C. Adler

Distributions of charged hadrons associated with high transverse momentum particles in pp and Au plus Au collisions at root(S)(NN)=200 GeV

Charged hadrons in 0.154 GeV/c are reconstructed in pp and Au+Au collisions at sqrt(s_NN)=200 GeV. The associated multiplicity and pt magnitude sum are found to increase from pp to central Au+Au collisions. The associated pt distributions, while similar in shape on the near side, are significantly softened on the away side in central Au+Au relative to pp and not much harder than that of inclusive hadrons. The results, consistent with jet quenching, suggest that the away-side fragments approach equilibration with the medium traversed.

Multiplicity Distribution and Spectra of Negatively Charged Hadrons in Au+Au Collisions at

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Elliptic Flow in Au + Au Collisions at sqrt(s_NN) = 130 GeV

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

The STAR level-3 trigger system

Abstract The STAR Level-3 trigger issues a trigger decision upon a complete online reconstruction of Au+Au collisions at relativistic heavy ion collider energies. Central interactions are processed up to a rate of 50 s −1 including a simple analysis of physics observables. The setup of the processor farm and the event reconstruction as well as experiences and the proposed trigger algorithms are described.

The ALICE transition radiation detector: construction, operation, and performance

The Transition Radiation Detector (TRD) was designed and built to enhance the capabilities of the ALICE detector at the Large Hadron Collider (LHC). While aimed at providing electron identification and triggering, the TRD also contributes significantly to the track reconstruction and calibration in the central barrel of ALICE. In this paper the design, construction, operation, and performance of this detector are discussed. A pion rejection factor of up to 410 is achieved at a momentum of 1 GeV/c in p–Pb collisions and the resolution at high transverse momentum improves by about 40% when including the TRD information in track reconstruction. The triggering capability is demonstrated both for jet, light nuclei, and electron selection. ∗See Appendix A for the list of collaboration members ar X iv :1 70 9. 02 74 3v 2 [ ph ys ic s. in sde t] 1 7 Ja n 20 19 The ALICE Transition Radiation Detector ALICE Collaboration

phi meson production in Au + Au and p + p collisions at root S-NN=200 GeV

We report the STAR measurement of Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi spectra and yields are obtained at mid-rapidity for five centrality bins in Au+Au collisions and for non-singly-diffractive p+p collisions. It is found that the Phi transverse momentum distributions from Au+Au collisions are better fitted with a single-exponential while the p+p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that Phi production in central Au+Au collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions. The systematics ofversus centrality and the constant Phi/K- ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for Phi production.

Event-wise fluctuations in Au-Au collisions at {radical}(s{sub NN})=130 GeV

We present the first large-acceptance measurement of event-wise mean transverse momentum fluctuations for Au-Au collisions at nucleon-nucleon center-of-momentum collision energy root s(NN) = 130 GeV. The observed nonstatistical fluctuations substantially exceed in magnitude fluctuations expected from the finite number of particles produced in a typical collision. The r.m.s. fractional width excess of the event-wise distribution is 13.7 +/- 0.1(stat) +/- 1.3(syst)% relative to a statistical reference, for the 15% most-central collisions and for charged hadrons within pseudorapidity range vertical bar eta vertical bar fluctuation excess is qualitatively larger than those observed at lower energies and differs markedly from theoretical expectations. Contributions to fluctuations from semihard parton scattering in the initial state and dissipation in the bulk colored medium are discussed.

Identified particle elliptic flow in √sNN = 130 GeV

We report first results on elliptic flow of identified particles at mid-rapidity in Au+Au collisions at

Pion Interferometry of

\sqrt{s_{_{NN}}}=130

From the Big Bang to Massive Data Flow: Parallel Computing in High Energy Physics Experiments

GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow. The fit to the data with a simple model gives information on the temperature and flow velocities at freeze-out.