy of the hadronic cluster is required to be at least
3.5$\mathrm{\,Ge\kern-1.00006ptV}$. The software trigger includes more
sophisticated requirements and operations, in particular a multivariate
algorithm to identify secondary vertices Gligorov:2012qt .

The analyses use simulated events generated by Pythia 8.1 Sjostrand:2008  with
a specific LHCb configuration LHCb-PROC-2010-056 . Decays of hadronic
particles are described by EvtGen Lange:2001uf  in which final state radiation
is generated using Photos Golonka:2005pn . The interaction of the generated
particles with the detector and its response are implemented using the Geant4
toolkit Allison:2006ve ; *Agostinelli:2002hh as described in Ref. LHCb-
PROC-2011-006 .

Figure 1: Global view of the LHCb detector. Figure 2: LHCb data acquisition
chain for Run I data.

##  III Brief reminder on quark couplings

Because the eigenstates of the weak interaction are different from the mass
eigenstates, the Cabibbo-Kobayashi-Maskawa (CKM) matrix CKM1 ; CKM2  involves
couplings within and between quark generations:

$V_{CKM}=\left[\begin{array}[]{c c c}V_{ud}&V_{us}&V_{ub}\\\
V_{cd}&V_{cs}&V_{cb}\\\ V_{td}&V_{ts}&V_{tb}\end{array}\right]$ (1)

However, the magnitude of its elements is not evenly distributed: the modules
of the diagonal elements (within-generation couplings) are one while the
strength decreases as one departs from the diagonal. The weakest couplings are
thus between the first and third generation, namely $V_{td}$ and $V_{ub}$. The
unitarity condition, $V_{CKM}V_{CKM}^{\dagger}=\mathbf{1}$, imposes six
independent relations, of which two are of particular interest since one of
them the “${B}^{0}$ triangle”,
$V_{ud}V_{ub}^{*}+V_{cd}V_{cb}^{*}+V_{td}V_{tb}^{*}=0$, involves a sum of
elements of similar magnitude, and the second one,
$V_{us}V_{ub}^{*}+V_{cs}V_{cb}^{*}+V_{ts}V_{tb}^{*}=0$, although being a
unbalanced squeezed triangle, involves the angle intervening in the
${B}^{0}_{s}$ meson oscillations,
$\beta_{s}=-\mathrm{arg}\left(\frac{-V_{ts}V_{tb}^{*}}{V_{cs}V_{cb}^{*}}\right)$.

For the ${B}^{0}$ triangle, the angle
$\beta=\mathrm{arg}\left(\frac{-V_{cd}V_{cb}^{*}}{V_{td}V_{tb}^{*}}\right)$ is
now measured at a very high precision even with LHCb measurement alone LHCb-
PAPER-2015-004 . The angle
$\gamma=\mathrm{arg}\left(\frac{-V_{ud}V_{ub}^{*}}{V_{cd}V_{cb}^{*}}\right)$,
however is much less known and is the subject of an extensive program
involving $B\rightarrow DK$ decays LHCb-CONF-2014-004 . The module of the
element $V_{ub}$ intervening in the latter, can be probed through the study of
the semileptonic decays $b\rightarrow u~{}\ell^{-}\overline{\nu}$. Finally,
the sides $V_{ts}V_{tb}^{*}$ and $V_{td}V_{tb}^{*}$ are involved in rare $B$
decays through flavour changing neutral currents $b\rightarrow s,d$.

##  IV Rare $b\rightarrow(s,d)\ell^{+}\ell^{-}$ decays

$b\rightarrow(s,d)\ell^{+}\ell^{-}$ decays proceed in the Standard Model
through flavour changing neutral currents (FCNC) involving loop or box
diagrams as in Fig.3. However, their dynamics could well be affected by the
intervention of heavy virtual particles coming from a higher mass scale.

Figure 3: Flavour changing electroweak $b\rightarrow s,d$ (top) loop and
(bottom) box transitions.

LHCb has studied all of ${{B}^{0}}\rightarrow K^{*0}\mu^{+}\mu^{-}$ LHCb-
CONF-2015-002 , ${{B}^{0}_{s}}\rightarrow\phi\mu^{+}\mu^{-}$ LHCb-
PAPER-2015-023 , ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{\mathchar
28931\relax}\mu^{+}\mu^{-}$ LHCb-PAPER-2015-009 , for $b\rightarrow
s\mu^{+}\mu^{-}$, and ${{B}^{+}}\rightarrow{{\pi}^{+}}\mu^{+}\mu^{-}$ LHCb-
PAPER-2015-035 , for $b\rightarrow d\mu^{+}\mu^{-}$. A consistent mismatch
between data and Standard Model(SM)-based predictions at low
$q^{2}=m^{2}(\mu^{+}\mu^{-})$ is exhibited for several observables in
$b\rightarrow s\mu^{+}\mu^{-}$ decays. This the case for the decay
${{B}^{0}}\rightarrow K^{*0}\mu^{+}\mu^{-}$ for which the variable
$P_{5}^{\prime}=S_{5}/\sqrt{F_{L}(1-F_{L})}$, which combines the coefficient
$S_{5}$ of the angular distribution LHCb-CONF-2015-002  and the fraction of
$K^{*0}$ longitudinal polarization $F_{L}$, shows a 3.7$\sigma$ combined
discrepancy with the SM predictions in the region
$4<q^{2}<8{\mathrm{\,Ge\kern-1.00006ptV^{2}\\!/}c^{4}}$. For
${{B}^{0}_{s}}\rightarrow\phi\mu^{+}\mu^{-}$ and ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{\mathchar 28931\relax}\mu^{+}\mu^{-}$, the
mismatch is seen for the differential branching fraction $d\mathcal{B}/dq^{2}$
in the region $q^{2}<8{\mathrm{\,Ge\kern-1.00006ptV^{2}\\!/}c^{4}}$. All these
trends will be followed up with more statistics. For the time being, no sign
of deviation is observed in any of the observables for
${{B}^{+}}\rightarrow{{\pi}^{+}}\mu^{+}\mu^{-}$.

##  V Semileptonics

Semileptonic decays $b\rightarrow(c,u)\ell^{-}\overline{\nu}$ have the
advantage of providing an exact factorization between the weak part of the
decay $\ell^{-}\overline{\nu}$ and the hadronic $b\rightarrow(c,u)$ transition
involving form factors of the type $b$-hadron ($H_{b}$) $\rightarrow$ open-
charm ($H_{c}$) or light-quarks hadron ($H_{q}$), $F(H_{b}\rightarrow
H_{c,q})(q^{2})$, where $q^{2}=(\tilde{p}_{b}-\tilde{p}_{c,q})^{2}$. The two
parts are connected through a $W$ boson in the SM with an intervention of the
CKM elements $V_{cb}$ and $V_{ub}$.

$V_{cb}\sim 4\times 10^{-2}$ is known to a typical relative accuracy of 2%
while the precision on $V_{ub}\sim[3-4]\times 10^{-3}$ is not better than 12%
PDG2014_SL . Measuring $V_{ub}$ is thus interesting in itself. It becomes even
more attractive with the persistence of a 3$\sigma$ discrepancy between
measurements from inclusive $B\rightarrow X_{u}\ell\overline{\nu}$ and
exclusive $B\rightarrow\pi\ell\overline{\nu}$ decays, with
$(V_{ub})_{incl}>(V_{ub})_{excl}$. The pattern
$(V_{cb})_{incl}>(V_{cb})_{excl}$ is also observed, though not as significant.
One explanation that has been put forward VubTh  is the possible existence of
a right-handed current brought by extra operators generated by a TeV-scale new
physics. LHCb has investigated the baryonic equivalent of
$B\rightarrow\pi\mu\overline{\nu}$, ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{p}\mu\overline{\nu}$ LHCb-PAPER-2015-013 ,
using ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{\mathchar
28931\relax}^{+}_{c}}(\rightarrow pK\pi)\mu\overline{\nu}$ as a control
channel. As there is no access to the missing neutrino energy, $q^{2}$ is
inferred from the ${\mathchar 28931\relax}^{0}_{b}$ flight vector, the visible
momentum, with a ${\mathchar 28931\relax}^{0}_{b}$ mass constraint. The
discriminating variable is the corrected mass,
$M_{corr}=\sqrt{M_{vis}^{2}+p_{\perp}^{2}}+p_{\perp}$ where $p_{\perp}$ is
inferred from the flight vector and the visible momentum. $M_{vis}=M_{p\mu}$
for ${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{p}\mu\overline{\nu}$ and
$M_{vis}=M_{pK\pi\mu}$ for ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{\mathchar 28931\relax}^{+}_{c}}(\rightarrow
pK\pi)\mu\overline{\nu}$. The distribution of this variable is shown in Fig.4
for both channels.

Figure 4: Corrected mass distributions of the (top) ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{p}\mu\overline{\nu}$ and (bottom)
${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{\mathchar
28931\relax}^{+}_{c}}(\rightarrow pK\pi)\mu\overline{\nu}$ candidates, showing
contributions of the signals and backgrounds.

From the efficiency-corrected $q^{2}$-integrated yields and the use of
${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{p}$ and ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{\mathchar 28931\relax}^{+}_{c}}$ form
factors calculated with lattice QCD pmunuTh , one can infer
$|V_{ub}|/|V_{cb}|=0.083\pm 0.004(\mathrm{exp})\pm 0.004(\mathrm{lattice})$.
This gives finally: $|V_{ub}|=(3.27\pm 0.15(\mathrm{exp})\pm
0.16(\mathrm{lattice})\pm 0.06(|V_{cb}|))\times 10^{-3}$.

Any beyond-SM heavy charged particle replacing the $W$ in
$W\rightarrow\ell^{-}\overline{\nu}$ would preferably couple to a $\tau$
lepton. Therefore, by studying e.g. the ratio of $b\rightarrow
c\tau^{-}\overline{\nu}_{\tau}$ to $b\rightarrow
c\mu^{-}\overline{\nu}_{\mu}$, a deviation induced by new physics could be
probed. This is done in LHCb by measuring $R(D^{*})=\mathcal{B}(B\rightarrow
D^{*}\tau^{-}\overline{\nu}_{\tau})/\mathcal{B}(B\rightarrow
D^{*}\mu^{-}\overline{\nu}_{\mu})$ LHCb-PAPER-2015-025 . The $D^{*}$ is
reconstructed in the chain $D^{*+}\rightarrow D^{0}(\rightarrow
K\pi){{\pi}^{+}}$ while the $\tau$ is considered in the decay
$\tau^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}\nu_{\tau}$ to allow for the
same final visible particles for both $D^{*}\tau^{-}\overline{\nu}_{\tau}$ and
$D^{*}\mu^{-}\overline{\nu}_{\mu}$. Apart from the the variable $q$, the muon
energy and the invariant mass of the invisible part of the decay are used as
discriminating variables. The latter one is important to separate
$D^{*}\tau^{-}\overline{\nu}_{\tau}$ which has a big invisible mass from
$D^{*}\mu^{-}\overline{\nu}_{\mu}$ for which this quantity is much smaller as
can be seen in Fig.5.

Figure 5: Squared missing mass distributions for (blue) $B\rightarrow
D^{*}\mu^{-}\overline{\nu}_{\mu}$ and (red) $B\rightarrow
D^{*}\tau^{-}\overline{\nu}_{\tau}$ reconstructed events from simulation.

The fits to the two channels, accounting for the corrections to the detection
and reconstruction efficiencies, permit to extract their ratio as
$R(D^{*})=0.336\pm 0.027(\mathrm{stat})\pm 0.030(\mathrm{syst})$, which
confirms (+2.1$\sigma$) the trend observed in the past above the SM-based
predictions RDst_Th , as shown in Fig.6.

Figure 6: Comparison of results on $R(D^{*})$ between past and current
measurements, and SM-based expectations.

##  VI CKM $\gamma$ angle

The easiest way to extract the angle $\gamma$ is to use the interference of
tree favored $b\rightarrow c(\overline{u}s)$ ($A_{B}$) and suppressed
$b\rightarrow u(\overline{c}s)$ ($A_{B}r_{B}e^{i(\delta_{B}-\gamma)}$, $r_{B}$
is the suppression factor and $\delta_{B}$ is the relative strong phase)
decays leading to final states of the type $B\rightarrow DX_{s}$ where $D$ is
a charm meson and $X_{s}$ a strange system ($K$, $K^{*}$, $K\pi$,
$K\pi\pi\pi$, …). The charm meson decays to a final state accessible by both
$D$ and $\overline{D}$ through allowed ($A_{D}$) and suppressed
($A_{D}r_{D}e^{i\delta_{D}}$). Since more than two decades, several methods
have initially been proposed for $B\rightarrow DK$ GLW ; ADS ; GGSZ ; GLS  to
extract the angle for observables including charge asymmetries and combination
of branching fractions which definition may vary depending on the type of $D$
decay ($C\\!P$ eigenstate, flavour eigenstate, multibody). Beside the
generalization of the paradigm to more complex $X_{s}$ system, alternative
methods have been developped with other $B$ mesons, such as
$B^{0}_{s}\rightarrow D^{\mp}_{s}K^{\pm}$ LHCb-PAPER-2014-038 .

Over the last years, the LHCb collaboration has been combining several
$B\rightarrow DK$ modes to extract a value of
$\gamma=(72.9^{+9.2}_{-9.9})^{\circ}$ LHCb-CONF-2014-004 . For multibody $D$
decays, the variation of the strong phase $\delta_{D}$ across the decay phase
space engenders a dilution factor in the extraction of the $\gamma$ angle.
This effect can be unfolded by dedicated amplitude analyses of this type of
decays. As an illustration, LHCb used a recent determination of the $C\\!P$
content of $D^{0}\rightarrow{{\pi}^{+}}{{\pi}^{-}}{{\pi}^{0}}$ and
$D^{0}\rightarrow{{K}^{+}}{{K}^{-}}{{\pi}^{0}}$ based on CLEO-c data
cleoc_dhhpi0  to perform an extraction of $r_{B}$, $\gamma$ and $\delta_{B}$
in $B\rightarrow D(\rightarrow h^{+}h^{-}{{\pi}^{0}})K$ decays LHCb-
PAPER-2015-014 . The accuracy of the results is not yet at the level of giving
a substantial contribution to the combined fit.

The other recent study involves a $B\rightarrow DX_{s}$ decay, $B\rightarrow
D(\rightarrow hh)K\pi\pi$ LHCb-PAPER-2015-020 . The two observables used to
extract the relevant information are charge averages based on the decay rates,
$\mathcal{B}({{B}^{\pm}}\rightarrow D(\rightarrow hh)X_{s}^{\pm})\propto
1+r_{B}^{2}+2\kappa r_{B}\cos(\delta_{B}\pm\gamma)$, and the charge asymmetry
$\mathcal{A}({{B}^{\pm}}\rightarrow D(\rightarrow hh)X_{s}^{\pm})\propto
2\kappa r_{B}\sin\delta_{B}\sin\gamma$, where $\kappa$ is a dilution factor
due to the multibody nature of the decay $B\rightarrow DX_{s}$. From
simultaneous fits to the signals $B\rightarrow D(\rightarrow K\pi)X_{s}$,
$B\rightarrow D(\rightarrow\pi\pi)X_{s}$, $B\rightarrow D(\rightarrow
KK)X_{s}$, the value $\gamma=(74^{+20}_{-18})^{\circ}$ is obtained, in
agreement with the combined average.

##  VII New quark bound states

The idea of hadronic bound states having more than three valence quarks has
been envisaged since already half a century gellmann , with subsequent
quantitative work including tetraquark and pentaquark states jaffe ; strottman
; lipkin . On the experimental side, various past claims of pentaquark
observation have been shown to rely on unconvincing signals hicks . Recently
however, the resonant nature of the tetraquark candidate $Z(4430)^{-}$ seen in
the $\psi^{\prime}{{\pi}^{-}}$ invariant mass distribution, first advertised
by the Belle collaboration in $B\rightarrow K\psi^{\prime}\pi$ decays
belletetra1 ; belletetra2 , has been finally established by LHCb LHCb-
PAPER-2014-014 . The Argand diagram of the amplitude is shown in Fig.7.
Current independent studies aim at consolidating the result LHCb-
PAPER-2015-038 .

While studying the baryonic counterpart of the aforementioned decays, which
are ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{p}K$ decays, the LHCb collaboration achieved a significant
breakthrough in the path of proving the existence of a pentaquark resonance
LHCb-PAPER-2015-029 . The ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p}$
invariant mass spectrum exhibits a peculiar peak near
4.4${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ as shown in Fig.8. A full
amplitude analysis involving the squared invariant masses of the
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p}$ and $K{p}$ systems, and
five decay angles, has been performed to investigate the decay spectrum. The
best fit leads to the data being compatible with the existence of two
resonances $P_{c}^{+}(4380)$ and $P_{c}^{+}(4450)$ of masses $(4380\pm 8\pm
29,~{}4449.8\pm 1.7\pm 2.5$ ${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ and
widths $(205\pm 18\pm 86,~{}39\pm 5\pm 19$, respectively, and spin-parities
equal to $(3/2^{-},5/2^{+})$. The signal of the narrower resonance is stronger
as already shown in Fig.8 and less likely to be sensitive to fluctuation of
other amplitudes. This is reflected in the Argand diagrams of Fig.9.

Both $Z$ and $P_{c}$ are built on charmonium and are thus labeled as
charmonium-tetraquark and charmonium-pentaquark states. The exact dynamics and
structure of these states are still subject to intense modelings and
investigations.

Figure 7: Fitted value of the $Z(4430)^{-}$ amplitude in six
$m^{2}(\psi^{\prime}{{\pi}^{-}})$ bins (increasing counterclockwise). The red
curve shows the prediction from a Breit-Wigner formula with mass and width of
4475 and 172 ${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, respectively.

Figure 8: Invariant masses of (top) $Kp$ and (bottom)
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p}$ combinations for the
signal decays ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}{p}K$. The peaking structure above
4.4${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ in
$m({{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p})$ is clearly visible. The
complex $Kp$ pattern below 2.0${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ is
produced by combinations (and interferences) of $\Lambda$ resonances. Figure
9: Fitted value of the (a) $P_{c}^{+}(4450)$ and (b) $P_{c}^{+}(4380)$
amplitudes in $m^{2}({{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{p})$ bins
(increasing counterclockwise). The red curve shows the predictions from
relativistic Breit-Wigner formulaes with masses, widths and spins
corresponding to values found in the amplitude analysis (see text).

##  VIII Forward physics

Over the past few years, there has been a significative number of LHCb studies
involving $W$ or $Z$ bosons, jets and searches for displaced vertices of long-
lived heavy particles in the forward region LHCb-PAPER-2014-062 ; LHCb-
PAPER-2015-002 . Since the first publications on inclusive electroweak bosons
production LHCb-PAPER-2012-008 ; LHCb-PAPER-2014-033 , the collaboration has
been particularly active in improving the quality of the identification of
heavy-flavoured jets LHCb-PAPER-2015-016  with the idea of studying the boson-
jet associated production LHCb-PAPER-2015-021 .

The search for top production in the $W+b$-jet associations comes as a natural
follow-up of this effort. In reference LHCb-PAPER-2015-022 , the muon from the
$W\rightarrow\mu\nu$ decay is combined with a jet, with further multivariate
discrimination between $W+q$-jet ($q$ denotes light-quark jets), $W+c$-jet and
$W+b$-jet categories. The inclusive $W+j$-jet production is used as a control
channel, since it has very low background and the ratio
$\sigma(Wb)/\sigma(Wj)$ is predicted to a very good accuracy in the Standard
Model. Using the latter quantity also permits to benefit from the cancelling
of several experimental uncertainties. The yields are extracted by a fit to
the transverse momentum ratio
$\mbox{$p_{\mathrm{T}}$}(\mu)/\mbox{$p_{\mathrm{T}}$}(j_{\mu})$, where
$j_{\mu}$ denotes the jet clustered around the muon, including the muon. This
variable is particularly useful to reject dijet events. Figure 10 shows the
fit results for $W+b$ yield and charge asymmetry
$(N(W^{+}b)-N(W^{-}b))/(N(W^{+}b)+N(W^{-}b))$ in bins of
$\mbox{$p_{\mathrm{T}}$}(\mu+b)$: the data favours the existence of the top
production over pure $W+b$-jet production by a significance of 5.4$\sigma$,
which establishes the observation.

For what concerns Higgs physics, a limit on Higgs decays to $\tau^{+}\tau^{-}$
has already been set by LHCb with the 2011 data sample LHCb-PAPER-2013-009 .
However, the experimental improvements that permitted the aforementioned
results on $Wb$, $Wc$ and top identification have opened the door to exciting
studies on boson + dijet production in the forward region with the hope of
probing the boson + Higgs forward production.

Figure 10: Fit results for the (top) $W+b$ yield and (bottom) $W+b$ charge
asymmetry in bins of $\mbox{$p_{\mathrm{T}}$}(\mu+b)$, compared to NLO level
SM predictions.

##  IX Current data taking and prospects

Run II data taking has started early June 2015 at a center of mass energy of
13 TeV with a proton bunch spacing of 50 ns. Since early September, the 25 ns
bunch spacing is used and the current status of the integrated luminosity is
shown in Fig.11. The main difference in the data acquisition with Run I is the
online calibration and alignment performed at the High Level Trigger step, and
a larger output rate to storage (12.5 kHz). The 50 ns data sample has already
given birth to several validation plots and studies, with the first early
publication being on the ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$
production LHCb-PAPER-2015-037  based on an integrated luminosity of
3$\mbox{\,pb}^{-1}$. A fit to the $\mu\mu$ invariant mass and vertex lifetime
distributions is performed to extract the prompt and
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$-from-$b$-hadron components, in
bins of transverse momentum $p_{\mathrm{T}}$ and rapidity $y$. Figure 12
illustrates the fit results for one kinematical bin.

The cross-sections extracted in the LHCb acceptance are
$\sigma_{\mathrm{prompt}{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}}(\mbox{$p_{\mathrm{T}}$}<14{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},2.0<y<4.5)=15.30\pm
0.03\pm 0.86{\mathrm{\,\upmu b}}$ and
$\sigma_{{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}-\mathrm{from}-b}(\mbox{$p_{\mathrm{T}}$}<14{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},2.0<y<4.5)=2.34\pm
0.01\pm 0.13{\mathrm{\,\upmu b}}$, where the firt and second uncertainties are
statistical and systematic, respectively. Using the
$b\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}X$ branching
fraction PDG2014  and an acceptance extrapolating factor from Pythia
simulation, the total cross-section is obtained $\sigma(pp\rightarrow
b\overline{b}X)=515\pm 2\pm 53{\mathrm{\,\upmu b}}$.

For Run II, the benchmark scenario predicts an integrated luminosity of
$\approx$ 5-6 $\mbox{\,fb}^{-1}$ by 2018, which will more than double the Run
I sample, given the $b\overline{b}$ production cross-section scaling with
energy. This is will certainly allow to converge on a final word for all the
deviations seen for several observables in the rare $B$ decays. In the case
where beyond-SM physics does not show up directly, the indirect presence of
new physics would permit to estimate its energy scale through the size of its
contribution to low-energy effective hamiltonians. Besides, the higher center-
of-mass energy of Run II (and further data taking) enhances the capabilities
of multiple-jets detection in LHCb and thus improves in particular the
sensitivity to associated Higgs and electroweak bosons production.

Figure 11: Integrated luminosity as a function of time for the beginning of
Run II data taking.

Figure 12: $\mu\mu$ invariant mass (top) and pseudo-decay time (bottom) for
the bin $2<\mbox{$p_{\mathrm{T}}$}<3{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$,
$3.0<y<3.5$. The prompt component is shown in blue cross-hatched area while
the solid black line exhibits the ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}$ mesons coming from $b$-hadrons.

##  X Conclusion

The harvest of physics results for Run I data has permitted to drastically
improve the knowledge of the weak $C\\!P$ violation in the quark sector with
in particular measurements of the $\beta_{s}$ and $\gamma$ angles. From the
improvements on rare decays, it has also shed light on the size of possible
contributions of new heavy particles in loops, with the remarkable observation
of $B\rightarrow{\mu^{+}}\mu^{-}$LHCb-PAPER-2014-049 . The LHCb collaboration
has also shown the potential for interesting prospects for electroweak physics
in the forward region with the first observation of the top quark production.

The upgrade of years 2019-2020 111See dedicated presentation, these
proceedings

is aimed at preparing the detector for the high luminosity run, where about 50
$\mbox{\,fb}^{-1}$ of data are expected to be recorded, which will project the
collaboration into a new era of discoveries and precision tests for rare
decays, heavy hadrons, $C\\!P$ violation and forward physics.

## References

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