| 61. |
- Abelev, B., et al.
(författare)
-
Inclusive photon production at forward rapidities in proton-proton collisions at root s=0.9, 2.76 and 7 TeV
- 2015
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:4
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Tidskriftsartikel (refereegranskat)abstract
- The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities (2.3 < eta < 3.9) in proton-proton collisions at three center-of-mass energies, root s = 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 +/- 0.3% (stat) +/- 8.8% (sys) and 61.2 +/- 0.3% (stat) +/- 7.6% (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
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| 62. |
- Abelev, B., et al.
(författare)
-
J/psi production and nuclear effects in p-Pb collisions at=5.02 TeV
- 2014
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/psi production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < y (cms) < 3.53 and -4.46 < y (cms) < -2.96, down to zero transverse momentum, studying the mu (+) mu (-) decay mode. In this paper, the J/psi production cross section and the nuclear modification factor R (pPb) for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/psi yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.
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| 63. |
- Abelev, B., et al.
(författare)
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Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=2.76 TeV
- 2015
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:1
-
Tidskriftsartikel (refereegranskat)abstract
- The p(T)-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at midrapidity in proton-proton collisions at root s = 2.76 TeV in the transverse momentum range 0.5 < p(T) < 12 GeV/c with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties.
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| 64. |
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| 65. |
- Abelev, B., et al.
(författare)
-
Measurement of visible cross sections in proton-lead collisions at root s(NN)=5.02 TeV in van der Meer scans with the ALICE detector
- 2014
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair root s(NN) = 5.02 TeV. Van der Meer scans were performed for both configurations of colliding beams, and the cross section was measured for two reference processes, based on particle detection by the T0 and V0 detectors, with pseudo-rapidity coverage 4.6 < eta < 4.9, -3.3 < eta < -3.0 and 2.8 < eta < 5.1, -3.7 < eta < -1.7, respectively. Given the asymmetric detector acceptance, the cross section was measured separately for the two configurations. The measured visible cross sections are used to calculate the integrated luminosity of the proton-lead and lead-proton data samples, and to indirectly measure the cross section for a third, configuration-independent, reference process, based on neutron detection by the Zero Degree Calorimeters.
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| 66. |
- Abelev, B., et al.
(författare)
-
Multiparticle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
- 2014
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:5
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of multiparticle azimuthal correlations (cumulants) for charged particles in p-Pb at root s(NN) = 5.02 TeV and Pb-Pb at root s(NN) = 2.76 TeV collisions are presented. They help address the question of whether there is evidence for global, flowlike, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a vertical bar Delta eta vertical bar gap is placed to suppress such correlations, the two-particle cumulants begin to rise at high multiplicity, indicating the presence of global azimuthal correlations. The Pb-Pb values are higher than the p-Pb values at similar multiplicities. In both systems, the second harmonic four-particle cumulants exhibit a transition from positive to negative values when the multiplicity increases. The negative values allow for a measurement of v(2){4} to be made, which is found to be higher in Pb-Pb collisions at similar multiplicities. The second harmonic six-particle cumulants are also found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find v(2){4} similar or equal to v(2){6} not equal 0 which is indicative of a Bessel-Gaussian function for the v(2) distribution. For very high-multiplicity Pb-Pb collisions, we observe that the four-and six-particle cumulants become consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and Pb-Pb are measured. These are found to be similar for overlapping multiplicities, when a vertical bar Delta eta vertical bar > 1.4 gap is placed.
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| 67. |
- Abelev, B., et al.
(författare)
-
Multiplicity dependence of jet-like two-particle correlation structures in p-Pb collisions at root s(NN)=5.02 TeV
- 2015
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 741, s. 38-50
-
Tidskriftsartikel (refereegranskat)abstract
- Two-particle angular correlations between unidentified charged trigger and associated particles 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 < p(T),(assoc) < p(T),(trig) < 5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range vertical bar eta vertical bar < 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 consistent 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 increase 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 only in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).
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| 68. |
- Abelev, B., et al.
(författare)
-
Neutral pion production at midrapidity in pp and Pb-Pb collisions at root(NN)-N-S=2.76 TeV
- 2014
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:10
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Tidskriftsartikel (refereegranskat)abstract
- Invariant yields of neutral pions at midrapidity in the transverse momentum range 0.6 < pT < 12 GeV/c measured in Pb-Pb collisions at root(NN)-N-s = 2.76 TeV are presented for six centrality classes. The pp reference spectrum was measured in the range 0.4 < pT < 10 GeV/c at the same center-of-mass energy. The nuclear modification factor, R-AA, shows a suppression of neutral pions in central Pb-Pb collisions by a factor of up to about 8-10 for 5 less than or similar to p(T) less than or similar to 7 GeV/c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations.
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| 69. |
- Abelev, B., et al.
(författare)
-
Performance of the ALICE experiment at the CERN LHC
- 2014
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Ingår i: International Journal of Modern Physics A. - 0217-751X. ; 29:24
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Forskningsöversikt (refereegranskat)abstract
- ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
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| 70. |
- Abelev, B., et al.
(författare)
-
Pion, Kaon, and Proton Production in Central Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:25
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter we report the first results on pi(+/-), K-+/-, p, and (p) over bar production at midrapidity (vertical bar y vertical bar < 0.5) in central Pb-Pb collisions at root s(NN) = 2.76 TeV, measured by the ALICE experiment at the LHC. The p(T) distributions and yields are compared to previous results at root s(NN) = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with root s(NN), which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/pi ratio is in line with predictions from the thermal model, the p/pi ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.
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