Browsing by Author "Tchekhovski, V."

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Development of Systematic Uncertainty-Aware Neural Network Trainings for Binned-Likelihood Analyses at the LHC
(Springer Nature, 2025) Druzhkin, D.; Borshch, V.; Babaev, A.; Uzunian, A.; Slabospitskii, S.; Kachanov, V.; Tchekhovski, V.
We propose a neural network training method capable of accounting for the effects of systematic variations of the data model in the training process and describe its extension towards neural network multiclass classification. The procedure is evaluated on the realistic case of the measurement of Higgs boson production via gluon fusion and vector boson fusion in the ττ decay channel at the CMS experiment. The neural network output functions are used to infer the signal strengths for inclusive production of Higgs bosons as well as for their production via gluon fusion and vector boson fusion. We observe improvements of 12 and 16% in the uncertainty in the signal strengths for gluon and vector-boson fusion, respectively, compared with a conventional neural network training based on cross-entropy. © CERN for the benefit of the CMS Collaboration 2025.
Citation - Scopus: 1
Measurements of the Higgs Boson Production Cross Section in the Four-Lepton Final State in Proton-Proton Collisions at = 13.6 TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
The measurements of the Higgs boson (H) production cross sections performed by the CMS Collaboration in the four-lepton (4ℓ, ℓ = e, μ) final state at a center-of-mass energy = 13.6 TeV are presented. These measurements are based on data collected with the CMS detector at the CERN LHC in 2022, corresponding to an integrated luminosity of 34.7 fb−1. Cross sections are measured in a fiducial region closely matching the experimental acceptance, both inclusively and differentially, as a function of the transverse momentum and the absolute value of the rapidity of the four-lepton system. The H → ZZ → 4ℓ inclusive fiducial cross section is measured to be fb, in agreement with the standard model expectation of fb. © The Author(s) 2025.
Observation of Coherent (Formula Presented) Meson Photoproduction in Ultraperipheral PbPb Collisions at (Formula Presented)
(American Physical Society, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
The first observation of coherent (Formula presented) meson photoproduction off heavy nuclei is presented using ultraperipheral lead-lead collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The data were collected by the CMS experiment and correspond to an integrated luminosity of (Formula presented). The (Formula presented) meson signals are reconstructed via the (Formula presented) decay channel. The production cross section is presented as a function of the (Formula presented) meson rapidity in the range (Formula presented), probing gluons that carry a fraction of the nucleon momentum ((Formula presented)) around (Formula presented). The observed cross section exhibits little dependence on rapidity and is significantly suppressed, by a factor of (Formula presented), compared to a baseline model that treats a nucleus as a collection of free nucleons. Theoretical models that incorporate the nuclear shadowing effect generally provide a better description of the (Formula presented) data than those incorporating gluon saturation. This study establishes a powerful new tool for exploring nuclear effects and nuclear gluonic structure in the small-(Formula presented) regime at a unique energy scale bridging the perturbative and nonperturbative quantum chromodynamics domains. © 2025 CERN, for the CMS Collaboration.
Search for a Heavy Pseudoscalar Higgs Boson Decaying To a 125 GeV Higgs Boson and a Z Boson in Final States with Two Tau and Two Light Leptons in Proton-Proton Collisions at TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
A search for a heavy pseudoscalar Higgs boson, A, decaying to a 125 GeV Higgs boson h and a Z boson is presented. The h boson is identified via its decay to a pair of tau leptons, while the Z boson is identified via its decay to a pair of electrons or muons. The search targets the production of the A boson via the gluon-gluon fusion process, gg → A, and in association with bottom quarks,. The analysis uses a data sample corresponding to an integrated luminosity of 138 fb−1 collected with the CMS detector at the CERN LHC in proton-proton collisions at a centre-of-mass energy of TeV. Constraints are set on the product of the cross sections of the A production mechanisms and the A → Zh decay branching fraction. The observed (expected) upper limit at 95% confidence level ranges from 0.049 (0.060) pb to 1.02 (0.79) pb for the gg → A process and from 0.053 (0.059) pb to 0.79 (0.61) pb for the process in the probed range of the A boson mass, mA, from 225 GeV to 1 TeV. The results of the search are used to constrain parameters within the benchmark scenario of the minimal supersymmetric extension of the standard model. Values of tan β below 2.2 are excluded in this scenario at 95% confidence level for all mA values in the range from 225 to 350 GeV. © The Author(s) 2025.
Search for Dark Matter Produced in Association with a Higgs Boson Decaying To a τ Lepton Pair in Proton-Proton Collisions at TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
A search for dark matter particles produced in association with a Higgs boson decaying into a pair of τ leptons is performed using data collected in proton-proton collisions at a center-of-mass energy of 13 TeV with the CMS detector. The analysis is based on a data set corresponding to an integrated luminosity of 101 fb−1 collected in 2017–2018. No significant excess over the expected standard model background is observed. This result is interpreted within the frameworks of the 2HDM+a and baryonic Z′ benchmark simplified models. The 2HDM+a model is a type-II two-Higgs-doublet model featuring a heavy pseudoscalar with an additional light pseudoscalar. Upper limits at 95% confidence level are set on the product of the production cross section and the branching fraction for each of these two simplified models. Heavy pseudoscalar boson masses between 400 and 700 GeV are excluded for a light pseudoscalar mass of 100 GeV. For the baryonic Z′ model, a statistical combination is made with an earlier search based on a data set of 36 fb−1 collected in 2016. In this model, Z′ boson masses up to 1050 GeV are excluded for a dark matter particle mass of 1 GeV. © The Author(s) 2025.
Citation - WoS: 1
Citation - Scopus: 1
Search for Jet Quenching With Dijets From High-Multiplicity ppb Collisions at = 8.16 TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Zhizhin, I.
The first measurement of the dijet transverse momentum balance xj in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of = 8.16 TeV is presented. The xj observable, defined as the ratio of the subleading over leading jet transverse momentum in a dijet pair, is used to search for jet quenching effects. The data, corresponding to an integrated luminosity of 174.6 nb−1, were collected with the CMS detector in 2016. The xj distributions and their average values are studied as functions of the charged-particle multiplicity of the events and for various dijet rapidity selections. The latter enables probing hard scattering of partons carrying distinct nucleon momentum fractions x in the proton- and lead-going directions. The former, aided by the high-multiplicity triggers, allows probing for potential jet quenching effects in high-multiplicity events (with up to 400 charged particles), for which collective phenomena consistent with quark-gluon plasma (QGP) droplet formation were previously observed. The ratios of xj distributions for high- to low-multiplicity events are used to quantify the possible medium effects. These ratios are consistent with simulations of the hard-scattering process that do not include QGP production. These measurements set an upper limit on medium-induced energy loss of the subleading jet of 1.26% of its transverse momentum at the 90% confidence level in high multiplicity pPb events. © The Author(s) 2025.
Citation - Scopus: 1
Search for the Rare Decay (Formula Presented) in Proton-Proton Collisions at (Formula Presented)
(American Physical Society, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
A search for the rare decay (Formula presented) is reported using proton-proton collision events at (Formula presented) collected by the CMS detector in 2022-2023, corresponding to an integrated luminosity of (Formula presented). This is the first analysis to use a newly developed inclusive dimuon trigger, expanding the scope of the CMS flavor physics program. The search uses (Formula presented) mesons obtained from (Formula presented) decays. No significant excess is observed. A limit on the branching fraction of (Formula presented) at 95% confidence level is set. This is the most stringent upper limit set on any flavor changing neutral current decay in the charm sector. © 2025 CERN, for the CMS Collaboration.
Search for Top Squarks in Final States with Many Light-Flavor Jets and 0, 1, or 2 Charged Leptons in Proton-Proton Collisions at TeV
(Springer Science and Business Media Deutschland GmbH, 2025) Tchekhovski, V.; Hayrapetyan, A.; Makarenko, V.; Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Druzhkin, D.
Several new physics models including versions of supersymmetry (SUSY) characterized by R-parity violation (RPV) or with additional hidden sectors predict the production of events with top quarks, low missing transverse momentum, and many additional quarks or gluons. The results of a search for top squarks decaying to two top quarks and six additional light-flavor quarks or gluons are reported. The search employs a novel machine learning method for background estimation from control samples in data using decorrelated discriminators. The search is performed using events with 0, 1, or 2 electrons or muons in conjunction with at least six jets. No requirement is placed on the magnitude of the missing transverse momentum. The result is based on a sample of proton-proton collisions at TeV corresponding to 138 fb−1 of integrated luminosity collected with the CMS detector at the LHC in 2016–2018. With no statistically significant excess of events observed beyond the expected contributions from the standard model, the data are used to determine upper limits on the top squark pair production cross section in the frameworks of RPV and stealth SUSY. Models with top squark masses less than 700 (930) GeV are excluded at 95% confidence level for RPV (stealth) SUSY scenarios. © The Author(s) 2025.