| 1. |
- Abelev, B., et al.
(författare)
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Beauty production in pp collisions at root s=2.76 TeV measured via semi-electronic decays
- 2014
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 738, s. 97-108
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y| < 0.8 and transverse momentum 1 < p(T)< 10 GeV/c, in pp collisions at root s = 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, sigma(b -> e) = 3.47 +/- 0.40(stat)(+1.12)(-1.33)(sys) +/- 0.07(norm) mu b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) calculations to obtain the total b (b) over bar production cross section, sigma(b (b) over bar) = 130 +/- 15.1(stat)(+42.1)(-49.8)(sys)(+3.4)(-3.1)(extr) +/- 2.5(norm) +/- 4.4(BR) mu b. (C) 2014 The Authors. Published by Elsevier B.V.
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| 2. |
- Abelev, B., et al.
(författare)
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Event-by-event mean p(T) fluctuations in pp and Pb-Pb collisions at the LHC
- 2014
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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
- Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at root s = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at root S-NN = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar-multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb-Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.
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| 3. |
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| 4. |
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| 5. |
- Abelev, B., et al.
(författare)
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Multiparticle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:5
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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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| 6. |
- Abelev, B., et al.
(författare)
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Neutral pion production at midrapidity in pp and Pb-Pb collisions at root(NN)-N-S=2.76 TeV
- 2014
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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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| 7. |
- Abelev, B., et al.
(författare)
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Suppression of Upsilon(1S) at forward rapidity in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2014
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 738, s. 361-372
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Tidskriftsartikel (refereegranskat)abstract
- We report on the measurement of the inclusive Upsilon(1S) production in Pb-Pb collisions at root s(NN) = 2.76 TeV carried out at forward rapidity (2.5 < y < 4) and down to zero transverse momentum using its mu(+)mu(-) decay channel with the ALICE detector at the Large Hadron Collider. Astrong suppression of the inclusive Upsilon(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleo-nnucleon collisions. The nuclear modification factor, for events in the 0-90% centrality range, amounts to 0.30 +/- 0.05(stat) +/- 0.04(syst). The observed Upsilon(1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence. (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/). Funded by SCOAP(3).
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| 8. |
- Abelev, B., et al.
(författare)
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Transverse momentum dependence of inclusive primary charged-particle production in p-Pb collisions at root S-NN=5.02 TeV
- 2014
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:9
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Tidskriftsartikel (refereegranskat)abstract
- The transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC in the range 0.15 < pT < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at root S-NN = 2.76 TeV.
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| 9. |
- Adare, A., et al.
(författare)
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Cross section and double helicity asymmetry for eta mesons and their comparison to pi(0) production in p plus p collisions at root s=200 GeV
- 2011
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 83:3
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of double-helicity asymmetries in inclusive hadron production in polarized p + p collisions are sensitive to helicity-dependent parton distribution functions, in particular, to the gluon helicity distribution, Delta g. This study focuses on the extraction of the double-helicity asymmetry in eta production ((p) over right arrow + (p) over right arrow -> eta + X), the eta cross section, and the eta/pi(0) cross section ratio. The cross section and ratio measurements provide essential input for the extraction of fragmentation functions that are needed to access the helicity-dependent parton distribution functions.
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| 10. |
- Adare, A., et al.
(författare)
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Detailed measurement of the e(+)e(-) pair continuum in p plus p and Au plus Au collisions at root s(NN)=200 GeV and implications for direct photon production
- 2010
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 81:3
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Tidskriftsartikel (refereegranskat)abstract
- PHENIX has measured the e(+)e(-) pair continuum in root s(NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e(+)e(-) yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c (c) over bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7 +/- 0.4(stat) +/- 1.5(syst) +/- 0.9(model). At low mass (m(ee) < 0.3 GeV/c(2)) and high p(T) (1 < p(T) < 5 GeV/c) an enhanced e(+)e(-) pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p(T), with inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar or equal to 300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p(T) < 1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T similar or equal to 100 MeV. Theoretical models underpredict the low-mass, low-p(T) enhancement.
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