Rectorate / Rektörlük
Permanent URI for this collectionhttps://hdl.handle.net/11147/6849
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Article Citation - WoS: 15Citation - Scopus: 19Study of J/Ψ Meson Production Inside Jets in pp Collisions at S=8 TeV(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Hensel, C.A study of the production of prompt J/ψ mesons contained in jets in proton-proton collisions at s=8TeV is presented. The analysis is based on data corresponding to an integrated luminosity of 19.1 fb−1 collected with the CMS detector at the LHC. For events with at least one observed jet, the angular separation between the J/ψ meson and the jet is used to test whether the J/ψ meson is part of 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 |η<inf>jet</inf>|<1. The differential distributions of the probability to have a J/ψ meson contained in a jet as a function of jet energy for a fixed J/ψ energy fraction are compared to a theoretical model using the fragmenting jet function approach. The data agree best with fragmenting jet function calculations that use a long-distance matrix element parameter set in which prompt J/ψ mesons are predicted to be unpolarized. This technique demonstrates a new way to test predictions for prompt J/ψ production using nonrelativistic quantum chromodynamics. © 2020 Elsevier B.V.Article Citation - WoS: 12Citation - Scopus: 37Running of the Top Quark Mass From Proton-Proton Collisions at S=13 TeV(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Alves, G.A.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 (MS‾) renormalization scheme is extracted from a comparison of the differential top quark-antiquark (tt¯) cross section as a function of the invariant mass of the tt¯ 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 tt¯ 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 35.9fb−1. 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. © 2020 The Author(s)Article Citation - WoS: 32Citation - Scopus: 49Measurement of the tt‾bb‾ Production Cross Section in the All-Jet Final State in pp Collisions at S=13 TeV(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Moraes, A.A measurement of the production cross section of top quark pairs in association with two b jets (tt‾bb‾) 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 35.9 fb−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 b quarks. 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)<inf>−1.3</inf> +1.6(syst)pb and also measured for two fiducial tt‾bb‾ 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. © 2020 The AuthorArticle Citation - WoS: 35Citation - Scopus: 93Search for Resonant and Nonresonant Higgs Boson Pair Production in the B B ¯final State in Proton-Proton Collisions at ?s=13 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerSearches for resonant and nonresonant pair-produced Higgs bosons (HH) decaying respectively into , through either W or Z bosons, and b b ¯ are presented. The analyses are based on a sample of proton-proton collisions at s=13 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb −1 . Data and predictions from the standard model are in agreement within uncertainties. For the standard model HH hypothesis, the data exclude at 95% confidence level a product of the production cross section and branching fraction larger than 72 fb, corresponding to 79 times the standard model prediction. Constraints are placed on different scenarios considering anomalous couplings, which could affect the rate and kinematics of HH production. Upper limits at 95% confidence level are set on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs, the latter produced with minimal gravity-like coupling.Article Citation - WoS: 24Citation - Scopus: 26Pseudorapidity Distributions of Charged Hadrons in Proton-Lead Collisions at ?snn=5.02 and 8.16 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerThe pseudorapidity distributions of charged hadrons in proton-lead collisions at nucleon-nucleon center-of-mass energies sNN=5.02 and 8.16 TeV are presented. The measurements are based on data samples collected by the CMS experiment at the LHC. The number of primary charged hadrons produced in non-single-diffractive proton-lead collisions is determined in the pseudorapidity range |η lab | < 2.4. The charged-hadron multiplicity distributions are compared to the predictions from theoretical calculations and Monte Carlo event generators. In the center-of-mass pseudorapidity range |η cm | < 0.5, the average charged-hadron multiplicity densities 〈dN ch /dη cm 〉 |ηcm| < 0.5 are 17.31 ± 0.01 (stat) ± 0.59 (syst) and 20.10 ± 0.01 (stat) ± 0.85(syst) at sNN=5.02 and 8.16 TeV, respectively. The particle densities per participant nucleon are compared to similar measurements in proton-proton, proton-nucleus, and nucleus-nucleus collisions.Article Citation - WoS: 5Citation - Scopus: 6Production of Leading Charged Particles and Leading Charged-Particle Jets at Small Transverse Momenta in Pp Collisions at Sqrt(s) = 8 Tev(American Physical Society, 2015) CMS Collaboration; Karapınar, GülerThe per-event yield of the highest transverse momentum charged particle and charged-particle jet, integrated above a given pTmin threshold starting at pTmin=0.8 and 1 GeV, respectively, is studied in pp collisions at s=8 TeV. The particles and the jets are measured in the pseudorapidity ranges |η|<2.4 and 1.9, respectively. The data are sensitive to the momentum scale at which parton densities saturate in the proton, to multiple partonic interactions, and to other key aspects of the transition between the soft and hard QCD regimes in hadronic collisions. © 2015 CERN, for the CMS Collaboration. Published by the American Physical Society under the terms of the »http://creativecommons.org/licenses/by/3.0/» Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Article Citation - WoS: 22Citation - Scopus: 38Combined Search for the Quarks of a Sequential Fourth Generation(American Physical Society, 2012) CMS Collaboration; Karapınar, GülerResults are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5fb-1 recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about ±20GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions. © 2012 CERN.Article Citation - WoS: 20Citation - Scopus: 45Search for Pair Production of First- and Second-Generation Scalar Leptoquarks in Pp Collisions at ?s=7tev(American Physical Society, 2012) CMS Collaboration; Karapınar, GülerResults are presented from a search for the pair production of first- and second-generation scalar leptoquarks in proton-proton collisions at √s=7TeV. The data sample corresponds to an integrated luminosity of 5.0fb -1, collected by the CMS detector at the LHC. The search signatures involve either two charged leptons of the same flavor (electrons or muons) and at least two jets or a single charged lepton (electron or muon), missing transverse energy, and at least two jets. If the branching fraction of the leptoquark decay into a charged lepton and a quark is assumed to be β=1, leptoquark pair production is excluded at the 95% confidence level for masses below 830 GeV and 840 GeV for the first and second generations, respectively. For β=0.5, masses below 640 GeV and 650 GeV are excluded. These limits are the most stringent to date. © 2012 CERN.