RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 1 Recent Results from STAR Nu Xu Lawrence...

RHIC & AGS Annual User’s Meeting, May 2003RHIC & AGS Annual User’s Meeting, May 2003 Nu XuNu Xu 11

Recent Results from STARRecent Results from STAR

Nu Xu Lawrence Berkeley National Laboratory

For the STAR Collaboration


PPhase diagram of strongly hase diagram of strongly interacting matterinteracting matter

CERN-SPS, RHIC, LHC: high temperature, low baryon density

AGS, GSI (SIS200): moderate temperature, high baryon density


Identify and study the properties of the matter with partonic degree of freedom:

- nuclear effects in the intermediate pT region

initial conditionsparton energy loss due to interaction of dense matter

- bulk properties

collision dynamicscollective motion with the partonic degree of freedomearly thermalization (c-quark)

Physics goals at RHICPhysics goals at RHIC


OutlineOutline

1) Introduction

2) Results from intermediate pT (< 10 GeV/c)

-- suppression of particle yields

-- ‘jet’ correlations

3) Results of bulk properties-- azimuthal anisotropy -- particle distributions and yields

4) Summary

http://www.star.bnl.gov/STAR/


IntroductionIntroduction

Initial Condition - initial scatterings - baryon transfer - ET production - parton dof

System Evolves - parton interaction - parton/hadron expansion

Bulk Freeze-out - hadron dof - interactions stop

J/D

K*

K

p

d, HBT

vv22

TT

Q2

time

partonic scatterings?early thermalization?


Key parameters at STAR (i)Key parameters at STAR (i)

Spokesperson:

John Harris 1991 - 2002 Tim Hallman 2002 - now

468 collaborators from 10 countries 49 Institutions 3 U.S. National Laboratories

~ 65 graduate students ~ 60 postdocs

Ph.D thesis: ~ 20 (May 2003)

Publications: 14 PRL / 3 PRC


Key parameters at STAR (ii)Key parameters at STAR (ii)

1) Magnetic field: 0.5 T

2) Acceptance: 2charge particle ||<1.5dE/dx id. |y|<0.5V0 id. |y|< 1.0

charged multiplicity: ~2000

3) dE/dx resolution~ 8%

4) Momentum resolutions:1.5% at pT ~ 2 GeV/c2% at pT ~ 4 GeV/c5% at pT ~ 10 GeV/c

5) Tracking efficiency> 80%

M. Anderson et al., STAR NIM A499, 659(03)

Events collected:

Au+Au 200 GeV

~ 3 M M.B. 2001

~ 3 M 10%2001

p+p 200 GeV

~13 M2001

d + Au 200 GeV

~ 28 M M.B.2003


The STAR detectorThe STAR detector

MagnetMagnet

CoilsCoils

Time Time Projection Projection ChamberChamber(TPC)(TPC)

ZCalZCal

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

RICHRICH

Year 2000Year 2000

Silicon Silicon Vertex Vertex Tracker Tracker (SVT)(SVT)

FTPCFTPCEndcapEndcapCalCal

FPDFPD

Barrel Barrel EM CalEM Cal(EMCal)(EMCal)

TOFpTOFpTOFrTOFr

Year 2001Year 2001Year 2003Year 2003 See talk by Richard Majka, 3:40 pm Friday


Particle Identification in STARParticle Identification in STAR

Reconstruct particles in full azimuthal acceptance of STAR!


Physics at intermediate pPhysics at intermediate pTT

Probes for studying the properties of bulk matter:

direct-, DY, and high pT particles – - Spectra and ratios RAA - Statistical & Correlations

hadronsleadingparticle suppressed

q

q

?

Gyulassy, Vitev, Wang, and Zhang, nucl-th/0302077


Jets from STAR at RHICJets from STAR at RHIC(STAR, PRL 90, 082302(2002))

Jets from p + p at 200 GeVJets from p + p at 200 GeV ‘‘Jets’ from Au + Au at 200 GeVJets’ from Au + Au at 200 GeV


Nuclear modification factor RNuclear modification factor RAAAA

ppTAA

AAT

TAAddpdT

ddpNdpR

/

/)(

2

2

1) R < 1, at low pT ‘soft’ physics, bulk production, different scaling

2) R = 1 at intermediate pT no effects

3) R 1 at intermediate pT nuclear effects

Note: No scaling has been observed up to pT ~ 12 GeV/c in hadron

production, from fix target p+A experiment.


Suppression at intermediate pSuppression at intermediate pTT

STAR Preliminary

Evidence of suppression early interactions partonic dof

? Cold matter or ‘QGP’? Parton-parton interaction or structure function

Number of binary collisions:

Number of participants:

Gyulassy, Wang, et al. nucl-th/0302077Kharzeev, Levin, McLerran, hep-ph/0210332

STAR measured p+p spectrum used for RAA!

STAR: 200 GeV Au + Au

STAR Preliminary


Suppression and correlationSuppression and correlationSTAR: 200 GeV Au+Au / p+pSTAR: 200 GeV Au+Au / p+p

Hadron suppression and disappearance of back-to-back ‘jet’ are correlated!STAR PRL 90, 082302

● Au+Au p + p

STAR Preliminary


d + Au results (i)d + Au results (i)

STAR Preliminary, May 2003

d+Au RdA is similar to the peripheral results of Au+Au collisions


d+Au results (ii)d+Au results (ii)Back-to-back correlationsBack-to-back correlations

•p+p: measured data•Au+Au: measured data - B*(1+2v2

2cos(2)•d+Au: measured data - dAu pedestal + pp pedestal

STAR Preliminary

- d+Au similar to p+p


Lesson learned – intermediate pLesson learned – intermediate pTT

(1) Spectra at intermediate pT show evidence of suppression and the ratios start to decrease at pT ~ 2 GeV/c (2) Jet-like behavior observed in correlations: - hard scatterings in AA collisions - disappearance of back-to-back correlations Consistent with the final state partonic

interactions – “jet quenching”


Transverse flow observablesTransverse flow observables

As a function of particle mass:• Directed flow (v1) – early• Elliptic flow (v2) – early• Radial flow – integrated over whole evolution

Note:1) Effect of collectivity is accumulative – sum of all processes as long as interactions are there. 2) No thermalization is needed – pressure gradient depends on density gradient and interactions.

1i

Ritttt

))ψcos(i(2v1dydpp

dN

2π

1

dyddpp

dN


Anisotropy parameter vAnisotropy parameter v22

)(tan,2cos 1222

22

x

y

p

pv

xy

xy

y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Initial/final conditions, dof, EOS


STAR:STAR: v v2 2 vs. pvs. pTT and centrality and centrality

1) Saturate at pT > 2.5 GeV/c for all centrality bins2) There are non-reaction plane related correlations ! It is up to 20% and could be pT dependent!3) Model comparisons should be careful !

Cha

rged

par

ticle

v2

Transverse momentum pT (GeV/c)

STAR Preliminary, Au+Au at 200 GeV

STAR Preliminary


STAR:STAR: PID v PID v2 2 vs. pvs. pTT

As in 130 GeV collision, the mass dependence of v2 at low pT (<1 GeV/c) is well described by hydro type calculations – early thermalization at RHIC (?)

Filled: Au + Au at 200 GeV

Open: Au +Au at 130 GeV

Lines: hydro-inspired blast wave fits

p

K


Strange hadron (KStrange hadron (K00 , , ) v) v22

1) High quality M.B. data!

2) At pt < 2 GeV/c, hydro behavior, v2() < v2(K)

3) At pt > 2.5 GeV/c, v2() > v2(K) !

- CGC ? - Coalescence ? - Energy loss ? Partonic dof relevant ?Partonic dof relevant ?

Model” P.Huovinen, et al., Phys. Lett. B503, 58 (2001)


Coalescence and multi-strange vCoalescence and multi-strange v22

Coalescence approach seems to work

Partonic collectivity at RHIC ?Partonic collectivity at RHIC ?

Z. Lin et al., PRL, 89, 202302(02)S. Voloshin, nucl-ex/0210014R. Fries et al., nucl-th/0301087D. Molnar et al. nucl-th/0302014

Multi-strange baryon () seems to flow ?

STAR preliminary

STAR Preliminary


Lesson learned – azimuthal anisotropyLesson learned – azimuthal anisotropy

1) Charged particle:i) M.B. events, saturated at ~ 15-17%, for pT > 2.5 GeV/c;

ii) Non-flow correlations are important, at higher pT region

2) Identified particle:i) pT < 2 GeV/c, M.B. events, hydro calculations fit v2() > v2(K) > v2(p) > v2() [ v2(heavy) < v2(light) ]ii) pT > 2 GeV/c, for all centrality bins,

v2(K) < v2(p, ) [ v2(heavy) > v2(light) ]

3) Coalescence: i) Seems work in the measured pT region ii) Multi-strange particle v2

Partonic collectivity ?


, K, p spectra from 200 GeV, K, p spectra from 200 GeV

1) Mid-rapidity transverse momentum distributions, lines are thermal fits.2) The shape depends on collision centrality and the particle mass.

STAR preliminary, |y|<0.1 Au+Au at 200 GeV

- K- p


Bulk rapidity distributionsBulk rapidity distributions

, K, p boost invariant within |y| < 0.5: for both dN/dy and <pT> !


transverse momentum spectratransverse momentum spectra

n

TT

p

ppp

T

mAuAu

0

1:)exp(:

200 GeV:

Au + Au collisions: exponential function fits no clear centrality dependence

p + p collisions: power-law function fits.

STAR Preliminary

KK


(a) , K, p mean transverse momentum <pT> increase in more central collisions - collective flow;(b) <pT> increases vs. beam energy;(c) and (d) N()/N(K) and N()/N(h-) ratios ~ constant vs. collision centrality and beam energy !

KK++ + K + K-- coalescence coalescence inconsistentinconsistent production sensitiveproduction sensitive to initial to initial collision (?)collision (?)

systematics vs. centrality and beam energysystematics vs. centrality and beam energy

STAR Preliminary


STAR preliminary

200 GeV Au + Au

STAR: KSTAR: K00, , , , , , spectra spectra


Nuclear modification factorNuclear modification factor

STAR preliminary

1) The pT dependence of R(K0) is different from that of R()

2) At pT ~ 5 GeV/c, R(K0), R(), and R(charge) are approaching each other

Flow 0< pT<2 GeV/c ?

Coalescence 2<pT<4 GeV/c ?

Independent fragmentation pT>5 GeV/c ?

)/(

)/()(

2

2

dydpNNd

dydpNNdpR

Tperipheralbinary

peripheral

Tcentralbinary

central

TCP


TTfofo vs. < vs. < > plane> plane

At given centrality, within this fits, the minimum for At given centrality, within this fits, the minimum for is different from is different from

, K, p. Freeze-out earlier than bulk produced ?reeze-out earlier than bulk produced ?

Sensitive to early partonic stage ! (?)Sensitive to early partonic stage ! (?)

STAR Preliminary! 130 GeV Au + Au central collisionsSTAR Preliminary! 130 GeV Au + Au central collisions


STAR: resonance programSTAR: resonance program

Au+Au 40% to 80%

1.2 pT 1.4 GeV/c

|y| 0.5

STAR Preliminary

K*0

*(1520)

STAR preliminary p+p at 200 GeV

, f, f00, , *(892), *(892),

, , *(1385)*(1385)*(1520)*(1520)

DD00, D*, D*

STAR Preliminary

0.8 pT 0.9 GeV/c

|y| 0.5

pp Minimum Bias


Resonances mass & widthResonances mass & width

In and K* results:

1) Width - pT independent

2) Mass - strong pT dependent

3) Evidence of hadronic rescattering and finite duration between Tch and Tfo

???Phase-spacePhase-spaceInterferenceInterferenceCollision broadeningCollision broadeningMedium effectMedium effect

STAR preliminary, 200 GeV Au + Au

K*


Number of events: ~ 20 M

STAR preliminary 200 GeV d + Au collisions

|y|<1, pT < 4 GeV/c|y|<0.25, 7< pT <10 GeV/c

Results from d + Au (iii)Results from d + Au (iii) Open CharmOpen Charm

KDD 00 KD

STAR Preliminary !


Bose-Einstein correlations Bose-Einstein correlations

STAR preliminary: 200 GeV Au+Au(- -) & (+ +) correlation results

1) Within 0.25 < kT <0.6 GeV/c, no clear kT dependence, why?

2) In coordinate space, -source at freeze-out ~ initial, why?

STAR Preliminary


Bose-Einstein correlationsBose-Einstein correlations

0)(2 Tpv

y

x

y

x

py

px

coordinate-space

momentum-space

02 s

1) v1) v22(p(pTT)) > 0 > 0 strong expansionstrong expansion

2) s2) s22 < 0 < 0 not much change in source not much change in source

Self-quenching limit not reach yet .Self-quenching limit not reach yet .


Top 15% Au+Au collisions at 130 GeVNon-statistical 14+0.5% !

N//p pTp̂TT

Gamma with increased rms

Gamma ref. from inclusive pT

STAR: Mean pSTAR: Mean pTT fluctuations fluctuations

Strong non-statistical fluctuationsCentrality dependencePHENIX null result is not inconsistent

STAR Preliminary


Lesson learned – bulk production Lesson learned – bulk production and collective motionand collective motion

1) , K, p (|y| < 0.5):i) <pT> and yields indicate large degree of thermalization;

ii) Within |y|<0.5, ‘boost invariant’

2) Multi-strange (|y| < 0.75):i) Transverse behavior differently from bulk

ii) Less sensitive to hadronic interactions Collectivity with partonic dof ?

3) Resonances, correlations, fluctuations: i) Strong pT dependence of the resonances mass (,K*0): Rescatterings at hadronic stage - Medium effect ? ii) Space-time structure of the freeze-out ‘viewed’ via HBT: Evidence of collective flow iii) Mean pT fluctuation increase compared with reference


STAR UPC ProgramSTAR UPC Program: : Interference in Au + Au Interference in Au + Au Au*Au* Au*Au*00

Au+Au at 200 GeV

1) Two indistinguishable possibilities: A photon from nucleus 1 scatters from 2 A photon from nucleus 2 scatters from 1

2) Negative parity – destructive inter.

~ |A1 - A2eip·b|2

- At y=0 =0[1-cos(pb)] - pT <<1/<b> - For 0 w/ XnXn <b> ~ 20 fm

- Clear signal of interference!Clear signal of interference!

- wave function non-local !wave function non-local !

- Wave functions contains all Wave functions contains all amplitudes long after the amplitudes long after the decay decaySTAR Preliminary, 200 GeV Au+Au

dN

/dt

(GeV

2)-1

Data (w/ fit) No Interference Interference

t = pT2 (GeV2)

STAR Preliminary


SummarySummary

STAR: Study matter under extreme STAR: Study matter under extreme conditionsconditions

Bulk properties – partonic collectivity and EOS- azimuthal anisotropy v2 : elliptic flow- spectra: radial expansion, multi-strange particles- resonances: medium effect and other effects- two-particle correlations: space-time structure

Penetrating probes – intermediate pT

- hadron suppression at intermediate pT region < 12 GeV/c RAA depends on particle type at pT < 5 GeV/c- disappearing back-to-back ‘jets’

Strong field QED – UPC program

RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 1 Recent Results from STAR Nu Xu Lawrence...

Documents

Transcript of RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 1 Recent Results from STAR Nu Xu Lawrence...