Browsing by Author "Chatterjee, S."
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Article Citation Count: 1Combined search for electroweak production of winos, binos, higgsinos, and sleptons in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A combination of the results of several searches for the electroweak production of the supersymmetric partners of standard model bosons, and of charged leptons, is presented. All searches use proton-proton collision data at root s = 13 TeV recorded with the CMS detector at the LHC in 2016-2018. The analyzed data correspond to an integrated luminosity of up to 137 fb(-1). The results are interpreted in terms of simplified models of supersymmetry. Two new interpretations are added with this combination: a model spectrum with the bino as the lightest supersymmetric particle together with mass-degenerate Higgsinos decaying to the bino and a standard model boson, and the compressed-spectrum region of a previously studied model of slepton pair production. Improved analysis techniques are employed to optimize sensitivity for the compressed spectra in the wino and slepton pair production models. The results are consistent with expectations from the standard model. The combination provides a more comprehensive coverage of the model parameter space than the individual searches, extending the exclusion by up to 125 GeV, and also targets some of the intermediate gaps in the mass coverage.Article Citation Count: 1Extracting the speed of sound in quark-gluon plasma with ultrarelativistic lead-lead collisions at the LHC(Iop Publishing Ltd, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.Ultrarelativistic nuclear collisions create a strongly interacting state of hot and dense quark-gluon matter that exhibits a remarkable collective flow behavior with minimal viscous dissipation. To gain deeper insights into its intrinsic nature and fundamental degrees of freedom, we determine the speed of sound in an extended volume of quark-gluon plasma using lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data were recorded by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 0.607 nb(-1). The measurement is performed by studying the multiplicity dependence of the average transverse momentum of charged particles emitted in head-on PbPb collisions. Our findings reveal that the speed of sound in this matter is nearly half the speed of light, with a squared value of 0.241 +/- 0.002 (stat) +/- 0.016 9(syst) in natural units. The effective medium temperature, estimated using the mean transverse momentum, is 219 +/- 8 The measured squared speed of sound at this temperature aligns precisely with predictions from lattice quantum chromodynamic (QCD) calculations. This result provides a stringent constraint on the equation of state of the created medium and direct evidence for a deconfined QCD phase being attained in relativistic nuclear collisions.Article Citation Count: 0Measurement of differential ZZ + jets production cross sections in pp collisions at s = 13 TeV(Springer Science and Business Media Deutschland GmbH, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Lasaosa García, C.Diboson production in association with jets is studied in the fully leptonic final states, pp → (Z/γ*)(Z/γ*) + jets → 2ℓ2ℓ′ + jets, (ℓ, ℓ′ = e or μ) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb−1 collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentum pT, pseudorapidity η, invariant mass and ∆η of the highest-pT and second-highest-pT jets, and as a function of invariant mass of the four-lepton system for events with various jet multiplicities. These differential cross sections are compared with theoretical predictions that mostly agree with the experimental data. However, in a few regions we observe discrepancies between the predicted and measured values. Further improvement of the predictions is required to describe the ZZ+jets production in the whole phase space. © The Author(s) 2024.Article Citation Count: 0Measurement of the Bs0→J/ψKS0 effective lifetime from proton-proton collisions at s = 13 TeV(Springer Science and Business Media Deutschland GmbH, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Vazquez Escobar, J.The effective lifetime of the Bs0 meson in the decay Bs0→J/ψKS0 is measured using data collected during 2016–2018 with the CMS detector in s = 13 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 140 fb−1. The effective lifetime is determined by performing a two-dimensional unbinned maximum likelihood fit to the Bs0 meson invariant mass and proper decay time distributions. The resulting value of 1.59 ± 0.07(stat) ± 0.03(syst) ps is the most precise measurement to date and is in good agreement with the expected value. © The Author(s) 2024.Article Citation Count: 0Nonresonant central exclusive production of charged-hadron pairs in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zich, J.The central exclusive production of charged-hadron pairs in pp collisions at a center-of-mass energy of 13 TeV is examined, based on data collected in a special high-beta* run of the LHC. The nonresonant continuum processes are studied with the invariant mass of the centrally produced twopion system in the resonance-free region, m(pi+pi-) < 0.7 or m(pi+pi-) > 1.8 GeV. Differential cross sections as functions of the azimuthal angle between the surviving protons, squared exchanged four- momenta, and m(pi+pi-) are measured in a wide region of scattered proton transverse momenta, between 0.2 and 0.8 GeV, and for pion rapidities |y| < 2. A rich structure of interactions related to double-pomeron exchange is observed. A parabolic minimum in the distribution of the two-proton azimuthal angle is observed for the first time. It can be interpreted as an effect of additional pomeron exchanges between the protons from the interference between the bare and the rescattered amplitudes. After model tuning, various physical quantities are determined that are related to the pomeron cross section, protonpomeron and meson-pomeron form factors, pomeron trajectory and intercept, and coefficients of diffractive eigenstates of the proton.Article Citation Count: 0Observation of double Formula Presented meson production in Formula Presented collisions at Formula Presented(American Physical Society, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Alvarez Gonzalez, B.The first observation of the concurrent production of two Formula Presented mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead (Formula Presented) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of Formula Presented. The two Formula Presented mesons are reconstructed in their Formula Presented decay channels with transverse momenta Formula Presented and rapidity Formula Presented. Events where one of the Formula Presented mesons is reconstructed in the dielectron channel are also considered in the search. The Formula Presented process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is Formula Presented. A fit of the data to the expected rapidity separation for pairs of Formula Presented mesons produced in single (SPS) and double (DPS) parton scatterings yields Formula Presented and Formula Presented, respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of Formula Presented at 95% confidence level. © 2024 CERN, for the CMS Collaboration.Article Citation Count: 1Observation of Enhanced Long-Range Elliptic Anisotropies Inside High-Multiplicity Jets in pp Collisions at √s = 13 TeV(American Physical Society, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Garcia, J.M.V.A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis ffiffi uses data collected at a center-of-mass energy of √s = 13 TeV, corresponding to an integrated luminosity of 138 fb−1. Jets are reconstructed with the anti-kT algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity (equation presented). Two-particle correlations among the charged particles within the jets are studied as functions of the particles' azimuthal angle and pseudorapidity separations (Δϕ* and Δη*) in a jet coordinate basis, where particles' η*, ϕ* are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to Njch ≈ 100. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for (equation presented). For low-Njch jets, the long-range elliptic anisotropic harmonic, v*2, is observed to decrease with Njch. This trend is well described by Monte Carlo event generators. However, a rising trend for v*2 emerges at (equation presented), hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum. © 2024 CERN, for the CMS Collaboration.Article Citation Count: 0Observation of the J/ψ → μ+μ-μ+μ- decay in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.The J/psi -> mu(+)mu(-)mu(+)mu(-) decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb(-1). Normalizing to the J/psi -> mu(+)mu(-) decay mode leads to a branching fraction of [10.1(-2.7)(+3.3)(stat) +/- 0.4(syst)] x 10(-7), a value that is consistent with the standard model prediction.Article Citation Count: 0Observation of the Λb0→J/ψΞ-K+ decay(Springer Nature, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Villalba, C.V.Using proton–proton collision data corresponding to an integrated luminosity of 140fb-1 collected by the CMS experiment at s=13TeV, the Λb0→J/ψΞ-K+ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the Λb0→ψ(2S)Λ decay, is measured to be B(Λb0→J/ψΞ-K+)/B(Λb0→ψ(2S)Λ)=[3.38±1.02±0.61±0.03]%, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in B(ψ(2S)→J/ψπ+π-) and B(Ξ-→Λπ-). © The Author(s) 2024.Article Citation Count: 0Search for a resonance decaying to a W boson and a photon in proton-proton collisions at s = 13 TeV using leptonic W boson decays(Springer Science and Business Media Deutschland GmbH, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Sánchez Navas, S.A search for a new charged particle X with mass between 0.3 and 2.0 TeV decaying to a W boson and a photon is presented, using proton-proton collision data at a center-of-mass energy of 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 138 fb−1. Particle X has electric charge ±1 and is assumed to have spin 0. The search is performed using the electron and muon decays of the W boson. No significant excess above the predicted background is observed. The upper limit at 95% confidence level on the product of the production cross section of the X and its branching fraction to a W boson and a photon is found to be 94 (137) fb for a 0.3 TeV resonance and 0.75 (0.81) fb for a 2.0 TeV resonance, for an X width-to-mass ratio of 0.01% (5%). This search presents the most stringent constraints to date on the existence of such resonances across the probed mass range. A statistical combination with an earlier study based on the hadronic decay mode of the W boson is also performed, and the upper limit at 95% confidence level for a 2.0 TeV resonance is reduced to 0.50 (0.63) fb for an X width-to-mass ratio of 0.01% (5%). © The Author(s) 2024.Article Citation Count: 0Search for flavor changing neutral current interactions of the top quark in final states with a photon and additional jets in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A search for the production of a top quark in association with a photon and additional jets via flavor changing neutral current interactions is presented. The analysis uses proton-proton collision data recorded by the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb(-1). The search is performed by looking for processes where a single top quark is produced in association with a photon, or a pair of top quarks where one of the top quarks decays into a photon and an up or charm quark. Events with an electron or a muon, a photon, one or more jets, and missing transverse momentum are selected. Multivariate analysis techniques are used to discriminate signal and standard model background processes. No significant deviation is observed over the predicted background. Observed (expected) upper limits are set on the branching fractions of top quark decays: B(t -> u gamma) < 0.95 x 10(-5) (1.20 x 10(-5)) and B(t -> c gamma) < 1.51 x 10(-5) (1.54 x 10(-5)) at 95% confidence level, assuming a single nonzero coupling at a time. The obtained limit for B(t -> u gamma) is similar to the current best limit, while the limit for B(t -> u gamma) is significantly tighter than previous results.Article Citation Count: 0Search for long-lived particles decaying to final states with a pair of muons in proton-proton collisions at s = 13.6 TeV(Springer Science and Business Media Deutschland GmbH, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Piedra Gomez, J.An inclusive search for long-lived exotic particles (LLPs) decaying to final states with a pair of muons is presented. The search uses data corresponding to an integrated luminosity of 36.6 fb−1 collected by the CMS experiment from the proton-proton collisions at s = 13.6 TeV in 2022, the first year of Run 3 of the CERN LHC. The experimental signature is a pair of oppositely charged muons originating from a secondary vertex spatially separated from the proton-proton interaction point by distances ranging from several hundred μm to several meters. The sensitivity of the search benefits from new triggers for displaced dimuons developed for Run 3. The results are interpreted in the framework of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons, and of an R-parity violating supersymmetry model, in which long-lived neutralinos decay to a pair of muons and a neutrino. The limits set on these models are the most stringent to date in wide regions of lifetimes for LLPs with masses larger than 10 GeV. © The Author(s) 2024.Article Citation Count: 0Search for long-lived particles using displaced vertices and missing transverse momentum in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A search for the production of long-lived particles in proton- proton collisions at a center-of-mass energy of 13 TeVat the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016-2018, corresponding to a total integrated luminosity of 137 fb(-1). This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 mm, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gaugemediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 mm.Article Citation Count: 0Search for pair production of scalar and vector leptoquarks decaying to muons and bottom quarks in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A search for pair production of scalar and vector leptoquarks (LQs) each decaying to a muon and a bottom quark is performed using proton-proton collision data collected at root s = 13 TeV with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 138 fb(-1). No excess above standard model expectation is observed. Scalar (vector) LQs with masses less than 1810 (2120) GeV are excluded at 95% confidence level, assuming a 100% branching fraction of the LQ decaying to a muon and a bottom quark. These limits represent the most stringent to date.Article Citation Count: 0Search for production of a single vectorlike quark decaying to tH or tZ in the all-hadronic final state in pp collisions at(American Physical Society, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Matorras, F.A search for electroweak production of a single vectorlike T quark in association with a bottom (b) quark in the all-hadronic decay channel is presented. This search uses proton-proton collision data at pffiffi s ¼ 13 TeV collected by the CMS experiment at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of 138 fb−1. The T quark is assumed to have charge 2=3 and decay to a top (t) quark and a Higgs (H) or Z boson. Hadronic decays of the t quark and the H or Z boson are reconstructed from the kinematic properties of jets, including those containing b hadrons. No deviation from the standard model prediction is observed in the reconstructed tH and tZ invariant mass distributions. The 95% confidence level upper limits on the product of the production cross section and branching fraction of a T quark produced in association with a b quark and decaying via tH or tZ range from 1260 to 68 fb for T quark masses of 600–1200 GeV. © 2024 CERN, for the CMS Collaboration.Article Citation Count: 3Search for supersymmetry in final states with disappearing tracks in proton-proton collisions at √s=13 TeV(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A search is presented for charged, long-lived supersymmetric particles in final states with one or more disappearing tracks. The search is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the CERN LHC between 2016 and 2018, corresponding to an integrated luminosity of 137 fb(-1). The search is performed over final states characterized by varying numbers of jets, b-tagged jets, electrons, and muons. The length of signal-candidate tracks in the plane perpendicular to the beam axis is used to characterize the lifetimes of wino- and Higgsino-like charginos produced in the context of the minimal supersymmetric standard model. The dE/dx energy loss of signal-candidate tracks is used to increase the sensitivity to charginos with a large mass and thus a small Lorentz boost. The observed results are found to be statistically consistent with the background-only hypothesis. Limits on the pair-production cross section of gluinos and squarks are presented in the framework of simplified models of supersymmetric particle production and decay, and for electroweakino production based on models of wino and Higgsino dark matter. The limits presented are the most stringent to date for scenarios with light third-generation squarks and a wino- or Higgsino-like dark matter candidate capable of explaining the observed dark matter relic density.Article Citation Count: 0Search for the lepton flavor violating τ → 3μ decay in proton-proton collisions at √s=13 TeV(Elsevier, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Zhokin, A.A search for the lepton flavor violating tau -> 3 mu decay is performed using proton-proton collision events at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2017-2018, corresponding to an integrated luminosity of 97.7 fb(-1). Tau leptons produced in both heavy-flavor hadron and W boson decays are exploited in the analysis. No evidence for the decay is observed. The results of this search are combined with an earlier null result based on data collected in 2016 to obtain a total integrated luminosity of 131 fb(-1). The observed (expected) upper limits on the branching fraction.( tau -> 3 mu) at confidence levels of 90 and 95% are 2.9 x 10(-8) (2.4 x 10(-8)) and 3.6 x 10(-8) (3.0 x 10(-8)), respectively.