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Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions
(Amer Physical Soc, 2023) Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Del Valle, A. Escalante; Fruhwirth, R.; Jeitler, M.
The structure of nucleons is multidimensional and depends on the transverse momenta, spatial geometry, and polarization of the constituent partons. Such a structure can be studied using high-energy photons produced in ultraperipheral heavy-ion collisions. The first measurement of the azimuthal angular correlations of exclusively produced events with two jets in photon-lead interactions at large momentum transfer is presented, a process that is considered to be sensitive to the underlying nuclear gluon polarization. This study uses a data sample of ultraperipheral lead-lead collisions at ffiffiffiffiffiffiffi p = 5.02 TeV, corresponding to sNN an integrated luminosity of 0.38 nb-1, collected with the CMS experiment at the LHC. The measured second harmonic of the correlation between the sum and difference of the two jet transverse momentum vectors is found to be positive, and rising, as the dijet transverse momentum increases. A well-tuned model that has been successful at describing a wide range of proton scattering data from the HERA experiments fails to describe the observed correlations, suggesting the presence of gluon polarization effects.
Constraints on anomalous HVV couplings from the production of Higgs bosons decaying to ? lepton pairs
(Amer Physical Soc, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
A study is presented of anomalous HVV interactions of the Higgs boson, including its CP properties. The study uses Higgs boson candidates produced mainly in vector boson fusion and gluon fusion that subsequently decay to a pair of tau leptons. The data were recorded by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 35.9 fb(-1). A matrix element technique is employed for the analysis of anomalous interactions. The results are combined with those from the H -> 4l decay channel presented earlier, yielding the most stringent constraints on anomalous Higgs boson couplings to electroweak vector bosons expressed as effective cross section fractions and phases: the CP-violating parameter f(a3) cos(phi(a3)) = (0.00 +/- 0.27) x 10(-3) and the CP-conserving parameters f(a2) cos(phi(a2)) = (0.08)(-0.21)(+1.04)) x 10(-3), f(Lambda 1) cos(phi(Lambda 1)) = (0.00)(-0.09)(+0.53)) x 10(-3), and f(Lambda 1)(Z gamma) cos(phi(Z gamma)(Lambda 1)) = (0.0(-1.3)(+1.1)) x 10(-3). The current dataset does not allow for precise constraints on CP properties in the gluon fusion process. The results are consistent with standard model expectations.
An embedding technique to determine ?? backgrounds in proton-proton collision data
(Iop Publishing Ltd, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).
First measurement of the forward rapidity gap distribution in pPb collisions at ?sNN=8.16 TeV
(Amer Physical Soc, 2023) Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Ero, J.; Del Valle, A. Escalante
For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of ffisffi than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the EPOS-LHC generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology, the EPOS-LHC, QGSJET II, and HIJING predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.
Hard color-singlet exchange in dijet events in proton-proton collisions at ?s=13 TeV
(Amer Physical Soc, 2021) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Ero, J.
Events where the two leading jets are separated by a pseudorapidity interval devoid of particle activity, known as jet-gap-jet events, are studied in proton-proton collisions at root s = 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum (p(T)) jets must have p(T)(jet) > 40 GeV and pseudorapidity 1.4 < vertical bar eta(jet)vertical bar < 4.7, with eta(jet1)eta(jet2) < 0, where jet1 and jet2 are the leading and subleading jets in p(T), respectively. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity, high-beta* run at the CERN LHC in 2015, with an integrated luminosity of 0.66 pb(-1). Events with a low number of charged particles with p(T) > 0.2 GeV in the interval vertical bar eta vertical bar < 1 between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, f(CSE), is measured as a function of p(T)(jet2), the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction f(CSE) has values of 0.4-1.0%. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the first study of jet-gap-jet events detected in association with an intact proton using a subsample of events with an integrated luminosity of 0.40 pb(-1) is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The f(CSE) in this sample is 2.91 +/- 0.70(stat)(-1.01)(+1.08)(syst) times larger than that for inclusive dijet production in dijets with similar kinematics.
Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV
(Iop Publishing Ltd, 2018) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, are presented. Heavy-flavour jet identification algorithms have been improved compared to those used previously at centre-of-mass energies of 7 and 8 TeV. For jets with transverse momenta in the range expected in simulated t (t) over bar events, these new developments result in an efficiency of 68% for the correct identification of a b jet for a probability of 1% of misidentifying a light-flavour jet. The improvement in relative efficiency at this misidentification probability is about 15%, compared to previous CMS algorithms. In addition, for the first time algorithms have been developed to identify jets containing two b hadrons in Lorentz-boosted event topologies, as well as to tag c jets. The large data sample recorded in 2016 at a centre-of-mass energy of 13 TeV has also allowed the development of new methods to measure the efficiency and misidentification probability of heavy-flavour jet identification algorithms. The b jet identification efficiency is measured with a precision of a few per cent at moderate jet transverse momenta (between 30 and 300 GeV) and about 5% at the highest jet transverse momenta (between 500 and 1000 GeV).
Measurement of b hadron lifetimes in pp collisions at ?s = 8TeV (vol 78, 2018)
(Springer, 2018) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
[Abstract Not Available]
Measurement of exclusive ? photoproduction from protons in pPb collisions at ?sNN = 5.02 TeV (vol 79, 277, 2019)
(Springer, 2022) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
[Abstract Not Available]
Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV (vol 78, 509, 2018)
(Springer, 2023) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
[Abstract Not Available]
Measurement of single-diffractive dijet production in proton-proton collisions at ?s = 8 TeV with the CMS and TOTEM experiments (vol 80, 1164, 2020)
(Springer, 2021) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
[Abstract Not Available]
Measurement of the average very forward energy as a function of the track multiplicity at central pseudorapidities in proton-proton collisions at ?s=13 TeV
(Springer, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
The average total energy as well as its hadronic and electromagnetic components are measured with the CMS detector at pseudorapidities -6.6 < eta < -5.2 in proton-proton collisions at a centre-of-mass energy root s = 13 TeV. The results are presented as a function of the charged particle multiplicity in the region vertical bar eta vertical bar < 2. This measurement is sensitive to correlations induced by the underlying event structure over a very wide pseudorapidity region. The predictions of Monte Carlo event generators commonly used in collider experiments and ultra-high energy cosmic ray physics are compared to the data. All generators considered overestimate the fraction of energy going into hadrons.
Measurement of the differential Drell-Yan cross section in proton-proton collisions at ?s=13 TeV
(Springer, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Measurements of the differential cross section for the Drell-Yan process, based on proton-proton collision data at a centre-of-mass energy of 13 TeV, collected by the CMS experiment, are presented. The data correspond to an integrated luminosity of 2.8 (2.3) fb(-1) in the dimuon (dielectron) channel. The total and fiducial cross section measurements are presented as a function of dilepton invariant mass in the range 15 to 3000 GeV, and compared with the perturbative predictions of the standard model. The measured differential cross sections are in good agreement with the theoretical calculations.
Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the dilepton final state in proton-proton collisions at ?s=13 TeV
(Amer Physical Soc, 2020) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Ero, J.
A measurement of the Higgs boson Yukawa coupling to the top quark is presented using proton-proton collision data at root s = 13 TeV, corresponding to an integrated luminosity of 137 fb(-1), recorded with the CMS detector. The coupling strength with respect to the standard model value, Y-t, is determined from kinematic distributions in t (t) over bar final states containing ee, mu mu, or e mu pairs. Variations of the Yukawa coupling strength lead to modified distributions for t (t) over bar production. In particular, the distributions of the t (t) over bar mass of the a system and the rapidity difference of the top quark and antiquark are sensitive to the value of Y-t. The measurement yields a best fit value of Y-t = 1.16(-0.35)(+0.24), bounding Y-t < 1.54 at a 95% confidence level.
Measurements of differential Z boson production cross sections in proton-proton collisions at ?s=13 TeV
(Springer, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Measurements are presented of the differential cross sections for Z bosons produced in proton-proton collisions at root 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 phi*(eta), 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 phi*(eta) < 0.5 and for p(T)(Z) < 50 GeV.
Measurements of properties of the Higgs boson decaying into the four-lepton final state in pp collisions at ?s=13 TeV
(Springer, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Properties of the Higgs boson are measured in the H -> ZZ -> 4l (l = e, mu) decay channel. A data sample of proton-proton collisions at root s = 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb(-1) is used. The signal strength modifier mu, defined as the ratio of the observed Higgs boson rate in the H -> ZZ -> 4l decay channel to the standard model expectation, is measured to be mu = 1.05(-0.17)(+0.19) at m(H) = 125.09 GeV, the combined ATLAS and CMS measurement of the Higgs boson mass. The signal strength modifiers for the individual Higgs boson production modes are also measured. The cross section in the fiducial phase space defined by the requirements on lepton kinematics and event topology is measured to be 2.92(-0.44)(+0.48)(stat) (+0.28)(-0.24)(syst) fb, which is compatible with the standard model prediction of 2.76 +/- 0.14 fb. Differential cross sections are reported as a function of the transverse momentum of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet. The Higgs boson mass is measured to be m(H) = 125.26 +/- 0.21 GeV and the width is constrained using the on-shell invariant mass distribution to be Gamma(H) < 1.10 GeV, at 95% confidence level.
Measurements of properties of the Higgs boson decaying to a Wboson pair in pp collisions at root s=13 TeV
(Elsevier, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Measurements of the production of the standard model Higgs boson decaying to a W boson pair are reported. The W+ W- candidates are selected in events with an oppositely charged lepton pair, large missing transverse momentum, and various numbers of jets. To select Higgs bosons produced via vector boson fusion and associated production with a W or Z boson, events with two jets or three or four leptons are also selected. The event sample corresponds to an integrated luminosity of 35.9 fb(-1), collected in pp collisions at root s = 13 TeV by the CMS detector at the LHC during 2016. Combining all channels, the observed cross section times branching fraction is 1.28(-0.17)(+0.18) times the standard model prediction for the Higgs boson with a mass of 125.09 GeV. This is the first observation of the Higgs boson decay to W boson pairs by the CMS experiment. (c) 2019 The Author(s). Published by Elsevier B.V.
Measurements of triple-differential cross sections for inclusive isolated-photon plus jet events in pp collisions at ?s=8 TeV
(Springer, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.
Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in pp collisions at root s = 8 TeV as a function of photon transverse momentum (p(T)(gamma)), photon pseudorapidity (eta(gamma)), and jet pseudorapidity (eta(jet)). The data correspond to an integrated luminosity of 19.7 fb(-1) that probe a broad range of the available phase space, for vertical bar eta(gamma)vertical bar < 1.44 and 1.57 < vertical bar eta(gamma)vertical bar < 2.50, vertical bar eta(jet)vertical bar < 2.5, 40 < p(T)(gamma) < 1000 GeV, and jet transverse momentum, p(T)(jet), > 25 GeV. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties.
Nuclear modification of Y states in pPb collisions at ?SNN=5.02 TeV
(Elsevier, 2022) Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Ero, J.; Del Valle, A. Escalante
Production cross sections of Y(1S), Y(2S), and Y(3S) states decaying into mu(+)mu(-) in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at root S-NN= 5.02 TeV. A comparison is made with corresponding cross sections obtained with ppdata measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for Y(1S) is found to be R-pPb(Y(1S)) = 0.806 +/- 0.024 (stat)+/- 0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that R-pPb(Y(1S)) > R-pPb(Y(2S)) > R-pPb(Y(3S)). The suppression of all states is much less pronounced in pPbthan in PbPbcollisions, and independent of transverse momentum p(T)(Y) and center-of-mass rapidity y(CM)(Y) of the individual Y state in the studied range p(T)(Y) < 30GeV/c and |y(CM)(Y)| < 1.93. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Observation of Two Excited Bc+ States and Measurement of the Bc+ (2S) Mass in pp Collisions at ?s=13 TeV
(Amer Physical Soc, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Dragicevic, M.
Signals consistent with the B-c(+)(2S) and B-c*(+)(2S) states are observed in proton-proton collisions at root s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb(-1), collected by the CMS experiment during the 2015-2018 LHC running periods. These excited (b) over barc states are observed in the B-c(+)pi(+)pi(-) invariant mass spectrum, with the ground state B-c(+) reconstructed through its decay to J/psi pi(+). The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 +/- 1.5(stat) +/- 0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B-c(+)(2S) meson is measured to be 6871.0 +/- 1.2(stat) +/- 0.8(syst) +/- 0.8(B-c(+)) MeV, where the last term corresponds to the uncertainty in the world-average B-c(+) mass.
Particle-flow reconstruction and global event description with the CMS detector
(Iop Publishing Ltd, 2017) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.; Brondolin, E.
The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic tau decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions.

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