Publications
1342 results found
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in in pp collisions at root s=13 TeV, The Journal of High Energy Physics, Vol: 2020, Pages: 1-56, ISSN: 1029-8479
The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d^t) and chromomagnetic (μ^t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable A(1)FB is used to approximate the asymmetry. Candidate tt¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for tt¯ final states. The values found for the parameters are A(1)FB=0.048+0.095−0.087(stat)+0.020−0.029(syst),μ^t=−0.024+0.013−0.009(stat)+0.016−0.011(syst), and a limit is placed on the magnitude of ∣∣d^t∣∣< 0.03 at 95% confidence level.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Strange hadron production in pp and pPb collisions at root(NN)-N-s=5.02 TeV, Physical Review C: Nuclear Physics, Vol: 101, Pages: 064906 – 1-064906 – 21, ISSN: 0556-2813
The transverse momentum (pT) distributions of Λ, Ξ−, and Ω− baryons, their antiparticles, and K0S mesons are measured in proton-proton (pp) and proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV over a broad rapidity range. The data, corresponding to integrated luminosities of 40.2 nb−1 and 15.6 μb−1 for pp and pPb collisions, respectively, were collected by the CMS experiment. The nuclear modification factor RpPb, which is defined as the ratio of the particle yield in pPb collisions and a scaled pp reference, is measured for each particle. A strong dependence on particle species is observed in the pT range from 2 to 7 GeV, where RpPb for K0S is consistent with unity, while an enhancement ordered by strangeness content and/or particle mass is observed for the three baryons. In pPb collisions, the strange hadron production is asymmetric about the nucleon-nucleon center-of-mass rapidity. Enhancements, which depend on the particle type, are observed in the direction of the Pb beam. The results are compared with predictions from epos lhc, which includes parametrized radial flow. The model is in qualitative agreement with the RpPb data, but fails to describe the dependence on particle species in the yield asymmetries measured away from midrapidity in pPb collisions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles in PbPb collisions at s NN =2.76 and 5.02TeV, European Physical Journal C: Particles and Fields, Vol: 80, ISSN: 1124-1861
Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in PbPb collisions at nucleon-nucleon center-of-mass energies s NN = 2.76 and 5.02 TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for dijet resonances using events with three jets in proton-proton collisions at root s=13 TeV, PHYSICS LETTERS B, Vol: 805, Pages: 1-23, ISSN: 0370-2693
A search for a narrow resonance with a mass between 350 and 700 GeV, and decaying into a pair of jets, is performed using proton-proton collision events containing at least three jets. The data sample corresponds to an integrated luminosity of 18.3 fb−1 recorded at with the CMS detector. Data are collected with a technique known as “data scouting”, in which the events are reconstructed, selected, and recorded at a high rate in a compact form by the high-level trigger. The three-jet final state provides sensitivity to lower resonance masses than in previous searches using the data scouting technique. The spectrum of the dijet invariant mass, calculated from the two jets with the largest transverse momenta in the event, is used to search for a resonance. No significant excess over a smoothly falling background is found. Limits at 95% confidence level are set on the production cross section of a narrow dijet resonance and compared with the cross section of a vector dark matter mediator coupling to dark matter particles and quarks. Translating to a model where the narrow resonance interacts only with quarks, upper limits on this coupling range between 0.10 and 0.15, depending on the resonance mass. These results represent the most stringent upper limits in the mass range between 350 and 450 GeV obtained with a flavor-inclusive dijet resonance search.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of the cross section for electroweak production of a Z boson, a photon and two jets in proton-proton collisions at root s=13TeV and constraints on anomalous quartic couplings, The Journal of High Energy Physics, Vol: 2020, Pages: 1-42, ISSN: 1029-8479
A measurement is presented of the cross section for electroweak production of a Z boson and a photon in association with two jets (Zγjj) in proton-proton collisions. The Z boson candidates are selected through their decay into a pair of electrons or muons. The process of interest, electroweak Zγjj production, is isolated by selecting events with a large dijet mass and a large pseudorapidity gap between the two jets. The measurement is based on data collected at the CMS experiment at s√ = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The observed significance of the signal is 3.9 standard deviations, where a significance of 5.2 standard deviations is expected in the standard model. These results are combined with published results by CMS at s√ = 8 TeV, which leads to observed and expected respective significances of 4.7 and 5.5 standard deviations. From the 13 TeV data, a value is obtained for the signal strength of electroweak Zγjj production and bounds are given on quartic vector boson interactions in the framework of dimension-eight effective field theory operators.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, A measurement of the Higgs boson mass in the diphoton decay channel, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 805, Pages: 1-25, ISSN: 0370-2693
A measurement of the mass of the Higgs boson in the diphoton decay channel is presented. This analysis is based on 35.9 fb−1of proton-proton collision data collected during the 2016 LHC running period, with the CMS detector at a centre-of-mass energy of 13 TeV. A refined detector calibration and new analysis techniques have been used to improve the precision of this measurement. The Higgs boson mass is measured to be mH=125.78 ±0.26 GeV. This is combined with a measurement of mHalready performed in the H→ZZ→4 decay channel using the same data set, giving mH=125.46 ±0.16 GeV. This result, when further combined with an earlier measurement of mHusing data collected in 2011 and 2012 with the CMS detector, gives a value for the Higgs boson mass of mH=125.38 ±0.14 GeV. This is currently the most precise measurement of the mass of the Higgs boson.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurements with silicon photomultipliers of dose-rate effects in the radiation damage of plastic scintillator tiles in the CMS hadron endcap calorimeter, Journal of Instrumentation, Vol: 15, Pages: 1-48, ISSN: 1748-0221
Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb−1. The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: a laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation campaigns using 60Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Determination of the strong coupling constant alpha(S)(m(Z)) from measurements of inclusive W-+/- and Z boson production cross sections in proton-proton collisions at root s=7 and 8 TeV, The Journal of High Energy Physics, Vol: 2020, Pages: 1-50, ISSN: 1029-8479
Twelve measurements of inclusive cross sections of W± and Z boson production, performed in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, are compared with perturbative quantum chromodynamics calculations at next-to-next- to-leading order (NNLO) accuracy obtained with the CT14, HERAPDF2.0, MMHT14, and NNPDF3.0 parton distribution functions (PDFs). Data and theory agree well for all PDF sets, taking into account the experimental and theoretical uncertainties. A novel procedure is employed to extract the strong coupling constant at the Z pole mass from a detailed comparison of all the experimental fiducial cross sections to the corresponding NNLO theoretical predictions, yielding αS(mZ)=0.1163+0.0024−0.0031 (CT14), 0.1072+0.0043−0.0040 (HERAPDF2.0), 0.1186 ± 0.0025 (MMHT14), and 0.1147 ± 0.0023 (NNPDF3.0). Using the results obtained with the CT14 and MMHT14 PDFs, which yield the most robust and stable αS(mZ) extractions, a value αS(mZ)=0.1175+0.0025−0.0028 is determined.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Identification of heavy, energetic, hadronically decaying particles using machine-learning techniques, Journal of Instrumentation, Vol: 15, Pages: 1-87, ISSN: 1748-0221
Machine-learning (ML) techniques are explored to identify and classify hadronic decays of highly Lorentz-boosted W/Z/Higgs bosons and top quarks. Techniques without ML have also been evaluated and are included for comparison. The identification performances of a variety of algorithms are characterized in simulated events and directly compared with data. The algorithms are validated using proton-proton collision data at √s = 13TeV, corresponding to an integrated luminosity of 35.9 fb−1. Systematic uncertainties are assessed by comparing the results obtained using simulation and collision data. The new techniques studied in this paper provide significant performance improvements over non-ML techniques, reducing the background rate by up to an order of magnitude at the same signal efficiency.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of the jet mass distribution and top quark mass in hadronic decays of boosted top quarks in pp collisions at root s=13 TeV, Physical Review Letters, Vol: 124, Pages: 202001-1-202001-19, ISSN: 0031-9007
A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at √s=13 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb−1. The measurement is performed in the lepton+jets channel of t¯t events, where the lepton is an electron or muon. The products of the hadronic top quark decay t→bW→bq¯q′ are reconstructed as a single jet with transverse momentum larger than 400 GeV. The t¯t cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6±2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of 3 relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at root s = 7TeV (vol 78, 242, 2018), European Physical Journal C: Particles and Fields, Vol: 80, Pages: 1-15, ISSN: 1124-1861
Events with no charged particles produced between the two leading jets are studied in proton–proton collisions at s√=7 TeV. The jets were required to have transverse momentum pjetT>40 GeV and pseudorapidity 1.5<|ηjet|<4.7, and to have values of ηjet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8pb−1. Events with no charged particles with pT>0.2 GeV in the interval −1<η<1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5–1% of the selected dijet sample, is measured as a function of the pT of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky–Fadin–Kuraev–Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions at root s=13 TeV, The Journal of High Energy Physics, Vol: 2020, Pages: 1-40, ISSN: 1029-8479
Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at s√ = 13 TeV, corresponding to an integrated luminosity of 77.4 fb−1. The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Study of J/psi meson production inside jets in pp collisions at N root s=8 TeV The CM Collaboration, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 804, Pages: 1-24, ISSN: 0370-2693
A study of the production of prompt J/ψ mesons contained in jets in proton-proton collisions at√s = 8 TeV is presented. The analysis is based on data corresponding to an integrated luminosity of19.1 fb−1 collected with the CMS detector at the LHC. For events with at least one observed jet, theangular separation between the J/ψ meson and the jet is used to test whether the J/ψ meson is partof the jet. The analysis shows that most prompt J/ψ mesons having energy above 15 GeV and rapidity|y| < 1 are contained in jets with pseudorapidity |ηjet| < 1. The differential distributions of the probabilityto have a J/ψ meson contained in a jet as a function of jet energy for a fixed J/ψ energy fraction arecompared to a theoretical model using the fragmenting jet function approach. The data agree best withfragmenting jet function calculations that use a long-distance matrix element parameter set in whichprompt J/ψ mesons are predicted to be unpolarized. This technique demonstrates a new way to testpredictions for prompt J/ψ production using nonrelativistic quantum chromodynamics.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for high mass dijet resonances with a new background prediction method in proton-proton collisions at root s=13 TeV, The Journal of High Energy Physics, Vol: 2020, Pages: 1-45, ISSN: 1029-8479
A search for narrow and broad resonances with masses greater than 1.8 TeV decaying to a pair of jets is presented. The search uses proton-proton collision data at s√ = 13 TeV collected at the LHC, corresponding to an integrated luminosity of 137 fb−1. The background arising from standard model processes is predicted with the fit method used in previous publications and with a new method. The dijet invariant mass spectrum is well described by both data-driven methods, and no significant evidence for the production of new particles is observed. Model independent upper limits are reported on the production cross sections of narrow resonances, and broad resonances with widths up to 55% of the resonance mass. Limits are presented on the masses of narrow resonances from various models: string resonances, scalar diquarks, axigluons, colorons, excited quarks, color-octet scalars, W′ and Z′ bosons, Randall-Sundrum gravitons, and dark matter mediators. The limits on narrow resonances are improved by 200 to 800 GeV relative to those reported in previous CMS dijet resonance searches. The limits on dark matter mediators are presented as a function of the resonance mass and width, and on the associated coupling strength as a function of the mediator mass. These limits exclude at 95% confidence level a dark matter mediator with a mass of 1.8 TeV and width 1% of its mass or higher, up to one with a mass of 4.8 TeV and a width 45% of its mass or higher.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for direct top squark pair production in events with one lepton, jets, and missing transverse momentum at 13 TeV with the CMS experiment, The Journal of High Energy Physics, Vol: 2020, Pages: 1-50, ISSN: 1029-8479
A search for direct top squark pair production is presented. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV recorded by the CMS experiment at the LHC during 2016, 2017, and 2018, corresponding to an integrated luminosity of 137 fb−1. The search is carried out using events with a single isolated electron or muon, multiple jets, and large transverse momentum imbalance. The observed data are consistent with the expectations from standard model processes. Exclusions are set in the context of simplified top squark pair production models. Depending on the model, exclusion limits at 95% confidence level for top squark masses up to 1.2 TeV are set for a massless lightest supersymmetric particle, assumed to be the neutralino. For models with top squark masses of 1 TeV, neutralino masses up to 600 GeV are excluded.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of differential cross sections and charge ratios for t-channel single top quark production in proton-proton collisions at mml:msqrts mml:msqrt=13 mml:mspace width="0.166667em"mml:mspaceTe mml:mspace width="0.333333em"mml:mspace, European Physical Journal C: Particles and Fields, Vol: 80, Pages: 1-37, ISSN: 1124-1861
A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton–proton collisions at a centre-of-mass energy of 13TeV by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9fb−1, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum (pT), rapidity, and polarisation angle, the charged lepton pT and rapidity, and the pT of the W boson from the top quark decay. In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and W boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be 0.440±0.070, in agreement with the standard model prediction.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Calibration of the CMS hadron calorimeters using proton-proton collision data at root s=13 TeV, Journal of Instrumentation, Vol: 15, Pages: 1-48, ISSN: 1748-0221
Methods are presented for calibrating the hadron calorimeter system of the CMS detector at the LHC. The hadron calorimeters of the CMS experiment are sampling calorimeters of brass and scintillator, and are in the form of one central detector and two endcaps. These calorimeters cover pseudorapidities |η| < 3 and are positioned inside the solenoidal magnet. An outer calorimeter, outside the magnet coil, covers |η| < 1.26, and a steel and quartz-fiber Cherenkov forward calorimeter extends the coverage to |η| < 5.19. The initial calibration of the calorimeters was based on results from test beams, augmented with the use of radioactive sources and lasers. The calibration was improved substantially using proton-proton collision data collected at √s = 7, 8, and 13 TeV, as well as cosmic ray muon data collected during the periods when the LHC beams were not present. The present calibration is performed using the 13 TeV data collected during 2016 corresponding to an integrated luminosity of 35.9 fb−1. The intercalibration of channels exploits the approximate uniformity of energy collection over the azimuthal angle. The absolute energy scale of the central and endcap calorimeters is set using isolated charged hadrons. The energy scale for the electromagnetic portion of the forward calorimeters is set using Z→ ee data. The energy scale of the outer calorimeters has been determined with test beam data and is confirmed through data with high transverse momentum jets. In this paper, we present the details of the calibration methods and accuracy.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Study of J/ψ meson production inside jets in pp collisions at s=8TeV, Physics Letters B, Vol: 804, Pages: 1-24, ISSN: 0370-2693
A study of the production of prompt J/ψ mesons contained in jets in proton-proton collisions at√s = 8 TeV is presented. The analysis is based on data corresponding to an integrated luminosity of19.1 fb−1 collected with the CMS detector at the LHC. For events with at least one observed jet, theangular separation between the J/ψ meson and the jet is used to test whether the J/ψ meson is partof the jet. The analysis shows that most prompt J/ψ mesons having energy above 15 GeV and rapidity|y| < 1 are contained in jets with pseudorapidity |ηjet| < 1. The differential distributions of the probabilityto have a J/ψ meson contained in a jet as a function of jet energy for a fixed J/ψ energy fraction arecompared to a theoretical model using the fragmenting jet function approach. The data agree best withfragmenting jet function calculations that use a long-distance matrix element parameter set in whichprompt J/ψ mesons are predicted to be unpolarized. This technique demonstrates a new way to testpredictions for prompt J/ψ production using nonrelativistic quantum chromodynamics
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of properties of B(s)(0)s -> mu(+)mu(-) decays and search for B-0 -> mu(+)mu(-) with the CMS experiment, The Journal of High Energy Physics, Vol: 2020, Pages: 1-49, ISSN: 1029-8479
Results are reported for the B0s→ μ+μ− branching fraction and effective lifetime and from a search for the decay B0→ μ+μ−. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb−1), 8 TeV (20 fb−1), and 13 TeV (36 fb−1). The branching fractions are determined by measuring event yields relative to B+→ J/ψK+ decays (with J/ψ → μ+μ−), which results in the reduction of many of the systematic uncertainties. The decay B0s→ μ+μ− is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be B(B0s→μ+μ−)=[2.9±0.7(exp)±0.2(frag)]×10−9, where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the B0s and the B+ fragmentation functions. No significant excess is observed for the decay B0→ μ+μ−, and an upper limit of ℬ(B0 → μ+μ−) < 3.6 × 10−10 is obtained at 95% confidence level. The B0s→ μ+μ− effective lifetime is measured to be τμ+μ−=1.70+0.61−0.44 ps. These results are consistent with standard model predictions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for heavy Higgs bosons decaying to a top quark pair in proton-proton collisions at √<i>s</i>=13 TeV, Publisher: SPRINGER
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Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Constraints on the χc1 versus χc2 polarizations in proton-proton collisions at √s=8 TeV, Physical Review Letters, Vol: 124, ISSN: 0031-9007
The polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e−, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ− decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Experimental study of different silicon sensor options for the upgrade of the CMS Outer Tracker, Journal of Instrumentation, Vol: 15, Pages: 1-34, ISSN: 1748-0221
During the high-luminosity phase of the LHC (HL-LHC), planned to start in 2027, the accelerator is expected to deliver an instantaneous peak luminosity of up to 7.5×1034 cm−2 s−1. A total integrated luminosity of 0300 or even 0400 fb−1 is foreseen to be delivered to the general purpose detectors ATLAS and CMS over a decade, thereby increasing the discovery potential of the LHC experiments significantly. The CMS detector will undergo a major upgrade for the HL-LHC, with entirely new tracking detectors consisting of an Outer Tracker and Inner Tracker. However, the new tracking system will be exposed to a significantly higher radiation than the current tracker, requiring new radiation-hard sensors. CMS initiated an extensive irradiation and measurement campaign starting in 2009 to systematically compare the properties of different silicon materials and design choices for the Outer Tracker sensors. Several test structures and sensors were designed and implemented on 18 different combinations of wafer materials, thicknesses, and production technologies. The devices were electrically characterized before and after irradiation with neutrons, and with protons of different energies, with fluences corresponding to those expected at different radii of the CMS Outer Tracker after 0300 fb−1. The tests performed include studies with β sources, lasers, and beam scans. This paper compares the performance of different options for the HL-LHC silicon sensors with a focus on silicon bulk material and thickness.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Running of the top quark mass from proton-proton collisions at root s=13 TeV, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 803, Pages: 1-24, ISSN: 0370-2693
The running of the top quark mass is experimentally investigated for the first time. The mass of the top quark in the modified minimal subtraction () renormalization scheme is extracted from a comparison of the differential top quark-antiquark () cross section as a function of the invariant mass of the system to next-to-leading-order theoretical predictions. The differential cross section is determined at the parton level by means of a maximum-likelihood fit to distributions of final-state observables. The analysis is performed using candidate events in the e± μ∓ channel in proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the CMS detector at the CERN LHC in 2016, corresponding to an integrated luminosity of 35.9. The extracted running is found to be compatible with the scale dependence predicted by the corresponding renormalization group equation. In this analysis, the running is probed up to a scale of the order of 1 TeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Measurement of the t(t)over-barb(b)over-bar production cross section in the all-jet final state in pp collisions at root s=13 TeV, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 803, Pages: 1-26, ISSN: 0370-2693
A measurement of the production cross section of top quark pairs in association with two bjets (ttbb) is presented using data collected in proton-proton collisions at √s=13 TeV by the CMS detector at the LHC corresponding to an integrated luminosity of 35.9fb−1. The cross section is measured in the all-jet decay channel of the top quark pair by selecting events containing at least eight jets, of which at least two are identified as originating from the hadronization of bquarks. A combination of multivariate analysis techniques is used to reduce the large background from multijet events not containing a top quark pair, and to help discriminate between jets originating from top quark decays and other additional jets. The cross section is determined for the total phase space to be 5.5 ±0.3 (stat)+1.6−1.3(syst) pb and also measured for two fiducial ttbb definitions. The measured cross sections are found to be larger than theoretical predictions by a factor of 1.5–2.4, corresponding to 1–2 standard deviations.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Production of Lambda(+)(c) baryons in proton-proton and lead-lead collisions at root S-NN=5.02 TeV, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 803, Pages: 1-23, ISSN: 0370-2693
The transverse momentum (pT) spectra of inclusively produced +cbaryons are measured via the exclusive decay channel +c→pK−π+using the CMS detector at the LHC. Spectra are measured as a function of transverse momentum in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measurement is performed within the +crapidity interval |y| <1in the pTrange of 5–20 GeV/cin pp and 10–20 GeV/cin PbPb collisions. The observed yields of +cfor pTof 10–20 GeV/csuggest a suppression in central PbPb collisions compared to ppcollisions scaled by the number of nucleon-nucleon (NN) interactions. The +c/D0production ratio in pp collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from pp collisions in their common pTrange.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Study of excited Lambda(0)(b) states decaying to Lambda(0)(b)pi(+)pi(-) in proton-proton collisions at root s=13TeV, Physics Letters B: Nuclear Physics and Particle Physics, Vol: 803, Pages: 1-22, ISSN: 0370-2693
A study of excited Λ0bbaryons is reported, based on a data sample collected in 2016–2018 with the CMS detector at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of up to 140 fb−1. The existence of four excited Λ0bstates: Λ0b(5912)0, Λ0b(5920)0, Λ0b(6146)0, and Λ0b(6152)0in the Λ0bπ+π−mass spectrum is confirmed, and their masses are measured. The Λ0bπ+π−mass distribution exhibits a broad excess of events in the region of 6040–6100 MeV, whose origin cannot be discerned with the present data.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for a narrow resonance lighter than 200 GeV decaying to a pair of muons in proton-proton collisions at sqrt[s]=13 TeV., Physical Review Letters`, Vol: 124, Pages: 131802-1-131802-17, ISSN: 0031-9007
A search is presented for a narrow resonance decaying to a pair of oppositely charged muons using sqrt[s]=13 TeV proton-proton collision data recorded at the LHC. In the 45-75 and 110-200 GeV resonance mass ranges, the search is based on conventional triggering and event reconstruction techniques. In the 11.5-45 GeV mass range, the search uses data collected with dimuon triggers with low transverse momentum thresholds, recorded at high rate by storing a reduced amount of trigger-level information. The data correspond to integrated luminosities of 137 and 96.6 fb^{-1} for conventional and high-rate triggering, respectively. No significant resonant peaks are observed in the probed mass ranges. The search sets the most stringent constraints to date on a dark photon in the ∼30-75 and 110-200 GeV mass ranges.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, Search for supersymmetry in pp collisions at root s=13 TeV with 137 fb(-1) in final states with a single lepton using the sum of masses of large-radius jets, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 052010-1-052010-33, ISSN: 1550-2368
Results are reported from a search for new physics beyond the standard model in proton-proton collisions in final states with a single lepton; multiple jets, including at least one jet tagged as originating from the hadronization of a bottom quark; and large missing transverse momentum. The search uses a sample of proton-proton collision data at √s=13 TeV, corresponding to 137 fb−1, recorded by the CMS experiment at the LHC. The signal region is divided into categories characterized by the total number of jets, the number of bottom quark jets, the missing transverse momentum, and the sum of masses of large-radius jets. The observed event yields in the signal regions are consistent with estimates of standard model backgrounds based on event yields in the control regions. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production in which each gluino decays into a top quark-antiquark pair and a stable, unobserved neutralino, which generates missing transverse momentum in the event. Scenarios with gluino masses up to about 2150 GeV are excluded at 95% confidence level (or more) for neutralino masses up to 700 GeV. The highest excluded neutralino mass is about 1250 GeV, which holds for gluino masses around 1850 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, A search for the standard model Higgs boson decaying to charm quarks, The Journal of High Energy Physics, Vol: 2020, Pages: 1-54, ISSN: 1029-8479
A direct search for the standard model Higgs boson, H, produced in association with a vector boson, V (W or Z), and decaying to a charm quark pair is presented. The search uses a data set of proton-proton collisions corresponding to an integrated luminosity of 35.9 fb−1, collected by the CMS experiment at the LHC in 2016, at a centre-of-mass energy of 13 TeV. The search is carried out in mutually exclusive channels targeting specific decays of the vector bosons: W → ℓν, Z → ℓℓ, and Z → νν, where ℓ is an electron or a muon. To fully exploit the topology of the H boson decay, two strategies are followed. In the first one, targeting lower vector boson transverse momentum, the H boson candidate is reconstructed via two resolved jets arising from the two charm quarks from the H boson decay. A second strategy identifies the case where the two charm quark jets from the H boson decay merge to form a single jet, which generally only occurs when the vector boson has higher transverse momentum. Both strategies make use of novel methods for charm jet identification, while jet substructure techniques are also exploited to suppress the background in the merged-jet topology. The two analyses are combined to yield a 95% confidence level observed (expected) upper limit on the cross section σ(VH)B(H→cc¯¯) of 4.5 (2.4+1.0−0.7) pb, corresponding to 70 (37) times the standard model prediction.
Sirunyan AM, Tumasyan A, Adam W, et al., 2020, A multi-dimensional search for new heavy resonances decaying to boosted WW , WZ , or ZZ boson pairs in the dijet final state at 13 Te, European Physical Journal C: Particles and Fields, Vol: 80, ISSN: 1124-1861
A search in an all-jet final state for new massive resonances decaying to W W , W Z , or Z Z boson pairs using a novel analysis method is presented. The analysis is performed on data corresponding to an integrated luminosity of 77.3 fb−1 recorded with the CMS experiment at the LHC at a centre-of-mass energy of 13 TeV. The search is focussed on potential narrow-width resonances with masses above 1.2 TeV, where the decay products of each W or Z boson are expected to be collimated into a single, large-radius jet. The signal is extracted using a three-dimensional maximum likelihood fit of the two jet masses and the dijet invariant mass, yielding an improvement in sensitivity of up to 30% relative to previous search methods. No excess is observed above the estimated standard model background. In a heavy vector triplet model, spin-1 Z′ and W′ resonances with masses below 3.5 and 3.8 TeV, respectively, are excluded at 95% confidence level. In a bulk graviton model, upper limits on cross sections are set between 27 and 0.2 fb for resonance masses between 1.2 and 5.2 TeV, respectively. The limits presented in this paper are the best to date in the dijet final state.
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