Browsing by Author "Anson, C"

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    Anomalous evolution of the Near-Side Jet Peak Shape in Pb-Pb Collisions at √sNN = 2.76 TeV
    (2017) 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; An, M; Andrei, C; Andrews, H A; Andronic, A; Anguelov, V; Anson, C; Antičić, T; Antinori, F
    The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a p T region inaccessible by direct jet identification. Here, the differences in the pseudorapidity (Δη) and azimuthal (Δφ) measurements are used to extract the shape of the near-side peak formed by particles associated with a higher pT trigger particle (1 < p T,trig < 8 GeV/c). A combined fit of the near-side peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at √ sNN=2.76 TeV. A significant broadening of the peak in the Δη direction at low pT is found from peripheral to central collisions, which vanishes above 4 GeV/c, while in the Δφ direction the peak is almost independent of centrality. For the 10% most central collisions and 1 < p T,assoc < 2 GeV/c, 1 < p T,trig < 3 GeV/c a novel feature is observed: a depletion develops around the center of the peak. Our results are compared to pp collisions at the same center of mass energy and ampt model simulations. The comparison to the investigated models suggests that the broadening and the development of themore » depletion is connected to the strength of radial and longitudinal flow.« less
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    Charge separation relative to the reaction plane in Pb-Pb collisions at√SNN = 2.76 TeV
    (2013) 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, N; Ahmad Masoodi, A; Ahn, S A; 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
    Measurements of charge dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at √SNN = 2.76 TeV.
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    First measurement of jet mass in Pb–Pb and p–Pb collisions at the LHC
    (2018) Acharya, S; Adamová, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, N; 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; Altsybeev, I; Alves Garcia Prado, C; An, M; Andrei, C; Andrews, H A; Andronic, A; Anguelov, V; Anson, C; Antičić, T; Antinori, F; Antonioli, P
    This letter presents the first measurement of jet mass in Pb–Pb and p–Pb collisions at √sNN = 2.76 TeV and √sNN = 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti-kT jet algorithm and resolution parameter R = 0.4. The jets are measured in the pseudorapidity range |ηjet| < 0.5 and in three intervals of transverse momentum between 60 GeV/c and 120 GeV/c. The measurement of the jet mass in central Pb–Pb collisions is compared to the jet mass as measured in p–Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb–Pb collisions is consistent within uncertainties with p–Pb reference measurements. Furthermore, the measured jet mass in Pb–Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties
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    Inclusive J/ψ production in pp collisions at √s = 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 Collaboration has measured inclusive J/ψ production in pp collisions at a center-of-mass energy √s = 2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges |y| < 0.9 and 2.5 < y < 4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are Le int = 1.1 nb−1 and L μ int = 19.9 nb−1, and the corresponding signal statistics are Ne+e− J/ψ = 59 ± 14 and Nμ+μ− J/ψ = 1364 ± 53. We present dσJ/ψ /dy for the two rapidity regions under study and, for the forward-y range, d2σJ/ψ /dy dpt in the transverse momentum domain 0 < pt < 8 GeV/c. The results are compared with previously published results at √s = 7 TeV and with theoretical calculations.
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    J/psi Polarization in pp Collisions at root s=7 TeV
    (2012) Abelev, B; Abrahantes Quintana, A; Adamová, D; Adare, A M; Aggarwal, M M; Aglieri Rinella, G; Agocs, A G; Agostinelli, A; Aguilar Salazar, S; Ahammed, Z; Ahmad, N; Ahmad Masoodi, A; Ahn, S U; Akindinov, A; Aleksandrov, D; Alessandro, B; Alfaro Molina, R; Alici, A; Alkin, A; Almaráz Aviña, E; Alt, T; Altini, V; Altinpinar, S; Altsybeev, I; Andrei, C; Andronic, A; Anguelov, V; Anson, C; Antičić, T; Antinori, F; Antonioli, P; Aphecetche, L
    The ALICE Collaboration has studied J/psi production in pp collisions at root s = 7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/psi polarization parameters lambda(theta) and lambda(phi) were obtained. The study was performed in the kinematic region 2: 5 < y < 4, 2 < p(t) < 8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.
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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.
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    J/ψ suppression at forward rapidity in Pb–Pb collisions at √sNN = 5.02 TeV
    (2017) 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; An, M; Andrei, C; Andrews, H A; Andronic, A; Anguelov, V; Anson, C; Antičić, T; Antinori, F
    The inclusive J/ ψ production has been studied in Pb–Pb and pp collisions at the centre-of-mass energy per nucleon pair sNN=5.02 TeV , using the ALICE detector at the CERN LHC. The J/ ψ meson is reconstructed, in the centre-of-mass rapidity interval 2.5 < y < 4 and in the transverse-momentum range pT < 12 GeV/c , via its decay to a muon pair. In this Letter, we present results on the inclusive J/ ψ cross section in pp collisions at s=5.02 TeV and on the nuclear modification factor RAA . The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum pT of the J/ ψ . The measured RAA values indicate a suppression of the J/ ψ in nuclear collisions and are then compared to our previous results obtained in Pb–Pb collisions at sNN=2.76 TeV . The ratio of the RAA values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0–10% centrality) is 1.17±0.04(stat)±0.20(syst) . In central events, as a function of pT , a slight increase of RAA with collision energy is visible in the region 2 < pT < 6 GeV/c . Theoretical calculations qualitatively describe the measurements, within uncertainties.
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    Multi-strange baryon production in pp collisions at √s = 7 TeV with ALICE
    (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, N; Ahmad Masoodi, A; 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
    A measurement of the multi-strange Ξ− and Ω− baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton–proton collisions at a centreof-mass energy of 7 TeV. The transverse momentum (pT) distributions were studied at mid-rapidity (|y| < 0.5) in the range of 0.6 < pT < 8.5 GeV/c for Ξ− and Ξ+ baryons, and in the range of 0.8 < pT < 5 GeV/c for Ω− and Ω+. Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current data has allowed us to measure a difference between the mean pT of Ξ− (Ξ+) and Ω− (Ω+). Particle yields, mean pT, and the spectra in the intermediate pT range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Ω− (Ω+). This PYTHIA tune approaches the pT spectra of Ξ− and Ξ+ baryons below pT < 0.85 GeV/c and describes the Ξ− and Ξ+ spectra above pT > 6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of (Ω− + Ω+)/(Ξ− + Ξ+) as a function of transverse mass.