WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
Browse
195 results
Search Results
Now showing 1 - 10 of 195
Article Citation - WoS: 13Citation - Scopus: 23Search for Top Squarks Decaying Via Four-Body or Chargino-Mediated Modes in Single-Lepton Final States in Proton-Proton Collisions at ?s=13 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerA search for the pair production of the lightest supersymmetric partner of the top quark (t ˜ 1) is presented. The search focuses on a compressed scenario where the mass difference between the top squark and the lightest supersymmetric particle, often considered to be the lightest neutralino (χ˜10), is smaller than the mass of the W boson. The proton-proton collision data were recorded by the CMS experiment at a centre-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb−1. In this search, two decay modes of the top squark are considered: a four-body decay into a bottom quark, two additional fermions, and a χ˜10; and a decay via an intermediate chargino. Events are selected using the presence of a high-momentum jet, significant missing transverse momentum, and a low transverse momentum electron or muon. Two analysis techniques are used, targeting different decay modes of the t ˜ 1: a sequential selection and a multivariate technique. No evidence for the production of top squarks is found, and mass limits at 95% confidence level are set that reach up to 560 GeV, depending on the m(t˜1)−m(χ˜10) mass difference and the decay mode.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: 20Citation - Scopus: 40Measurement of the Inclusive T T ¯ Cross Section in Pp Collisions at ?s=5.02 Tev Using Final States With at Least One Charged Lepton(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerThe top quark pair production cross section (σtt ¯) is measured for the first time in pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected by the CMS experiment at the LHC and correspond to an integrated luminosity of 27.4 pb−1. The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is σtt ¯ = 69.5 ± 6.1 (stat) ± 5.6 (syst) ± 1.6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impact of the presented measurement on the determination of the gluon distribution function is investigated.Article Citation - WoS: 83Citation - Scopus: 139Search for Electroweak Production of Charginos and Neutralinos in Multilepton Final States in Proton-Proton Collisions at ?s=13 Tev(Springer Verlag, 2018) Karapınar, GülerResults are presented from a search for the direct electroweak production of charginos and neutralinos in signatures with either two or more leptons (electrons or muons) of the same electric charge, or with three or more leptons, which can include up to two hadronically decaying tau leptons. The results are based on a sample of proton-proton collision data collected at s=13 TeV, recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The observed event yields are consistent with the expectations based on the standard model. The results are interpreted in simplified models of supersymmetry describing various scenarios for the production and decay of charginos and neutralinos. Depending on the model parameters chosen, mass values between 180 GeV and 1150 GeV are excluded at 95% CL. These results significantly extend the parameter space probed for these particles in searches at the LHC. In addition, results are presented in a form suitable for alternative theoretical interpretations.Article Citation - WoS: 18Citation - Scopus: 24Comparing Transverse Momentum Balance of B Jet Pairs in Pp and Pbpb Collisions at ?snn=5.02 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerThe transverse momentum balance of pairs of back-to-back b quark jets in PbPb and pp collisions recorded with the CMS detector at the LHC is reported. The center-of-mass energy in both collision systems is 5.02TeV per nucleon pair. Compared to the pp collision baseline, b quark jets have a larger imbalance in the most central PbPb collisions, as expected from the jet quenching e ect. The data are also compared to the corresponding measurement with inclusive dijets. In the most central collisions, the imbalance of b quark dijets is comparable to that of inclusive dijets.Article Citation - WoS: 16Citation - Scopus: 12Search for Zz Resonances in the 2l2? Final State in Proton-Proton Collisions at 13 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerA search for heavy resonances decaying to a pair of Z bosons is performed using data collected with the CMS detector at the LHC. Events are selected by requiring two oppositely charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum, which is interpreted as arising from the decay of a second Z boson to two neutrinos. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The hypothesis of a spin-2 bulk graviton (X) decaying to a pair of Z bosons is examined for 600 ≤ mX ≤ 2500 GeV and upper limits at 95% confidence level are set on the product of the production cross section and branching fraction of X → ZZ ranging from 100 to 4 fb. For bulk graviton models characterized by a curvature scale parameter k˜ = 0.5 in the extra dimension, the region mXOpenSPiltSPi 800 GeV is excluded, providing the most stringent limit reported to date. Variations of the model considering the possibility of a wide resonance produced exclusively via gluon-gluon fusion or q q ¯ annihilation are also examined.Article Citation - WoS: 1Citation - Scopus: 1Search for Natural Supersymmetry in Events With Top Quark Pairs and Photons in Pp Collisions at ?s=8 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerResults are presented from a search for natural gauge-mediated supersymmetry (SUSY) in a scenario in which the top squark is the lightest squark, the next-to-lightest SUSY particle is a bino-like neutralino, and the lightest SUSY particle is the gravitino. The strong production of top squark pairs can produce events with pairs of top quarks and neutralinos, with each bino-like neutralino decaying to a photon and a gravitino. The search is performed using a sample of pp collision data accumulated by the CMS experiment at s=8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The final state consists of a lepton (electron or muon), jets, and one or two photons. The imbalance in transverse momentum in the events is compared with the expected spectrum from standard model processes. No excess event yield is observed beyond the expected background, and the result is interpreted in the context of a general model of gauge-mediated SUSY breaking that leads to exclusion of top squark masses below 650–730 GeV.Article Citation - WoS: 48Citation - Scopus: 37Measurement of the W-Boson Helicity in Top-Quark Decays From Tt¯ Production in Lepton+jets Events in Pp Collisions At?s = 7 Tev Th(Springer Verlag, 2013) CMS Collaboration; Karapınar, GülerThe W-boson helicity fractions in top-quark decays are measured with tt̄ events in the lepton+jets final state, using proton-proton collisions at a centre-of-mass energy of 7TeV, collected in 2011 with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 5.0 fb -1. The measured fractions of longitudinal, left-, and right-handed helicity are F0 = 0:682±0:030 (stat.)± 0:033 (syst.), F= 0:310 ±0:022 (stat.)± 0:022 (syst.), and F= 0:008± 0:012 (stat.) ± 0:014 (syst.), consistent with the standard model predictions. The measured fractions are used to probe the existence of anomalous Wtb couplings. Exclusion limits on the real components of the anomalous couplings gL; gR are also derived.Article Citation - WoS: 34Citation - Scopus: 42Measurements of Tt¯ Cross Sections in Association With B Jets and Inclusive Jets and Their Ratio Using Dilepton Final States in Pp Collisions at S=13tev(Elsevier Ltd., 2018) CMS Collaboration; Karapınar, GülerThe cross sections for the production of tt¯bb¯ and tt¯jj events and their ratio σtt¯bb¯/σtt¯jj are measured using data corresponding to an integrated luminosity of 2.3 fb−1collected in pp collisions at s=13 TeV with the CMS detector at the LHC. Events with two leptons (e or μ) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022±0.003(stat)±0.006(syst), the cross section σtt¯bb¯ is 4.0±0.6(stat)±1.3(syst) pb and σtt¯jj is 184±6(stat)±33(syst) pb. The measurements are compared with the standard model expectations obtained from a POWHEG simulation at next-to-leading-order interfaced with PYTHIA.Article Citation - WoS: 29Citation - Scopus: 33Constraints on the Double-Parton Scattering Cross Section From Same-Sign W Boson Pair Production in Proton-Proton Collisions at ?s=8 Tev(Springer Verlag, 2018) CMS Collaboration; Karapınar, GülerA first search for same-sign WW production via double-parton scattering is performed based on proton-proton collision data at a center-of-mass energy of 8 TeV using dimuon and electron-muon final states. The search is based on the analysis of data corresponding to an integrated luminosity of 19.7 fb−1. No significant excess of events is observed above the expected single-parton scattering yields. A 95% confidence level upper limit of 0.32 pb is set on the inclusive cross section for same-sign WW production via the double-parton scattering process. This upper limit is used to place a 95% confidence level lower limit of 12.2 mb on the effective double-parton cross section parameter, closely related to the transverse distribution of partons in the proton. This limit on the effective cross section is consistent with previous measurements as well as with Monte Carlo event generator predictions.