WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 97Citation - Scopus: 96Constraints on the Chiral Magnetic Effect Using Charge-Dependent Azimuthal Correlations in P Pb and Pbpb Collisions at the Cern Large Hadron Collider(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerCharge-dependent azimuthal correlations of same- and opposite-sign pairs with respect to the second- and third-order event planes have been measured in pPb collisions at sNN=8.16TeV and PbPb collisions at 5.02 TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chiral magnetic effect (CME) in heavy ion collisions. Three- and two-particle azimuthal correlators are extracted as functions of the pseudorapidity difference, the transverse momentum (pT) difference, and the pT average of same- and opposite-charge pairs in various event multiplicity ranges. The data suggest that the charge-dependent three-particle correlators with respect to the second- and third-order event planes share a common origin, predominantly arising from charge-dependent two-particle azimuthal correlations coupled with an anisotropic flow. The CME is expected to lead to a v2-independent three-particle correlation when the magnetic field is fixed. Using an event shape engineering technique, upper limits on the v2-independent fraction of the three-particle correlator are estimated to be 13% for pPb and 7% for PbPb collisions at 95% confidence level. The results of this analysis, both the dominance of two-particle correlations as a source of the three-particle results and the similarities seen between PbPb and pPb, provide stringent constraints on the origin of charge-dependent three-particle azimuthal correlations and challenge their interpretation as arising from a chiral magnetic effect in heavy ion collisions.Article Citation - WoS: 24Citation - Scopus: 30Principal-Component Analysis of Two-Particle Azimuthal Correlations in Pbpb and Ppb Collisions at Cms(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerFor the first time a principle-component analysis is used to separate out different orthogonal modes of the two-particle correlation matrix from heavy ion collisions. The analysis uses data from sNN=2.76TeV PbPb and sNN=5.02TeV pPb collisions collected by the CMS experiment at the CERN Large Hadron Collider. Two-particle azimuthal correlations have been extensively used to study hydrodynamic flow in heavy ion collisions. Recently it was shown that the expected factorization of two-particle results into a product of the constituent single-particle anisotropies is broken. The new information provided by these modes may shed light on the breakdown of flow factorization in heavy ion collisions. The first two modes ("leading" and "subleading") of two-particle correlations are presented for elliptical and triangular anisotropies in PbPb and pPb collisions as a function of pT over a wide range of event activity. The leading mode is found to be essentially equivalent to the anisotropy harmonic previously extracted from two-particle correlation methods. The subleading mode represents a new experimental observable and is shown to account for a large fraction of the factorization breaking recently observed at high transverse momentum. The principle-component analysis technique was also applied to multiplicity fluctuations. These also show a subleading mode. The connection of these new results to previous studies of factorization is discussed.Article Citation - WoS: 22Citation - Scopus: 22Pseudorapidity Dependence of Long-Range Two-Particle Correlations in Ppb Collisions at Sqrt(s[nn]) =5.02 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerTwo-particle correlations in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV are studied as a function of the pseudorapidity separation (Δη) of the particle pair at small relative azimuthal angle (|Δφ|<π/3). The correlations are decomposed into a jet component that dominates the short-range correlations (|Δη|<1), and a component that persists at large Δη and may originate from collective behavior of the produced system. The events are classified in terms of the multiplicity of the produced particles. Finite azimuthal anisotropies are observed in high-multiplicity events. The second and third Fourier components of the particle-pair azimuthal correlations, V2 and V3, are extracted after subtraction of the jet component. The single-particle anisotropy parameters v2 and v3 are normalized by their laboratory frame midrapidity value and are studied as a function of ηc.m.. The normalized v2 distribution is found to be asymmetric about ηc.m.=0, with smaller values observed at forward pseudorapidity, corresponding to the direction of the proton beam, while no significant pseudorapidity dependence is observed for the normalized v3 distribution within the statistical uncertainties. © 2017 CERN.Article Citation - WoS: 70Citation - Scopus: 118Measurement of Inclusive Jet Cross Sections in Pp and Pbpb Collisions at Sqrt(s[nn])=2.76 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerInclusive jet spectra from pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76TeV, collected with the CMS detector at the CERN Large Hadron Collider, are presented. Jets are reconstructed with three different distance parameters (R=0.2, 0.3, and 0.4) for transverse momentum (pT) greater than 70GeV/c and pseudorapidity |η|<2. Next-to-leading-order quantum chromodynamic calculations with nonperturbative corrections are found to overpredict jet production cross sections in pp for small distance parameters. The jet nuclear modification factors for PbPb compared to pp collisions, show a steady decrease from peripheral to central events, along with a weak dependence on the jet pT. They are found to be independent of the distance parameter in the measured kinematic range. ©2017 CERN, for the CMS Collaboration. Published by the American Physical Society under the terms of the 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.Article Citation - WoS: 44Citation - Scopus: 40Measurements of the Tt¯ Production Cross Section in Lepton+jets Final States in Pp Collisions at 8 Tev and Ratio of 8 To 7 Tev Cross Sections(Springer Verlag, 2017) CMS Collaboration; Karapınar, GülerA measurement of the top quark pair production (tt¯) cross section in proton–proton collisions at the centre-of-mass energy of 8TeV is presented using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.6fb-1. This analysis is performed in the tt¯ decay channels with one isolated, high transverse momentum electron or muon and at least four jets, at least one of which is required to be identified as originating from hadronization of a b quark. The calibration of the jet energy scale and the efficiency of b jet identification are determined from data. The measured tt¯ cross section is 228.5±3.8(stat)±13.7(syst)±6.0(lumi) pb. This measurement is compared with an analysis of 7TeV data, corresponding to an integrated luminosity of 5.0fb-1, to determine the ratio of 8TeV to 7TeV cross sections, which is found to be 1.43±0.04(stat)±0.07(syst)±0.05(lumi). The measurements are in agreement with QCD predictions up to next-to-next-to-leading order.Article Citation - WoS: 17Citation - Scopus: 20Measurement of Dijet Azimuthal Decorrelation in Pp Collisions at ?s=8tev(Springer Verlag, 2016) CMS Collaboration; Karapınar, GülerA measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8TeV corresponding to an integrated luminosity of 19.7fb-1. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.Article Citation - WoS: 34Citation - Scopus: 26Forward–backward Asymmetry of Drell–yan Lepton Pairs in Pp Collisions at ?s = 8 Tev(Springer Verlag, 2016) CMS Collaboration; Karapınar, GülerA measurement of the forward–backward asymmetry AFB of oppositely charged lepton pairs (μμ and ee) produced via Z / γ∗ boson exchange in pp collisions at √s = 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.7 fb-1 collected with the CMS detector at the LHC. The measurement of AFB is performed for dilepton masses between 40 GeV and 2TeV and for dilepton rapidity up to 5. The AFB measurements as a function of dilepton mass and rapidity are compared with the standard model predictions.Article Citation - WoS: 18Citation - Scopus: 18Search for Lepton Flavour Violating Decays of Heavy Resonances and Quantum Black Holes To an Eµ Pair in Proton–proton Collisions at ?s = 8 Tev(Springer Verlag, 2016) CMS Collaboration; Karapınar, GülerA search for narrow resonances decaying to an electron and a muon is presented. The eμ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 fb-1 collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected eμ pairs, upper limits are set at 95 % confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of τ sneutrino in R-parity violating supersymmetry is considered. The τ sneutrino is excluded for masses below 1.28 TeV for couplings λ132= λ231= λ311 ′= 0.01 , and below 2.30 TeV for λ132= λ231= 0.07 and λ311 ′= 0.11. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the Z boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the eμ mass spectrum excludes QBH production below a threshold mass Mth of 1.99 TeV. In models that invoke extra dimensions, the bounds range from 2.36 TeV for one extra dimension to 3.63 TeV for six extra dimensions. This is the first search for QBHs decaying into the eμ final state. © 2016, CERN for the benefit of the CMS collaboration.Article Citation - WoS: 33Citation - Scopus: 30Search for Massive Wh Resonances Decaying Into the L?bb¯ Final State at ?s = 8 Tev(Springer Verlag, 2016) CMS Collaboration; Karapınar, GülerA search for a massive resonance W ′decaying into a W and a Higgs boson in the ℓνb b ¯ (ℓ= e , μ) final state is presented. Results are based on data corresponding to an integrated luminosity of 19.7fb - 1 of proton–proton collisions at s= 8 TeV , collected using the CMS detector at the LHC. For a high-mass (≳ 1TeV) resonance, the two bottom quarks coming from the Higgs boson decay are reconstructed as a single jet, which can be tagged by placing requirements on its substructure and flavour. Exclusion limits at 95 % confidence level are set on the production cross section of a narrow resonance decaying into WH, as a function of its mass. In the context of a little Higgs model, a lower limit on the W ′ mass of 1.4TeV is set. In a heavy vector triplet model that mimics the properties of composite Higgs models, a lower limit on the W ′ mass of 1.5TeV is set. In the context of this model, the results are combined with related searches to obtain a lower limit on the W ′ mass of 1.8TeV , the most restrictive to date for decays to a pair of standard model bosons.Article Citation - WoS: 50Citation - Scopus: 49Measurement of the Inclusive Jet Cross Section in Pp Collisions at ?s = 2.76 Tev(Springer Verlag, 2016) Karapınar, GülerThe double-differential inclusive jet cross section is measured as a function of jet transverse momentum pT and absolute rapidity |y|, using proton-proton collision data collected with the CMS experiment at the LHC, at a center-of-mass energy of √s = 2.76 TeV and corresponding to an integrated luminosity of 5.43 pb-1. Jets are reconstructed within the pT range of 74 to 592 GeV and the rapidity range |y|<3.0. The reconstructed jet spectrum is corrected for detector resolution. The measurements are compared to the theoretical prediction at next-to-leading-order QCD using different sets of parton distribution functions. This inclusive cross section measurement explores a new kinematic region and is consistent with QCD predictions. © 2016, CERN for the benefit of the CMS collaboration.