Rectorate / Rektörlük
Permanent URI for this collectionhttps://hdl.handle.net/11147/6849
Browse
37 results
Search Results
Article Citation - WoS: 13Evidence for Ww/Wz Vector Boson Scattering in the Decay Channel <i>l</I>νqq Produced in Association With Two Jets in Proton-Proton Collisions at √<i>s</I>=13tev(Elsevier, 2022) Karapınar, Güler; CMS Collaboration; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Dragicevic, M.; Vetens, W.; 01. Izmir Institute of TechnologyEvidence is reported for electroweak (EW) vector boson scattering in the decay channel l nu qq of two weak vector bosons WV(V = Wor Z), produced in association with two parton jets. The search uses a data set of proton-proton collisions at 13TeVcollected with the CMS detector during 2016-2018 with an integrated luminosity of 138fb(-1). Events are selected requiring one lepton (electron or muon), moderate missing transverse momentum, two jets with a large pseudorapidity separation and a large dijet invariant mass, and a signature consistent with the hadronic decay of a W/Zboson. The cross section is computed in a fiducial phase space defined at parton level requiring all parton transverse momenta p(T)> 10 GeVand at least one pair of outgoing partons with invariant mass mqq> 100 GeV. The measured and expected EW WVproduction cross sections are 1.90(-0.46)(+0.5)3 pb and 2.23(-0.11)(+0.08)(scale) +/- 0.05(PDF) pb, respectively, where PDF is the parton distribution function. The observed EW signal strength is mu EW= 0.85 +/- 0.12 (stat)(-0.17)(+0.19)(syst), corresponding to a signal significance of 4.4 standard deviations with 5.1 expected, and it is measured keeping the quantum chromodynamics (QCD) associated diboson production fixed to the standard model prediction. This is the first evidence of vector boson scattering in the l nu qq decay channel at LHC. The simultaneous measurement of the EW and QCD associated diboson production agrees with the standard model prediction. (C) 2022 The Author(s). Published by Elsevier B.V.Article Citation - WoS: 20Citation - Scopus: 31Search for Flavor-Changing Neutral Current Interactions of the Top Quark and Higgs Boson in Final States With Two Photons in Proton-Proton Collisions at S =13 Tev(American Physical Society, 2022) Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Dragicevic, M.; Bunichev, V.; 01. Izmir Institute of TechnologyProton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks (t) and Higgs bosons (H). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb-1. No significant excess above the background prediction is observed. Upper limits on the branching fractions (B) of the top quark decaying to a Higgs boson and an up (u) or charm (c) quark are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019% (0.031%) for B(t→Hu) and 0.073% (0.051%) for B(t→Hc). These are the strictest upper limits yet determined. © 2022 CERN.Article Citation - WoS: 22Citation - Scopus: 25Observation of the Bc+ Meson in Pb-Pb and Pp Collisions at Snn =5.02 Tev and Measurement of Its Nuclear Modification Factor(American Physical Society, 2022) Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Dragicevic, M.; Boos, E.; 01. Izmir Institute of TechnologyThe Bc+ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the Bc+ meson in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of sNN=5.02 TeV, via the Bc+→(J/ψ→μ+μ-)μ+νμ decay. The Bc+ nuclear modification factor, derived from the Pb-Pb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the Pb-Pb collision centrality. The Bc+ meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma. © 2022 CERN.Article Citation - WoS: 51Citation - Scopus: 60Identification of Hadronic Tau Lepton Decays Using a Deep Neural Network(Institute of Physics, 2022) Tumasyan, A.; Adam, W.; Andrejkovic, J.W.; Bergauer, T.; Chatterjee, S.; Dragicevic, M.; Andreev, V.; 01. Izmir Institute of TechnologyA new algorithm is presented to discriminate reconstructed hadronic decays of tau leptons (τ h) that originate from genuine tau leptons in the CMS detector against τ h candidates that originate from quark or gluon jets, electrons, or muons. The algorithm inputs information from all reconstructed particles in the vicinity of a τ h candidate and employs a deep neural network with convolutional layers to efficiently process the inputs. This algorithm leads to a significantly improved performance compared with the previously used one. For example, the efficiency for a genuine τ h to pass the discriminator against jets increases by 10-30% for a given efficiency for quark and gluon jets. Furthermore, a more efficient τ h reconstruction is introduced that incorporates additional hadronic decay modes. The superior performance of the new algorithm to discriminate against jets, electrons, and muons and the improved τ h reconstruction method are validated with LHC proton-proton collision data at s = 13 TeV. © 2022 CERN.Article Citation - WoS: 13Citation - Scopus: 16Observation of Bs 0 Mesons and Measurement of the Bs 0/B+ Yield Ratio in Pbpb Collisions at [formula Presented] Tev(Elsevier B.V., 2022) Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Erö, J.; Kirakosyan, M.; 01. Izmir Institute of TechnologyThe Bs 0 and B+ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb−1. The mesons are reconstructed in the exclusive decay channels B→s0J/ψ(μ+μ−)ϕ(K+K−) and B→+J/ψ(μ+μ−)K+, in the transverse momentum range 7–50 GeV/c and absolute rapidity 0–2.4. The Bs 0 meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of Bs 0 and B+ is measured and compared to theoretical models that include quark recombination effects. © 2022 The Author(s)Article Citation - WoS: 5Citation - Scopus: 7Search for Wγ Resonances in Proton-Proton Collisions at S=13 TeV Using Hadronic Decays of Lorentz-Boosted W Bosons(Elsevier B.V., 2022) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Alves, G.A.; 01. Izmir Institute of TechnologyA search for Wγ resonances in the mass range between 0.7 and 6.0 TeV is presented. The W boson is reconstructed via its hadronic decays, with the final-state products forming a single large-radius jet, owing to a high Lorentz boost of the W boson. The search is based on proton-proton collision data at s=13 TeV, corresponding to an integrated luminosity of 137 fb−1, collected with the CMS detector at the LHC in 2016–2018. The Wγ mass spectrum is parameterized with a smoothly falling background function and examined for the presence of resonance-like signals. No significant excess above the predicted background is observed. Model-specific upper limits at 95% confidence level on the product of the cross section and branching fraction to the Wγ channel are set. Limits for narrow resonances and for resonances with an intrinsic width equal to 5% of their mass, for spin-0 and spin-1 hypotheses, range between 0.17 fb at 6.0 TeV and 55 fb at 0.7 TeV. These are the most restrictive limits to date on the existence of such resonances over a large range of probed masses. In specific heavy scalar (vector) triplet benchmark models, narrow resonances with masses between 0.75 (1.15) and 1.40 (1.36) TeV are excluded for a range of model parameters. Model-independent limits on the product of the cross section, signal acceptance, and branching fraction to the Wγ channel are set for minimum Wγ mass thresholds between 1.5 and 8.0 TeV. © 2022 The Author(s)Article Citation - WoS: 239Citation - Scopus: 291Performance of the Cms Level-1 Trigger in Proton-Proton Collisions at √s = 13 Tev(Institute of Physics, 2020) Sirunyan, A.M.; Karapınar, Güler; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Bunichev, V.; 01. Izmir Institute of TechnologyAt the start of Run 2 in 2015, the LHC delivered proton-proton collisions at a center-of-mass energy of 13 TeV. During Run 2 (years 2015-2018) the LHC eventually reached a luminosity of 2.1 × 1034 cm-2s-1, almost three times that reached during Run 1 (2009-2013) and a factor of two larger than the LHC design value, leading to events with up to a mean of about 50 simultaneous inelastic proton-proton collisions per bunch crossing (pileup). The CMS Level-1 trigger was upgraded prior to 2016 to improve the selection of physics events in the challenging conditions posed by the second run of the LHC. This paper describes the performance of the CMS Level-1 trigger upgrade during the data taking period of 2016-2018. The upgraded trigger implements pattern recognition and boosted decision tree regression techniques for muon reconstruction, includes pileup subtraction for jets and energy sums, and incorporates pileup-dependent isolation requirements for electrons and tau leptons. In addition, the new trigger calculates high-level quantities such as the invariant mass of pairs of reconstructed particles. The upgrade reduces the trigger rate from background processes and improves the trigger efficiency for a wide variety of physics signals. © 2020 CERN for the benefit of the CMS collaboration.Article Citation - WoS: 205Citation - Scopus: 159Search for Resonances and Quantum Black Holes Using Dijet Mass Spectra in Proton-Proton Collisions at S =8tev(American Physical Society, 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Hegeman, J.; 01. Izmir Institute of TechnologyA search for resonances and quantum black holes is performed using the dijet mass spectra measured in proton-proton collisions at s=8TeV with the CMS detector at the LHC. The data set corresponds to an integrated luminosity of 19.7fb-1. In a search for narrow resonances that couple to quark-quark, quark-gluon, or gluon-gluon pairs, model-independent upper limits, at 95% confidence level, are obtained on the production cross section of resonances, with masses above 1.2 TeV. When interpreted in the context of specific models the limits exclude string resonances with masses below 5.0 TeV; excited quarks below 3.5 TeV; scalar diquarks below 4.7 TeV; W′ bosons below 1.9 TeV or between 2.0 and 2.2 TeV; Z′ bosons below 1.7 TeV; and Randall-Sundrum gravitons below 1.6 TeV. A separate search is conducted for narrow resonances that decay to final states including b quarks. The first exclusion limit is set for excited b quarks, with a lower mass limit between 1.2 and 1.6 TeV depending on their decay properties. Searches are also carried out for wide resonances, assuming for the first time width-to-mass ratios up to 30%, and for quantum black holes with a range of model parameters. The wide resonance search excludes axigluons and colorons with mass below 3.6 TeV, and color-octet scalars with mass below 2.5 TeV. Lower bounds between 5.0 and 6.3 TeV are set on the masses of quantum black holes. © 2015 CERN, for the CMS Collaboration.Article Citation - WoS: 72Citation - Scopus: 72Measurement of J /Ψ and Ψ (2s) Prompt Double-Differential Cross Sections in Pp Collisions at S =7tev(American Physical Society, 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Innocente, V.; 01. Izmir Institute of TechnologyThe double-differential cross sections of promptly produced J/ψ and ψ(2S) mesons are measured in pp collisions at s=7TeV, as a function of transverse momentum pT and absolute rapidity |y|. The analysis uses J/ψ and ψ(2S) dimuon samples collected by the CMS experiment, corresponding to integrated luminosities of 4.55 and 4.90fb-1, respectively. The results are based on a two-dimensional analysis of the dimuon invariant mass and decay length, and extend to pT=120 and 100 GeV for the J/ψ and ψ(2S), respectively, when integrated over the interval |y|<1.2. The ratio of the ψ(2S) to J/ψ cross sections is also reported for |y|<1.2, over the range 10<pT<100GeV. These are the highest pT values for which the cross sections and ratio have been measured. © 2015 CERN, for the CMS Collaboration.Article Citation - WoS: 518Citation - Scopus: 550Precise Determination of the Mass of the Higgs Boson and Tests of Compatibility of Its Couplings With the Standard Model Predictions Using Proton Collisions at 7 and 8 Tev(Springer Nature, 2015) Khachatryan, V.; Karapınar, Güler; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Janot, P.; 01. Izmir Institute of TechnologyProperties of the Higgs boson with mass near 125 GeV are measured in proton-proton collisions with the CMS experiment at the LHC. Comprehensive sets of production and decay measurements are combined. The decay channels include γγ, ZZ, WW, ττ, bb, and μμ pairs. The data samples were collected in 2011 and 2012 and correspond to integrated luminosities of up to 5.1fb-1at 7TeV and up to 19.7fb-1at 8 TeV. From the high-resolution γγ and ZZ channels, the mass of the Higgs boson is determined to be (Formula presented) GeV. For this mass value, the event yields obtained in the different analyses tagging specific decay channels and production mechanisms are consistent with those expected for the standard model Higgs boson. The combined best-fit signal relative to the standard model expectation is (Formula presented) at the measured mass. The couplings of the Higgs boson are probed for deviations in magnitude from the standard model predictions in multiple ways, including searches for invisible and undetected decays. No significant deviations are found. © 2015, CERN for the benefit of the CMS collaboration.