CIPANP '03Jets and high pT hadrons in STAR1 Jets and high p T hadrons: results from STAR Peter Jacobs Lawrence Berkeley National Laboratory STAR Collaboration

CIPANP '03 Jets and high pT hadrons in STAR 1

Jets and high pT hadrons: results from STARPeter Jacobs

Lawrence Berkeley National LaboratorySTAR Collaboration

• Au+Au at 200 GeV:• inclusive hadron distributions

confrontation with theory• two-particle correlations

• first results from d+Au

STARSTAR

Other STAR high pT talks:A.Tang: Anisotropic Flow (Session 4, Thurs.)M. Miller: High pT correlations (Session 6, Fri.)J. Klay: High pT spectra (Session 6, Fri.)


E-M Calorimeter

Time of Flight

Projection Chamber

STAR


Partonic energy loss in dense matter

Thick plasma (Baier et al.):

glueSglue

Debye

sRBDMS

q

vLqC

E

2

2

ˆ

~ˆ4

Strong dependence of energy loss on gluon density gluemeasure color charge density at early hot, dense phase

Gluon bremsstrahlung

Thin plasma (GLV, WW):

32

2( , ( )) jet

A a s glue

EE C C d r Log

L


Jets at RHIC

p+p jet+jet (STAR@RHIC)

Au+Au ??? (STAR@RHIC)

nucleon nucleonparton

jet

Find this……….in this


Jet energy loss via leading hadrons

-

Wang and Gyulassy: partonic energy loss effective softening of fragmentation suppression of leading hadron yield


Au+Au and p+p: inclusive charged hadrons

STAR PRL 89, 202301 nucl-ex/0305015

p+p spectrum measured at RHIC


Measuring hadron suppression

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbinary>/inelp+p

p+p cross section

1. Au+Au yield relative to binary-scaled nucleon-nucleon cross section:

2. Au+Au central/peripheral yields scaled by <Nbinary>

Nuclear geometry via Glauber model <Nbinary>


Au+Au relative to measured p+p

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Central collisions: factor ~4-5 suppression

nucl-ex/0305015


Binary-scaled central/peripheral

• central collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT

nucl-ex/0305015


Central/peripheral: dependence on particle species

STAR preliminary

• 1.5<pT<3.5 GeV/c: scales ~Nbinary, K0s suppressed

• pT~ 6 GeV/c: , K0s, charged hadrons scale similarly

• “baryon enhancement”: partonic flow? modified fragmentation? Cronin effect? …


Jets and two-particle correlations

p+p dijet

Two-particle azimuthal correlations:

• select highest pT track

• distribution of other tracks (pT>2 GeV/c) in the event

• normalize to # of triggers …


High pT correlations: Au+Au vs p+pPRL 90, 082302 (2003)

Central Au + Au

Peripheral Au + Au

Back-to-back jets are suppressed in central collisions

22 2 2( ) ( ) (1 cos(2 ))D Au Au D p p B v

near side

away side

peripheral central


Theory vs. Data pQCD-I: Wang, nucl-th/0305010pQCD-II: Vitev and Gyulassy, PRL 89, 252301Saturation: KLM, Phys Lett B561, 93

pT>5 GeV/c: well described by saturation model (up to 60% central) and pQCD+jet quenching

nucl-ex/0305015


Do we see jet quenching?

• Independent of particular model calculations:

Can we distinguish experimentally between initial and final state effects? measure partonic energy loss

• d+Au at 200 GeV: high pT hadrons

• 2-particle correlations: back-to-back jets observed?

• inclusive yield relative to p+p: enhancement (pQCD+Cronin) or suppression (saturation)?


d+Au centrality tagging

ZDCW

FTPCE

Au d

1. Neutron spectator from deuteron:• Observed via single neutron in ZDCW • Measured to be 20% of minbias • Glauber w/ Hulthen wavefn: also 20% of minbias

peripheral events2. Forward charged particle multiplicity (Au direction):

• FTPCE: -3.8<<-2.8


d+Au centrality tagging cont’d

• quantitative study in progress <Nbinary>• for now: use FTPCE multiplicity to bias towards central events

Cross check: FTPCE multiplicity for ZDCW peripheral events

strong correlation across 8 rapidity units

FTPCE mult sensitive to collision geometry

uncorrected FTPCE multiplicity

minbiasZDCW

peripheral

20% “central”


d+Au: two-particle correlations

• no normalization to underlying event

• “central”: top 20% FTPCE multiplicity

• near-side: correlation strength and width similar• underlying event grows: p+p d+Au minbias d+Au central•away-side: d+Au peak broadens but little centrality dependence

Back-to-back jets are observed in central d+Au


d+Au: minbias charged hadron yield

• compatible with expectations from Cronin enhancement• to do: centrality dependence

Charged hadron yield is enhanced in minbias d+Au

2

2

/

/

2 197

2.2

dAuT

dAu ppdAu T

dAu

d N dp dR

T d dp d

Tb


Summary

central Au+Au

Binary-scaled inclusive hadron yield:strong suppression central Au+Aumodest enhancement in minbias d+Au

Back-to-back jets:strong suppression central Au+Auno suppression in minbias and central d+Au


• Are initial state effects excluded as the dominant mechanisms of strong hadron suppression in heavy ion collisions?

• If so, have we therefore measured large partonic energy loss in very dense matter?


Russia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino

U.S. Laboratories:ArgonneBerkeleyBrookhaven

U.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinWashington UniversityWayne State UniversityYale University

Brazil: Universidade de Sao Paulo

China: IHEP – BeijingIMP - LanzouIPP – WuhanUSTCSINR – ShanghaiTsinghua University

Great Britain: University of Birmingham

France:IReS StrasbourgSUBATECH - Nantes

Germany: MPI – MunichUniversity of Frankfurt

India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC – Kolcata

Poland:Warsaw University of Tech.

The STAR Collaboration


Extra slides


Theory vs data IILietava, Pisut, Pisutova and Tomasik, Eur. Phys. J. C28, 119

• similar pT dependence also expected from hadronic formation time effects (Gallmeister, Greiner and Xu, hep-ph/0212295)

Jet attenuation in cold matter

Documents

CIPANP '03Jets and high pT hadrons in STAR1 Jets and high p T hadrons: results from STAR Peter Jacobs Lawrence Berkeley National Laboratory STAR Collaboration