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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.)
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CIPANP '03 Jets and high pT hadrons in STAR 2
E-M Calorimeter
Time of Flight
Projection Chamber
STAR
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CIPANP '03 Jets and high pT hadrons in STAR 3
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
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CIPANP '03 Jets and high pT hadrons in STAR 4
Jets at RHIC
p+p jet+jet (STAR@RHIC)
Au+Au ??? (STAR@RHIC)
nucleon nucleonparton
jet
Find this……….in this
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CIPANP '03 Jets and high pT hadrons in STAR 5
Jet energy loss via leading hadrons
-
Wang and Gyulassy: partonic energy loss effective softening of fragmentation suppression of leading hadron yield
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CIPANP '03 Jets and high pT hadrons in STAR 6
Au+Au and p+p: inclusive charged hadrons
STAR PRL 89, 202301 nucl-ex/0305015
p+p spectrum measured at RHIC
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CIPANP '03 Jets and high pT hadrons in STAR 7
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>
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CIPANP '03 Jets and high pT hadrons in STAR 8
Au+Au relative to measured p+p
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
Central collisions: factor ~4-5 suppression
nucl-ex/0305015
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CIPANP '03 Jets and high pT hadrons in STAR 9
Binary-scaled central/peripheral
• central collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT
nucl-ex/0305015
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CIPANP '03 Jets and high pT hadrons in STAR 10
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? …
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CIPANP '03 Jets and high pT hadrons in STAR 11
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 …
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CIPANP '03 Jets and high pT hadrons in STAR 12
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
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CIPANP '03 Jets and high pT hadrons in STAR 13
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
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CIPANP '03 Jets and high pT hadrons in STAR 14
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)?
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CIPANP '03 Jets and high pT hadrons in STAR 15
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
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CIPANP '03 Jets and high pT hadrons in STAR 16
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”
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CIPANP '03 Jets and high pT hadrons in STAR 17
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
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CIPANP '03 Jets and high pT hadrons in STAR 18
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
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CIPANP '03 Jets and high pT hadrons in STAR 19
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
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CIPANP '03 Jets and high pT hadrons in STAR 20
• 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?
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CIPANP '03 Jets and high pT hadrons in STAR 21
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
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CIPANP '03 Jets and high pT hadrons in STAR 22
Extra slides
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CIPANP '03 Jets and high pT hadrons in STAR 23
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