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Measurement of the t-channel single top quark production cross section in pp collisions at √s=7TeV

Physical Review Letters 107:9 (2011)

Authors:

S Chatrchyan, V Khachatryan, AM Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Erö, C Fabjan, M Friedl, R Frühwirth, VM Ghete, J Hammer, S Hänsel, M Hoch, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, M Krammer, D Liko, I Mikulec, M Pernicka, H Rohringer, R Schöfbeck, J Strauss, A Taurok, F Teischinger, P Wagner, W Waltenberger, G Walzel, E Widl, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, S Bansal, L Benucci, EA De Wolf, X Janssen, J Maes, T Maes, L Mucibello, S Ochesanu, B Roland, R Rougny, M Selvaggi, H Van Haevermaet, P Van Mechelen, N Van Remortel, F Blekman, S Blyweert, J D'hondt, O Devroede, R Gonzalez Suarez, A Kalogeropoulos, M Maes, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, O Charaf, B Clerbaux, G De Lentdecker, V Dero, APR Gay, GH Hammad, T Hreus, PE Marage, L Thomas, C Vander Velde, P Vanlaer, V Adler, A Cimmino, S Costantini, M Grunewald, B Klein, J Lellouch, A Marinov, J Mccartin, D Ryckbosch, F Thyssen, M Tytgat, L Vanelderen, P Verwilligen, S Walsh, N Zaganidis, S Basegmez, G Bruno, J Caudron, L Ceard, E Cortina Gil, J De Favereau De Jeneret, C Delaere, D Favart, A Giammanco, G Grégoire, J Hollar, V Lemaitre, J Liao

Abstract:

Electroweak production of the top quark is measured for the first time in pp collisions at √s=7TeV, using a data set collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 36pb-1. With an event selection optimized for t-channel production, two complementary analyses are performed. The first one exploits the special angular properties of the signal, together with background estimates from the data. The second approach uses a multivariate analysis technique to probe the compatibility with signal topology expected from electroweak top-quark production. The combined measurement of the cross section is 83.6±29.8(stat+syst)±3.3(lumi) pb, consistent with the standard model expectation. © 2011 CERN.
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On the DAMA and CoGeNT modulations

Physical Review D - Particles, Fields, Gravitation and Cosmology 84:4 (2011)

Authors:

MT Frandsen, F Kahlhoefer, J March-Russell, C McCabe, M McCullough, K Schmidt-Hoberg

Abstract:

DAMA observes an annual modulation in their event rate, as might be expected from dark matter scatterings, while CoGeNT has reported evidence for a similar modulation. The simplest interpretation of these findings in terms of dark matter-nucleus scatterings is excluded by other direct detection experiments. We consider the robustness of these exclusions with respect to assumptions regarding the scattering and find that isospin-violating inelastic dark matter helps alleviate this tension and allows marginal compatibility between experiments. Isospin violation can significantly weaken the XENON constraints, while inelasticity enhances the annual modulation fraction of the signal, bringing the CoGeNT and CDMS results into better agreement. © 2011 American Physical Society.
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Branching fractions for γ(3S)→π0hb and ψ(2S)→πp0hc

Physical Review D - Particles, Fields, Gravitation and Cosmology 84:3 (2011)

Authors:

JY Ge, DH Miller, IPJ Shipsey, B Xin, GS Adams, J Napolitano, KM Ecklund, J Insler, H Muramatsu, CS Park, LJ Pearson, EH Thorndike, S Ricciardi, C Thomas, M Artuso, S Blusk, R Mountain, T Skwarnicki, S Stone, LM Zhang, G Bonvicini, D Cinabro, A Lincoln, MJ Smith, P Zhou, J Zhu, P Naik, J Rademacker, DM Asner, KW Edwards, K Randrianarivony, G Tatishvili, RA Briere, H Vogel, PUE Onyisi, JL Rosner, JP Alexander, DG Cassel, S Das, R Ehrlich, L Gibbons, SW Gray, DL Hartill, BK Heltsley, DL Kreinick, VE Kuznetsov, JR Patterson, D Peterson, D Riley, A Ryd, AJ Sadoff, X Shi, WM Sun, J Yelton, P Rubin, N Lowrey, S Mehrabyan, M Selen, J Wiss, J Libby, M Kornicer, RE Mitchell, CM Tarbert, D Besson, TK Pedlar, D Cronin-Hennessy, J Hietala, S Dobbs, Z Metreveli, KK Seth, A Tomaradze, T Xiao, L Martin, A Powell, G Wilkinson

Abstract:

Using e+e- collision data corresponding to 5.88×106γ(3S) [25.9×106ψ(2S)] decays and acquired by the CLEO III [CLEO-c] detectors operating at the Cornell Electron Storage Ring, we study the single-pion transitions from γ(3S)[ψ(2S)] to the respective spin-singlet states hb[c]. Utilizing only the momentum of suitably selected transition-π0 candidates, we obtain the upper limit B(γ(3S)→π0h b)<1.2×10-3 at 90% confidence level, and measure B(ψ(2S)→π0hc)=(9.0±1.5±1.3) ×10-4. Signal sensitivities are enhanced by excluding very asymmetric π0→γγ candidates. © 2011 American Physical Society.
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Measurement of the t t-bar Production Cross Section in pp Collisions at 7 TeV in Lepton + Jets Events Using b-quark Jet Identification

ArXiv 1108.3773 (2011)
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Observation and studies of jet quenching in PbPb collisions at √sNN=2.76 TeV

Physical Review C - Nuclear Physics 84:2 (2011)

Authors:

S Chatrchyan, V Khachatryan, AM Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Erö, C Fabjan, M Friedl, R Frühwirth, VM Ghete, J Hammer, S Hänsel, C Hartl, M Hoch, N Hörmann, J Hrubec, M Jeitler, G Kasieczka, W Kiesenhofer, M Krammer, D Liko, I Mikulec, M Pernicka, H Rohringer, R Schöfbeck, J Strauss, F Teischinger, P Wagner, W Waltenberger, G Walzel, E Widl, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, L Benucci, EA De Wolf, X Janssen, T Maes, L Mucibello, S Ochesanu, B Roland, R Rougny, M Selvaggi, H Van Haevermaet, P Van Mechelen, N Van Remortel, S Beauceron, F Blekman, S Blyweert, J D'Hondt, O Devroede, R Gonzalez Suarez, A Kalogeropoulos, J Maes, M Maes, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, O Charaf, B Clerbaux, G De Lentdecker, V Dero, APR Gay, GH Hammad, T Hreus, PE Marage, L Thomas, C Vander Velde, P Vanlaer, J Wickens, V Adler, S Costantini, M Grunewald, B Klein, A Marinov, J McCartin, D Ryckbosch, F Thyssen, M Tytgat, L Vanelderen, P Verwilligen, S Walsh, N Zaganidis, S Basegmez, G Bruno, J Caudron, L Ceard, E Cortina Gil, C Delaere, D Favart, A Giammanco, G Grégoire, J Hollar, V Lemaitre, J Liao, O Militaru

Abstract:

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7μb-1. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet pT=120 GeV/c) up to the statistical limit of the available data sample (jet pT≈210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet. © 2011 American Physical Society.
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