The STAR Collaboration

doi:10.1016/J.NUCLPHYSA.2009.10.156

Journal Article•DOI•

The STAR Collaboration

B. I. Abelev¹, Madan M. Aggarwal², Zubayer Ahammed³, A. V. Alakhverdyants⁴ +345 more•Institutions (49)

01 Nov 2009-Nuclear Physics (Elsevier)-Vol. 830, pp 1088-1091

About: This article is published in Nuclear Physics.The article was published on 2009-11-01. It has received 1696 citations till now. The article focuses on the topics: Star (graph theory).

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Journal Article•DOI•

The ALICE Collaboration

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K. Aamodt¹, N. Abel², A. Abrahantes Quintana, A. Acero +989 more•Institutions (76)

01 Nov 2009-Nuclear Physics

TL;DR: In this paper, the production of mesons containing strange quarks (KS, φ) and both singly and doubly strange baryons (,, and − + +) are measured at mid-rapidity in pp collisions at √ s = 0.9 TeV with the ALICE experiment at the LHC.

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1,176 citations

Cites background from "The STAR Collaboration"

...Just two month later, based on 22k events, the paper reporting the surprising large values of elliptic flow, indicating early-time thermalization, was published [17]....
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Journal Article•DOI•

Tuning Monte Carlo Generators: The Perugia Tunes

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Peter Skands¹•Institutions (1)

CERN¹

20 Oct 2010-Physical Review D

TL;DR: In this article, the p{sub perpendicular}-ordered shower and underlying event model in Pythia 6.4 is updated and supersede the older "S0" family, and a set of 8 related "Perugia variations" that attempt to systematically explore soft, hard, parton density, and color structure variations in the theoretical parameters.

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Abstract: We present 9 new tunes of the p{sub perpendicular}-ordered shower and underlying-event model in Pythia 6.4. These 'Perugia' tunes update and supersede the older 'S0' family. The data sets used to constrain the models include hadronic Z{sup 0} decays at LEP, Tevatron min-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In addition to the central parameter set, called 'Perugia 0', we introduce a set of 8 related 'Perugia variations' that attempt to systematically explore soft, hard, parton density, and color structure variations in the theoretical parameters. Based on these variations, a best-guess prediction of the charged track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC is made. Note that these tunes can only be used with Pythia 6, not with Pythia 8.

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1,056 citations

Cites background or methods from "The STAR Collaboration"

..., in the Rivet framework, see [29], most notably underlying-event observables from the Tevatron, but also recently some fragmentation spectra from RHIC [47,48]....
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...Also, since the Professor parameters were originally optimized for theQ(2)-ordered parton shower in PYTHIA, the newest (2010) Perugia tune goes slightly further, by changing the other fragmentation parameters (by order of 5%–10% relative to their Professor values) in an attempt to improve the description of high-z fragmentation and strangeness yields reported at LEP [45,46] and at RHIC [47,48], relative to the Professor p?-ordered tuning....
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...We acknowledge many fruitful interactions with the RHIC, Tevatron, and LHC experimental com- munities, and are particularly grateful to B. Cooper, L. Galtieri, B. Heinemann, G. Hesketh, D. Kar, P. Lenzi, A. Messina, and L. Tomkins for detailed counter-checks and feedback....
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...We hope these tunes will be useful to the RHIC, Tevatron, and LHC communities....
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...We expect a programme of such measurements to gradually develop as it becomes possible to extract more detailed information from the LHC data and note that some such observables, from earlier experiments, have already been included, e.g., in the Rivet framework, see [29], most notably underlying-event observables from the Tevatron, but also recently some fragmentation spectra from RHIC [47, 48]....
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Journal Article•DOI•

Systematic measurements of identified particle spectra in pp, d+Au, and Au+Au collisions at the star detector.

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B. I. Abelev¹, Madan M. Aggarwal², Zubayer Ahammed³, B. D. Anderson⁴ +367 more•Institutions (47)

03 Mar 2009-Physical Review C

TL;DR: In this article, the authors measured the charged-particle spectra at the BNL Relativistic Heavy Ion Collider (RHIC) time projection chamber and reported the average transverse momenta, total particle production, particle yield ratios, strangeness, and baryon production rates as a function of collision system and centrality.

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Abstract: Identified charged-particle spectra of pi(+/-), K(+/-), p, and (p) over bar at midrapidity (vertical bar y vertical bar < 0.1) measured by the dE/dx method in the STAR (solenoidal tracker at the BNL Relativistic Heavy Ion Collider) time projection chamber are reported for pp and d + Au collisions at root s(NN) = 200 GeV and for Au + Au collisions at 62.4, 130, and 200 GeV. Average transverse momenta, total particle production, particle yield ratios, strangeness, and baryon production rates are investigated as a function of the collision system and centrality. The transverse momentum spectra are found to be flatter for heavy particles than for light particles in all collision systems; the effect is more prominent for more central collisions. The extracted average transverse momentum of each particle species follows a trend determined by the total charged-particle multiplicity density. The Bjorken energy density estimate is at least several GeV/fm(3) for a formation time less than 1 fm/c. A significantly larger net-baryon density and a stronger increase of the net-baryon density with centrality are found in Au + Au collisions at 62.4 GeV than at the two higher energies. Antibaryon production relative to total particle multiplicity is found to be constant over centrality, but increases with the collision energy. Strangeness production relative to total particle multiplicity is similar at the three measured RHIC energies. Relative strangeness production increases quickly with centrality in peripheral Au + Au collisions, to a value about 50% above the pp value, and remains rather constant in more central collisions. Bulk freeze-out properties are extracted from thermal equilibrium model and hydrodynamics-motivated blast-wave model fits to the data. Resonance decays are found to have little effect on the extracted kinetic freeze-out parameters because of the transverse momentum range of our measurements. The extracted chemical freeze-out temperature is constant, independent of collision system or centrality; its value is close to the predicted phase-transition temperature, suggesting that chemical freeze-out happens in the vicinity of hadronization and the chemical freeze-out temperature is universal despite the vastly different initial conditions in the collision systems. The extracted kinetic freeze-out temperature, while similar to the chemical freeze-out temperature in pp, d + Au, and peripheral Au + Au collisions, drops significantly with centrality in Au + Au collisions, whereas the extracted transverse radial flow velocity increases rapidly with centrality. There appears to be a prolonged period of particle elastic scatterings from chemical to kinetic freeze-out in central Au + Au collisions. The bulk properties extracted at chemical and kinetic freeze-out are observed to evolve smoothly over the measured energy range, collision systems, and collision centralities.

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784 citations

Cites background or methods from "The STAR Collaboration"

...4 GeV are measured at relatively high p⊥ by the TOF detector in STAR [46, 47]....
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...4 GeV central Au+Au collisions (b) measured by dE/dx together with those by TOF [46, 47]....
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...The measured fractions of the total cross-section are determined to be 97 ± 3% [47, 162], 95±5% [23, 25], and 97±3% [13, 163] for minimum bias Au+Au collisions at 62....
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...Blast-wave fits are also performed including the large p⊥ ranges from TOF [46, 47] and the spectra obtained by the extended particle identification method (rdE/dx) [16]....
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Journal Article•DOI•

Observation and studies of jet quenching in PbPb collisions at √sNN=2.76 TeV

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S. Chatrchyan, Vardan Khachatryan, Albert M. Sirunyan, Armen Tumasyan +2177 more•Institutions (156)

12 Aug 2011-Physical Review C

TL;DR: In this article, the authors studied the effect of collision centrality on the transverse momentum of PbPb collisions at the LHC with a data sample of 6.7 inverse microbarns.

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Abstract: Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

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621 citations

Journal Article•DOI•

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

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K. Aamodt¹, A. Abrahantes Quintana, Dagmar Adamová², Andrew Marshall Adare³ +938 more•Institutions (80)

20 Jan 2011-Physical Review Letters

TL;DR: In this paper, the centrality dependence of the chargedparticle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented.

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Abstract: The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.

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553 citations