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Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at √SNN = 2.76 Tev

European Physical Journal C 72:5 (2012) 1-26

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, M Hoch, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, A Knapitsch, M Krammer, D Liko, I Mikulec, M Pernicka, B Rahbaran, C Rohringer, 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, T Cornelis, EA de Wolf, X Janssen, S Luyckx, T Maes, L Mucibello, S Ochesanu, B Roland, R Rougny, M Selvaggi, 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, O Charaf, B Clerbaux, G de Lentdecker, V Dero, APR Gay, GH Hammad, T Hreus, A Léonard, PE Marage, L Thomas, C Vander Velde, P Vanlaer, J Wickens, 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, L Vanelderen, P Verwilligen, S Walsh, N Zaganidis, S Basegmez, G Bruno, J Caudron

Abstract:

Measurements from the CMS experiment at the LHC of dihadron correlations for charged particles produced in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2. 76 TeV are presented. The results are reported as a function of the particle transverse momenta (pT) and collision centrality over a broad range in relative pseudorapidity (Δη) and the full range of relative azimuthal angle (Δφ). The observed two-dimensional correlation structure in Δη and Δφ is characterised by a narrow peak at (Δη,Δφ)≈(0,0) from jet-like correlations and a long-range structure that persists up to at least {pipe}Δη{pipe}=4. An enhancement of the magnitude of the short-range jet peak is observed with increasing centrality, especially for particles of pT around 1-2 GeV/c. The long-range azimuthal dihadron correlations are extensively studied using a Fourier decomposition analysis. The extracted Fourier coefficients are found to factorise into a product of single-particle azimuthal anisotropies up to pT≈3-3. 5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Various orders of the single-particle azimuthal anisotropy harmonics are extracted for associated particle pT of 1-3 GeV/c, as a function of the trigger particle pT up to 20 GeV/c and over the full centrality range. © 2012 CERN for the benefit of the CMS collaboration.
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Combined inclusive diffractive cross sections measured with forward proton spectrometers in deep inelastic ep scattering at HERA

European Physical Journal C 72:10 (2012) 1-17

Authors:

FD Aaron, H Abramowicz, I Abt, L Adamczyk, M Adamus, R Aggarwal, C Alexa, V Andreev, S Antonelli, P Antonioli, A Antonov, M Arneodo, O Arslan, V Aushev, Y Aushev, O Bachynska, S Backovic, A Baghdasaryan, S Baghdasaryan, A Bamberger, AN Barakbaev, G Barbagli, G Bari, F Barreiro, E Barrelet, W Bartel, N Bartosik, D Bartsch, M Basile, K Begzsuren, O Behnke, J Behr, U Behrens, L Bellagamba, A Belousov, P Belov, A Bertolin, S Bhadra, M Bindi, JC Bizot, C Blohm, V Bokhonov, K Bondarenko, EG Boos, K Borras, D Boscherini, D Bot, V Boudry, I Bozovic-Jelisavcic, T Bołd, N Brümmer, J Bracinik, G Brandt, M Brinkmann, V Brisson, D Britzger, I Brock, E Brownson, R Brugnera, D Bruncko, A Bruni, G Bruni, B Brzozowska, A Bunyatyan, PJ Bussey, A Bylinkin, B Bylsma, L Bystritskaya, A Caldwell, AJ Campbell, KB Cantun Avila, M Capua, R Carlin, CD Catterall, F Ceccopieri, K Cerny, V Cerny, S Chekanov, V Chekelian, J Chwastowski, J Ciborowski, R Ciesielski, L Cifarelli, F Cindolo, A Contin, JG Contreras, AM Cooper-Sarkar, N Coppola, M Corradi, F Corriveau, M Costa, JA Coughlan, J Cvach, G D'Agostini, JB Dainton, F Dal Corso, K Daum, B Delcourt, J Delvax, RK Dementiev

Abstract:

A combination of the inclusive diffractive cross section measurements made by the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples of diffractive deep inelastic ep scattering data at a centre-of-mass energy √s= 318 Gev where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an improved precision of the cross section measurement which reaches 6 % for the most precise points. The combined data cover the range 2.5 < Q2 < 200 GeV2 in photon virtuality, 0.00035 < xP < 0.09 in proton fractional momentum loss, 0.09 <{pipe}t{pipe}< 0.55 GeV2 in squared four-momentum transfer at the proton vertex and 0.0018 < β <0.816 in β=x/xP, where x is the Bjorken scaling variable. © 2012 The Author(s).
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Exclusive electroproduction of two pions at HERA

European Physical Journal C 72:1 (2012) 1-12

Authors:

H Abramowicz, I Abt, L Adamczyk, M Adamus, R Aggarwal, S Antonelli, P Antonioli, A Antonov, M Arneodo, D Ashery, V Aushev, Y Aushev, O Bachynska, A Bamberger, AN Barakbaev, G Barbagli, G Bari, F Barreiro, N Bartosik, D Bartsch, M Basile, O Behnke, J Behr, U Behrens, L Bellagamba, A Bertolin, S Bhadra, M Bindi, C Blohm, V Bokhonov, T Bołd, K Bondarenko, EG Boos, K Borras, D Boscherini, D Bot, I Brock, E Brownson, R Brugnera, N Brümmer, A Bruni, G Bruni, B Brzozowska, PJ Bussey, B Bylsma, A Caldwell, M Capua, R Carlin, CD Catterall, S Chekanov, J Chwastowski, J Ciborowski, R Ciesielski, L Cifarelli, F Cindolo, A Contin, AM Cooper-Sarkar, N Coppola, M Corradi, F Corriveau, M Costa, G D'Agostini, F Dal Corso, J del Peso, RK Dementiev, S de Pasquale, M Derrick, RCE Devenish, D Dobur, BA Dolgoshein, G Dolinska, AT Doyle, V Drugakov, LS Durkin, S Dusini, Y Eisenberg, PF Ermolov, S Eskreys, S Fang, S Fazio, J Ferrando, MI Ferrero, J Figiel, M Forrest, B Foster, G Gach, A Galas, E Gallo, A Garfagnini, A Geiser, I Gialas, LK Gladilin, D Gladkov, C Glasman, O Gogota, YA Golubkov, P Göttlicher, I Grabowska-Bołd, J Grebenyuk, I Gregor

Abstract:

The exclusive electroproduction of two pions in the mass range 0.4
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Exclusive γγ →+μμ- production in proton-proton collisions at √s = 7 TeV

Journal of High Energy Physics 2012:1 (2012)

Authors:

S Chatrchyan, V Khachatryan, AM Sirunyan, A Tumasyan, W Adam, T Bergauer, M Dragicevic, J Erö, C Fabjan, M Friedl, R Fruḧwirth, VM Ghete, J Hammer, S Hänsel, M Hoch, N Hörmann, J Hrubec, M Jeitler, W Kiesenhofer, M Krammer, D Liko, I Mikulec, M Pernicka, B Rahbaran, H Rohringer, R Schöfbeck, J Strauss, A Taurok, F Teischinger, C Trauner, P Wagner, W Waltenberger, G Walzel, E Widl, CE Wulz, V Mossolov, N Shumeiko, J Suarez, S Bansal, L Benucci, EA De Wolf, X Janssen, S Luyckx, 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, R Gonzalez Suarez, A Kalogeropoulos, M Maes, A Olbrechts, 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, A Léonard, PE Marage, L Thomas, C Vander Velde, P Vanlaer, J Wickens, V Adler, K Beernaert, A Cimmino, S Costantini, M Grunewald, B Klein, J Lellouch, A Marinov, J McCartin, D Ryckbosch, N Strobbe, 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

Abstract:

A measurement of the exclusive two-photon production of muon pairs in proton-proton collisions at √s = 7TeV, pp → pμ+μ -p, is reported using data corresponding to an integrated luminosity of 40 pb-1. For muon pairs with invariant mass greater than 11:5 GeV, transverse momentum p (μ) > 4 GeV and pseudorapidity σ(μ) < 2:1, a t to the dimuon pT(μ+μ-) distribution results in a measured cross section of η(p → pμ+μ -p) = 3:38+0:580:55 (stat:)±0:16 (syst:)±0:14 (lumi:) pb, consistent with the theoretical prediction evaluated with the event generator Lpair. The ratio to the predicted cross section is 0:83+0:14 -0:13 (stat:) ± 0:04 (syst:) ± 0:03 (lumi:). The characteristic distributions of the muon pairs produced via fusion, such as the muon acoplanarity, the muon pair invariant mass and transverse momentum agree with those from the theory. Copyright © CERN.
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Forward energy flow, central charged-particle multiplicities, and pseudorapidity gaps in W and Z boson events from pp collisions at √s = 7 TeV

European Physical Journal C 72:1 (2012) 1-28

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, B Rahbaran, H Rohringer, R Schöfbeck, J Strauss, A Taurok, F Teischinger, C Trauner, 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, 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, A Raval, L Thomas, G Vander Marcken, 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

Abstract:

A study of forward energy flow and central charged-particle multiplicity in events with W and Z bosons decaying into leptons is presented. The analysis uses a sample of 7 TeV pp collisions, corresponding to an integrated luminosity of 36 pb-1, recorded by the CMS experiment at the LHC. The observed forward energy depositions, their correlations, and the central charged-particle multiplicities are not well described by the available non-diffractive soft-hadron production models. A study of about 300 events with no significant energy deposited in one of the forward calorimeters, corresponding to a pseudorapidity gap of at least 1. 9 units, is also presented. An indication for a diffractive component in these events comes from the observation that the majority of the charged leptons from the W(Z) decays are found in the hemisphere opposite to the gap. When fitting the signed lepton pseudorapidity distribution of these events with predicted distributions from an admixture of diffractive (pompyt) and non-diffractive (pythia) Monte Carlo simulations, the diffractive component is determined to be (50. 0 ± 9. 3 (stat.) ± 5. 2 (syst.))%. © 2012 CERN for the benefit of the CMS collaboration.
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