Browsing by Author "Ahmed, I"

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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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    Charged jet cross sections and properties in proton-proton collisions at √s =7 TeV
    (2015) Abelev, B; Adam, J; Adamová, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmad, N; Ahmed, I; Ahn, S U; Ahn, S A; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; Alici, A; Alkin, A; Alme, J; Alt, T; Altinpinar, S; Altsybeev, I; Alves Garcia Prado, C; Andrei, C; Andronic, A; Anguelov, V; Anielski, J
    The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at center-of-mass energy √s=7 TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the midrapidity region using the sequential recombination kT and anti-kT as well as the SISCone jet finding algorithms with several resolution parameters in the range R ¼ 0.2–0.6. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum (pT) interval 20 < pjet;ch T < 100 GeV=c. They are also consistent with prior measurements carried out at the LHC by the ATLAS Collaboration. The jet charged particle multiplicity rises monotonically with increasing jet pT, in qualitative agreement with prior observations at lower energies. The transverse profiles of leading jets are investigated using radial momentum density distributions as well as distributions of the average radius containing 80% (hR80i) of the reconstructed jet pT. The fragmentation of leading jets with R ¼ 0.4 using scaled pT spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and hR80i distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.
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    Multiplicity dependence of jet-like two-particle correlation structures in p–Pb collisions at √sNN = 5.02 TeV
    (2015) Abelev, B; Adam, J; Adamová, D; Aggarwal, M M; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmad, N; Ahmed, I; Ahn, S U; Ahn, S A; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; 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
    Two-particle angular correlations between unidentified charged trigger and associated par- ticles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre- of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 < pT, assoc < pT, trig < 5.0 GeV/c is examined, to include correlations induced by jets originating from low momen- tum-transfer scatterings (minijets). The correlations expressed as associated yield per trig- ger particle are obtained in the pseudorapidity range η < 0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p–Pb collisions are subtracted from both near- side short-range and away-side correlations in order to remove the non- jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consis- tent with the particles being produced via the incoherent fragmentation of multiple parton– parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to in- crease linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p–Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon–nucleon collisions estimated with a Glauber Monte-Carlo simulation.
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    Multiplicity dependence of the average transverse momentum in pp, p–Pb, and Pb–Pb collisions at the LHC
    (2013) 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 Masoodi, A; Ahmad, N; Ahmed, I; Ahn, S A; Ahn, S U; Aimo, I; Ajaz, M; Akindinov, A; Aleksandrov, D; Alessandro, B; Alexandre, D; Alici, A; Alkin, A; Alme, J; Alt, T; Altini, V; Altinpinar, S; Altsybeev, I; Andrei, C; Andronic, A; Anguelov, V; Anielski, J
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    Production of inclusive Υ (1S) and Υ (2S) in p–Pb collisions at √sNN = 5.02 TeV
    (2015) Abelev, B; Adam, J; Adamová, D; Aggarwal, M M; Aglieri Rinella, G; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmad, N; Ahmed, I; Ahn, S U; Ahn, S A; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; Alici, A; Alkin, A; Alme, J; Alt, T; Altinpinar, S; Altsybeev, I; Alves Garcia Prado, C; Andrei, C; Andronic, A; Anguelov, V; Anielski, J
    International audience; We report on the production of inclusive Υ (1S) and Υ (2S) in p–Pb collisions at √ s NN = 5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46 < y cms < −2.96) and forward (2.03 < y cms < 3.53) rapidity down to zero transverse momentum. The production cross sections of the Υ (1S) and Υ (2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of Υ (1S). A suppression of the inclusive Υ (1S) yield in p–Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon–nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects. (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP 3 .
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    Suppression of Υ(1S)at forward rapidity in Pb–Pb collisions at √sNN=2.76TeV
    (2014) Abelev, B; Adam, J; Adamová, D; Aggarwal, M M; Agnello, M; Agostinelli, A; Agrawal, N; Ahammed, Z; Ahmad, N; Ahmed, I; Ahn, S U; Ahn, S A; Aimo, I; Aiola, S; Ajaz, M; Akindinov, A; Alam, S N; Aleksandrov, D; Alessandro, B; Alexandre, D; 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
    We report on the measurement of the inclusive $Upsilon$(1S) production in Pb-Pb collisions at $sqrt{s_{rm NN}}=2.76$ TeV carried out at forward rapidity ($2.5