| 1. |
- Acharya, S, et al.
(författare)
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J /ψ Elliptic Flow in Pb-Pb Collisions at sNN =5.02 TeV
- 2017
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Ingår i: Physical Review Letters. - 1079-7114. ; 119:24
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Tidskriftsartikel (refereegranskat)abstract
- We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|
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| 2. |
- Acharya, S, et al.
(författare)
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Measurement of D-meson production at mid-rapidity in pp collisions at √s=7 TeV
- 2017
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:8
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Tidskriftsartikel (refereegranskat)abstract
- The production cross sections for prompt charmed mesons D 0, D +, D ∗ + and Ds+ were measured at mid-rapidity in proton–proton collisions at a centre-of-mass energy s=7TeV with the ALICE detector at the Large Hadron Collider (LHC). D mesons were reconstructed from their decays D 0→ K -π+, D +→ K -π+π+, D ∗ +→ D 0π+, Ds++→K-K+π+, and their charge conjugates.With respect to previous measurements in the same rapidity region, the coverage in transverse momentum (pT) is extended and the uncertainties are reduced by a factor of about two. The accuracy on the estimated total c c ¯ production cross section is likewise improved. The measured pT-differential cross sections are compared with the results of three perturbative QCD calculations. © 2017, CERN for the benefit of the ALICE collaboration.
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| 3. |
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| 4. |
- Acharya, S, et al.
(författare)
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Production of π0 and η mesons up to high transverse momentum in pp collisions at 2.76 TeV
- 2017
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:5
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Tidskriftsartikel (refereegranskat)abstract
- The invariant differential cross sections for inclusive π0 and η mesons at midrapidity were measured in pp collisions at s=2.76 TeV for transverse momenta 0.4 < pT< 40 GeV/c and 0.6 < pT< 20 GeV/c, respectively, using the ALICE detector. This large range in pT was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a new single-cluster, shower-shape based method was developed for the identification of high-pT neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured cross sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the π0, and between 30–50% for the η meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10–30%, except at pT< 1 GeV/c. The new data can therefore be used to further improve the theoretical description of π0 and η meson production. © 2017, CERN for the benefit of the ALICE collaboration.
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| 5. |
- Adam, J., et al.
(författare)
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Anomalous Evolution of the Near-Side Jet Peak Shape in Pb-Pb Collisions at sNN =2.76 TeV
- 2017
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Ingår i: Physical Review Letters. - 1079-7114. ; 119:10
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a pT region inaccessible by direct jet identification. In these measurements pseudorapidity (Δη) and azimuthal (Δφ) differences are used to extract the shape of the near-side peak formed by particles associated with a higher pT trigger particle (1
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| 6. |
- Adam, J., et al.
(författare)
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Centrality dependence of the pseudorapidity density distribution for charged particles in Pb–Pb collisions at sNN=5.02 TeV
- 2017
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 772, s. 567-577
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Tidskriftsartikel (refereegranskat)abstract
- We present the charged-particle pseudorapidity density in Pb–Pb collisions at sNN=5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from −3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0–5%) collisions we find 21400±1300, while for the most peripheral (80–90%) we find 230±38. This corresponds to an increase of (27±4)% over the results at sNN=2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations — none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. © 2017 The Author(s)
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| 7. |
- Adam, J., et al.
(författare)
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Enhanced production of multi-strange hadrons in high-multiplicity proton-proton collisions
- 2017
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 13:6, s. 535-539
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Tidskriftsartikel (refereegranskat)abstract
- At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP). Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed. Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions, is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions, but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results, indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
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| 8. |
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| 9. |
- Adam, J., et al.
(författare)
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Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC
- 2017
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Ingår i: Physical Review Letters. - 1079-7114. ; 118:16
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Tidskriftsartikel (refereegranskat)abstract
- We present the first measurement of the two-particle transverse momentum differential correlation function, P2≡ ΔpTΔpT/ pT2, in Pb-Pb collisions at sNN=2.76 TeV. Results for P2 are reported as a function of the relative pseudorapidity (Δη) and azimuthal angle (Δφ) between two particles for different collision centralities. The Δφ dependence is found to be largely independent of Δη for |Δη|≥0.9. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around Δφ=π (i.e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of P2, studied as a function of the collision centrality, show that correlations at |Δη|≥0.9 can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system. © 2017 CERN, for the ALICE Collaboration.
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| 10. |
- Adam, J., et al.
(författare)
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Insight into particle production mechanisms via angular correlations of identified particles in pp collisions at √s=7 TeV
- 2017
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:8
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Tidskriftsartikel (refereegranskat)abstract
- Two-particle angular correlations were measured in pp collisions at s=7 TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon–baryon and anti-baryon–anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question. © 2017, CERN for the benefit of the ALICE collaboration.
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