Mathematics / Matematik
Permanent URI for this collectionhttps://hdl.handle.net/11147/8
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Article Citation - WoS: 52Citation - Scopus: 56Search for New Phenomena in Monophoton Final States in Proton–proton Collisions at S=8 Tev(Elsevier B.V., 2016) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Meschi, E.Results are presented from a search for new physics in final states containing a photon and missing transverse momentum. The data correspond to an integrated luminosity of 19.6 fb−1 collected in proton–proton collisions at s=8 TeV with the CMS experiment at the LHC. No deviation from the standard model predictions is observed for these final states. New, improved limits are set on dark matter production and on parameters of models with large extra dimensions. In particular, the first limits from the LHC on branon production are found and significantly extend previous limits from LEP and the Tevatron. An upper limit of 14.0 fb on the cross section is set at the 95% confidence level for events with a monophoton final state with photon transverse momentum greater than 145 GeV and missing transverse momentum greater than 140 GeV. © 2016 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 54Citation - Scopus: 54Search for New Resonances Decaying Via Wz To Leptons in Proton–proton Collisions at S=8tev(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Racz, A.A search is performed in proton–proton collisions at s=8 TeV for exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an integrated luminosity of 19.5 fb−1. No significant excess is observed above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of a W′ boson as predicted by an extended gauge model, and on the W′WZ coupling. The expected and observed mass limits for a W′ boson, as predicted by this model, are 1.55 and 1.47 TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters. © 2014 The AuthorsArticle Citation - WoS: 96Citation - Scopus: 109Long-Range Two-Particle Correlations of Strange Hadrons With Charged Particles in Ppb and Pbpb Collisions at Lhc Energies(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Masetti, L.Measurements of two-particle angular correlations between an identified strange hadron (KS 0 or Λ/Λ‾) and a charged particle, emitted in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 35 nb−1, were collected at a nucleon–nucleon center-of-mass energy (sNN) of 5.02 TeV with the CMS detector at the LHC. The results are compared to semi-peripheral PbPb collision data at sNN=2.76 TeV, covering similar charged-particle multiplicities in the events. The observed azimuthal correlations at large relative pseudorapidity are used to extract the second-order (v2) and third-order (v3) anisotropy harmonics of KS 0 and Λ/Λ‾ particles. These quantities are studied as a function of the charged-particle multiplicity in the event and the transverse momentum of the particles. For high-multiplicity pPb events, a clear particle species dependence of v2 and v3 is observed. For pT<2 GeV, the v2 and v3 values of KS 0 particles are larger than those of Λ/Λ‾ particles at the same pT. This splitting effect between two particle species is found to be stronger in pPb than in PbPb collisions in the same multiplicity range. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, both v2 and v3 for KS 0 particles are observed to be consistent with those for Λ/Λ‾ particles at the 10% level in pPb collisions. This consistency extends over a wide range of particle transverse kinetic energy and event multiplicities. © 2015 The AuthorsArticle Citation - WoS: 29Citation - Scopus: 33Measurement of the Cross Section Ratio Σtt¯bb¯/Σtt¯jj in Pp Collisions at S=8 Tev(Elsevier B.V., 2015) Karapınar, Güler; CMS Collaboration; Bergauer, T.; Dragicevic, M.; Malgeri, L.; Tumasyan, A.The first measurement of the cross section ratio σtt¯bb¯/σtt¯jj is presented using a data sample corresponding to an integrated luminosity of 19.6 fb−1 collected in pp collisions at s=8 TeV with the CMS detector at the LHC. Events with two leptons (e or μ) and four reconstructed jets, including two identified as b quark jets, in the final state are selected. The ratio is determined for a minimum jet transverse momentum pT of both 20 and 40 GeV/c. The measured ratio is 0.022±0.003(stat)±0.005(syst) for pT>20 GeV/c. The absolute cross sections σtt¯bb¯ and σtt¯jj are also measured. The measured ratio for pT>40 GeV/c is compatible with a theoretical quantum chromodynamics calculation at next-to-leading order. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 43Citation - Scopus: 48Search for Narrow High-Mass Resonances in Proton–proton Collisions at S=8 Tev Decaying To a Z and a Higgs Boson(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Kousouris, K.A search for a narrow, high-mass resonance decaying into Z and Higgs (H) bosons is presented. The final state studied consists of a merged jet pair and a τ pair resulting from the decays of Z and H bosons, respectively. The analysis is based on a data sample of proton–proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS experiment in 2012, and corresponding to an integrated luminosity of 19.7 fb−1. In the resonance mass range of interest, which extends from 0.8 to 2.5 TeV, the Z and H bosons are produced with large momenta, which implies that the final products of the two quarks or the two τ leptons must be detected within a small angular interval. From a combination of all possible decay modes of the τ leptons, production cross sections in a range between 0.9 and 27.8 fb are excluded at 95% confidence level, depending on the resonance mass. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 78Citation - Scopus: 96Measurement of the Z Boson Differential Cross Section in Transverse Momentum and Rapidity in Proton–proton Collisions at 8 Tev(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Eugster, J.We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy s=8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the FEWZ program. The results are also compared to the commonly used leading-order MADGRAPH and next-to-leading-order POWHEG generators. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 219Citation - Scopus: 242Search for Lepton-Flavour Decays of the Higgs Boson(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Lecoq, P.The first direct search for lepton-flavour-violating decays of the recently discovered Higgs boson (H) is described. The search is performed in the H→μτe and H→μτh channels, where τe and τh are tau leptons reconstructed in the electronic and hadronic decay channels, respectively. The data sample used in this search was collected in pp collisions at a centre-of-mass energy of s=8 TeV with the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 19.7 fb−1. The sensitivity of the search is an order of magnitude better than the existing indirect limits. A slight excess of signal events with a significance of 2.4 standard deviations is observed. The p-value of this excess at MH=125 GeV is 0.010. The best fit branching fraction is B(H→μτ)=(0.84−0.37 +0.39)%. A constraint on the branching fraction, B(H→μτ)<1.51% at 95% confidence level is set. This limit is subsequently used to constrain the μ–τ Yukawa couplings to be less than 3.6×10−3. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 39Citation - Scopus: 40Measurements of the ϒ(1s), ϒ(2s), and ϒ(3s) Differential Cross Sections in Pp Collisions at S=7tev(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Krajczar, K.Differential cross sections as a function of transverse momentum pT are presented for the production of ϒ(nS) (n = 1, 2, 3) states decaying into a pair of muons. Data corresponding to an integrated luminosity of 4.9fb−1 in pp collisions at s=7TeV were collected with the CMS detector at the LHC. The analysis selects events with dimuon rapidity |y| <1.2 and dimuon transverse momentum in the range 10 <pT <100GeV. The measurements show a transition from an exponential to a power-law behavior at pT≈20GeV for the three ϒ states. Above that transition, the ϒ(3S) spectrum is significantly harder than that of the ϒ(1S). The ratios of the ϒ(3S) and ϒ(2S) differential cross sections to the ϒ(1S) cross section show a rise as pT increases at low pT, then become flatter at higher pT. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 52Citation - Scopus: 65Study of W Boson Production in Ppb Collisions at Snn=5.02 Tev(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Masetti, L.The first study of W boson production in pPb collisions is presented, for bosons decaying to a muon or electron, and a neutrino. The measurements are based on a data sample corresponding to an integrated luminosity of 34.6 nb−1 at a nucleon–nucleon centre-of-mass energy of sNN=5.02 TeV, collected by the CMS experiment. The W boson differential cross sections, lepton charge asymmetry, and forward–backward asymmetries are measured for leptons of transverse momentum exceeding 25 GeV/c, and as a function of the lepton pseudorapidity in the |ηlab|<2.4 range. Deviations from the expectations based on currently available parton distribution functions are observed, showing the need for including W boson data in nuclear parton distribution global fits. © 2015 CERN for the benefit of the CMS CollaborationArticle Citation - WoS: 98Citation - Scopus: 108Angular Coefficients of Z Bosons Produced in Pp Collisions at S=8 Tev and Decaying To Μ+μ− as a Function of Transverse Momentum and Rapidity(Elsevier B.V., 2015) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Gigi, D.Measurements of the five most significant angular coefficients, A0 through A4, for Z bosons produced in pp collisions at s=8 TeV and decaying to μ+μ− are presented as a function of the transverse momentum and rapidity of the Z boson. The integrated luminosity of the dataset collected with the CMS detector at the LHC corresponds to 19.7fb−1. These measurements provide comprehensive information about the Z boson production mechanisms, and are compared to the QCD predictions at leading order, next-to-leading order, and next-to-next-to-leading order in perturbation theory. © 2015 CERN for the benefit of the CMS Collaboration