# 54TH RENCONTRES DE MORIOND
QCD AND HIGH ENERGY INTERACTIONS
EXPERIMENTAL SUMMARY

Vincenzo M. Vagnoni  Istituto Nazionale di Fisica Nucleare, Sezione di
Bologna,
via Irnerio 46, 40126 Bologna, Italy

###### Abstract

The conference included about 90 talks covering a plethora of different
sectors, like Higgs physics, electroweak physics, top physics, BSM physics,
soft QCD, jets, PDFs, heavy ions, heavy flavours, spectroscopy, etc. A few
experimental results are here highlighted.

##  1 Introduction

The Standard Model of particle physics (SM) has been working beautifully, up
to a few hundred GeV so far, yet we know that it must be an effective theory
valid up to some energy scale. There are many compelling reasons to believe
that the SM in an incomplete theory; we can mention the hierarchy problem, the
lack of a dark matter candidate, the unification of gauge couplings, the need
for new sources of $C\\!P$ violation to explain the dynamical generation of
the baryon asymmetry in the universe, the reason for the existence of three
generations of quarks and leptons, the origins of mass and CKM hierarchies,
etc. The SM has proven to be very solid, well beyond any expectation, but we
have powerful tools to go on with the investigations. For example, despite
some operational issues, the LHC reached a performance record in 2018, with a
peak luminosity steadily at about $2\times 10^{34}\leavevmode\nobreak\
\mathrm{cm}^{-2}\mathrm{s}^{-2}$, that is two times larger then the design
value.

##  2 Higgs physics

Although it seems with us since ages, we have not to forget that the discovery
of the Higgs boson took place only seven years ago. Measurements of Higgs
properties with increasing precision are now a formidable tool to look for
new-physics manifestations. A framework for cross-section measurements with
reduced model dependence targeting Higgs production, namely simplified
template cross-sections (STXS), has been developed and deployed. Within this
framework, Higgs production is split into the main production modes and
further into fine-grain kinematic regions of phase space.

The associated production of $H\to b\bar{b}$ and $W$ or $Z$ bosons decaying
into leptons as a function of $p_{\mathrm{T}}(W/Z)$ with STXS has been
measured, using a data sample corresponding to $80\leavevmode\nobreak\
\mathrm{fb}^{-1}$ at 13 TeV [1]. Cross-sections are used to constrain
parameters in an effective Lagrangian framework. Another relevant measurement
is that of the Higgs coupling to the top quark using $H\to\gamma\gamma$
decays. A simultaneous fit in seven signal-enriched event categories is
performed, and $t\bar{t}H$ production is observed at $4.9\sigma$, using
$140\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of data at 13 TeV [2].

Several new measurements in the four-lepton final state have been performed.
All main production modes have been studied, _i.e._ $ggH$, vector-boson
fusion, associated production of gauge bosons and $t\bar{t}H$. There is little
sensitivity to $b\bar{b}H$ or $tH$, but these processes have been also
considered explicitly. Differential cross-sections have been measured as a
function of the Higgs $p_{\mathrm{T}}$ and $y$, the number of associated jets,
and the $p_{\mathrm{T}}$ of the leading associated jet, using
$137\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of data at 13 TeV [3]. The
distribution of the reconstructed four-lepton invariant mass with 2018 data is
shown in Fig. 1.

Figure 1: Distribution of the reconstructed four-lepton invariant mass with
2018 data [3].

With more and more statistics, searches for Higgs rare decays are becoming
increasingly important. Exclusive decays of the Higgs boson to mesons, such as
$H\to J/\psi J\psi$ or $\Upsilon\Upsilon$, recently measured using
$37.5\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [4], are interesting to
study Yukawa couplings to quarks and for beyond-the-SM (BSM) searches. New
physics could affect direct $Hq\bar{q}$ couplings or enter through loops, and
modify interference patterns between the various amplitudes. However, SM
predictions are very small and uncertain.

We have not yet found evidence for non-SM behaviour of the Higgs particle. But
the transition from observation to detailed measurements has only started, and
now also in the STXS framework with finer granularity to probe deviations from
the SM. Several new Higgs results have been presented at winter conferences,
many with partial Run-2 statistics and only a few with full Run-2 statistics.
Significant improvements with the full set of analyses and the full Run-2 data
set are anticipated.

##  3 Top physics

The LHC is also a powerful top factory. Top quarks are produced predominantly
in pairs, with $\sigma(t\bar{t})\simeq 0.8\leavevmode\nobreak\ \mathrm{nb}$ at
13 TeV. Single-top production via electroweak interactions is rarer, but
theoretically very clean. The top quark is the heaviest known fundamental
particle by far, with a mass of about 173 GeV. An interesting question is
whether the similarity in mass scale to $H$, $W$ and $Z$ is related to
electroweak symmetry breaking. Due to the short lifetime, order of
$10^{-25}\leavevmode\nobreak\ \mathrm{s}$, the top decays before
hadronisation. For this reason it provides a unique opportunity to study a
quasi-free quark. Furthermore, spin decorrelation time is much longer, and
then one can study spin correlation via decay products [5]. The top quark
decays almost exclusively to $Wb$ in the SM. Events are categorised by the
decays of the $W$ boson: all hadronic, lepton plus jets and di-lepton.

The mass of the Higgs at 125 GeV is close to the minimum value that ensures
absolute vacuum stability within the SM. Precise top-mass measurements are
very relevant, and several different techniques are adopted

  * •

ideogram method, measured with $35.9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at
13 TeV [6];

  * •

all-jets final state, $35.9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV
[7];

  * •

differential cross-section, $35.9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13
TeV [8];

  * •

inclusive cross-section, $35.9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV
[8].

Concerning associated production of $t\bar{t}$ pairs with $W$ and $Z$ bosons,
these are rare processes with cross-sections of about $1\leavevmode\nobreak\
\mathrm{pb}$ at 13 TeV. Such measurements are very useful to test QCD
predictions, as deviations might indicate the presence of new physics, like
vector-like quarks, strongly coupled Higgs bosons, exotic quarks with charge
$-4/3$ and anomalous dipole moments of the top quark. Several measurements
have been performed recently, _e.g._ by ATLAS with $36.1\leavevmode\nobreak\
\mathrm{fb^{-1}}$ at 13 TeV [9], and by CMS with $35.9\leavevmode\nobreak\
\mathrm{fb^{-1}}$ and $77.5\leavevmode\nobreak\ \mathrm{fb^{-1}}$ at 13 TeV
[10, 11]. Results are in line with NLO predictions. The CMS result on
$t\bar{t}Z$ has better precision than NLO, but resummed calculations are now
reaching NNLL+NLO accuracy.

An interesting search is that of four-top production. This is a very rare
process, with a cross-section of about $10\leavevmode\nobreak\ \mathrm{fb}$ at
13 TeV. Events are characterised by very large jets, b-jet multiplicities and
hadronic activity. The latest search by CMS is for same-sign di-lepton and
multi-lepton events using $137\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV
[12]. A multivariate analysis yields a significance of
$2.6\leavevmode\nobreak\ \sigma$ relative to the background-only hypothesis,
and a cross-section of $12.6^{5.8}_{-5.2}\leavevmode\nobreak\ \mathrm{fb}$.
The results are used to constrain the top Yukawa coupling with respect to the
SM value.

The top quark is also a tool to look directly for BSM physics. In FCNC
processes the top quark can couple to a light quark (up or charm) and a
neutral boson ($\gamma$, $Z$, $H$, $g$). These processes are forbidden at
tree-level in the SM, and not observable with present data unless new physics
is at play. Observation of FCNC would be indicative of new physics. A recent
measurement by ATLAS in $t\to uH$ and $t\to cH$, using
$36.1\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [13], did not find
evidence for these processes. Combining the search with other ATLAS searches
in di-photon and multi-lepton final states, at 95% C.L. one gets $BR(t\to
uH)<1.1\times 10^{-3}$ and $BR(t\to cH)<1.2\times 10^{-3}$. There is nothing
unexpected in exotic physics with top quarks yet, but the full Run-2 data set
has still to be analysed.

To conclude this section, a peculiar measurement of top production that is
also worth mentioning is that performed by LHCb, using
$1.9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [14]. The forward
acceptance of the LHCb detector allows measurements in a phase space
inaccessible to ATLAS and CMS. In this analysis, events containing a
high-$p_{\mathrm{T}}$ muon and electron of opposite charge in addition to a
high-$p_{\mathrm{T}}$ jet have been selected. No discrepancy from the SM
expectation has been found.

##  4 Electroweak physics

In the SM, three parameters define the electroweak sector, namely U(1) and
SU(2) couplings and vacuum expectation value. The electroweak sector of the SM
is over-constrained and the strength of global fits can be exploited to
predict key observables, such as the $W$ mass and the effective electroweak
mixing angle, with a precision exceeding that of direct measurements.

The $W$ mass is sensitive to the Higgs and top masses via radiative
corrections. The precise determination of the $W$ mass is of great importance
in testing the internal consistency of the SM. The global electroweak fit
yields the mass of the $W$ with an uncertainty of 8 MeV, to be compared with
the experimental precision of 15 MeV. Therefore there is the need to improve
the experimental uncertainty. The only $W$ mass measurement at the LHC to date
has been performed by ATLAS: $M_{W}=80370\pm 7\,(\mathrm{stat.})\pm
11\,(\mathrm{exp.syst.})\pm 14\,(\mathrm{mod.syst.})$ MeV. The dominating
uncertainty stems from theory. This lone ATLAS measurement competes with the
Tevatron combination. It is worth reminding that the measurement at the LHC is
affected by PDF uncertainties more than at the Tevatron.

In the SM, $ZZ$ production proceeds mainly through quark-antiquark $t$\- and
$u$-channel scattering diagrams. At higher orders in QCD also $gg$ fusion
contributes via box diagrams with quark loops. There has been a recent CMS
study of four-lepton production, $pp\to(Z/\gamma^{\ast})(Z/\gamma^{\ast})\to
4l$, where $l=e\leavevmode\nobreak\ \mathrm{or}\leavevmode\nobreak\ \mu$,
using $101\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [15]. By combining
with the 2016 results, the measured cross-section value is found to be
consistent with the SM prediction.

##  5 BSM searches

BSM searches are amongst the most important (and challenging) analyses at the
LHC. As first searches, BSM models predict new resonances decaying to a pair
of objects, _i.e._ two-body resonances like di-photons, di-leptons, di-bosons,
di-jets. When the multiplicity of the final states gets larger, or one goes
for exotic signatures like long-lived particles (LLPs), analyses become
increasingly more complex and model-dependent, requiring better understanding
of the underlying physics models being tested and of the detector response.
Many signatures have been probed already with full Run-2 statistics. First
analyses did not reveal evidence for new physics yet, but a lot of phase space
has still to be explored. In the following, a few examples of recent analyses
presented during the conference will be highlighted.

A recent search for new resonances decaying to electron and muon pairs has
been performed by ATLAS using $139\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of
data at 13 TeV [16]. The background fit with a parametric function exhibits an
excellent description of the di-lepton spectra up to several TeV. The
distributions of the di-electron and di-muon invariant masses are shown in
Fig. 2. No significant excess over the SM expectation is found. Cross-section
limits are set for generic resonances with a relative natural width between
zero and 10%.

Figure 2: Distributions of the (left) di-electron and (right) di-muon
invariant masses. Zero-width signal shapes, scaled to 20 times the value of
the corresponding expected upper limit at 95% CL on the fiducial cross-section
times branching ratio, are superimposed [16].

New heavy particles that decay to partons are predicted in many BSM models.
For example, excited quarks are predicted in compositeness models and are a
typical benchmark used in many di-jet searches. Partons shower and hadronise,
creating collimated jets. BSM phenomena may produce a di-jet signal up to
masses that are a significant fraction of the total collision energy. Two
recent searches for new resonances in the di-jet invariant mass by ATLAS (with
$139\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [17]) and CMS (with
$77.8\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [18]) show no
significant excess from the SM expectation. Moving to a more complex analysis,
with three or more electrons and muons in the final state, one looks for non-
resonant excesses in the tails of the sum of lepton $p_{\mathrm{T}}$ plus
missing transverse momentum (with $137\leavevmode\nobreak\ \mathrm{fb}^{-1}$
at 13 TeV [19]). Observed data are consistent with the SM expectation.

While the phase space for an easy discovery is reducing, growing interest is
emerging for new-physics searches with unconventional signatures, like
emerging jets, heavy charged LLPs, delayed jets, displaced jets, disappearing
tracks, displaced muons. A community white paper has been released recently
[20]. At low energy, a search for a spin-0 boson using prompt decays to
$\mu^{+}\mu^{-}$ has been performed by LHCb, with $3\leavevmode\nobreak\
\mathrm{fb}^{-1}$ of data at 7 and 8 TeV [21]. The LHCb detector has good
sensitivity to light spin-0 particles due to its high-precision spectrometer
and its capability of triggering on objects with small transverse momenta. No
evidence for a signal is observed and limits are placed.

In conclusion, BSM searches are very challenging as they look for corners and
tails of SM physics. The community working in the sector is continuously
developing new techniques and adding new models, phase-space regions and
correlations with SM backgrounds. Many results are anticipated to come out
soon with Run-2 statistics, while preparing for Run 3. The phase space has
been narrowed down for some models, but there are many others to study, and
the end of the searches is still very far to come.

##  6 (Some) hard and soft QCD processes

Genuine QCD measurements at the LHC are important for the good modelling of
hadronic collisions and obviously to test our understanding of QCD: probing
PDFs and NLO predictions; studying event topologies in interesting phase space
regions, _i.e._ multi-jet production, di-jet decorrelations, and very forward
region; studying jet substructure; understanding backgrounds for electroweak
analyses, BSM searches, etc.; studying multiple parton interactions, _e.g._
double parton scattering (DPS); etc. In addition, accurate knowledge is
crucial for the development of future projects, like ATLAS and CMS phase-2
upgrades. Several recent measurements have been performed by ATLAS and CMS,
the latter also using CASTOR to study very forward energy flow and jets.

A measurement of simultaneous Drell-Yan production with four leptons in the
final state has been performed using $20.2\leavevmode\nobreak\
\mathrm{fb}^{-1}$ of data at 8 TeV [22]. The process is particularly relevant
as a background in the Higgs analysis with four-lepton decays. A simplified
model for a DPS cross-section can be written as
$\sigma^{\mathrm{DPS}}_{\mathrm{AB}}\simeq\sigma_{\mathrm{A}}\sigma_{\mathrm{B}}/{\sigma_{\mathrm{eff}}}$,
where $\sigma_{\mathrm{eff}}$ is assumed to be process- and energy-
independent. No signal of DPS is observed. The upper limit on the fraction of
the DPS contribution to the inclusive four-lepton final state translates into
a lower limit of $1.0\leavevmode\nobreak\ \mathrm{mb}$ on the effective cross-
section.

Another DPS measurement has been performed by looking for same sign $WW$
production with $77\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of data at 13 TeV
[23]. This is an important channel to test DPS predictions. Both hard
scatterings lead to the production of a $W$ boson, and particularly
interesting is the final state with two same-charge $W$ bosons. The $W$ decay
provides a relatively clean signal, with well-understood background processes.
In particular, $WZ$ production constitutes the main background. A fit is
performed in different flavour-sign categories separately,
$\mu^{\pm}\mu^{\pm}$ and $e^{\pm}e^{\pm}$. This result represents the first
experimental evidence of the DPS $WW$ process.

Production of prompt photons in $pp\to\gamma X$ allows pQCD tests with a hard
colourless probe. The dominant production mechanism at the LHC is $qg\to
q\gamma$. The cross-section is sensitive to the gluon density in the proton.
An isolation cut is needed to reduce background from neutral-hadron decays and
from fragmentation where the emitted photon is close to a jet. An analysis of
$20.2\leavevmode\nobreak\ \mathrm{fb}^{-1}$ and $3.2\leavevmode\nobreak\
\mathrm{fb}^{-1}$ of data at 8 and 13 TeV has been performed [24]. The ratio
between cross-sections at 13 and 8 TeV is measured as a function of the energy
of the photon in different photon pseudorapidity ranges. Predictions using
several PDFs agree well with data.

##  7 Heavy ions

Hard probes are one of the pillars to study hot and dense QCD matter created
in heavy ion collisions. Perturbative processes take place before the QGP
forms, _e.g._ heavy-quark production. On the other hand, heavy quarks decay
weakly such that their lifetime is greater than that of the QGP and so they
experience the full system evolution. In addition, quarkonium states have
binding energies of the order of a few hundred MeV, and interactions with hard
gluons in a QGP can overcome this threshold breaking the quarkonium system.
The modification of the jet structures while traversing the hot medium is also
another relevant example (jet quenching).

The production of $J/\psi$ mesons at high $p_{\mathrm{T}}$ is strongly
suppressed in PbPb with respect to $pp$ collisions. The suppression increases
as a function of the centrality of the collision. Also strong $\Upsilon$
suppression is observed (see Fig. 3), and higher $\Upsilon$ states are even
more suppressed: $R_{AA}(\Upsilon(2S))/R_{AA}(\Upsilon(1S))=0.28\pm
0.12\,(\mathrm{stat.})\pm 0.06\,(\mathrm{syst.})$, as measured by ALICE [25].
Also CMS observes a similar spectacular behaviour. The $R_{AA}$ of the
$\Upsilon(3S)$ state is measured to be below 0.096 at 95% C.L. [26]. This is
the strongest suppression observed for a quarkonium state in heavy ion
collisions to date. By contrast, at low $p\mathrm{T}$, smaller $J/\psi$
suppression at the LHC than at RHIC is found, owing to measurements by ALICE,
PHENIX and STAR. New regenerated $J/\psi$ mesons are produced by recombination
of charm quarks, with larger regeneration occurring at higher $c\bar{c}$ pair
density and higher energy density.

Figure 3: Nuclear modification factor for $\Upsilon$ production as a function
of centrality [25].

The ratio of $\Lambda_{c}$ to $D^{0}$ production has been measured by ALICE in
$pp$, $p$Pb, and PbPb collisions [27]. A similar ratio in $pp$ and $p$Pb
collisions is found, whereas enhanced production of $\Lambda_{c}$ baryons with
respect to $D^{0}$ mesons is observed in PbPb collisions. The measurement is
still limited in precision, but appears to be intriguing. Also STAR seems to
observe a larger $\Lambda_{c}$ to $D^{0}$ ratio in AuAu collisions. In the
forward region, as a dedicated heavy-flavour experiment, LHCb has obvious
advantages in measuring $b$-hadron decays (at pPb event multiplicities).
Beauty hadrons are cleanly reconstructed in exclusive decay modes [28]. First
measurements in nuclear collisions are made down to very low $p_{\mathrm{T}}$
values. The $R_{p\mathrm{Pb}}$ suppression pattern seen in $J/\psi$ from $b$
is confirmed. LHCb can also inject gas into the beampipe to measure cross-
sections in fixed-target mode, see e.g. antiproton production in pHe [29] or
charm production in pAr and pHe [30] collisions.

ATLAS measured the flow of muons from heavy flavour decays in $pp$ and PbPb
collisions at 2.76 TeV [31]. The value of $R_{\mathrm{AA}}$ is found to be
less than unity, hence observing suppressed production of heavy-flavour muons
in PbPb collisions. In particular, for the 10% most central PbPb events,
$R_{\mathrm{AA}}$ is about 0.35. Furthermore, lower values of the elliptic
flow are found for particles with heavy quarks than with the lighter quarks.
This is a useful information for the analysis of quark interactions in the
medium. Charged hadron production in PbPb and XeXe collisions has been studied
at 5.02 and 5.44 TeV by ALICE. The production of (most of) light-flavour
hadrons in PbPb at 5.02 TeV is described by the thermal model. The differences
between protons and the strangeness sector are confirmed. Hydrodynamic
properties are studied with spectral shape and azimuthal anisotropy.
Hydrodynamics works at low $p_{\mathrm{T}}$ for central collisions, with the
agreement worsening towards peripheral collisions.

In recent years, momentum anisotropies have been measured in $pp$ and $p$A
collisions, despite expectations that the volume and lifetime of the medium
would be too small. PHENIX observed elliptic and triangular flow patterns in
$p$Au, $d$Au and 3HeAu collisions [32]. The three initial geometries and two
flow patterns provide powerful model discrimination. In the PHENIX analysis,
hydrodynamic models, based on the formation of short-lived QGP droplets,
provide the best simultaneous description of the measurements.

##  8 Heavy flavours

The present consistency of global CKM fits is displayed in Fig. 4.

Figure 4: Results of global CKM fits from (left) CKMfitter and (right) UTfit
groups.

Each coloured band defines the allowed region of the apex of the unitarity
triangle, according to the measurement of a specific process. Such a
consistency represents a tremendous success of the CKM paradigm in the SM: all
of the available measurements agree in a highly profound way. In presence of
BSM physics affecting the measurements, the various contours would not cross
each other into a single point. Hence the quark-flavour sector is generally
very well described by the CKM mechanism, and one must look for small
discrepancies.

In the charm sector, using $6\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV
[33], LHCb measured the difference $\Delta A_{C\\!P}$ of the $C\\!P$-violating
asymmetries in the decays $D^{0}\to K^{-}K^{+}$ and $D^{0}\to\pi^{-}\pi^{+}$.
To perform the measurement, the flavour of the $D^{0}$ meson is tagged either
by using the charge of the pion in $D^{\ast+}\to D^{0}\pi^{+}$ decays, or the
charge of the muon in $B\to D^{0}\mu\nu X$ decays. The invariant-mass
distributions are shown in Fig. 5. Run-2 results are well compatible with
previous LHCb results and the world average. The combination of Run-1 and
Run-2 data gives $\Delta A_{C\\!P}=(-15.4\pm 2.9)\times 10^{-4}$, resulting in
the first observation of $C\\!P$ violation in the charm sector, with a
significance of $5.3\sigma$. The result is roughly compatible with the SM,
whose prediction however is way more uncertain than data.

Figure 5: Mass distributions of selected (top) $\pi^{\pm}$-tagged and (bottom)
$\mu^{\pm}$-tagged candidates for (left) $K^{+}K^{-}$ and (right)
$\pi^{+}\pi^{-}$ final states of the $D^{0}$-meson decays, with fit
projections overlaid [33].

The golden mode $B^{0}_{s}\to J/\psi\phi$ is the $B^{0}_{s}$ analogue of
$B^{0}\to J/\psi K^{0}_{\mathrm{S}}$, and one measures the interference
between $B^{0}_{s}$ mixing and decay graphs through the phase-difference
$\phi_{s}$ between the two processes, precisely predicted in the SM to be
$\phi_{s}=-37.4\pm 0.7$ mrad. This is very small, but can receive sizeable
contributions from new physics. New measurements by ATLAS (with
$80.5\leavevmode\nobreak\ \mathrm{fb}^{-1}$ at 13 TeV [34]) using
$B^{0}_{s}\to J/\psi\phi$ and LHCb (with $1.9\leavevmode\nobreak\
\mathrm{fb}^{-1}$ at 13 TeV [35, 36]) using $B^{0}_{s}\to J/\psi\phi$ and
$B^{0}_{s}\to J/\psi\pi\pi$ decays have been performed. The combination of
Run-1 and Run-2 data gives $\phi_{s}=-0.076\pm 0.034\,(\mathrm{stat})\pm
0.019\,(\mathrm{syst})$ rad for ATLAS and $\phi_{s}=-0.040\pm
0.025\,(\mathrm{stat+syst})$ rad for LHCb. The new world average provided by
HFLAV is $\phi_{s}=-0.0544\pm 0.0205$ rad. The experimental precision is
quickly approaching the sensitivity to observe a nonzero SM value. For this
reason, the ATLAS and LHCb analyses with full Run-2 statistics and Run-2 CMS
results are now eagerly awaited.

Another recent measurement is that of the radiative decay
$B^{0}_{s}\to\phi\gamma$, performed by LHCb with $3\leavevmode\nobreak\
\mathrm{fb}^{-1}$ of data at 7 and 8 TeV [37]. The chiral structure of the $W$
boson leads to a photon polarisation mostly left-handed in the SM, with a
small right-handed component. New physics might significantly alter the
contribution of the right-handed component to the total amplitude. LHCb has
measured now for the first time direct and mixing-induced $C\\!P$ violation in
$B^{0}_{s}\to\phi\gamma$ decays, with values compatible with the SM, albeit
with large uncertainties.

Moving to rare $B$ decays, $B\to\mu^{+}\mu^{-}$ decays are FCNC- and helicity-
suppressed, proceeding via $Z$ penguin and $W$ box diagrams. The value of the
branching fraction is particularly sensitive to new-physics scalar
contributions, such as extra Higgs doublets. CMS and LHCb performed in 2015 a
combined fit to their full Run-1 data sets, observing the
$B^{0}_{s}\to\mu^{+}\mu^{-}$ decay for the first time at $6.2\sigma$ [38]. In
2016 ATLAS published with Run-1 data [39] and in 2017 LHCb performed the first
measurement using Run-2 data [40]. A new measurement by ATLAS, using
$26.3\leavevmode\nobreak\ \mathrm{fb}^{-}1$ at 13 TeV, has been published
recently [41]. By combining Run-1 and Run-2 results, the branching fractions
are found to be compatible with the SM at $2.4\sigma$. The analysis of 2016
and 2017 data by CMS is in preparation. In total, 433 $B^{0}_{s}$ and 54
$B^{0}$ candidates are expected with full Run-2 statistics.

The sector of lepton-flavour universality (LFU) tests has received great
attention during the last few years. Focusing on $b\to sl^{+}l^{-}$
transitions, one measure the ratios $R_{K}=\mathrm{BR}(B^{+}\to
K^{+}\mu^{+}\mu^{-})/\mathrm{BR}(B^{+}\to K^{+}e^{+}e^{-})$ and
$R_{K^{\ast}}=\mathrm{BR}(B^{0}\to K^{\ast
0}\mu^{+}\mu^{-})/\mathrm{BR}(B^{0}\to K^{\ast 0}e^{+}e^{-})$. The theoretical
predictions of such ratios are very clean, hence an observation of non-LFU
would be a clear sign of new physics. The measurements are presently at about
$3\sigma$ from the SM, complementing a range of other anomalies in $b\to
sl^{+}l^{-}$ transitions, namely branching fractions in various decays and the
angular analysis of $B\to K^{\ast}\mu\mu$ decays. A new measurement of $R_{K}$
has been performed by LHCb, adding $2\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of
Run-2 data to $3\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of Run-1 data [42]. The
statistics has been doubled with respect to the previous measurement, and the
result is $R_{K}=0.846^{+0.060+0.016}_{-0.054-0.014}$. In practice, the
significance of the discrepancy from the SM is unchanged after the new
measurement, as the uncertainty has been reduced but the central value has
moved closer to the SM. The outlook is to include also 2017 and 2018 data, for
further doubling the statistics, and to add more channels, first to measure
$R_{K^{\ast}}$ with full Run-2 statistics, but also to provide first
measurements with $B^{0}_{s}$ and $\Lambda_{b}$ channels.

LFU tests are also performed with semitauonic $B\to D^{(\ast)}\tau\nu$ decays.
Here one measures the ratios $R_{D^{(\ast)}}=\mathrm{BR}(B\to
D^{(\ast)}\tau\nu/\mathrm{BR}(B\to D^{(\ast)}\mu\nu$, sensitive to new physics
at tree level. Measurements of $R_{D}$ and $R_{D^{\ast}}$ have been performed
by BaBar, Belle and LHCb. The overall average shows a discrepancy from the SM
by about $3.8\sigma$. LHCb can also perform measurements with other $b$
hadrons: _e.g._ $B^{0}_{s}$, $B_{c}$ and $\Lambda_{b}$ decays will help better
understand the global picture. A new measurement from Belle has been performed
recently, reporting the most precise determination of $R(D)$ and $R(D^{\ast})$
to date, and in particular the first $R(D)$ measurement realised using the
semileptonic tag. The new results are compatible with the SM at $1.2\sigma$.
The $R(D)-R(D^{\ast})$ Belle average is now at $2\sigma$ from the SM
prediction, and the overall tension with the SM expectation decreases to about
$3.1\sigma$.

Concerning the upcoming future, Belle II has concluded successfully the
phase-2 pilot run. The basic detector performance is as good as expected, and
the nano-beam scheme of the collision point has been tested with encouraging
results. The target for phase 3 is to have a full physics run and collect
$20\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of luminosity by summer 2019. These
are crucial years to demonstrate the capability of the machine to provide the
required luminosity while keeping background under control.

##  9 Kaon physics

While waiting for the measurement of $\mathrm{BR}(K^{+}\to\pi^{+}\nu\nu)$,
NA62 performed a measurement using the kaon beam as a source of $\pi^{0}$s to
search for an invisible massive dark photon, $A^{\prime}$ [43]. No significant
excess is detected, using only 1% of the available statistics collected in
2016-2018. Upper limits are set at 90% C.L., compatible with fluctuations from
the background-only hypothesis. The analysis improves on previous limits over
the mass range 60–110 MeV/$c^{2}$.

Another new measurement in the kaon sector has been performed by NA48 with the
$K^{\pm}\to\pi^{\pm}\pi^{0}e^{+}e^{-}$ decay [44]. This is a rare decay
proceeding through virtual photon exchange. The first observation has been
achieved, and the branching fraction determined to be $(4.237\pm
0.063\,(\mathrm{stat.})\pm 0.033\,(\mathrm{syst.})\pm
0.126\,(\mathrm{ext.})\times 10^{-6}$. Several $C\\!P$-violating asymmetries
and a long-distance $P$-violating asymmetry have been measured and found to be
consistent with zero.

##  10 Muon magnetic anomaly

In the SM, the theoretical uncertainty on $a_{\mu}$ is dominated by hadron
vacuum polarisation and hadronic light-by-light scattering. E821 measured
$a_{\mu}$ with a precision of 550 ppb, observing a (statistically dominated)
discrepancy from the SM expectation at $3.7\sigma$. E989 is now taking data to
reduce the experimental uncertainty to 140 ppb. With such an experimental
precision, the reduction of the hadronic theoretical uncertainties will become
mandatory. The contribution of hadron vacuum polarisation to $a_{\mu}$ is
calculated through a dispersion relation using the experimental information on
the cross-section $\sigma(e^{+}e^{-})\to\mathrm{hadrons}$, as the relevant
energy scale is too low for applying perturbative QCD. A reduction of about
20% in the uncertainty has been achieved since 2013, mostly owing to results
from BaBar and VEPP-2000. By contrast, the hadronic light-by-light scattering
contribution remains as an open issue, and can be determined with lattice QCD
calculations or via further experimental measurements like the proposed MUonE,
which aims at measuring the elastic reaction $\mu e\to\mu e$ to constrain
$a_{\mu}^{\mathrm{HLO}}$ from data. Additional physics motivations for light-
resonance spectroscopy are the study of hadronic decays of charmonium, via
$e^{+}e^{-}\to\gamma\psi(\to\mathrm{hadrons})$, the study of other hadronic
resonances, searches for dark-photon decays, etc.

##  11 Spectroscopy

A renaissance of QCD in the non-perturbative regime has been taking place
during the last decade. A recent measurement with the observation of excited
$B_{c}$ mesons has been performed by CMS, using $140\leavevmode\nobreak\
\mathrm{fb}^{-1}$ of data at 13 TeV [45]. Two excited $B_{c}$ states have been
observed in the $B_{c}\pi\pi$ final state, with $B_{c}\to J/\psi(\mu\mu)\pi$
(see Fig. 6). The result has been also confirmed by LHCb, with an analysis on
$8.5\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of data at 7, 8 and 13 TeV [46].

Figure 6: Invariant $B_{c}\pi\pi$ mass showing two peaks of excited $B_{c}$
states [45].

Figure 7: Invariant $J/\psi p$ mass with the three pentaquark states observed
by LHCb [49].

One of the most active experiments in spectroscopy measurements with charm
quarks is BESIII. BESIII is a dedicated $e^{+}e^{-}$ open charm and charmonium
factory at BEPC. A plethora of spectroscopy measurements have been performed
through the years, notably including tetraquark states. For example, the
observation of $X(3872)\to\omega J/\psi$ has been recently reported [47].
Furthermore, the cross-section measurement of $\gamma X(3872)$ suggests a
connection between $X(3872)$ and $Y(4260)$. BESIII is also very active in
searching for and studying glueball candidates.

Also LHCb is extremely active, with novel spectroscopy measurements being
performed at an impressive rate. LHCb has observed recently a new state,
likely to be $\psi(1^{3}D_{3})$, _i.e._ achieving the first observation of a
spin-3 charmonium state [48]. LHCb has also got relevant news on pentaquarks.
First pentaquarks were observed by LHCb four years ago using $\Lambda_{b}\to
J/\psi pK$ decays as a proxy. Two charged states were determined: one narrow,
dubbed $P_{c}(4450)$, and one broader, dubbed $P_{c}(4380)$, both decaying
into $J/\psi p$. The measurement triggered great theoretical interest to
understand the nature of the new resonances, _i.e._ whether they are tightly
bound or molecular states. LHCb has now updated the same pentaquark analysis
using $9\leavevmode\nobreak\ \mathrm{fb}^{-1}$ of data at 7, 8 and 13 TeV
[49]. The overall statistics has increased by a factor nine with respect to
the the Run-1 analysis. Only a narrow bump-hunting analysis with empirical
background shape has been performed so far. As shown in Fig. 7, the previously
found $P_{c}(4450)$ reveals a finer structure with two close peaks, and a new
peak is found at 4312 MeV. This constitutes an important novel input to shed
light into the nature of pentaquarks. A full amplitude analysis is ongoing,
especially needed to confirm the $P_{c}(4380)$ state.

##  12 Conclusions

Despite the formidable attempts performed so far by high-energy physics
experiments, the Standard Model of particle physics still proves to be
unbreakable. In the current state of fundamental physics, it is of paramount
importance to maintain and further develop a diversified programme, ranging
from the high-energy frontier to the intensity frontier, from astrophysics and
cosmology to dark matter detection. We know that the Standard Model will
capitulate in the end, the only question is when and how. Meanwhile, long live
Rencontres de Moriond!

## Acknowledgments

I wish to express my cordial thanks to the organisers of the conference for
the kind invitation and for the pleasant environment.

## References

## References

  * [1] M. Aaboud et al. [ATLAS Collaboration], “Measurement of $VH$, $H\to b\bar{b}$ production as a function of the vector-boson transverse momentum in 13 TeV $pp$ collisions with the ATLAS detector”, JHEP 1905 (2019) 141, arXiv:1903.04618 [hep-ex].
  * [2] [ATLAS Collaboration], “Measurement of Higgs boson production in association with a $t\overline{t}$ pair in the diphoton decay channel using 139 fb-1 of LHC data collected at $\sqrt{s}=13$ TeV by the ATLAS experiment”, ATLAS-CONF-2019-004.
  * [3] [CMS Collaboration], “Measurements of properties of the Higgs boson in the four-lepton final state in proton-proton collisions at $\sqrt{s}=13\leavevmode\nobreak\ \mathrm{TeV}$”, CMS-PAS-HIG-19-001.
  * [4] [CMS Collaboration], “Search for Higgs and $Z$ boson decays to $J/\psi$ or $\Upsilon$ pairs in proton-proton collisions at $\sqrt{s}=13\leavevmode\nobreak\ \mathrm{TeV}$”, CMS-PAS-HIG-18-025.
  * [5] M. Aaboud et al. [ATLAS Collaboration], “Measurements of top-quark pair spin correlations in the $e\mu$ channel at $\sqrt{s}=13$ TeV using $pp$ collisions in the ATLAS detector”, arXiv:1903.07570 [hep-ex].
  * [6] A. M. Sirunyan et al. [CMS Collaboration], “Measurement of the top quark mass with lepton+jets final states using $pp$ collisions at $\sqrt{s}=13$ TeV”, Eur. Phys. J. C 78 (2018) 891, arXiv:1805.01428 [hep-ex].
  * [7] A. M. Sirunyan et al. [CMS Collaboration], “Measurement of the top quark mass in the all-jets final state at $\sqrt{s}=$ 13 TeV and combination with the lepton+jets channel”, Eur. Phys. J. C 79 (2019) 313, arXiv:1812.10534 [hep-ex].
  * [8] A. M. Sirunyan et al. [CMS Collaboration], “Measurement of the $\mathrm{t}\overline{\mathrm{t}}$ production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at $\sqrt{s}=$ 13 TeV”, Eur. Phys. J. C 79 (2019) 368, arXiv:1812.10505 [hep-ex].
  * [9] M. Aaboud et al. [ATLAS Collaboration], “Measurement of the $t\bar{t}Z$ and $t\bar{t}W$ cross sections in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector”, Phys. Rev. D 99 (2019) 072009, arXiv:1901.03584 [hep-ex].
  * [10] A. M. Sirunyan et al. [CMS Collaboration], “Measurement of the cross section for top quark pair production in association with a W or Z boson in proton-proton collisions at $\sqrt{s}=$ 13 TeV”, JHEP 1808 (2018) 011, arXiv:1711.02547 [hep-ex].
  * [11] [CMS Collaboration], “Measurement of top quark pair production in association with a Z boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV”, CMS-PAS-TOP-18-009.
  * [12] [CMS Collaboration], “Search for standard model production of four top quarks in final states with same-sign and multiple leptons in proton-proton collisions at $\sqrt{s}=13\leavevmode\nobreak\ \mathrm{TeV}$”, CMS-PAS-TOP-18-003.
  * [13] M. Aaboud et al. [ATLAS Collaboration], “Search for top-quark decays $t\to Hq$ with 36 fb-1 of $pp$ collision data at $\sqrt{s}=13$ TeV with the ATLAS detector”, JHEP 05 (2019) 123, arXiv:1812.11568 [hep-ex].
  * [14] R. Aaij et al. [LHCb Collaboration], “Measurement of forward top pair production in the dilepton channel in $pp$ collisions at $\sqrt{s}=13$ TeV”, JHEP 08 (2018) 174, arXiv:1803.05188 [hep-ex].
  * [15] [CMS Collaboration], “Measurement of the $\textrm{pp}\rightarrow\textrm{Z}\textrm{Z}$ production cross section at $\sqrt{s}=13$ TeV with the Run 2 data set”, CMS-PAS-SMP-19-001.
  * [16] G. Aad et al. [ATLAS Collaboration], “Search for high-mass dilepton resonances using 139 fb-1 of $pp$ collision data collected at $\sqrt{s}=$13 TeV with the ATLAS detector”, arXiv:1903.06248 [hep-ex].
  * [17] [ATLAS Collaboration], “Search for New Phenomena in Dijet Events using 139 fb−1 of $pp$ collisions at $\sqrt{s}$ = 13TeV collected with the ATLAS Detector”, ATLAS-CONF-2019-007.
  * [18] [CMS Collaboration], “Searches for dijet resonances in pp collisions at $\sqrt{s}=13\leavevmode\nobreak\ \mathrm{TeV}$ using the 2016 and 2017 datasets”, CMS-PAS-EXO-17-026.
  * [19] [CMS Collaboration], “Search for new physics in multilepton final states in pp collisions at $\sqrt{s}=13\leavevmode\nobreak\ \mathrm{TeV}$”, CMS-PAS-EXO-19-002.
  * [20] J. Alimena et al., “Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider”, arXiv:1903.04497 [hep-ex].
  * [21] R. Aaij et al. [LHCb Collaboration], “Search for a dimuon resonance in the $\Upsilon$ mass region”, JHEP 09 (2018) 147, arXiv:1805.09820 [hep-ex].
  * [22] M. Aaboud et al. [ATLAS Collaboration], “Study of the hard double-parton scattering contribution to inclusive four-lepton production in $pp$ collisions at $\sqrt{s}=$ 8 TeV with the ATLAS detector”, Phys. Lett. B 790 (2019) 595, arXiv:1811.11094 [hep-ex].
  * [23] [CMS Collaboration], “Evidence for WW production from double-parton interactions in proton-proton collisions at $\sqrt{s}$ = 13 TeV”, CMS-PAS-SMP-18-015.
  * [24] M. Aaboud et al. [ATLAS Collaboration], “Measurement of the ratio of cross sections for inclusive isolated-photon production in $pp$ collisions at $\sqrt{s}=13$ and $8$ TeV with the ATLAS detector”, JHEP 1904 (2019) 093, arXiv:1901.10075 [hep-ex].
  * [25] S. Acharya et al. [ALICE Collaboration], “$\Upsilon$ suppression at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV”, Phys. Lett. B 790 (2019) 89, arXiv:1805.04387 [nucl-ex].
  * [26] A. M. Sirunyan et al. [CMS Collaboration], “Measurement of nuclear modification factors of $\Upsilon$(1S), $\Upsilon$(2S), and $\Upsilon$(3S) mesons in PbPb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=$ 5.02 TeV”, Phys. Lett. B 790 (2019) 270, arXiv:1805.09215 [hep-ex].
  * [27] S. Acharya et al. [ALICE Collaboration], “$\Lambda_{\mathrm{c}}^{+}$ production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV”, Phys. Lett. B 793 (2019) 212, arXiv:1809.10922 [nucl-ex].
  * [28] R. Aaij et al. [LHCb Collaboration], “Measurement of $B^{+}$, $B^{0}$ and $\Lambda_{b}^{0}$ production in $p\mkern 1.0mu\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=8.16\,{\rm TeV}$”, Phys. Rev. D 99 (2019) 052011, arXiv:1902.05599 [hep-ex].
  * [29] R. Aaij et al. [LHCb Collaboration], “Measurement of Antiproton Production in ${\rm pHe}$ Collisions at $\sqrt{s_{NN}}=110$ GeV”, Phys. Rev. Lett. 121 (2018) 222001, arXiv:1808.06127 [hep-ex].
  * [30] R. Aaij et al. [LHCb Collaboration], “First Measurement of Charm Production in its Fixed-Target Configuration at the LHC”, Phys. Rev. Lett. 122 (2019) 132002, arXiv:1810.07907 [hep-ex].
  * [31] M. Aaboud et al. [ATLAS Collaboration], “Measurement of the suppression and azimuthal anisotropy of muons from heavy-flavor decays in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS detector”, Phys. Rev. C 98 (2018) 044905, arXiv:1805.05220 [nucl-ex].
  * [32] C. Aidala et al. [PHENIX Collaboration], “Creation of quark–gluon plasma droplets with three distinct geometries”, Nature Phys. 15 (2019) 214, arXiv:1805.02973 [nucl-ex].
  * [33] R. Aaij et al. [LHCb Collaboration], “Observation of $C\\!P$ violation in charm decays”, Phys. Rev. Lett. 122 (2019) 211803, arXiv:1903.08726 [hep-ex].
  * [34] [ATLAS Collaboration], “Measurement of the CP violation phase $\phi_{s}$ in $B_{s}\to J/\psi\phi$ decays in ATLAS at 13 TeV”, ATLAS-CONF-2019-009.
  * [35] R. Aaij et al. [LHCb Collaboration], “Search for lepton-universality violation in $B^{+}\to K^{+}\ell^{+}\ell^{-}$ decays”, Phys. Rev. Lett. 122 (2019) 191801, arXiv:1903.09252 [hep-ex].
  * [36] R. Aaij et al. [LHCb Collaboration], “Measurement of the $CP$-violating phase $\phi_{s}$ from $B_{s}^{0}\to J/\psi\pi^{+}\pi^{-}$ decays in 13 TeV $pp$ collisions”, arXiv:1903.05530 [hep-ex].
  * [37] R. Aaij et al. [LHCb Collaboration], “Measurement of $CP$-violating and mixing-induced observables in $B_{s}^{0}\to\phi\gamma$ decays”, arXiv:1905.06284 [hep-ex].
  * [38] V. Khachatryan et al. [CMS and LHCb Collaborations], “Observation of the rare $B^{0}_{s}\to\mu^{+}\mu^{-}$ decay from the combined analysis of CMS and LHCb data”, Nature 522 (2015) 68, arXiv:1411.4413 [hep-ex].
  * [39] M. Aaboud et al. [ATLAS Collaboration], “Study of the rare decays of $B^{0}_{s}$ and $B^{0}$ into muon pairs from data collected during the LHC Run 1 with the ATLAS detector”, Eur. Phys. J. C 76 (2016) 513, arXiv:1604.04263 [hep-ex].
  * [40] R. Aaij et al. [LHCb Collaboration], “Measurement of the $B^{0}_{s}\to\mu^{+}\mu^{-}$ branching fraction and effective lifetime and search for $B^{0}\to\mu^{+}\mu^{-}$ decays”, Phys. Rev. Lett. 118 (2017) 191801, arXiv:1703.05747 [hep-ex].
  * [41] M. Aaboud et al. [ATLAS Collaboration], “Study of the rare decays of $B^{0}_{s}$ and $B^{0}$ mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector”, JHEP 1904 (2019) 098, arXiv:1812.03017 [hep-ex].
  * [42] R. Aaij et al. [LHCb Collaboration], “Search for lepton-universality violation in $B^{+}\to K^{+}\ell^{+}\ell^{-}$ decays”, Phys. Rev. Lett. 122 (2019) 191801, arXiv:1903.09252 [hep-ex].
  * [43] E. Cortina Gil et al. [NA62 Collaboration], “Search for production of an invisible dark photon in $\pi^{0}$ decays”, arXiv:1903.08767 [hep-ex].
  * [44] J. R. Batley et al. [NA48/2 Collaboration], “First observation and study of the $K^{\pm}\to\pi^{\pm}\pi^{0}e^{+}e^{-}$ decay”, Phys. Lett. B 788 (2019) 552, arXiv:1809.02873 [hep-ex].
  * [45] A. M. Sirunyan et al. [CMS Collaboration], “Observation of Two Excited B${}^{+}_{\mathrm{c}}$ States and Measurement of the B${}^{+}_{\mathrm{c}}$(2S) Mass in pp Collisions at $\sqrt{s}=$ 13 TeV”, Phys. Rev. Lett. 122 (2019) 132001, arXiv:1902.00571 [hep-ex].
  * [46] R. Aaij et al. [LHCb Collaboration], “Observation of an excited $B_{c}^{+}$ state”, arXiv:1904.00081 [hep-ex].
  * [47] M. Ablikim et al. [BESIII Collaboration], “Study of $e^{+}e^{-}\to\gamma\omega J/\psi$ and Observation of $X(3872)\to\omega J/\psi$”, arXiv:1903.04695 [hep-ex].
  * [48] R. Aaij et al. [LHCb Collaboration], “Near-threshold $D\bar{D}$ spectroscopy and observation of a new charmonium state”, arXiv:1903.12240 [hep-ex].
  * [49] R. Aaij et al. [LHCb Collaboration], “Observation of a narrow pentaquark state, $P_{c}(4312)^{+}$, and of two-peak structure of the $P_{c}(4450)^{+}$”, arXiv:1904.03947 [hep-ex].