andr é mischke for the star collaboration
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André Mischke
for the
STAR Collaboration
Rencontres de Moriond, La Thuile, Italy, March 18-25, 2006
Amsterdam
Recent STAR results on hard probes
Andre Mischke (Utrecht) 2
• Parton scattering in the early stage of the collision
• Traverse through the medium and interact strongly
• In-medium fragmentation
• Model expectations:- Collisional energy loss (small effect ?!)- Partonic energy loss via medium induced gluon Bremsstrahlung (jet-quenching)
- Jet broadening due to parton rescattering - Modification of the FF (softening)
• Energy loss sensitive to the medium density 2ˆ4
LqC
E RSmedium
modified
modified
q q
q
qhadronic
partonic
q ?
Probing QCD matter with jets
Andre Mischke (Utrecht) 3
• Two concentric rings
• 3.8 km circumference
• Counter-rotating ion beams
• 4 experiments
- Au+Au @ sNN = 19.6, 62.4, 130, 200 GeV
- Cu+Cu @ sNN = 200 GeV
- d+Au @ sNN = 200 GeV
- polarized p+p @ s = 200 GeV
STAR
PHENIX
PHOBOSBRAHMS
RHIC
The RHIC accelerator at BNLSTAR detector
Andre Mischke (Utrecht) 4
Most 200 GeV Au+Au results are from the FY04 run
RHIC performance
Ldt = 241 b-1
Andre Mischke (Utrecht) 5
20.7m
8.2m
7.9m
Solenoidal Tracker at RHICLarge acceptance magnetic spectrometer
The STAR detector
• Particle identification and tracking (TPC, ToF, SVT)• Energy measurement (EMC)
Andre Mischke (Utrecht) 6
p+p jet+jet Au+Au ???
?
sNN = 200 GeV, STAR-TPC profile
Jet measurements in Au+Au
Jet-like correlation Statistical reconstruction using angular correlations
Andre Mischke (Utrecht) 7
• Strong high-pT particle suppression
• Disappearance of the away-side jet
Jet quenching is a final state effect
Initial medium density is high
Results so far
NNinelastCollAA
TNN
AA
TAA
TAA
NT
ddpdT
ddpNdpR
/ where
/
/)(
2
2
factor 4-5
Inclusive hadron spectra di-hadron correlation
Nuclear modification factor:
Nucl. Phys. A757, 102 (2005)
4 < pTtrig < 6 GeV/c
pTasso > 2 GeV/c
Andre Mischke (Utrecht) 8
Outline
• Inclusive identified particle spectra (particle ratio)
- modification of jet fragmentation
• Low-pT recoil and three particle correlation
(Mach-like cones ?)
- jet-medium interplay
• Di-hadron correlation at higher pT
- reappearance of the away-side jet
Andre Mischke (Utrecht) 9
Identified particle ratios
Au+Au 0-10%
p+p
Au+Au 0-10%
p+p
/K
0 s
Au+Au 0-5%
p+p
vacuum fragmentation
• Significant baryon enhancement in central Au+Au collisions with a maximum around 2-3 GeV/c
• Additional effects besides jet fragmentation
• Vacuum fragmentation approach at pT > ~6 GeV/c
Andre Mischke (Utrecht) 10
4 < pTtrig < 6 GeV/c
pTasso > 0.15 GeV/c
Where does the deposited energy go?
cos()
pTasso > 2 GeV/c
• Suppression of high-pT hadrons enhancement of low-pT hadrons
• Broadening and softening of the recoil distribution momentum balance shape (cos )
Andre Mischke (Utrecht) 11
4 < pTtrig < 6 GeV/c
pTasso > 0.15 GeV/c
• Softening of the associate hadrons in the cone opposite to leading trigger hadron
• Indication for thermal equilibration with the bulk medium
Mean-pT of away-side asso. hadrons
central Au+Au
Andre Mischke (Utrecht) 12
Mediumaway
near
Deflected jets
1
2
1
2
• Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315• Stoecker, Nucl. Phys A750, 121 (2005)• Ruppert and Muller, PLB 618, 123 (2005)
away
near
Medium
Conical flow
Indication for Mach-like cones ?
• Does a shock wave form?
• Three-particle correlations, two scenarios:
- Conical flow: associated particles may appear on opposite sides of Δφ = π
- Deflected jets: associated particles on the same side of Δφ = π
Andre Mischke (Utrecht) 13
pTtrig = 3-4 GeV/c, pT
asso = 1-2 GeV/c2-particle corr., bg, v2 subtracted
φ2=φ2-φtrig d+Au min-bias
dN2/d
Δφ1dΔφ2/Ntrig
φ1=φ1-φtrig
φ2=φ2-φtrig Au+Au 10%
Mediumaway
near
Deflected jets
away
near
Medium
Conical flow
Three-particle correlations
• Elongated along diagonal: kT effect?
deflected jets?
• Distinctive features of conical flow are not seen in present data within these pT
windows.
Andre Mischke (Utrecht) 148 < pT
trig < 15 GeV/c
• Correlation peak visible at near- and away-side
• Away-side peak is - finite suppressed - not broadened
• Limits on parton energy loss
Di-hadron azimuthal correlation at higher pT
Large year-4 Au+Au dataset
Andre Mischke (Utrecht) 15
Width of the away-side peak8 < pT
trig < 15 GeV/c
• Away-side widths similar for central and peripheral collisions
• Fragmentation similar as in the vacuum?
Andre Mischke (Utrecht) 16
Away-side yields
• Away-side suppression similar to RAA measurement
• No zT dependencetrigT
assoT
T p
pz
Andre Mischke (Utrecht) 17
X-N Wang, PLB 595, 165 (2004)
STAR preliminary
Comparison to model prediction
• Model (recoil fragmentation) with modified di-hadron fragmentation function
• Suppression factor
shows no zT dependence
• Qualitative but not quantitative agreement with measurement
Andre Mischke (Utrecht) 18
Conclusion• Inclusive hadron spectra and di-hadron correlations - strong suppression in central Au+Au - final state modification of jets
• Baryon enhancement - non-perturbative effects dominates at intermediate pT
• Low-pT recoil - away-side correlation widely dispersed - strong coupling effects of jets to bulk matter
• Three particle correlation using intermediate trigger-pT particle - Mach-cone like patterns not observed in present data
• correlations at higher pT
- reappearance of the away-side jet - no modification of the fragmentation distribution (width and slope) - stringent constraints for model descriptions
Andre Mischke (Utrecht) 19
Back-up slides
Andre Mischke (Utrecht) 20
50 institutes from 13 countries, 545 participants
The STAR collaboration
Andre Mischke (Utrecht) 21
Experimental and theoreticalchallenges in the search for the QGP
• Strong evidence for a dense, opaque, non-viscous, pre-hadronic liquid state of matter at RHIC
• Open question: do the quarks and gluon reach thermal equilibration with each other in this matter before confinement
The STAR collaboration's critical assessment of the evidence from RHIC collisions, Nucl. Phys. A757, 102 (2005)
Andre Mischke (Utrecht) 22
Identified particle RCP
peripheralbinaryperipheral
centralbinarycentral
Nyield
Nyield
//
• Φ follows mesons at intermediate pT no mass dependence
• All particles consistent for pT larger than ~5 GeV/c
• Coalescence of valence quarks?
Andre Mischke (Utrecht) 23
• Parton energy loss depends on the path length traversed • Qualitatively consistent with jet-quenching picture:
in-plane
out-of-plane
4 < pTtrig < 6 GeV/c
2 GeV/c < pTasso < pT
trig 2ˆLqCE RSmedium
Azimuthal correlations wrt. to the reaction plane
Andre Mischke (Utrecht) 24
In vacuo fragmentation of a high momentum quark to producehadrons competes with the in medium recombination of lower momentum quarks to produce hadrons
Example:• Fragmentation: Dq→h(z) produces
a 6 GeV/c proton from a 10 GeV/c quark
• Recombination:
- produces a 6 GeV/c proton from two 3 GeV/c quarks
- produces a 6 GeV/c proton from three 2 GeV/c quarks
Recombination models
Andre Mischke (Utrecht) 25
STAR preliminary , ||<1
0-5% 5-10%
10-20% 20-40%
40-60% 60-80%
pTtrig = 2.5-4.0 GeV/c
pTasso = 1.0-2.5 GeV/c
Conical flow
Andre Mischke (Utrecht) 26
away
syst. error
pT spectra of associate hadrons
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