Rectorate / Rektörlük
Permanent URI for this collectionhttps://hdl.handle.net/11147/6849
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Article Citation - WoS: 56Citation - Scopus: 60Search for Lepton Flavour Violating Decays of the Higgs Boson To Eτ and Eμ in Proton–proton Collisions at S=8 Tev(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Trevisani, N.; 01. Izmir Institute of TechnologyA direct search for lepton flavour violating decays of the Higgs boson (H) in the H→eτ and H→eμ channels is described. The data sample used in the search was collected in proton–proton collisions at s=8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb−1. No evidence is found for lepton flavour violating decays in either final state. Upper limits on the branching fractions, B(H→eτ)<0.69% and B(H→eμ)<0.035%, are set at the 95% confidence level. The constraint set on B(H→eτ) is an order of magnitude more stringent than the existing indirect limits. The limits are used to constrain the corresponding flavour violating Yukawa couplings, absent in the standard model. © 2016 The Author(s)Article Citation - WoS: 8Citation - Scopus: 10ϒ(ns) Polarizations Versus Particle Multiplicity in Pp Collisions at S=7 Tev(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Flix, J.; 01. Izmir Institute of TechnologyThe polarizations of the ϒ(1S), ϒ(2S), and ϒ(3S) mesons are measured as a function of the charged particle multiplicity in proton–proton collisions at s=7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The results are extracted from the dimuon decay angular distributions, in two ranges of ϒ(nS) transverse momentum (10–15 and 15–35 GeV), and in the rapidity interval |y|>1.2. The results do not show significant changes from low- to high-multiplicity pp collisions, although large uncertainties preclude definite statements in the ϒ(2S) and ϒ(3S) cases. © 2016 The Author(s)Article Citation - WoS: 24Citation - Scopus: 22Search for Top Squark Pair Production in Compressed-Mass Scenarios in Proton-Proton Collisions at S=8 Tev Using the Αt Variable(Elsevier B.V., 2017) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Cabrillo, I.J.; 01. Izmir Institute of TechnologyAn inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, p→T miss, due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated luminosity of 18.5 fb−1. The dimensionless kinematic variable αT is used to discriminate between events with genuine p→T miss associated with unobserved particles and spurious values of p→T miss arising from jet energy mismeasurements. No excess of event yields above the expected standard model backgrounds is observed. The results are interpreted in terms of constraints on the parameter space of several simplified models of supersymmetry that assume the pair production of top squarks. The search provides sensitivity to a broad range of top squark (t˜) decay modes, including the two-body decay t˜→cχ˜1°, where c is a charm quark and χ˜1° is the lightest neutralino, as well as the four-body decay t˜→bff¯′χ˜1°, where b is a bottom quark and f and f¯′ are fermions produced in the decay of an intermediate off-shell W boson. These modes dominate in scenarios in which the top squark and lightest neutralino are nearly degenerate in mass. For these modes, top squarks with masses as large as 260 and 225 GeV are excluded, respectively, for the two- and four-body decays. © 2017 The AuthorArticle Citation - WoS: 90Citation - Scopus: 107Suppression of ϒ(1s), ϒ(2s), and ϒ(3s) Quarkonium States in Pbpb Collisions at Snn=2.76tev(Elsevier B.V., 2017) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Gomez, G.; 01. Izmir Institute of TechnologyThe production yields of ϒ(1S), ϒ(2S), and ϒ(3S) quarkonium states are measured through their decays into muon pairs in the CMS detector, in PbPb and pp collisions at the centre-of-mass energy per nucleon pair of 2.76 TeV. The data correspond to integrated luminosities of 166μb−1 and 5.4pb−1 for PbPb and pp collisions, respectively. Differential production cross sections are reported as functions of ϒ rapidity y up to 2.4, and transverse momentum pT up to 20GeV/c. A strong centrality-dependent suppression is observed in PbPb relative to pp collisions, by factors of up to ≈2 and 8, for the ϒ(1S) and ϒ(2S) states, respectively. No significant dependence of this suppression is observed as a function of y or pT. The ϒ(3S) state is not observed in PbPb collisions, which corresponds to a suppression for the centrality-integrated data by at least a factor of ≈7 at a 95% confidence level. The observed suppression is in agreement with theoretical scenarios modeling the sequential melting of quarkonium states in a quark gluon plasma. © 2017 The Author(s)Article Citation - WoS: 6Citation - Scopus: 6Search for Supersymmetry in Events With Photons and Missing Transverse Energy in Pp Collisions at 13 Tev(Elsevier B.V., 2017) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Milosevic, J.; 01. Izmir Institute of TechnologyThe results of a search for new physics in final states with photons and missing transverse energy are reported. The study is based on a sample of proton–proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 fb−1. Final states with two photons and significant missing transverse energy are used to search for supersymmetric particles in models of supersymmetry (SUSY) with general gauge-mediated (GGM) supersymmetry breaking. No excess is observed with respect to the standard model expectation, and the results are used to set limits on gluino pair production and squark pair production in the GGM SUSY framework. Gluino masses below 1.65 TeV and squark masses below 1.37 TeV are excluded at a 95% confidence level. © 2017 The Author(s)Article Citation - WoS: 44Citation - Scopus: 53Measurement of the Cross Section for Electroweak Production of Zγ in Association With Two Jets and Constraints on Anomalous Quartic Gauge Couplings in Proton–proton Collisions at S=8 Tev(Elsevier B.V., 2017) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Piedra Gomez, J.; 01. Izmir Institute of TechnologyA measurement is presented of the cross section for the electroweak production of a Z boson and a photon in association with two jets in proton–proton collisions at s=8 TeV. The Z bosons are identified through their decays to electron or muon pairs. The measurement is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 fb−1. The electroweak contribution has a significance of 3.0 standard deviations, and the measured fiducial cross section is 1.86−0.75 +0.90(stat)−0.26 +0.34(syst)±0.05(lumi) fb, while the summed electroweak and quantum chromodynamic total cross section in the same region is observed to be 5.94−1.35 +1.53(stat)−0.37 +0.43(syst)±0.13(lumi) fb. Both measurements are consistent with the leading-order standard model predictions. Limits on anomalous quartic gauge couplings are set based on the Zγ mass distribution. © 2017 The AuthorArticle Citation - WoS: 13Citation - Scopus: 14Search for R-Parity Violating Decays of a Top Squark in Proton–proton Collisions at √s=8 Tev(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Gomez, G.; 01. Izmir Institute of TechnologyThe results of a search for a supersymmetric partner of the top quark (top squark), pair-produced in proton–proton collisions at s=8 TeV, are presented. The search, which focuses on R-parity violating, chargino-mediated decays of the top squark, is performed in final states with low missing transverse momentum, two oppositely charged electrons or muons, and at least five jets. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in 2012. The data are found to be in agreement with the standard model expectation, and upper limits are placed on the top squark pair production cross section at 95% confidence level. Assuming a 100% branching fraction for the top squark decay chain, t˜→tχ˜1 ±,χ˜1 ±→ℓ±+jj, top squark masses less than 890 (1000) GeV for the electron (muon) channel are excluded for the first time in models with a single nonzero R-parity violating coupling λijk ′ (i,j,k≤2), where i,j,k correspond to the three generations. © 2016 The Author(s)Article Citation - WoS: 81Citation - Scopus: 88Search for Neutral Resonances Decaying Into a Z Boson and a Pair of B Jets or Τ Leptons(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Garcia-Ferrero, J.; 01. Izmir Institute of TechnologyA search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged τ leptons or a bb‾ pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 fb−1. No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models. © 2016 The AuthorArticle Citation - WoS: 8Citation - Scopus: 9Search for Supersymmetry in Electroweak Production With Photons and Large Missing Transverse Energy in Pp Collisions at √s=8tev(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Fernandez, M.; 01. Izmir Institute of TechnologyResults are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy (ET miss) were examined. The data sample was collected in pp collisions at s=8TeV with the CMS detector at the LHC and corresponds to 7.4fb−1. The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, ET miss, and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10GeV above that of the bino, wino masses below 710GeV are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles. © 2016 The AuthorArticle Citation - WoS: 23Citation - Scopus: 26Search for Supersymmetry in Events With Soft Leptons, Low Jet Multiplicity, and Missing Transverse Energy in Proton–proton Collisions at √s=8 Tev(Elsevier B.V., 2016) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Palencia Cortezon, E.; 01. Izmir Institute of TechnologyResults are presented from a search for supersymmetric particles in scenarios with small mass splittings. The data sample corresponds to 19.7 fb−1 of proton–proton collisions recorded by the CMS experiment at s=8 TeV. The search targets top squark (t˜) pair production in scenarios with mass differences Δm=m(t˜)−m(χ˜1 0) below the W-boson mass and with top-squark decays in the four-body mode (t˜→bℓνχ˜1 0), where the neutralino (χ˜1 0) is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pT) jet associated with initial-state radiation, one or two low-pT leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the t˜ and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for Δm=25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino–neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common χ˜1 +/χ˜2 0 mass and the LSP mass of 20 GeV and a τ-enriched decay scenario, masses in the range m(χ˜1 +)<307 GeV are excluded at 95% CL. © 2016 The Author
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