Yazar "Brandstetter, J." seçeneğine göre listele
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Öğe Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root s(NN)=5.02 TeV(Elsevier, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; CERN CollaborationEvidence for the light-by-light scattering process, gamma gamma -> gamma gamma, in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390 mu b(-1) recorded by the CMS experiment at the LHC. Light-by-light scattering processes are selected in events with two photons exclusively produced, each with transverse energy E-T(gamma) > 2 GeV, pseudorapidity vertical bar eta(gamma)vertical bar < 2.4, diphoton invariant mass m(gamma gamma) > 5 GeV, diphoton transverse momentum p(T)(gamma gamma) < 1 GeV, and diphoton acoplanarity below 0.01. After all selection criteria are applied, 14 events are observed, compared to expectations of 9.0 +/- 0.9 (theo) events for the signal and 4.0 +/- 1.2 (stat) for the background processes. The excess observed in data relative to the background-only expectation corresponds to a significance of 3.7 standard deviations, and has properties consistent with those expected for the light-by-light scattering signal. The measured fiducial light-by-light scattering cross section, sigma(fid)(gamma gamma -> gamma gamma) = 120 +/- 46(stat) +/- 28(syst) +/- 12(theo) nb, is consistent with the standard model prediction. The m(gamma gamma) distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the gamma gamma -> a -> gamma gamma process, in the mass range m(a) = 5-90 GeV. (C) 2019 The Author(s). Published by Elsevier B.V.Öğe Measurement of nuclear modification factors of ?(1S), ?(2S), and ?(3S) mesons in PbPb collisions at sNN=5.02 TeV(Elsevier B.V., 2019) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.The cross sections for ?(1S), ?(2S), and ?(3S) production in lead–lead (PbPb) and proton–proton (pp) collisions at sNN=5.02 TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, RAA, derived from the PbPb-to-pp ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, RAA(?(1S))>RAA(?(2S))>RAA(?(3S)). The suppression of ?(1S) is larger than that seen at sNN=2.76TeV, although the two are compatible within uncertainties. The upper limit on the RAA of ?(3S) integrated over pT, rapidity and centrality is 0.096 at 95% confidence level, which is the strongest suppression observed for a quarkonium state in heavy ion collisions to date. © 2019 The Author(s)Öğe Measurement of the WZ production cross section in pp collisions at s=13 TeV(Elsevier B.V., 2017) Khachatryan, V.; Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Asilar, E.; Bergauer, T.; Brandstetter, J.The WZ production cross section in proton–proton collisions at s=13 TeV is measured with the CMS experiment at the LHC using a data sample corresponding to an integrated luminosity of 2.3 fb?1. The measurement is performed in the leptonic decay modes WZ???????, where ?,??=e,?. The measured cross section for the range 60Öğe Search for long-lived particles using delayed photons in proton-proton collisions at root s=13 TeV(American Physical Society, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.A search for long-lived particles decaying to photons and weakly interacting particles, using protonproton collision data at root s = 13 TeV collected by the CMS experiment in 2016-2017 is presented. The data set corresponds to an integrated luminosity of 77.4 fb(-1). Results are interpreted in the context of supersymmetry with gauge-mediated supersymmetry breaking, where the neutralino is long-lived and decays to a photon and a gravitino. Limits are presented as a function of the neutralino proper decay length and mass. For neutralino proper decay lengths of 0.1, 1, 10, and 100 m, masses up to 320, 525, 360, and 215 GeV are excluded at 95% confidence level, respectively. We extend the previous best limits in the neutralino proper decay length by up to one order of magnitude, and in the neutralino mass by up to 100 GeV.Öğe Search for physics beyond the standard model in events with overlapping photons and jets(American Physical Society, 2019) Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Sağır, SinanResults are reported from a search for new particles that decay into a photon and two gluons, in events with jets. Novel jet substructure techniques are developed that allow photons to be identified in an environment densely populated with hadrons. The analyzed proton-proton collision data were collected by the CMS experiment at the LHC, in 2016 at root s = 13 TeV, and correspond to an integrated luminosity of 35.9 fb(-1). The spectra of total transverse hadronic energy of candidate events are examined for deviations from the standard model predictions. No statistically significant excess is observed over the expected background. The first cross section limits on new physics processes resulting in such events are set. The results are interpreted as upper limits on the rate of gluino pair production, utilizing a simplified stealth supersymmetry model. The excluded gluino masses extend up to 1.7 TeV, for a neutralino mass of 200 GeV and exceed previous mass constraints set by analyses targeting events with isolated photons.Öğe Search for supersymmetry in proton-proton collisions at 13 TeV in final states with jets and missing transverse momentum(Springer Science and Business Media Deutschland GmbH, 2019) Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Brandstetter, J.; Dragicevic, M.Results are reported from a search for supersymmetric particles in the final state with multiple jets and large missing transverse momentum. The search uses a sample of proton-proton collisions at s = 13 TeV collected with the CMS detector in 2016–2018, corresponding to an integrated luminosity of 137 fb?1, representing essentially the full LHC Run 2 data sample. The analysis is performed in a four-dimensional search region defined in terms of the number of jets, the number of tagged bottom quark jets, the scalar sum of jet transverse momenta, and the magnitude of the vector sum of jet transverse momenta. No significant excess in the event yield is observed relative to the expected background contributions from standard model processes. Limits on the pair production of gluinos and squarks are obtained in the framework of simplified models for supersymmetric particle production and decay processes. Assuming the lightest supersymmetric particle to be a neutralino, lower limits on the gluino mass as large as 2000 to 2310 GeV are obtained at 95% confidence level, while lower limits on the squark mass as large as 1190 to 1630 GeV are obtained, depending on the production scenario. [Figure not available: see fulltext.]. © 2019, The Author(s).
