Rectorate / Rektörlük
Permanent URI for this collectionhttps://hdl.handle.net/11147/6849
Browse
63 results
Search Results
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.The 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.A 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: 15Citation - Scopus: 19Study of J/Ψ Meson Production Inside Jets in pp Collisions at S=8 TeV(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Hensel, C.A study of the production of prompt J/ψ mesons contained in jets in proton-proton collisions at s=8TeV is presented. The analysis is based on data corresponding to an integrated luminosity of 19.1 fb−1 collected with the CMS detector at the LHC. For events with at least one observed jet, the angular separation between the J/ψ meson and the jet is used to test whether the J/ψ meson is part of the jet. The analysis shows that most prompt J/ψ mesons having energy above 15 GeV and rapidity |y|<1 are contained in jets with pseudorapidity |η<inf>jet</inf>|<1. The differential distributions of the probability to have a J/ψ meson contained in a jet as a function of jet energy for a fixed J/ψ energy fraction are compared to a theoretical model using the fragmenting jet function approach. The data agree best with fragmenting jet function calculations that use a long-distance matrix element parameter set in which prompt J/ψ mesons are predicted to be unpolarized. This technique demonstrates a new way to test predictions for prompt J/ψ production using nonrelativistic quantum chromodynamics. © 2020 Elsevier B.V.Article Citation - WoS: 70Citation - Scopus: 75Search for Singly and Pair-Produced Leptoquarks Coupling To Third-Generation Fermions in Proton-Proton Collisions at S=13 Tev(Elsevier B.V., 2021) Sirunyan,A.M.; Tumasyan,A.; Adam,W.; Ambrogi,F.; Bergauer,T.; Dragicevic,M.; Chistov,R.A search for leptoquarks produced singly and in pairs in proton-proton collisions is presented. We consider the leptoquark (LQ) to be a scalar particle of charge −1/3e coupling to a top quark plus a tau lepton (tτ) or a bottom quark plus a neutrino (bν), or a vector particle of charge +2/3e, coupling to tν or bτ. These choices are motivated by models that can explain a series of anomalies observed in the measurement of B meson decays. In this analysis the signatures tτνb and tτν are probed, using data recorded by the CMS experiment at the CERN LHC at s=13 TeV and that correspond to an integrated luminosity of 137 fb−1. These signatures have not been previously explored in a dedicated search. The data are found to be in agreement with the standard model prediction. Lower limits at 95% confidence level are set on the LQ mass in the range 0.98–1.73 TeV, depending on the LQ spin and its coupling λ to a lepton and a quark, and assuming equal couplings for the two LQ decay modes considered. These are the most stringent constraints to date on the existence of leptoquarks in this scenario. © 2021 The Author(s)Article Citation - WoS: 40Citation - Scopus: 57Measurements of Production Cross Sections of Polarized Same-Sign W Boson Pairs in Association With Two Jets in Proton-Proton Collisions at S=13 Tev(Elsevier B.V., 2021) Sirunyan,A.M.; Tumasyan,A.; Adam,W.; Ambrogi,F.; Bergauer,T.; Dragicevic,M.; Chistov,R.The first measurements of production cross sections of polarized same-sign W±W± boson pairs in proton-proton collisions are reported. The measurements are based on a data sample collected with the CMS detector at the LHC at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 137fb−1. Events are selected by requiring exactly two same-sign leptons, electrons or muons, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass to enhance the contribution of same-sign W±W± scattering events. An observed (expected) 95% confidence level upper limit of 1.17 (0.88) fbis set on the production cross section for longitudinally polarized same-sign W±W± boson pairs. The electroweak production of same-sign W±W± boson pairs with at least one of the W bosons longitudinally polarized is measured with an observed (expected) significance of 2.3 (3.1) standard deviations. © 2020 The Author(s)Article Citation - WoS: 34Citation - Scopus: 47Measurement of the Cp-Violating Phase Φs in the Bs 0→j/Ψϕ(1020)→μ+μ−k+k− Channel in Proton-Proton Collisions at S=13tev(Elsevier B.V., 2021) Sirunyan,A.M.; Tumasyan,A.; Adam,W.; Ambrogi,F.; Bergauer,T.; Dragicevic,M.; Chistov,R.The CP -violating weak phase ϕs and the decay width difference ΔΓs between the light and heavy Bs 0 mass eigenstates are measured with the CMS detector at the LHC in a sample of 48500 reconstructed Bs 0→J/ψϕ(1020)→μ+μ−K+K− events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4fb−1, collected in proton-proton collisions at s=13TeV in 2017–2018. To extract the values of ϕs and ΔΓs, a time-dependent and flavor-tagged angular analysis of the μ+μ−K+K− final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ϕs=−11±50(stat)±10(syst)mrad and ΔΓs=0.114±0.014(stat)±0.007(syst)ps−1, in agreement with the standard model predictions. When combined with the previous CMS measurement at s=8TeV, the following values are obtained: ϕs=−21±44(stat)±10(syst)mrad, ΔΓs=0.1032±0.0095(stat)±0.0048(syst)ps−1, a significant improvement over the 8 TeV result. © 2021 The Author(s)Article Citation - WoS: 16Citation - Scopus: 68Measurement of the Y(1s) Pair Production Cross Section and Search for Resonances Decaying To Y(1s)μ+μ− in Proton-Proton Collisions at S=13tev(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Dudko, L.The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb−1. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)μ+μ− in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b¯ antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass. © 2020 The Author(s)Article Citation - WoS: 20Citation - Scopus: 28Measurement of Ckm Matrix Elements in Single Top Quark T-Channel Production in Proton-Proton Collisions at S=13 Tev(Elsevier B.V., 2020) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Sobol, A.The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |η|Vtb, |η|Vtd, and |η|Vts, in final states enriched in single top quark t-channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of |η|Vtb>0.970 is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values |η|Vtb=0.988±0.024, and |η|Vtd 2+|η|Vts 2=0.06±0.06, where the uncertainties include both statistical and systematic components, are measured. © 2020 The AuthorArticle 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.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Trevisani, N.A 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.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Flix, J.The 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)