Browsing by Subject "Lhc"

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    Centrality dependence of particle production in p–Pb collisions at √sNN= 5.02 TeV
    (2015) Adam, J; Adamová, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmed, I; Ahn, S U; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; Alfaro Molina, R; Alici, A; Alkin, A; Alme, J; Alt, T; Altinpinar, S; Altsybeev, I; Alves Garcia Prado, C; Andrei, C; Andronic, A; Anguelov, V; Anielski, J; Antičić, T; Antinori, F
    We report measurements of the primary charged particle pseudorapidity density and transverse momentum distributions in p–Pb collisions at √sNN = 5.02 TeV, and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined using different event activity estimators, i.e. charged particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero-degree). The procedures to determine the centrality, quantified by the number of participants (Npart), or the number of nucleon-nucleon binary collisions (Ncoll), are described. We show that, in contrast to Pb–Pb collisions, in p–Pb collisions large multiplicity fluctuations together with the small range of participants available, generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy centrality classes, the Npart dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb-participants, an approximate independence of the multiplicity per participating nucleon measured at midrapitity of the number of participating nucleons is observed. Furthermore, at high-pT the p–Pb spectra are found to be consistent with the pp spectra scaled by Ncoll for all centrality classes. Our results represent valuable input for the study of the event activity dependence of hard probes in p–Pb collision and, hence, help to establish baselines for the interpretation of the Pb–Pb data.
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    D-meson production in p-Pb collisions at √sNN = 5.02 TeV and in pp collisions at √s = 7 TeV
    (2016) Adam, J; Adamová, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Aiola, S; Akindinov, A; Alam, S N; Albuquerque, D S D; Aleksandrov, D; Alessandro, B; Alexandre, D; Alfaro Molina, R; Alici, A; Alkin, A; Alme, J; Alt, T; Altinpinar, S; Altsybeev, I; Alves Garcia Prado, C; Andrei, C; Andronic, A; Anguelov, V; Antičić, T; Antinori, F; Antonioli, P; Aphecetche, L; Appelshäuser, H
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    J/psi Elliptic Flow in Pb-Pb Collisions at root s(NN)=2.76 TeV ????????? Title not correct
    (2013) Abbas, E; Abelev, B; Adam, J; Adamová, D; Adare, A M; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agocs, A G; Agostinelli, A; Ahammed, Z; Ahmad, N; Ahmad Masoodi, A; Ahn, S A; Ahn, S U; Aimo, I; Ajaz, M; Akindinov, A; Aleksandrov, D; Alessandro, B; Alici, A; Alkin, A; Almaráz Aviña, E; Alme, J; Alt, T; Altini, V; Altinpinar, S; Altsybeev, I; Andrei, C; Andronic, A; Anguelov, V; Anielski, J
    We report on the first measurement of inclusive J/psi elliptic flow v(2) in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at root s(NN) = 2.76 TeV in the rapidity range 2.5 < y < 4.0. The dependence of the J/psi v(2) on the collision centrality and on the J/psi transverse momentum is studied in the range 0 <= p(T) < 10 GeV/c. For semicentral Pb-Pb collisions at root s(NN) = 2.76 TeV, an indication of nonzero v(2) is observed with a largest measured value of v(2) = 0.116 +/-0.046(stat) +/- 0.029(syst) for J/psi in the transverse momentum range 2 <= p(T) < 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/psi nuclear modification factor and favors the scenario of a significant fraction of J/psi production from charm quarks in a deconfined partonic phase.
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    J/psi Suppression at Forward Rapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV
    (2012) Abelev, B; Adam, J; Adamová, D; Adare, A M; Aggarwal, M M; Aglieri Rinella, G; Agocs, A G; Agostinelli, A; Aguilar Salazar, S; Ahammed, Z; Ahmad Masoodi, A; Ahmad, N; Ahn, S U; Akindinov, A; Aleksandrov, D; Alessandro, B; Alfaro Molina, R; Alici, A; Alkin, A; Almaráz Aviña, E; Alme, J; Alt, T; Altini, V; Altinpinar, S; Altsybeev, I; Andrei, C; Andronic, A; Anguelov, V; Anielski, J; Anson, C; Antičić, T; Antinori, F
    The ALICE experiment has measured the inclusive J/psi production in Pb-Pb collisions at root s(NN) = 2.76 TeV down to zero transverse momentum in the rapidity range 2.5 < y < 4. A suppression of the inclusive J/psi yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%-80% most central collisions, is 0.545 +/- 0.032(stat) +/- 0.083dsyst_ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/psi production from charm quarks in a deconfined partonic phase can describe our data.