Browsing by Author "Benato, L."

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Citation - WoS: 1
Angular Analysis of the B0 → K*(892)0μ+μ- Decay in Proton-Proton Collisions at √s=13 TeV
(Elsevier, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Kumar, A.
A full set of optimized observables is measured in an angular analysis of the decay B-0 -> K*(892)(0)mu(+)mu(-) using a sample of proton-proton collisions at root s = 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 140 fb(-1). The analysis is performed in six bins of the squared invariant mass of the dimuon system, q(2), over the range 1.1 < q(2) < 16 GeV2. The results are among the most precise experimental measurements of the angular observables for this decay and are compared to a variety of predictions based on the standard model. Some of these predictions exhibit tension with the measurements.
Measurement of the W Boson Decay Branching Fraction Ratio B(W → c q)/B(w → Q(q)over-Bar′) in Proton-Proton Collisions at √s=13 TeV
(Elsevier, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Kim, J.
The most precise measurement to date of the W boson hadronic decay branching fraction ratio R-c(W) = B(W -> cq)/B(W -> q (q) over bar') is presented. The measurement is based on a sample of proton-proton collision data from the CERN LHC collected by the CMS experiment at a center-of-mass energy of 13TeV in 2016-2018 with an integrated luminosity of 138 fb(-1). The large cross section of top quark-antiquark production at the LHC offers a sizable high-purity sample of W bosons suitable for this measurement. Events with one charged lepton (electron or muon) and at least four jets, two tagged as bottom quark jets, are analyzed. Charm jets are tagged using the presence of a muon inside the jet. The result, R-c(W) = 0.489 +/- 0.020, is consistent with the standard model prediction and is twice as precise as the current world-average value.
Measurement of Wwz and Zh Production Cross Sections at √s=13 and 13.6 TeV
(American Physical Society, 2025) Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Choi, J.
A measurement is presented of the cross section in proton-proton collisions for the production of two W bosons and one Z boson. It is based on data recorded by the CMS experiment at the CERN LHC at center-of-mass energies root s = 13 and 13.6 TeV, corresponding to an integrated luminosity of 200 fb(-1). Events with four charged leptons (electrons or muons) in the final state are selected. Both nonresonant WWZ production and ZH production, with the Higgs boson decaying into two W bosons, are reported. For the first time, the two processes are measured separately in a simultaneous fit. Combining the two modes, signal strengths relative to the standard model (SM) predictions of 0.75(-0.29)(+0.34) and 1.74(-0.60)(+0.71) are measured for root s = 13 and 13.6 TeV, respectively. The observed (expected) significance for the triboson signal is 3.8 (2.5) standard deviations for root s = 13.6 TeV, thus providing the first evidence for triboson production at this center-of-mass energy. Combining the two modes and the two center-of-mass energies, the inclusive signal strength relative to the SM prediction is measured to be 1.03(-0.28)(+0.31), with an observed (expected) significance of 4.5 (5.0) standard deviations.
Citation - Scopus: 1
Measurements of Inclusive and Differential Higgs Boson Production Cross Sections at √s=13.6 TeV in the H → Γγ Decay Channel
(Springer, 2025) Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Sosnov, D.
Inclusive and differential cross sections for Higgs boson production in proton-proton collisions at a centre-of-mass energy of 13.6TeV are measured using data collected with the CMS detector at the LHC in 2022, corresponding to an integrated luminosity of 34.7 fb(-1). Events with the diphoton final state are selected, and the measured inclusive fiducial cross section is sfid = 74 +/- 11 (stat)(-4)(+5) (syst) fb, in agreement with the standard model prediction of 67.8 +/- 3.8 fb. Differential cross sections are measured as functions of several observables: the Higgs boson transverse momentum and rapidity, the number of associated jets, and the transverse momentum of the leading jet in the event. Within the uncertainties, the differential cross sections agree with the standard model predictions.
Citation - WoS: 22
Citation - Scopus: 20
Measurements of Polarization and Spin Correlation and Observation of Entanglement in Top Quark Pairs Using Lepton Plus Jets Events From Proton-Proton Collisions at √s=13 Tev
(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Druzhkin, D.
Measurements of the polarization and spin correlation in top quark pairs (t (t) over bar) are presented using events with a single electron or muon and jets in the final state. The measurements are based on proton-proton collision data from the LHC at root s = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb(-1). All coefficients of the polarization vectors and the spin correlation matrix are extracted simultaneously by performing a binned likelihood fit to the data. The measurement is performed inclusively and in bins of additional observables, such as the mass of the t (t) over bar system and the top quark scattering angle in the t (t) over bar rest frame. The measured polarization and spin correlation are in agreement with the standard model. From the measured spin correlation, conclusions on the t (t) over bar spin entanglement are drawn by applying the Peres-Horodecki criterion. The standard model predicts entangled spins for t (t) over bart states at the production threshold and at high masses of the t (t) over bart system. Entanglement is observed for the first time in events at high t (t) over bar mass, where a large fraction of the t (t) over bar decays are spacelike separated, with an expected and observed significance of above 5 standard deviations.
A Method for Correcting the Substructure of Multiprong Jets using the Lund Jet Plane
(Springer Science and Business Media Deutschland GmbH, 2025) Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Benato, L.; Sosnov, D.
Many analyses at the CERN LHC exploit the substructure of jets to identify heavy resonances produced with high momenta that decay into multiple quarks and/or gluons. This paper presents a new technique for correcting the substructure of simulated large-radius jets from multiprong decays. The technique is based on reclustering the jet constituents into several subjets such that each subjet represents a single prong, and separately correcting the radiation pattern in the Lund jet plane of each subjet using a correction derived from data. The data presented here correspond to an integrated luminosity of 138 fb−1 collected by the CMS experiment between 2016–2018 at a center-of-mass energy of 13 TeV. The correction procedure improves the agreement between data and simulation for several different substructure observables of multiprong jets. This technique establishes, for the first time, a robust calibration for the substructure of jets with four or more prongs, enabling future measurements and searches for new phenomena containing these signatures. © The Author(s) 2025.
Observation of Λ Hyperon Local Polarization in P-Pb Collisions at √snn=8.16 Tev
(American Physical Society, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Druzhkin, D.
The polarization of the Lambda and (Lambda) over bar hyperons along the beam direction has been measured in proton-lead (p-Pb) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of 186.0 +/- 6.5 nb(-1). A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient P-z,P-s2, is observed. The P-z,P-s2 values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed P-z,P-s2 values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the p-Pb results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.
Citation - WoS: 17
Citation - Scopus: 10
Performance of the Cms High-Level Trigger During Lhc Run 2
(Iop Publishing Ltd, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Druzhkin, D.
The CERN LHC provided proton and heavy ion collisions during its Run 2 operation period from 2015 to 2018. Proton-proton collisions reached a peak instantaneous luminosity of 2.1 x 10(34) cm(-2)s(-1), twice the initial design value, at root s = 13 TeV. The CMS experiment records a subset of the collisions for further processing as part of its online selection of data for physics analyses, using a two-level trigger system: the Level-1 trigger, implemented in custom-designed electronics, and the high-level trigger, a streamlined version of the offline reconstruction software running on a large computer farm. This paper presents the performance of the CMS high-level trigger system during LHC Run 2 for physics objects, such as leptons, jets, and missing transverse momentum, which meet the broad needs of the CMS physics program and the challenge of the evolving LHC and detector conditions. Sophisticated algorithms that were originally used in offline reconstruction were deployed online. Highlights include a machine-learning b tagging algorithm and a reconstruction algorithm for tau leptons that decay hadronically.
Proton Reconstruction With the TOTEM Roman Pot Detectors for High-Β* LHC Data
(IOP Publishing Ltd, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Zich, J.
The TOTEM Roman pot detectors are used to reconstruct the transverse momentum of scattered protons and to estimate the transverse location of the primary interaction. This paper presents new methods of track reconstruction, measurements of strip-level detection efficiencies, cross-checks of the LHC beam optics, and detector alignment techniques, along with their application in the selection of signal collision events. The track reconstruction is performed by exploiting hit cluster information through a novel method using a common polygonal area in the intercept-slope plane. The technique is applied in the relative alignment of detector layers with mu m precision. A tag-and-probe method is used to extract strip-level detection efficiencies. The alignment of the Roman pot system is performed through time-dependent adjustments, resulting in a position accuracy of 3 mu m in the horizontal and 60 mu m in the vertical directions. The goal is to provide an optimal reconstruction tool for central exclusive physics analyses based on the high-beta* data-taking period at root s = 13 TeV in 2018.
Citation - WoS: 1
Citation - Scopus: 1
Reweighting Simulated Events Using Machine-Learning Techniques in the CMS Experiment
(Springer, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Druzhkin, D.
Data analyses in particle physics rely on an accurate simulation of particle collisions and a detailed simulation of detector effects to extract physics knowledge from the recorded data. Event generators together with a geant-based simulation of the detectors are used to produce large samples of simulated events for analysis by the LHC experiments. These simulations come at a high computational cost, where the detector simulation and reconstruction algorithms have the largest CPU demands. This article describes how machine-learning (ML) techniques are used to reweight simulated samples obtained with a given set of parameters to samples with different parameters or samples obtained from entirely different simulation programs. The ML reweighting method avoids the need for simulating the detector response multiple times by incorporating the relevant information in a single sample through event weights. Results are presented for reweighting to model variations and higher-order calculations in simulated top quark pair production at the LHC. This ML-based reweighting is an important element of the future computing model of the CMS experiment and will facilitate precision measurements at the High-Luminosity LHC.
Citation - WoS: 5
Search for a Neutral Gauge Boson With Nonuniversal Fermion Couplings in Vector Boson Fusion Processes in Proton-Proton Collisions at √s=13 TeV
(American Physical Society, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Warden, A.
The first search for a heavy neutral spin-1 gauge boson (Z ') with nonuniversal fermion couplings produced via vector boson fusion processes and decaying to tau leptons or W bosons is presented. The analysis is performed using LHC data at root s = 13 TeV, collected from 2016 to 2018 with the CMS experiment and corresponding to an integrated luminosity of 138 fb(-1). The data are consistent with the standard model predictions. Upper limits are set on the product of the cross section for production of the Z ' boson and its branching fraction to tau tau or WW. The presence of a Z ' boson decaying to tau(+)tau(-) (W+W-) is excluded for masses up to 2.45(1.60) TeV, depending on the Z ' boson coupling to standard model weak bosons, and assuming a Z ' -> tau(+)tau(-) (W+W-) branching fraction of 50%.
Search for CP Violation in Events with Top Quarks and Z Bosons at √s=13 and 13.6 Tev
(Elsevier, 2025) Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Sosnov, D.
A search for the violation of the charge-parity (CP) symmetry in the production of top quarks in association with Z bosons is presented, using events with at least three charged leptons and additional jets. The search is performed in a sample of proton-proton collision data collected by the CMS experiment at the CERN LHC in 2016-2018 at a center-of-mass energy of 13 TeV and in 2022 at 13.6 TeV, corresponding to a total integrated luminosity of 173 fb(-1). For the first time in this final state, observables that are odd under the CP transformation are employed. Also for the first time, physics-informed machine-learning techniques are used to construct these observables. While for standard model (SM) processes the distributions of these observables are predicted to be symmetric around zero, CP-violating modifications of the SM would introduce asymmetries. Two CP-odd operators O-Wt(I) and O-tZ(I) in the SM effective field theory are considered that may modify the interactions between top quarks and electroweak bosons. The obtained results are consistent with the SM prediction within two standard deviations, and exclusion limits on the associated Wilson coefficients of -2.7 < c(tW)(I) < 2.5 and -0.2 < c(tZ)(I) < 2.0 are set at 95% confidence level. The largest discrepancy is observed in CtZI where data is consistent with positive values, with an observed local significance with respect to the SM hypothesis of 2.5 standard deviations, when only linear terms are considered.
Citation - Scopus: 2
Search for Excited Tau Leptons in the Ττγ Final State in Proton-Proton Collisions √s=13 TeV
(Springer, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Makarenko, V.
Results are presented for a test of the compositeness of the heaviest charged lepton, tau, using data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC. The data were collected in 2016-2018 and correspond to an integrated luminosity of 138 fb(-1). This analysis searches for tau lepton pair production in which one of the tau leptons is produced in an excited state and decays to a ground state tau lepton and a photon. The event selection consists of two isolated tau lepton decay candidates and a high-energy photon. The mass of the excited tau lepton is reconstructed using the missing transverse momentum in the event, assuming the momentum of the neutrinos from each tau lepton decay are aligned with the visible decay products. No excess of events above the standard model background prediction is observed. This null result is used to set lower bounds on the excited tau lepton mass. For a compositeness scale Lambda equal to the excited tau lepton mass, excited tau leptons with masses below 4700 GeV are excluded at 95% confidence level; for Lambda = 10 TeV this exclusion is set at 2800 GeV. This is the first experimental result covering this production and decay process in the excited tau mass range above 175 GeV.
Search for Heavy Neutral Higgs Bosons a and H in the T(t)over-Barz Channel in Proton-Proton Collisions at 13 TeV
(Elsevier, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Lee, J.
A direct search for new heavy neutral Higgs bosons A and H in the t (t) over barZ channel is presented, targeting the process pp -> A -> ZH with H -> t (t) over bar. For the first time, the channel with decays of the Z boson to muons or electrons in association with all-hadronic decays of the t (t) over bar system is targeted. The analysis uses proton-proton collision data collected at the CERN LHC with the CMS experiment at root s = 13 TeV, which correspond to an integrated luminosity of 138 fb(-1). No signal is observed. Upper limits on the product of the cross section and branching fractions are derived for narrow resonances A and H with masses up to 2100 and 2000GeV, respectively, assuming A boson production through gluon fusion. The results are also interpreted within two-Higgs-doublet models, where A and H are CP-odd and CP-even states, respectively, complementing and substantially extending the reach of previous searches.
Search for Heavy Neutral Resonances Decaying to Tau Lepton Pairs in Proton-Proton Collisions at √s=13 TeV
(Amer Physical Soc, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Makarenko, V.
A search for heavy neutral gauge bosons (Z ') decaying into a pair of tau leptons is performed in proton-proton collisions at root s =13 TeV at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of 138 fb(-1). The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the Z ' production cross section and its branching fraction to tau lepton pairs for a range of Z ' boson masses. For a narrow resonance in the sequential standard model scenario, a Z ' boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search.
Search for High-Mass Resonances in a Final State Comprising a Gluon and Two Hadronically Decaying W Bosons in Proton-Proton Collisions at S = 13 TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Benato, L.; Bergauer, T.; Chatterjee, S.
A search for high-mass resonances decaying into a gluon, g, and two W bosons is presented. A Kaluza-Klein gluon, gKK, decaying in cascade via a scalar radion R, gKK → gR → gWW, is considered. The final state studied consists of three large-radius jets, two of which contain the products of hadronically decaying W bosons, and the third one the hadronization products of the gluon. The analysis is performed using proton-proton collision data at s = 13 TeV collected by the CMS experiment at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of 138 fb−1. The masses of the gKK and R candidates are reconstructed as trijet and dijet masses, respectively. These are used for event categorization and signal extraction. No excess of data events above the standard model background expectation is observed. Upper limits are set on the product of the gKK production cross section and its branching fraction via a radion R to gWW. This is the first analysis examining the resonant WW+jet signature and setting limits on the two resonance masses in an extended warped extra-dimensional model. © 2025 Elsevier B.V., All rights reserved.
Search for the Z Boson Decay To Ττμμ in Proton-Proton Collisions at √s=13 Tev
(Amer Physical Soc, 2024) Hayrapetyan, A.; Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Benato, L.; Bergauer, T.; Druzhkin, D.
The first search for the Z boson decay to tau tau mu mu at the CERN LHC is presented, based on data collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb(-1). The data are compatible with the predicted background. For the first time, an upper limit at the 95% confidence level of 6.9 times the standard model expectation is placed on the ratio of the Z -> tau tau mu mu to Z -> 4 mu branching fractions. Limits are also placed on the six flavor-conserving four-lepton effective-field-theory operators involving two muons and two tau leptons, for the first time testing all such operators.