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Rashmi Raniwala Department of Physics University of Rajasthan Jaipur

Rashmi Raniwala Department of Physics University of Rajasthan Jaipur. HYDRO & FREEZEOUT FROM STAR DATA. For STAR collaboration. Time. Initial conditions. Dense Partonic Matter Hydro description. Kinetic freeze-out. Initial hard interactions. Hadronization and chemical freeze-out.

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Rashmi Raniwala Department of Physics University of Rajasthan Jaipur

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  1. Rashmi Raniwala Department of Physics University of Rajasthan Jaipur HYDRO & FREEZEOUT FROM STAR DATA For STAR collaboration

  2. Time Initial conditions Dense Partonic Matter Hydro description Kinetic freeze-out Initial hard interactions Hadronization and chemical freeze-out EVOLUTION OF A HEAVY ION COLLISION AT RHIC Bulk of this produced matter is soft Some experimental handles on Bulk Properties at various stages: • Anisotropic flow : develops in early expansion stage (EoS,e,) • Hadron Yield ratios : are fixed at Chemical Freezeout (Tchemical, mB,gS) • Identified particle pT spectra reflect the random and collective motion at kinetic freezeout: (Tf,bT)

  3. PLAN OF THE TALK STAR results on: • Freezeout parameters from identified particle spectra • Freezeout parameters from integrated particle ratios • Elliptic flow

  4. STAR : A SUITE OF DETECTORS Time Projection Chamber Magnet Coils Silicon Tracker SVT & SSD TPC Endcap & MWPC FTPCs Endcap Calorimeter Beam Beam Counters Barrel EM Calorimeter Central Trigger Barrel & TOF Not Shown: pVPDs, ZDCs, and FPDs PMD 4.2 meters A TPC lies at the heart of STAR

  5. SOME EXPERIMENTAL ASPECTS TO DETERMINE THE SPECTRA A bulk of the identified particle information comes from TPC. • Particle identification accomplished through • dE/dx at low pT (π±, K±, p and p-bar) • Decay topology with invariant mass reconstruction (Ks0, Λ, Λ-bar, Ξ, Ξ-bar, Ω + Ω-bar) • Combinatorial invariant mass reconstruction (φ,K*) • Corrections applied for tracking inefficiency, detector acceptance, hadronic interactions and particle decays. These corrections obtained from embedding MC tracks. • Spectra integrated over all phase space to obtain total particle yields

  6. SPECTRA OF IDENTIFIED PARTICLES IN AuAu AT 200GEV • pT spectra of identified particles in AuAu 200GeV at various centralities. • These spectra are flatter than the spectra at SPS and also for pp collisions. • Mass dependent hardening of the spectra : collective radial motion STAR data : N.P.A 757(2005) 102 PHENIX data: P.R.C 69(2004) 034909 Inspired by the thermal equilibrium scenario of hydrodynamics, a Blast-wave model is fit to Spectra of all hadrons simultaneously to give a common radial flow velocity bT & freeze-out temperature Tf The multi-strange hadrons do not fit to the common values of Tf and bT : Different production mechanism? Decouple at a different time ?

  7. where and FREEZE-OUT PARAMETERS Blast-wave model: (E.Schnedermann et al, PRC48 (1993) 2462) , K, p  T= 90MeV, b=0.6 X,   T=160MeV, b=0.45 STAR Preliminary

  8. SYSTEMATICS OF KINETIC FREEZEOUT PARAMETERS: CENTRALITY AND SYSTEM SIZE DEPENDENCE STAR Preliminary STAR Preliminary STAR has fit the spectra of π±,K±, p,pbar for AuAu and CuCu collisions at 62.4 GeV and 200 GeV to Blast-Wave model STAR Preliminary 10% central, Cu+Cu @ 200 GeV Freeze-out parameters Tf and βTare extracted for each centrality • for different colliding systems • for different colliding energies Fall on a narrow band with overlapping values STAR Preliminary STAR Preliminary STAR Preliminary

  9. STAR Preliminary SYSTEMATICS OF KINETIC FREEZE-OUT VALUES As a function of dNch/dη : Tf decreases & bT increases Peripheral collisions are slower and hotter & central collisions are faster and cooler Freezeout parameters for different systems and different energy scale with dNch/dη Consistent with hydrodynamic expectations: fireball in peripheral collision is short lived -> radial flow does not build up so particles decouple earlier at a higher temperature STAR Preliminary

  10. HADRON YIELDS AT STAR Hadron Yield Ratios are fit to statistical model to derive the properties of a macroscopic system at chemical freezeout Statistical model characterizes this stage by 4 parameters : Tchemical, μB, μS, gS gS approaching 1 in central collisions : strangeness saturation Tchemical is constant for all dNch/dh: universal chemical freeze-out (Tkinetic for multistrange hadrons ~ Tchemical: freezeout soon after hadronization Universal temperature STAR Preliminary

  11. CONCLUSIONS FROM SPECTRA AND HADRONIC YIELDS • Hadron ratios fit to statistical model show that the strangeness is saturated at chemical freezeout • Tchemical is independent of system size and energy for AuAu and CuCu at 200 and 62.4 GeV and is close to the critical temperature predicted by Lattice QCD. The universality of Tchemical indicates a “critical energy density” at which hadrons are formed • Tchemical > Tkinetic : Tkinetic decreases with increasing dNch/dh.With increasing centrality the system expands more rapidly after chemical freezeout. • A larger and denser system is therefore faster and colder at kinetic freeze-out

  12. WHY IS ANISOTROPIC FLOW IMPORTANT? • Anisotropic overlap geometry of collision -> causes anisotropic pressure gradients -> momentum anisotropy • Reaction zone expands faster in the reaction plane -> decrease spatial eccentricity (self quenching) • Elliptic flow develops before spatial eccentricity vanishes. So elliptic flow is sensitive to early stages of evolution P.F.Kolb & U.Heinz Nucl.Phys.A 71(2003) 653c

  13. First Elliptic Flow Results at RHIC Centrality Dependence of elliptic flow results: hydrodynamic predictions agree for more central collisions and show deviations for peripheral collisions. In addition to initial state anisotropy, magnitude of v2 controlled by : • Time of thermalization • Amount of re-scattering • Softness of the equation of state Large values of v2 at RHIC indicate early thermalization time (t ~ 1fm/c): presence of a strongly interacting medium AuAu √sNN = 130GeV STAR Coll. PRL 86(2001) 402

  14. FLOW FOR IDENTIFIED PARTICLES: TRANSVERSE MOM. DEPENDENCE v2 increases with pT as predicted by hydrodynamical model. Mass ordering of v2 for identified particles as expected from hydro. Data for p,K,p,L is plotted for 200GeV along with ideal hydro predictions: match within 30% Hydrodynamics fails to predict the v2 behaviour above pT>1.5GeV: v2 saturates at two different values for mesons and baryons.

  15. v2 OF IDENTIFIED PARTICLES AT INTERMEDIATE TRANSVERSE MOM. The mass ordering and the saturation values of v2 for mesons and baryons seems to obey an interesting scaling. Here we show v2 scaled by number of constituent quarks, nq, as a function of pT also scaled by nq Results for different particles fall on a single curve: indicating that the flow originates at the partonic level, and that hadrons are seemingly formed by a coalescence of partons.

  16. Transverse kinetic energy: mT – m = (pT)2 + m2 - m CENTRALITY DEPENDENCE OF v2FORSTRANGEIDENTIFIED PARTICLES STAR Preliminary Transverse momentum 200 GeV Au+Au • All centralities: mass ordering at low pTmT-m scaling at low mT-m. • All centralities: baryon v2 > meson v2 at intermediate pT or mT-m. Hydro: P. Huovinen, private communications, 2007

  17. (c) ECCENTRICITY SCALING(?) 200 GeV Au+Au 200 GeV Au+Au • v2/nq is scaled by epart to remove initial geometric effects • Larger v2/part indicates stronger flow in more central collisions. • We do not observe the epart scaling claimed by PHENIX • Divided v2 by <v2>ch instead of part, it appears that the scaling works better STAR Preliminary PHENIX: Phys. Rev. Lett 98, 162301 (2007) Phys. Lett. B 503, 58 (2001)

  18.   p   pT-INTEGRATED v2/εpart STAR Preliminary • v2/part versus Npart  data: increasing trend indicates stronger flow in more central collisions.  hydro: little sensitivity to the collision centrality as expected in equilibrium scenario. • v2/part for a given centrality  data for diff. hadrons: not clear due to large errors  hydro: a clear hadron mass dependence • Above Npart ~ 170, integrated v2 consistent with hydro prediction local thermalization? 200 GeV Au+Au Charge particle data: STAR, Phys. Rev. C 72, 014904, 2005.

  19. SYSTEM SIZE DEPENDENCE OF ELLIPTIC FLOW STAR Preliminary PHENIX: Phys. Rev. Lett 98, 162301 (2007) • A given colliding system ; clear scaling with nq. • System size dependence: - No part scaling claimed by PHENIX - v2 seems to fall at lower pT in Cu+Cu than in Au+Au

  20. FLOW IN F MESONS fmesons: small hadronic cross-section Expected to provide information about the early partonic stages of the system evolution . v2(f) measured using minv (K+ +K-)Centrality dependence of v2 consistent with charged hadrons At low pT, v2 shows hydro mass ordering and follows nq scaling for mesons at intermediate pT s quarks flow as strongly as lighter quarksthermalized hot dense matter with parton collectivity has been formed at RHIC-> STAR: Phys. Rev. Lett., 99, 112301(07), nucl-ex/0703033

  21. FLOW IN INCLUSIVE PHOTONS MEASURED IN PMD • PMD measures photons by preshower reconstruction in rapidity range -2.3 to -3.7 for AuAu and CuCu collisions at 200GeV • Centrality and h dependence similar to charge particles • v2/e{2} scaled with Npart for different colliding systems: equilibration?

  22. CONCLUSIONS FROM ELLIPTIC FLOW RESULTS • Large values of Integrated v2 indicate an early thermalization and is seen to agree with hydro predictions for central collisions • Elliptic flow at low pT fits ideal hydro-predictions with Tc= 165MeV and Tfreezeout = 100MeV which are close to the values suggested by Blast wave model fits to data • At intermediate pT : v2 saturates deviating from ideal hydro predictions • At intermediate pT, v2/nq scales with pT/nq indicating hadron production by quark coalescence model => observed flow orginates in pre-hadronic stage and partonic collectivity is observed • v2/e is seen to increase for small Npart and tend to saturate for large Npart indicating a possible equilibrium as predicted by hydro.

  23. Extra Slides

  24. How (in)complete is the thermalization? h=0.46 σ=4.3 h=0.25 σ=5.7 0.46, 4.3 0.25, 5.7 Even central Au+Au collisions are about 30-50% away from ideal hydro limit! Note: assumed constant speed of sound - no phase transitions, change in initial conditions with energy, 2d, boost invariance, etc.. note that there is a difference of a factor of “2” in the definitions of S page 24 QM’08, Jaipur, India, February 4-10, 2008. Anisotropic flow:…

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