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Measurement of Z boson production in Pb-Pb collisions at √SNN = 2.76 TeV with the ATLAS detector

Physical Review Letters 110:2 (2013) 022301-1-022301-18

Authors:

G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, AA Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, OS Abou Zeid, H Abramowicz, H Abreu, BS Acharya, L Adamczyk, DL Adams, TN Addy, J Adelman, S Adomeit, P Adragna, T Adye, S Aefsky, JA Aguilar-Saavedra, M Agustoni, M Aharrouche, SP Ahlen, F Ahles, A Ahmad, M Ahsan, G Aielli, T Akdogan, TPA Åkesson, G Akimoto, AV Akimov, MS Alam, MA Alam, J Albert, S Albrand, M Aleksa, IN Aleksandrov, F Alessandria, C Alexa, G Alexander, G Alexandre, T Alexopoulos, M Alhroob, M Aliev, G Alimonti, J Alison, BMM Allbrooke, PP Allport, SE Allwood-Spiers, J Almond, A Aloisio, R Alon, A Alonso, F Alonso, A Altheimer, B Alvarez Gonzalez, MG Alviggi, K Amako, C Amelung, VV Ammosov, SP Amor Dos Santos, A Amorim, N Amram, C Anastopoulos, LS Ancu, N Andari, T Andeen, CF Anders, G Anders, KJ Anderson, A Andreazza, V Andrei, ML Andrieux, XS Anduaga, P Anger, A Angerami, F Anghinolfi, A Anisenkov, N Anjos, A Annovi, A Antonaki, M Antonelli, A Antonov, J Antos, F Anulli, M Aoki, S Aoun, L Aperio Bella, R Apolle, G Arabidze, I Aracena, Y Arai, ATH Arce, S Arfaoui, JF Arguin, E Arik, M Arik

Abstract:

The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0:15 nb-1 of integrated luminosity obtained in the 2011 LHC Pb + Pb run at √SNN = 2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
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Measurement of differential top-quark-pair production cross sections in pp collisions at √s = 7TeV

European Physical Journal C 73:3 (2013) 1-29

Authors:

S Chatrchyan, V Khachatryan, AM Sirunyan, A Tumasyan, W Adam, E Aguilo, T Bergauer, M Dragicevic, J Erö, C Fabjan, M Friedl, R Frühwirth, VM Ghete, J Hammer, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, V Knünz, M Krammer, I Krätschmer, D Liko, I Mikulec, M Pernicka, B Rahbaran, C Rohringer, H Rohringer, R Schöfbeck, J Strauss, A Taurok, W Waltenberger, G Walzel, E Widl, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, M Bansal, S Bansal, T Cornelis, EA de Wolf, X Janssen, S Luyckx, L Mucibello, S Ochesanu, B Roland, R Rougny, M Selvaggi, Z Staykova, H Van Haevermaet, P Van Mechelen, N Van Remortel, A Van Spilbeeck, F Blekman, S Blyweert, J D'Hondt, R Gonzalez Suarez, A Kalogeropoulos, M Maes, A Olbrechts, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, B Clerbaux, G de Lentdecker, V Dero, APR Gay, T Hreus, A Léonard, PE Marage, A Mohammadi, T Reis, L Thomas, G Vander Marcken, C Vander Velde, P Vanlaer, J Wang, V Adler, K Beernaert, A Cimmino, S Costantini, G Garcia, M Grunewald, B Klein, J Lellouch, A Marinov, J Mccartin, AA Ocampo Rios, D Ryckbosch, N Strobbe, F Thyssen, M Tytgat, S Walsh, E Yazgan, N Zaganidis, S Basegmez, G Bruno, R Castello, L Ceard

Abstract:

Normalised differential top-quark-pair production cross sections are measured in pp collisions at a centre-of-mass energy of 7 TeVat the LHC with the CMS detector using data recorded in 2011 corresponding to an integrated luminosity of 5. 0 fb-1. The measurements are performed in the lepton+jets decay channels (e+jets and μ+jets) and the dilepton decay channels (e+}e-, μ+μ-, and μ±e∓). The tt̄ differential cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the tt̄ system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed. © 2013 CERN for the benefit of the CMS collaboration.
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Measurement of the W+W- cross section in pp collisions at √s = 7 TeV and limits on anomalous WWγ and WWZ couplings

European Physical Journal C 73:10 (2013) 1-22

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, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, V Knünz, M Krammer, I Krätschmer, D Liko, I Mikulec, D Rabady, B Rahbaran, C Rohringer, H Rohringer, R Schöfbeck, J Strauss, A Taurok, W Treberer-Treberspurg, W Waltenberger, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, S Alderweireldt, M Bansal, S Bansal, T Cornelis, EA De Wolf, X Janssen, A Knutsson, S Luyckx, L Mucibello, S Ochesanu, B Roland, R Rougny, H Van Haevermaet, P Van Mechelen, N Van Remortel, A Van Spilbeeck, F Blekman, S Blyweert, J D'Hondt, A Kalogeropoulos, J Keaveney, M Maes, A Olbrechts, S Tavernier, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, B Clerbaux, G De Lentdecker, L Favart, APR Gay, T Hreus, A Léonard, PE Marage, A Mohammadi, L Perniè, T Reis, T Seva, L Thomas, C Vander Velde, P Vanlaer, J Wang, V Adler, K Beernaert, L Benucci, A Cimmino, S Costantini, S Dildick, G Garcia, B Klein, J Lellouch, A Marinov, J Mccartin, AA Ocampo Rios, D Ryckbosch, M Sigamani, N Strobbe, F Thyssen, M Tytgat, S Walsh, E Yazgan, N Zaganidis, S Basegmez, C Beluffi, G Bruno

Abstract:

A measurement of W+W- production in pp collisions at √s = 7 TeV is presented. The data were collected with the CMS detector at the LHC, and correspond to an integrated luminosity of 4.92±0.11 fb-1. The W+W- candidates consist of two oppositely charged leptons, electrons or muons, accompanied by large missing transverse energy. The W+W- production cross section is measured to be 52.4±2.0 (stat.)±4.5 (syst.)±1.2 (lum.) pb. This measurement is consistent with the standard model prediction of 47.0±2.0 pb at next-to-leading order. Stringent limits on the WWγ and WWZ anomalous triple gauge-boson couplings are set. © 2013 CERN for the benefit of the CMS collaboration.
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Measurement of the production cross section of jets in association with a Z boson in pp collisions at √s=7 TeV with the ATLAS detector

Journal of High Energy Physics 2013:7 (2013)

Authors:

G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, AA Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, OS Abouzeid, H Abramowicz, H Abreu, Y Abulaiti, BS Acharya, L Adamczyk, DL Adams, TN Addy, J Adelman, S Adomeit, T Adye, S Aefsky, JA Aguilar-Saavedra, M Agustoni, SP Ahlen, F Ahles, A Ahmad, M Ahsan, G Aielli, TPA Åkesson, G Akimoto, AV Akimov, MA Alam, J Albert, S Albrand, M Aleksa, IN Aleksandrov, F Alessandria, C Alexa, G Alexander, G Alexandre, T Alexopoulos, M Alhroob, M Aliev, G Alimonti, J Alison, BMM Allbrooke, LJ Allison, PP Allport, SE Allwood-Spiers, J Almond, A Aloisio, R Alon, A Alonso, F Alonso, A Altheimer, B Alvarez Gonzalez, MG Alviggi, K Amako, C Amelung, VV Ammosov, SP Amor Dos Santos, A Amorim, S Amoroso, N Amram, C Anastopoulos, LS Ancu, N Andari, T Andeen, CF Anders, G Anders, KJ Anderson, A Andreazza, V Andrei, XS Anduaga, S Angelidakis, P Anger, A Angerami, F Anghinolfi, A Anisenkov, N Anjos, A Annovi, A Antonaki, M Antonelli, A Antonov, J Antos, F Anulli, M Aoki, L Aperio Bella, R Apolle, G Arabidze, I Aracena, Y Arai, ATH Arce, S Arfaoui, JF Arguin, S Argyropoulos, E Arik, M Arik, AJ Armbruster

Abstract:

Measurements of the production of jets of particles in association with a Z boson in pp collisions at √s=7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb-1 collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p T > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers. [Figure not available: see fulltext.] © 2013 CERN for the benefit of the ATLAS collaboration.
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Measurement of the ratio of the inclusive 3-jet cross section to the inclusive 2-jet cross section in pp collisions at √s = 7 TeV and first determination of the strong coupling constant in the TeV range

European Physical Journal C 73:10 (2013) 1-21

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, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, V Knünz, M Krammer, I Krätschmer, D Liko, I Mikulec, D Rabady, B Rahbaran, C Rohringer, H Rohringer, R Schöfbeck, J Strauss, A Taurok, W Treberer-Treberspurg, W Waltenberger, CE Wulz, V Mossolov, N Shumeiko, J Suarez Gonzalez, S Alderweireldt, M Bansal, S Bansal, T Cornelis, EA De Wolf, X Janssen, A Knutsson, S Luyckx, L Mucibello, S Ochesanu, B Roland, R Rougny, H Van Haevermaet, P Van Mechelen, N Van Remortel, A Van Spilbeeck, F Blekman, S Blyweert, J D'Hondt, A Kalogeropoulos, J Keaveney, M Maes, A Olbrechts, S Tavernier, W Van Doninck, P Van Mulders, GP Van Onsem, I Villella, B Clerbaux, G De Lentdecker, L Favart, APR Gay, T Hreus, A Léonard, PE Marage, A Mohammadi, T Reis, L Thomas, C Vander Velde, P Vanlaer, J Wang, V Adler, K Beernaert, L Benucci, A Cimmino, S Costantini, S Dildick, G Garcia, B Klein, J Lellouch, A Marinov, J Mccartin, AA Ocampo Rios, D Ryckbosch, M Sigamani, N Strobbe, F Thyssen, M Tytgat, S Walsh, E Yazgan, N Zaganidis, S Basegmez, C Beluffi, G Bruno, R Castello, A Caudron

Abstract:

A measurement is presented of the ratio of the inclusive 3-jet cross section to the inclusive 2-jet cross section as a function of the average transverse momentum, 〈pT1,2〉, of the two leading jets in the event. The data sample was collected during 2011 at a proton-proton centre-of-mass energy of 7 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 5.0 fb-1. The strong coupling constant at the scale of the Z boson mass is determined to be αS(MZ)=0.1148±0.0014 (exp.)±0.0018 (PDF)±0.0050(theory), by comparing the ratio in the range 0.42 < 〈pT1,2〉 < 1.39 TeV to the predictions of perturbative QCD at next-to-leading order. This is the first determination of αS(M Z) from measurements at momentum scales beyond 0.6 TeV. The predicted ratio depends only indirectly on the evolution of the parton distribution functions of the proton such that this measurement also serves as a test of the evolution of the strong coupling constant. No deviation from the expected behaviour is observed. © 2013 CERN for the benefit of the CMS collaboration.
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