The nuclear modification factor
R
AA
and the azimuthal anisotropy coefficient
v
2
of prompt and nonprompt (i.e. those from decays of b hadrons)
J
/
ψ
mesons, measured from PbPb and pp collisions at
s
...NN
=
2.76
TeV
at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta
p
T
>
6.5
GeV
/
c
and rapidity
|
y
|
<
2.4
, extending down to
p
T
=
3
GeV
/
c
in the
1.6
<
|
y
|
<
2.4
range. The
v
2
of prompt
J
/
ψ
is found to be nonzero, but with no strong dependence on centrality, rapidity, or
p
T
over the full kinematic range studied. The measured
v
2
of nonprompt
J
/
ψ
is consistent with zero. The
R
AA
of prompt
J
/
ψ
exhibits a suppression that increases from peripheral to central collisions but does not vary strongly as a function of either
y
or
p
T
in the fiducial range. The nonprompt
J
/
ψ
R
AA
shows a suppression which becomes stronger as rapidity or
p
T
increases. The
v
2
and
R
AA
of open and hidden charm, and of open charm and beauty, are compared.
A search for standard model production of four top quarks (
t
t
¯
t
t
¯
) is reported using events containing at least three leptons (
e
,
μ
) or a same-sign lepton pair. The events are produced in ...proton–proton collisions at a center-of-mass energy of 13
TeV
at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9
fb
-
1
. Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant backgrounds. The observed and expected signal significances are, respectively, 1.6 and 1.0 standard deviations, and the
t
t
¯
t
t
¯
cross section is measured to be
16
.
9
-
11.4
+
13.8
fb
, in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling between the top quark and the Higgs boson to be less than 2.1 times its expected standard model value at 95% confidence level.
A
bstract
A search for a charged Higgs boson is performed with a data sample corresponding to an integrated luminosity of 19.7 ± 0.5 fb
−1
collected with the CMS detector in proton-proton collisions ...at
s
=
8
,TeV. The charged Higgs boson is searched for in top quark decays for
m
H
± <
m
t
−
m
b
, and in the direct production pp → t(b)H
±
for
m
H
± >
m
t
−
m
b
. The H
±
→
τ
±
ν
τ
and H
±
→ tb decay modes in the final states
τ
h
+jets,
μτ
h
,
ℓ
+jets, and
ℓℓ
’ (
ℓ
=e,
μ
) are considered in the search. No signal is observed and 95% confidence level upper limits are set on the charged Higgs boson production. A model-independent upper limit on the product branching fraction
ℬ
t
→
H
±
b
ℬ
H
±
→
τ
±
ν
τ
=
1.2
−
0.15
%
is obtained in the mass range
m
H
± = 80–160 GeV, while the upper limit on the cross section times branching fraction
σ
pp
→
t
b
H
±
ℬ
H
±
→
τ
±
ν
τ
=
0.38
−
0.025
pb is set in the mass range
m
H
+ = 180–600 GeV. Here,
σ
(pp → t(b)H
±
) stands for the cross section sum
σ
pp
→
t
¯
b
H
+
+
σ
pp
→
t
b
¯
H
−
. Assuming
ℬ
H
±
→
t
b
=
1
, an upper limit on
σ
(pp → t(b)H
±
) of 2.0–0.13 pb is set for
m
H
± = 180–600 GeV. The combination of all considered decay modes and final states is used to set exclusion limits in the
m
H
±−tan
β
parameter space in different MSSM benchmark scenarios.
A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton–proton collisions at s=13 TeV collected with the CMS detector. The ...integrated luminosity for the dielectron sample is 2.7 fb−1 and for the dimuon sample 2.9 fb−1. The sensitivity of the search is increased by combining these data with a previously analyzed set of data obtained at s=8 TeV and corresponding to a luminosity of 20 fb−1. No evidence for non-standard-model physics is found, either in the 13 TeV data set alone, or in the combined data set. Upper limits on the product of production cross section and branching fraction have also been calculated in a model-independent manner to enable interpretation in models predicting a narrow dielectron or dimuon resonance structure. Limits are set on the masses of hypothetical particles that could appear in new-physics scenarios. For the ZSSM′ particle, which arises in the sequential standard model, and for the superstring inspired Zψ′ particle, 95% confidence level lower mass limits for the combined data sets and combined channels are found to be 3.37 and 2.82 TeV, respectively. The corresponding limits for the lightest Kaluza–Klein graviton arising in the Randall–Sundrum model of extra dimensions with coupling parameters 0.01 and 0.10 are 1.46 and 3.11 TeV, respectively. These results significantly exceed the limits based on the 8 TeV LHC data.
The differential cross section and charge asymmetry for inclusive
p
p
→
W
±
+
X
→
μ
±
ν
+
X
production at
s
=
8
TeV
are measured as a function of muon pseudorapidity. The data sample corresponds to ...an integrated luminosity of 18.8
fb
-
1
recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable
x
from
10
-
3
to
10
-
1
.
The observation of the production of four top quarks in proton-proton collisions is reported, based on a data sample collected by the CMS experiment at a center-of-mass energy of 13 TeV in 2016–2018 ...at the CERN LHC and corresponding to an integrated luminosity of 138fb−1. Events with two same-sign, three, or four charged leptons (electrons and muons) and additional jets are analyzed. Compared to previous results in these channels, updated identification techniques for charged leptons and jets originating from the hadronization of b quarks, as well as a revised multivariate analysis strategy to distinguish the signal process from the main backgrounds, lead to an improved expected signal significance of 4.9 standard deviations above the background-only hypothesis. Four top quark production is observed with a significance of 5.6 standard deviations, and its cross section is measured to be 17.7−3.5+3.7(stat)−1.9+2.3(syst)fb, in agreement with the available standard model predictions.
Results are presented of a search for heavy particles decaying into two photons. The analysis is based on a 19.7fb−1 sample of proton–proton collisions at s=8TeV collected with the CMS detector at ...the CERN LHC. The diphoton mass spectrum from 150 to 850GeV is used to search for an excess of events over the background. The search is extended to new resonances with natural widths of up to 10% of the mass value. No evidence for new particle production is observed and limits at 95% confidence level on the production cross section times branching fraction to diphotons are determined. These limits are interpreted in terms of two-Higgs-doublet model parameters.
Normalized double-differential cross sections for top quark pair (
t
t
¯
) production are measured in pp collisions at a centre-of-mass energy of 8
TeV
with the CMS experiment at the LHC. The ...analyzed data correspond to an integrated luminosity of 19.7
fb
-
1
. The measurement is performed in the dilepton
e
±
μ
∓
final state. The
t
t
¯
cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and
t
t
¯
system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured
t
t
¯
cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.
A search for a new high-mass resonance decaying to a τ lepton and a neutrino is reported. The analysis uses proton-proton collision data collected by the CMS experiment at the LHC at s=13TeV, ...corresponding to an integrated luminosity of 35.9fb−1. The search utilizes hadronically decaying τ leptons. No excess in the event yield is observed at high transverse masses of the τ and missing transverse momentum. An interpretation of results within the sequential standard model excludes W′ boson masses below 4.0 TeV at 95% confidence level. Existing limits are also improved on models in which the W′ boson decays preferentially to fermions of the third generation. Heavy W′ bosons with masses less than 1.7–3.9 TeV, depending on the coupling in the non-universal G(221) model, are excluded at 95% confidence level. These are the most stringent limits on this model to date.
A
bstract
Pair production of Y(1S) mesons is observed at the LHC in proton-proton collisions at
s
=
8
TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb
...−1
. Both Y(1S) candidates are fully reconstructed via their decays to
μ
+
μ
−
. The fiducial acceptance region is defined by an absolute Y(1S) rapidity smaller than 2.0. The fiducial cross section for the production of Y(1S) pairs, assuming that both mesons decay isotropically, is measured to be 68.8±12.7 (stat)±7.4 (syst)±2.8 (
ℬ
) pb, where the third uncertainty comes from the uncertainty in the branching fraction of Y(1S) decays to
μ
+
μ
−
. Assuming instead that the Y(1S) mesons are produced with different polarizations leads to variations in the measured cross section in the range from −38% to +36%.
PDF
