Collision Dynamics at RHIC Olga Barannikova Purdue University

Collision Dynamics at RHIC Olga Barannikova (Purdue University) For the STAR Collaboration Olga Barannikova Lake Louise Winter Institute, Feb. 2004

Collision Evolution Tc=170 Me. V e. C=0. 5 Ge. V/fm 3 F. Karsch, Nucl. Phys. A 698, 199 c (2002). QCD predicts phase transition from hadronic matter to QGP at high energy density initial state QGP and Hydro. expansion pre-equilibrium Olga Barannikova Tc Hadronic interaction and chemical freeze-out Hadronization Tch ? Elastic scattering and kinetic freeze-out Tkin ? Lake Louise Winter Institute, Feb. 2004 2

Collision Dynamics Search for final state QGP signals in Bulk properties of the collision Spectral shapes: kinetic freeze-out properties transverse radial flow Tkin @ kinetic freeze-out Flavor composition: chemical freeze-out properties strangeness&baryon production Tch @ chemical freeze-out Olga Barannikova Lake Louise Winter Institute, Feb. 2004 3

Particle Identification Topological method ( -) X+ (X-) d. E/dx method 4

Transverse Mass Spectra d. N/(2π dy p. Tdp. T) [c 4/Ge. V 2] Spectra shape similar in p+p, different in A+A. Au+Au central Variety of hadron species: , K 0 s, K*, , p, , , pp and Au+Au collisions Same experimental setup! Olga Barannikova d 2 N/(2 m. Tdy) pp Lake Louise Winter Institute, Feb. 2004 m. T-m 0 5

Kinetic Freeze-out Blast-wave model: Kinetic freeze-out temperature E. Schnedermann et al, PRC 48 (1993) 2462. where and - Au+Au central Radial flow velocity K- – Tkin decreases with centrality – < > increases with centrality Olga Barannikova p Lake Louise Winter Institute, Feb. 2004 6

Particle Production Increase with centrality Olga Barannikova Little centrality dependence Enhanced strangeness and (anti)baryon production Lake Louise Winter Institute, Feb. 2004 7

Statistical Model Fit Tc Tch 200 Ge. V STAR – Tch is insensitive to centrality – Tch ~ Tc: No much interaction from hadronization to chemical freeze-out What about other particle species? Olga Barannikova Lake Louise Winter Institute, Feb. 2004 8

Kinetic Freeze-out Evolution Sequential kinetic freeze-out: , , Tc , , K, p, K* , : Tkin independent of centrality Tkin ~ Tch~ 160 Me. V ~ 0. 45 c Initial state broadening? String fusion? Partonic flow? Tch ~ 160 Me. V, ~ 0. 45, <E > ~ 620 Me. V rescattering Tkin ~ 90 Me. V, ~ 0. 6, <E > ~ 580 Me. V Tch Tkin : Dt(ch kin) ~6 fm/c What about initial state? Olga Barannikova Lake Louise Winter Institute, Feb. 2004 9

Initial Conditions Gluon saturation scale: J. P. Blaizot and A. H. Mueller, Nucl. Phys. B 289, 847 (1987) D. Kharzeev and E. Levin, Phys. Lett. B 523, 79 (2001). Nch RHIC Dynamics at RHIC: – different initial conditions – same chemical freeze-out condition – cooling and expansion with a sequential decoupling of particles Olga Barannikova Lake Louise Winter Institute, Feb. 2004 10

Summary • Initial conditions vary with centrality • Constant Tch ~160 Me. V ~ TC • Kinetic freeze-out parameters have centrality dependence: Blast wave model fit (central collisions): - Tkin , b - sequential kinetic freeze-out: X, W, f , K, p, L, K* • Multistrange baryons: Tkin ~ Tch bch ~ 0. 45 c • Tch Tkin : Olga Barannikova Dt(ch kin) ~6 fm/c Lake Louise Winter Institute, Feb. 2004 11

Back-up Olga Barannikova Lake Louise Winter Institute, Feb. 2004 12

Blast-wave Model Fit All data were studied within the same framework, Blast Wave model (E. Schnedermann et. al. PRC 48 (1993) 2462). The model assumes a boosted thermal source in transverse and longitudinal directions. There are three fit parameters: β – the flow velocity, Tkin – the kinetic freeze out temperature, and n – that describes the shape of the flow profile. R r R Olga Barannikova Lake Louise Winter Institute, Feb. 2004 13

Particle Production _ p/ 200 Ge. V 130 Ge. V SPS/NA 49 AGS/E 866(x 50) d. N -/dy Increase with centrality Olga Barannikova (Anti)baryon enhancement Lake Louise Winter Institute, Feb. 2004 14

K-/ Particle Production d. N -/dy Increase with centrality Olga Barannikova Little centrality dependence -- different at lower energies! Lake Louise Winter Institute, Feb. 2004 15

Freeze-out Conditions Central events: Statistical model fit results: – , K, p: Tch ~ 160 Me. V B ~ 20 Me. V s ~ 4 Me. V ~ 0. 9 – , K, p, , , : Tch ~ 160 Me. V B ~ 24 Me. V s ~ 1 Me. V Olga Barannikova ~ 1. 0 Lake Louise Winter Institute, Feb. 2004 16

Kinetic Freeze-out Evolution p, K, p fit with p, K, p , , fit Au+Au @ 130 Ge. V , : Less flow and hotter p, K, p: Strong flow but cool Olga Barannikova Lake Louise Winter Institute, Feb. 2004 17

Collision Dynamics QGP Initial state broadening? String fusion? Partonic flow? Tc ~ 170± 10 Me. V Hadronization Chemical freeze-out Tch ~ 160 Me. V, ~ 0. 45, <E > ~ 620 Me. V rescattering Tkin ~ 90 Me. V, ~ 0. 6, <E > ~ 580 Me. V Kinetic freeze-out <E > ~ 600 Me. V /particle g g 600 Me. V / parton Olga Barannikova T~300 Me. V Lake Louise Winter Institute, Feb. 2004 18

Time Scale Tch Tkin For massless particles in equilibrium: Entropy density ~ T 3 Olga Barannikova Lake Louise Winter Institute, Feb. 2004 19