Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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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: 42Citation - Scopus: 35Search for Supersymmetry in Proton-Proton Collisions at 13 Tev Using Identified Top Quarks(American Physical Society, 2018) CMS Collaboration; Karapınar, GülerA search for supersymmetry is presented based on proton-proton collision events containing identified hadronically decaying top quarks, no leptons, and an imbalance pTmiss in transverse momentum. The data were collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb-1. Search regions are defined in terms of the multiplicity of bottom quark jet and top quark candidates, the pTmiss, the scalar sum of jet transverse momenta, and the mT2 mass variable. No statistically significant excess of events is observed relative to the expectation from the standard model. Lower limits on the masses of supersymmetric particles are determined at 95% confidence level in the context of simplified models with top quark production. For a model with direct top squark pair production followed by the decay of each top squark to a top quark and a neutralino, top squark masses up to 1020 GeV and neutralino masses up to 430 GeV are excluded. For a model with pair production of gluinos followed by the decay of each gluino to a top quark-antiquark pair and a neutralino, gluino masses up to 2040 GeV and neutralino masses up to 1150 GeV are excluded. These limits extend previous results.Article Citation - WoS: 30Citation - Scopus: 56Observation of Top Quark Production in Proton-Nucleus Collisions(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerThe first observation of top quark production in proton-nucleus collisions is reported using proton-lead data collected by the CMS experiment at the CERN LHC at a nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. The measurement is performed using events with exactly one isolated electron or muon candidate and at least four jets. The data sample corresponds to an integrated luminosity of 174 nb-1. The significance of the tt signal against the background-only hypothesis is above 5 standard deviations. The measured cross section is σtt=45±8 nb, consistent with predictions from perturbative quantum chromodynamics.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: 44Search for Evidence of the Type-Iii Seesaw Mechanism in Multilepton Final States in Proton-Proton Collisions at ?s =13 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerA search for a signal consistent with the type-III seesaw mechanism in events with three or more electrons or muons is presented. The data sample consists of proton-proton collisions at s=13 TeV collected by the CMS experiment at the LHC in 2016 and corresponds to an integrated luminosity of 35.9 fb-1. Selection criteria based on the number of leptons and the invariant mass of oppositely charged lepton pairs are used to distinguish the signal from the standard model background. The observations are consistent with the expectations from standard model processes. The results are used to place limits on the production of heavy fermions of the type-III seesaw model as a function of the branching ratio to each lepton flavor. In the scenario of equal branching fractions to each lepton flavor, heavy fermions with masses below 840 GeV are excluded. This is the most sensitive probe to date of the type-III seesaw mechanism.Article Citation - WoS: 29Citation - Scopus: 48Measurement of the Differential Cross Sections for the Associated Production of a W Boson and Jets in Proton-Proton Collisions at Sqrt(s) =13 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerA measurement of the differential cross sections for a W boson produced in association with jets in the muon decay channel is presented. The measurement is based on 13 TeV proton-proton collision data corresponding to an integrated luminosity of 2.2 fb-1, recorded by the CMS detector at the LHC. The cross sections are reported as functions of jet multiplicity, jet transverse momentum pT, jet rapidity, the scalar pT sum of the jets, and angular correlations between the muon and each jet for different jet multiplicities. The measured cross sections are in agreement with predictions that include multileg leading-order (LO) and next-to-LO matrix element calculations interfaced with parton showers, as well as a next-to-next-to-LO calculation for the W boson and one jet production.Article Citation - WoS: 17Citation - Scopus: 43A Search for Higgs Boson Pair Production in the Bb Tau Tau Final State in Proton-Proton Collisions at Sqrt(s) = 8 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerResults are presented from a search for production of Higgs boson pairs (HH) where one boson decays to a pair of b quarks and the other to a τ lepton pair. This work is based on proton-proton collision data collected by the CMS experiment at s=8 TeV, corresponding to an integrated luminosity of 18.3 fb-1. Resonant and nonresonant modes of HH production have been probed and no significant excess relative to the background-only hypotheses has been found in either mode. Upper limits on cross sections of the two HH production modes have been set. The results have been combined with previously published searches at s=8 TeV, in decay modes to two photons and two b quarks, as well as to four b quarks, which also show no evidence for a signal. Limits from the combination have been set on resonant HH production by an unknown particle X in the mass range mX=300 GeV to mX=1000 GeV. For resonant production of spin 0 (spin 2) particles, the observed 95% CL upper limit is 1.13 pb (1.09 pb) at mX=300 GeV and to 21 fb (18 fb) at mX=1000 GeV. For nonresonant HH production, a limit of 43 times the rate predicted by the standard model has been set.Article Citation - WoS: 61Citation - Scopus: 111Measurement of the B± Meson Nuclear Modification Factor in Pb-Pb Collisions at ??snn =5.02 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerThe differential production cross sections of B± mesons are measured via the exclusive decay channels B±→J/ψK±→μ+μ-K± as a function of transverse momentum in pp and Pb-Pb collisions at a center-of-mass energy sNN=5.02 TeV per nucleon pair with the CMS detector at the LHC. The pp(Pb-Pb) data set used for this analysis corresponds to an integrated luminosity of 28.0 pb-1 (351 μb-1). The measurement is performed in the B± meson transverse momentum range of 7 to 50 GeV/c, in the rapidity interval |y|<2.4. In this kinematic range, a strong suppression of the production cross section by about a factor of 2 is observed in the Pb-Pb system in comparison to the expectation from pp reference data. These results are found to be roughly compatible with theoretical calculations incorporating beauty quark diffusion and energy loss in a quark-gluon plasma.Article Citation - WoS: 41Citation - Scopus: 71Search for Charged Higgs Bosons Produced Via Vector Boson Fusion and Decaying Into a Pair of W and Z Bosons Using Pp Collisions at ?s =13 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerA search for charged Higgs bosons produced via vector boson fusion and decaying into W and Z bosons using proton-proton collisions at s=13 TeV is presented. The data sample corresponds to an integrated luminosity of 15.2 fb-1 collected with the CMS detector in 2015 and 2016. The event selection requires three leptons (electrons or muons), two jets with large pseudorapidity separation and high dijet mass, and missing transverse momentum. The observation agrees with the standard model prediction. Limits on the vector boson fusion production cross section times branching fraction for new charged physical states are reported as a function of mass from 200 to 2000 GeV and interpreted in the context of Higgs triplet models.Article Citation - WoS: 14Citation - Scopus: 38Search for Low Mass Vector Resonances Decaying To Quark-Antiquark Pairs in Proton-Proton Collisions at √s =13 Tev(American Physical Society, 2017) CMS Collaboration; Karapınar, GülerA search is reported for a narrow vector resonance decaying to quark-antiquark pairs in proton-proton collisions at s=13 TeV, collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.7 fb-1. The vector resonance is produced at large transverse momenta, with its decay products merged into a single jet. The resulting signature is a peak over background in the distribution of the invariant mass of the jet. The results are interpreted in the framework of a leptophobic vector resonance and no evidence is found for such particles in the mass range of 100-300 GeV. Upper limits at 95% confidence level on the production cross section are presented in a region of mass-coupling phase space previously unexplored at the LHC. The region below 140 GeV has not been explored by any previous experiments.