178 research outputs found

    Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy

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    A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.Comment: Published in Physical Review Letter

    Performance and Operation of the CMS Electromagnetic Calorimeter

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    The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented

    Design, performance, and calibration of CMS forward calorimeter wedges

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    We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region (3 <= vertical bar eta vertical bar <= 5), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h approximate to 5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as a/root E circle plus b. The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%

    The transverse momentum dependence of charged kaon Bose-Einstein correlations in the SELEX experiment

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    CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOWe report the measurement of the one-dimensional charged kaon correlation functions using 600GeV/c σ-, π- and 540GeV/c p beams from the SELEX (E781) experiment at the Fermilab Tevatron. K±K± correlation functions are studied for three transverse pair momentum, kT, ranges and parameterized by a Gaussian form. The emission source radii, R, and the correlation strength, λ, are extracted. The analysis shows a decrease of the source radii with increasing kaon transverse pair momentum for all beam types. © 2015 The Authors.We report the measurement of the one-dimensional charged kaon correlation functions using 600GeV/c σ-, π- and 540GeV/c p beams from the SELEX (E781) experiment at the Fermilab Tevatron. K±K± correlation functions are studied for three transverse pair momentum, kT, ranges and parameterized by a Gaussian form. The emission source radii, R, and the correlation strength, λ, are extracted. The analysis shows a decrease of the source radii with increasing kaon transverse pair momentum for all beam types.753458464CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOSem informaçãoSem informaçãoRuss, J.S., Akchurin, N., Andreev, V.A., First charm hadroproduction results from SELEX (1998) ICHEP'98 Proc. Int. Conf. on High Energy Physics II, p. 1259. , arxiv:hep-ex/9812031Goldhaber, G., Fowler, W.B., Goldhaber, S., Hoang, T.F., Kalogeropoulos, T.E., Powell, W.M., Pion-pion correlations in antiproton annihilation events (1959) Phys. Rev. Lett., 3, pp. 181-183Goldhaber, G., Goldhaber, S., Lee, W., Pais, A., Influence of Bose-Einstein statistics on the antiproton-proton annihilation process (1960) Phys. Rev., 120, pp. 300-312Kopylov, G.I., Podgoretsky, M.I., Correlations of identical particles emitted by highly excited nuclei (1972) Sov. J. Nucl. Phys., 15, pp. 219-223Kopylov, G.I., Podgoretsky, M.I., Multiple production and interference of particles emitted by moving sources (1974) Sov. J. Nucl. Phys., 18, pp. 336-341Kopylov, G.I., Like particle correlations as a tool to study the multiple production mechanism (1974) Phys. Lett. B, 50, pp. 472-474Abbiendi, G., Transverse and longitudinal Bose-Einstein correlations in hadronic Z0 decays (2000) Eur. Phys. J. C, 16, pp. 423-433. , arxiv:hep-ex/0002062Chekanov, S., Bose-Einstein correlations in one and two dimensions in deep inelastic scattering (2004) Phys. Lett. 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Phys., 37, pp. 871-876. , arxiv:nucl-th/0612006Lednický, R., Finite-size effect on two-particle production (2008) J. Phys. G, Nucl. Part. Phys., 35Lednický, R., Lyuboshitz, V.V., Lyuboshitz, V.L., Final-state interactions in multichannel quantum systems and pair correlations of nonidentical and identical particles at low relative velocities (1998) Phys. At. Nucl., 61, pp. 2050-2063Bowler, M.G., Coulomb corrections to Bose-Einstein corrections have greatly exaggerated (1991) Phys. Lett. B, 270, pp. 69-74Sinyukov, Y., Lednický, R., Akkelin, S.V., Pluta, J., Erazmus, B., Coulomb corrections to Bose-Einstein corrections have greatly exaggerated (1998) Phys. Lett. B, 432, pp. 248-257Adams, J., Pion interferometry in Au+Au collisions at sNN=200GeV (2005) Phys. Rev. C, 71. , arxiv:nucl-ex/0411036Skands, P.Z., Tuning Monte Carlo generators: the Perugia tunes (2010) Phys. Rev. D, 82. , arxiv:1005.3457Abelev, B., Charged kaon femtoscopic correlations in pp collisions at s=7TeV (2013) Phys. Rev. D, 87. , arxiv:1212.5958v2Khachatryan, V., Measurement of Bose-Einstein correlations in pp collisions at s = 0.9 and 7 TeV (2011) J. High Energy Phys., 5. , arxiv:1101.3518Akkelin, S.V., Sinyukov, Y.M., Deciphering nonfemtoscopic two-pion correlations in p+p collisions with simple analytical models (2012) Phys. Rev. D, 85. , arxiv:1106.5120Lednický, R., Progulova, T.B., Influence of resonances on Bose-Einstein correlations of identical pions (1992) Z. Phys. C, 55, pp. 295-305Lisa, M., Pratt, S., Soltz, R., Wiedemann, U., Femtoscopy in relativistic heavy ion collisions: two decades of progress (2005) Annu. Rev. Nucl. Part. Sci., 55, pp. 357-402. , arxiv:nucl-ex/0505014Pratt, S., Pion interferometry for exploding sources (1984) Phys. Rev. Lett., 53, pp. 1219-1221Abbiendi, G., Bose-Einstein study of position-momentum correlations of charged pions in hadronic Z0 decays (2007) Eur. Phys. J. C, 52, pp. 787-803. , arxiv:0708.1122Achard, P., Test of the τ-model of Bose-Einstein correlations and reconstruction of the source function in hadronic Z-boson decay at LEP (2011) Eur. Phys. J. C, 71, p. 1648. , arxiv:1105.4788Aamodt, K., Femtoscopy of pp collisions at s = 0.9 and 7 TeV at the LHC with two-pion Bose-Einstein correlations (2011) Phys. Rev. D, 84. , arxiv:1101.3665Wiedemann, U.A., Heinz, U.W., Resonance contributions to Hanbury-Brown-Twiss correlation radii (1997) Phys. Rev. C, 56, pp. 3265-3286. , arxiv:nucl-th/9611031Werner, K., Karpenko, I., Pierog, T., Bleicher, M., Mikhailov, K., Evidence for hydrodynamic evolution in proton-proton scattering at 900 GeV (2011) Phys. Rev. C, 83. , arxiv:1010.0400Humanic, T.J., Predictions for two-pion correlations for s=14TeV proton-proton collisions (2007) Phys. Rev. C, 76. , arxiv:nucl-th/0612098Alexopoulos, T., Study of source size in pp- collisions at s=1.8TeV using pion interferometry (1993) Phys. Rev. D, 48, pp. 1931-1942Csorgo, T., Kittel, W., Metzger, W.J., Novák, T., Parametrization of Bose-Einstein correlations and reconstruction of the space-time evolution of pion production in e+e- annihilation (2008) Phys. Lett. B, 663, pp. 214-216. , arxiv:0803.3528Bialas, A., Kucharczyk, M., Palka, H., Zalewski, K., Mass dependence of HBT correlations in e+e- annihilation (2000) Phys. Rev. D, 62. , arxiv:hep-ph/0006290Alexander, G., Open questions related to Bose-Einstein correlations in e+e- → hadrons (2004) Acta Phys. Pol. B, 35, pp. 69-76. , arxiv:hep-ph/0311114Alexander, G., Mass and transverse mass effects on the hadron emitter size (2001) Phys. Lett. B, 506, pp. 45-51. , arxiv:hep-ph/0101319The authors are indebted to the staff of Fermi National Accelerator Laboratory and for invaluable technical support from the staffs of collaborating institutions. This project was supported in part by Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Consejo Nacional de Ciencia y Tecnología (CONACyT), Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fondo de Apoyo a la Investigación (UASLP), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities, Istituto Nazionale di Fisica Nucleare (INFN), the International Science Foundation (ISF), the National Science Foundation, NATO, the Russian Academy of Sciences, the Russian Ministry of Science and Technology, the Russian Foundation for Basic Research (research project No. 11-02-01302-a), the Secretaría de Educación Pública (Mexico), the Turkish Scientific and Technological Research Board (TÜBİTAK), and the U.S. Department of Energy. We thank ITEP and National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) for providing computing powers and support for data analysis and simulations. The authors also would like to thank Prof. Michael Lisa and Prof. Richard Lednický for helpful comments and fruitful discussions

    Evidence for the 125 GeV Higgs boson decaying to a pair of tau leptons

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    Observation of Top Quark Production in Proton-Nucleus Collisions

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    Evidence for the 125 GeV Higgs boson decaying to a pair of tau leptons

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    A search for a standard model Higgs boson decaying into a pair of &#964; leptons is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. The dataset corresponds to an integrated luminosity of 4.9 fb &#8722;1 at a centre-of-mass energy of 7 TeV and 19.7 fb &#8722;1 at 8 TeV. Each &#964; lepton decays hadronically or leptonically to an electron or a muon, leading to six different final states for the &#964; -lepton pair, all considered in this analysis. An excess of events is observed over the expected background contributions, with a local significance larger than 3 standard deviations for m H values between 115 and 130 GeV. The best fit of the observed H &#8594; &#964; &#964; signal cross section times branching fraction for m H = 125 GeV is 0 . 78 ± 0 . 27 times the standard model expectation. These observations constitute evidence for the 125 GeV Higgs boson decaying to a pair of &#964; leptons

    Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV

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    The nuclear modification factors of J/psi and psi(2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of root S-NN = 5.02 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 mu b(-1) and 28 pb(-1), respectively. The measurements are performed in the dimuon rapidity range of vertical bar y vertical bar 25 GeV/c is seen with respect to that observed at intermediate p(T). The prompt psi(2S) meson yield is found to be more suppressed than that of the prompt J/psi mesons in the entire p(T) range.Peer reviewe

    Search for charged Higgs bosons in the H± → τ±ν_τ decay channel in proton-proton collisions at √s= 13 TeV

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    A search is presented for charged Higgs bosons in the H-+/- -> tau(+/-)nu(tau) decay mode in the hadronic final state and in final states with an electron or a muon. The search is based on proton-proton collision data recorded by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). The results agree with the background expectation from the standard model. Upper limits at 95% confidence level are set on the production cross section times branching fraction to tau(+/-)nu(tau) for an H-+/- in the mass range of 80GeV to 3TeV, including the region near the top quark mass. The observed limit ranges from 6 pb at 80 GeV to 5 fb at 3 TeV. The limits are interpreted in the context of the minimal supersymmetric standard model m(h)(mod-) scenario.Peer reviewe

    Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states

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