A
bstract
A search for phenomena beyond the standard model in final states with two oppositely charged same-flavor leptons and missing transverse momentum is presented. The search uses a data sample ...of proton-proton collisions at
s
= 13 TeV, corresponding to an integrated luminosity of 137 fb
−
1
, collected by the CMS experiment at the LHC. Three potential signatures of physics beyond the standard model are explored: an excess of events with a lepton pair, whose invariant mass is consistent with the Z boson mass; a kinematic edge in the invariant mass distribution of the lepton pair; and the nonresonant production of two leptons. The observed event yields are consistent with those expected from standard model backgrounds. The results of the first search allow the exclusion of gluino masses up to 1870 GeV, as well as chargino (neutralino) masses up to 750 (800) GeV, while those of the searches for the other two signatures allow the exclusion of light-flavor (bottom) squark masses up to 1800 (1600) GeV and slepton masses up to 700 GeV, respectively, at 95% confidence level within certain supersymmetry scenarios.
The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013–2014 in preparation for running at higher LHC collision energy and ...instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy s=13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously. We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.
A
bstract
A search is presented for additional neutral Higgs bosons in the
τ τ
final state in proton-proton collisions at the LHC. The search is performed in the context of the minimal supersymmetric ...extension of the standard model (MSSM), using the data collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb
−1
. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes production of the Higgs boson in association with b quarks. No significant deviation above the expected background is observed. Model-independent limits at 95% confidence level (CL) are set on the product of the branching fraction for the decay into τ leptons and the cross section for the production via gluon fusion or in association with b quarks. These limits range from 18 pb at 90 GeV to 3.5 fb at 3.2 TeV for gluon fusion and from 15 pb (at 90 GeV) to 2.5 fb (at 3.2 TeV) for production in association with b quarks, assuming a narrow width resonance. In the
m
h
hod +
scenario these limits translate into a 95% CL exclusion of tan
β >
6 for neutral Higgs boson masses below 250 GeV, where tan
β
is the ratio of the vacuum expectation values of the neutral components of the two Higgs doublets. The 95% CL exclusion contour reaches 1.6 TeV for tan
β
= 60.
The standard model (SM) production of four top quarks (
t
t
¯
t
t
¯
) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of ...the LHC, corresponds to an integrated luminosity of 137
fb
-
1
at a center-of-mass energy of 13
TeV
. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the
t
t
¯
t
t
¯
signal are respectively 2.6 and 2.7 standard deviations, and the
t
t
¯
t
t
¯
cross section is measured to be
12
.
6
-
5.2
+
5.8
fb
. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson,
y
t
, yielding a limit of
|
y
t
/
y
t
SM
|
<
1.7
at
95
%
confidence level, where
y
t
SM
is the SM value of
y
t
. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework,
H
^
<
0.12
. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470
GeV
and 350–550
GeV
for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
Results are presented from a search for the direct electroweak production of charginos and neutralinos in signatures with either two or more leptons (electrons or muons) of the same ...electric charge, or with three or more leptons, which can include up to two hadronically decaying tau leptons. The results are based on a sample of proton-proton collision data collected at
s
=
13
TeV, recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb
−1
. The observed event yields are consistent with the expectations based on the standard model. The results are interpreted in simplified models of supersymmetry describing various scenarios for the production and decay of charginos and neutralinos. Depending on the model parameters chosen, mass values between 180 GeV and 1150 GeV are excluded at 95% CL. These results significantly extend the parameter space probed for these particles in searches at the LHC. In addition, results are presented in a form suitable for alternative theoretical interpretations.
A
bstract
The spectra of charged particles produced within the pseudorapidity window |
η
| < 1 at
s
N
N
=
5.02
TeV are measured using 404
μ
b
−1
of PbPb and 27.4 pb
−1
of pp data collected by the CMS ...detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0
.
5
< p
T
<
400 GeV in pp and 0
.
7
< p
T
<
400 GeV in PbPb collisions. The corresponding nuclear modification factor,
R
AA
, is measured in bins of collision centrality. The
R
AA
in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the
p
T
region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest
p
T
measured, and approaches unity in the vicinity of
p
T
= 200 GeV. The
R
AA
is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor,
R
pA
, up to 120 GeV. For
p
T
>
20 GeV,
R
pA
exhibits weak momentum dependence and shows a moderate enhancement above unity.
A
bstract
Measurements of Higgs boson properties in the H →
γγ
decay channel are reported. The analysis is based on data collected by the CMS experiment in proton-proton collisions at
s
=
13
TeV ...during the 2016 LHC running period, corresponding to an integrated luminosity of 35.9 fb
−1
. Allowing the Higgs mass to float, the measurement yields a signal strength relative to the standard model prediction of 1.18
− 0.14
+ 0.17
= 1.18
− 0.11
+ 0.12
(stat)
− 0.07
+ 0.09
(syst)
− 0.06
+ 0.07
(theo), which is largely insensitive to the exact Higgs mass around 125 GeV. Signal strengths associated with the different Higgs boson production mechanisms, couplings to bosons and fermions, and effective couplings to photons and gluons are also measured.
A
bstract
Measurements are presented of the differential cross sections for Z bosons produced in proton-proton collisions at
s
= 13 TeV and decaying to muons and electrons. The data analyzed were ...collected in 2016 with the CMS detector at the LHC and correspond to an integrated luminosity of 35
.
9 fb
−
1
. The measured fiducial inclusive product of cross section and branching fraction agrees with next-to-next-to-leading order quantum chromodynamics calculations. Differential cross sections of the transverse momentum
p
T
, the optimized angular variable
ϕ
η
∗
, and the rapidity of lepton pairs are measured. The data are corrected for detector effects and compared to theoretical predictions using fixed order, resummed, and parton shower calculations. The uncertainties of the measured normalized cross sections are smaller than 0.5% for
ϕ
η
∗
<
0
.
5 and for
p
T
Z
<
50 GeV.
A search for dark matter particles is performed using events with a Z boson candidate and large missing transverse momentum. The analysis is based on proton–proton collision data at a center-of-mass ...energy of 13
Te
, collected by the CMS experiment at the LHC in 2016–2018, corresponding to an integrated luminosity of 137
fb
-
1
. The search uses the decay channels
Z
→
e
e
and
Z
→
μ
μ
. No significant excess of events is observed over the background expected from the standard model. Limits are set on dark matter particle production in the context of simplified models with vector, axial-vector, scalar, and pseudoscalar mediators, as well as on a two-Higgs-doublet model with an additional pseudoscalar mediator. In addition, limits are provided for spin-dependent and spin-independent scattering cross sections and are compared to those from direct-detection experiments. The results are also interpreted in the context of models of invisible Higgs boson decays, unparticles, and large extra dimensions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
A search is presented for new high-mass resonances decaying into electron or muon pairs. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ...CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 36 fb
−1
. Observations are in agreement with standard model expectations. Upper limits on the product of a new resonance production cross section and branching fraction to dileptons are calculated in a model-independent manner. This permits the interpretation of the limits in models predicting a narrow dielectron or dimuon resonance. A scan of different intrinsic width hypotheses is performed. Limits are set on the masses of various hypothetical particles. For the
Z
S
S
M
′
Z
ψ
′
particle, which arises in the sequential standard model (superstring-inspired model), a lower mass limit of 4.50 (3.90) TeV is set at 95% confidence level. The lightest Kaluza-Klein graviton arising in the Randall-Sundrum model of extra dimensions, with coupling parameters
k
/
M
Pl
of 0.01, 0.05, and 0.10, is excluded at 95% confidence level below 2.10, 3.65, and 4.25 TeV, respectively. In a simplified model of dark matter production via a vector or axial vector mediator, limits at 95% confidence level are obtained on the masses of the dark matter particle and its mediator.
PDF
