Rashmi Raniwala Department of Physics University of Rajasthan Jaipur

Rashmi Raniwala Hot & Dense Matter in RHIC-LHC Era, February 12-14, 2008, TIFR, Mumbai1

Rashmi RaniwalaDepartment of PhysicsUniversity of Rajasthan

Jaipur

HYDRO & FREEZEOUT FROM STAR DATA

For STAR collaboration


PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Time

Initial conditions

Initial hard interactions

Dense Partonic Matter Hydro description

Hadronization and chemical freeze-out

Kinetic freeze-out

Some experimental handles on Bulk Properties at various stages:● Anisotropic flow : develops in early expansion stage (EoS,)● Hadron Yield ratios : are fixed at Chemical Freezeout (Tchemical, B,S)● Identified particle pT spectra reflect the random and collective motion at kinetic freezeout: (Tf,

EVOLUTION OF A HEAVY ION COLLISION AT RHIC

Bulk of this produced matter is soft


PLAN OF THE TALK

STAR results on:

● Freezeout parameters from identified particle spectra

● Freezeout parameters from integrated particle ratios

● Elliptic flow


STAR : A SUITE OF DETECTORS

Barrel EM Calorimeter

FTPCs

Time Projection Chamber

Silicon TrackerSVT & SSD

Endcap Calorimeter

Magnet

Coils

TPC Endcap & MWPC

Central Trigger Barrel & TOF

Beam Beam Counters

4.2 meters

Not Shown: pVPDs, ZDCs, and FPDs

A TPC lies at the heart of STAR

PMD


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(Ks

0, 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


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 motionSTAR data : N.P.A 757(2005) 102PHENIX 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

T & freeze-out temperature T

f

The multi-strange hadrons do not fit to the common values of Tf and

T : Different

production mechanism? Decouple at a different time ?


FREEZE-OUT PARAMETERS

(E.Schnedermann et al, PRC48 (1993) 2462)

T

pI

T

mKmdrr

dmm

dn TR

TT

TT

sinh

cosh

0

0

1 tanh 1 r r (r) s f (r)where and

Blast-wave model:

, K, p T= 90MeV,

T=160MeV,

STAR Preliminary


SYSTEMATICS OF KINETIC FREEZEOUT PARAMETERS: CENTRALITY AND SYSTEM SIZE DEPENDENCE

STAR PreliminarySTAR Preliminary

Freeze-out parameters Tf and βT are extracted for each centrality● for different colliding systems● for different colliding energiesFall on a narrow band with overlapping values

STAR PreliminarySTAR 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

10% central, Cu+Cu @ 200 GeV

STAR Preliminary


As a function of dNch/dη : Tf decreases & T increases

Peripheral collisions are slower and hotter & central collisions are faster and cooler Freezeout parameters for different systems and different energy scale with dNch/dηConsistent 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

SYSTEMATICS OF KINETIC FREEZE-OUT VALUES

STAR Preliminary


HADRON YIELDS AT STAR

Hadron Yield Ratios are fit to statistical model to derive the properties of a macroscopic system at chemical freezeoutStatistical model characterizes this stage by 4 parameters : T

chemical, μB, μS, S

S approaching 1 in central collisions : strangeness saturation

Tchemical is constant for all dNch/d: universal chemical freeze-out

(Tkinetic for multistrange hadrons ~ Tchemical: freezeout soon after hadronization

STAR Preliminary

Universal temperature


● 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/dWith increasing centrality the system expands more rapidly after chemical freezeout.

● A larger and denser system is therefore faster and colder at kinetic freeze-out

CONCLUSIONS FROM SPECTRA AND HADRONIC YIELDS


•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

WHY IS ANISOTROPIC FLOW IMPORTANT?


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


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 ,K,p, 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.


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.


• 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.

STAR PreliminaryTransverse kinetic energy: mT – m = (pT)2 + m2 - mTransverse momentum

Hydro: P. Huovinen, private communications, 2007

200 GeV Au+Au

CENTRALITY DEPENDENCE OF

v2 FOR STRANGE IDENTIFIED PARTICLES


ECCENTRICITY SCALING(?)

STAR Preliminary

•v2/nq is scaled by part to remove initial geometric effects•Larger v2/part indicates stronger flow in more central collisions.•We do not observe the part scaling claimed by PHENIX•Divided v2 by <v2>ch instead of part, it appears that the scaling works better

PHENIX: Phys. Rev. Lett 98, 162301 (2007)Phys. Lett. B 503, 58 (2001)

200 GeV Au+Au200 GeV Au+Au

(c)


STAR Preliminary

Charge particle data: STAR, Phys. Rev. C 72, 014904, 2005.

• 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

p

pT-INTEGRATED v2/εpart


SYSTEM SIZE DEPENDENCE OF ELLIPTIC FLOW

STAR Preliminary

• 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

PHENIX: Phys. Rev. Lett 98, 162301 (2007)


FLOW IN MESONS

mesons: small hadronic cross-section Expected to provide information about the early partonic stages of the system evolution . v

2() measured using m

inv (K+ +K-)

Centrality dependence of v2

consistent with charged hadronsAt low p

T, v

2 shows hydro mass

ordering and follows nq scaling for

mesons at intermediate pT

s quarks flow as strongly as lighter quarks thermalized hot dense matter with parton collectivity has been formed at RHIC-> STAR: Phys. Rev. Lett., 99, 112301(07), nucl-ex/0703033


●PMD measures photons by preshower reconstruction in rapidity range -2.3 to -3.7 for AuAu and CuCu collisions at 200GeV●Centrality and dependence similar to charge particles●v2/{2} scaled with Npart for different colliding systems: equilibration?

FLOW IN INCLUSIVE PHOTONS MEASURED IN PMD


● 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/ is seen to increase for small Npart and tend to saturate for large Npart indicating a possible equilibrium as predicted by hydro.

CONCLUSIONS FROM ELLIPTIC FLOW RESULTS


Extra Slides

Rashmi Raniwala Hot & Dense Matter in RHIC-LHC Era, February 12-14, 2008, TIFR, Mumbai24QM’08, Jaipur, India, February 4-10, 2008. Anisotropic flow:… page24

How (in)complete is the thermalization?

note that there is a difference of a factor of “2” in the definitions of S

Even central Au+Au collisions are about 30-50% away fromideal hydro limit!

Note: assumed constant speed of sound - no phase transitions, change in initial conditions with energy, 2d, boost invariance, etc..

0.46, 4.30.25, 5.7

h=0.46σ=4.3

h=0.25σ=5.7

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Rashmi Raniwala Department of Physics University of Rajasthan Jaipur