High-pT results from STAR – what did we learn?
Jana Bielcikova for the STAR Collaboration
NPI ASCR and Center for physics of ultra-relativistic heavy-ion collisions, Prague, Czech Republic
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 2
Outline:
• Introduction• Baryon/meson enhancement, quark vs gluon energy loss • Di-hadron correlations: system size dependence • “Jet”-medium interaction via 2- and 3-particle correlations - conical emission - ridge
- path length effects• Emerging and future studies: -jet, full jet reconstruction • Summary
Jana Bielcikova 3
Probing QCD matter with high-pT particles and jets
What happens to high-pT particles/jets which pass through the medium?Are they similar to p+p or modified by the medium?
p+pAu+Au
4th workshop "High-pT at LHC", Prague
Tools:• inclusive pT spectra• di-hadron correlations• multi-hadron correlations• jets, -jets
C. Natrass
O. Barannikova
J. PutschkeA. Hamed
See also talks by:
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 4
• large enhancement of B/M ratio in Au+Au relative to p+p collisions - reaches maximum at pT~3 GeV/c
• particle production via parton coalescence/recombination
Baryon/meson ratios at RHIC
d+A
u, Au+
Au: S
TA
R, P
RL 97 (152301) 2006
p+p: P
. Fachini (S
TA
R), Q
M2008
Au+Au: p/ ~ 1 Λ/K0S ~ 1.8
p+p: p/ ~ 0.3 Λ/K0S
~ 0.6e++e-: p/ ~ 0.1-0.2
M. Lam
ont (ST
AR
), SQ
M2006
Gluon jet contribution factor increases from , K, p towards: e.g. pT = 8 GeV/c: 50% for 90% for p
If
and
At high pT for same beam energy, system and centrality:
RCP() > RCP(p) RCP(K) > RCP()
Gluon vs quark energy loss (I)
4
9~
E
E
q
g
2 ˆ LqCE Rs
B. Mohanty (STAR), arXiv: 0705.0953
AKK (Albino-Kniehl-Kramer): NPB 734, 50 (2006)
Jana Bielcikova 54th workshop "High-pT at LHC", Prague
High-pT (pT > 6 GeV/c): RCP()~RCP(p)
Gluon vs quark energy loss (II)
no color factor effect of 9/4 observed up to pT ~ 12 GeV/c ?
I. Vitev, QM2008
non-asymptotic limit: q and g losses are closer to each other
Jana Bielcikova 64th workshop "High-pT at LHC", Prague
B.
Moh
anty
, P
. F
achi
ni (
ST
AR
), Q
M20
08
System size dependence of di-hadron yields6 < pT
trig < 10 GeV/c, pTassoc >3 GeV/c
Parton Quenching Model (PQM): BDMPS energy loss, Glauber geometry, bin scaling C. Loizides, Eur. Phys. J. C 49, 339 (2007)
Modified Fragmentation Model: NLO, higher twist, hard sphere geometry, part scaling Zhang, Owens, Wang, Wang, PRL 98, 212301
More model calculations needed to disentangle effects fromenergy loss and density scaling/profile
O. C
atu
(ST
AR
), QM
08
Near-side peak Away-side peak
zT=pTassoc/pTtrig
Jana Bielcikova 74th workshop "High-pT at LHC", Prague
Jana Bielcikova 8
Conical emission in A+A collisions?2.5 < p
Ttrig< 4 GeV/c and 1< p
Tassoc < 2.5 GeV/c
40-60%
0-12%
Preliminary
• Mach cone in heavy-ion physics introduced in1970’s (Hofmann, Stöcker, Heinz, Scheid, Greiner) • a supersonic parton creates shock waves: - hydrodynamics Stöcker et al., NPA750 (2005) 121 Casalderrey-Solana et al., NPA774 (2006) 577 Renk, Ruppert, PRC73 (2006) 011901
- colored plasma Ruppert, Mueller, PLB618 (2005) 123
- AdS/CFT Gubser, Pufu, Yarom, PRL100, (2008) 012301
• Čerenkov gluon radiation by a superluminal parton Dremin, NPA750 (2006) 233 Koch et. al., PRL96 (2006) 172302
To distinguish from other mechanisms 3-particle correlation studies needed
4th workshop "High-pT at LHC", Prague
M. H
orn
er (S
TA
R), J.P
hys.G
34
, S9
95
,20
07
4th workshop "High-pT at LHC", Prague 9
Conical flow or deflected jets? (I)
Mediumaway
near
deflected jets
away
near
Medium
mach cone
Medium
away
near
di-jets 00
π
π
Jana Bielcikova
deflected jets (by the collective movement, “flow”, of the expanding medium)
Armesto , Salgado, Wiedemann, PRL 93, (2004) 242301
conical emission
di-jets
cartoons of 3-particle azimuthal correlations(1 trigger + 2 associated particles)
courtesy to J. Ulery
10
Conical flow or deflected jets? (II)
STAR uses 2 methods:1. Jet+flow background - model dependent analysis- evidence for conical emission
2. Cumulant methodC. Pruneau (STAR),J.Phys.G34 (667),2007;C. Pruneau, PRC 74 (2006) 064910
- unambiguous evidence for 3-particle correlations- strength and shape of away-side structures depend on magnitude of flow coefficients- no conclusive evidence for conical emission- an improved analysis with rotating EP shows conical structures
3 < pT,trig
< 4 GeV/c
1 < pT,assoc < 2 GeV/c
3 < pT,trig
< 4 GeV/c
1 < pT,assoc < 2 GeV/c
Abelev et al (STAR), arXiv:0805.0622
d+Au central Au+Au
central Au+AuC3
Subtraction of v2v2v4 termsusing v2 = 0.06
Subtraction of v2v2v4 term using v2 = 0.12
STAR Preliminary
central Au+Au
Note: Large and complicated backgrounds
STAR Preliminary
11
pT dependence of cone angle
Cone angle
independent of pTassoc
Jana Bielcikova 4th workshop "High-pT at LHC", Prague
Čerenkov gluon emission: cone angle decreases with pT
assoc
BUT! Hydro: expects pT dependence as well (G. Torrieri, priv.comm.)
Con
e an
gle
(rad
ians
)
pT (GeV/c)
STAR preliminary
Koch, Majumder, Wang, PRL96 172302 (2006)
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 12
Momentum conservation in correlation analysesC3 cumulant pT conservation 3-particle correlation
Calculation by N. Borghini:momentum conservation sizable correlation between pairs or triplets of high-pT particles in central Au+Au collisions at RHIC C3(pT) ~ C3(flow) jet “distorts” the event Data: possibly a fraction of stat. conservation: assuming bkg follows exp. drop a small effect for pT
trig~3-4 GeV/c
N. Borghini, PRC 75 (2007) 021904
2-particle correlation after v2 subtraction
Calculation for:<p
T,trig > = 3.2 GeV/c
<pT,assoc >= 1.2 GeV/c
Calculation for:<p
T,trig > = 3.2 GeV/c
<pT,assoc >= 1.2 GeV/c
N. Borghini, arXiv:0710.2588
out-of-plane S=90oin-plane S=0o
3< pTtrig < 4 GeV/c, pT
assoc=1.0-1.5 GeV/c
trigger in-plane
trigger out-of-plane
• 20-60% : away-side evolves from single (φS=0o) to double peak (φS=90o)• 0-5% : double peak shows up at smaller φS
• at large φS there is little difference between two centrality bins
Centrality and φS dependence:A.Feng (STAR), QM2008
Au+Au 200 GeV STAR Preliminary
STAR Preliminary
d+Au20-60%
0-5% Au+Au 200 GeV
d+Au
Away-side peak: path-length effects?
RMS
Jana Bielcikova 134th workshop "High-pT at LHC", Prague
shoulder
in-plane:similar to d+Au in 20-60%broader than d+Au in central collisions
out-of-plane:small difference between the two centralities
Away-side features reveal path-length effects
STAR Preliminary
v2{4}
v2{EP}
v2 syst. error
Di-hadron correlations: path-length effects
3< pTtrig < 4 GeV/c, pT
assoc=1.0-1.5 GeV/c
Au+Au 200 GeV
A.Feng (STAR), QM2008
Jana Bielcikova 144th workshop "High-pT at LHC", Prague
A.Feng (STAR), QM2008
Yield in shoulder region independent of s
Yield in peak region decreases with s
“shoulder”
A closer look at the near-side peak …
Jana Bielcikova 15
Additional near-sidecorrelation in observed in central Au+Au collisions
pTtrig=3-4 GeV/c, 2 GeV/c <pT
assoc< pTtrig
“jet”ridge
d+Au, 200 GeV Au+Au, 200 GeV
The ridgeology …1) Medium heating and parton recombination Chiu & Hwa PRC 72 (2005) 034903
2) Radial flow + high-pT trigger particle Shuryak, Phys.Rev.C76 (2007) 047901
Voloshin, nucl-th/0312065 NPA 749, (2005) 287 Gavin, Pruneau, Voloshin , NPA 802, 107 (2008)
3) Parton radiation and its coupling to the longitudinal flow Armesto, Salgado, Wiedemann, PRL 93 (2004) 242301
4) Momentum broadening in anisotropic QGP Romatschke, PRC 75 (2007) 014901
5) Longitudinal broadening of quenched jets in turbulent color fields Majumder, Mueller, Bass, PRL 99 (2007) 042301
6) Momentum kick imparted on partons in medium Wong, PRC PRC 76 (2007) 054908
7) Glasma flux tubes Dumitru, Gelis, McLerran, Venugopalan, arXiv: 0804.3858
…
4th workshop "High-pT at LHC", Prague
STAR preliminary
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 16
Ridge properties
Ridge yield: • increases steeply with centrality• ~ independent of pT
trigger
• baryon/meson ratios and pT -spectra are ‘bulk-like’
• system size and energy dependence see talk by C. Nattrass
STAR preliminary
Rid
ge y
ield
pTtrig (GeV/c)
pTassoc> 2 GeV/c
h-h, Au+Au 200 GeV Ridge: solid symbolsJet: open symbols
STAR preliminary
Ridge
Jet
inclusive
out-of-plane S=90oin-plane S=0o
3< pTtrig < 4 GeV/c, pT
assoc=1.0-1.5 GeV/c
Near-side peak: path-length effects?
Jana Bielcikova 174th workshop "High-pT at LHC", Prague
trigger in-plane
trigger out-of-plane
Ridge component ||>0.7
“Jet” component
Au+Au 200 GeV
20-60%
STAR Preliminary
“jet” part, near-side
ridge part, near-side
ridge yield decreases with φS ridge larger in-plane “jet” yield: slight increase with φS magnitude similar
to d+Au
Jana Bielcikova 18
1) Jet fragmentation in vacuum
d+Au Au+Au
3<pTtrig<10 GeV/c, 1<pT
assoc<3 GeV/c, ||<0.7
STAR Preliminary
Uniform overall excess of associated particles observed at intermediate pT - more data needed - studies at higher pT
assoc
and pTtrigger
Note: Involves complicated background subtraction
3-particle xcorrelations2) In medium radiated gluons diffused in
3) In medium radiated gluons collimated
by longitudinal flow
4th workshop "High-pT at LHC", Prague
Data:STAR Preliminary
P.
Ne
tra
kan
ti (S
TA
R),
QM
20
08
4) Combination of jet fragmentation and diffused gluons
The ‘soft’ ridge in non-triggered correlations
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 19
M. Daugherity (STAR), QM08
stat. errors only, syst.errors 9% (correlation amplitude)
M. D
augherity (ST
AR
), QM
08
• “Minijet” near-side peak amplitude and widthexperience a sharp transition at ~55% centralityfor 200 GeV and ~40% for 62 GeV Au+Au data. x• width is const. from mid-central to central Au+Au collisions
# correlated pairs/particle
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 20
Emerging and future high-pT studies
Full jet reconstruction in Au+Au collisions
The first full jet reconstruction in heavy-ion collisions!
J. Putschke (STAR)Hard Probes 2008
Jana Bielcikova 214th workshop "High-pT at LHC", Prague
Jet spectrum and fragmentation function in Au+Au
• Jet spectrum: need to understand HT trigger bias
• Fragmentation function: no apparent modification with respect to p+p
Leading Order High Seed Cone(LOHSC)R=0.4, pT = 1 GeV/c, seed = 4.6 GeV/c
See talk by J. Putschke
Jana Bielcikova 224th workshop "High-pT at LHC", Prague
-hadron correlations
• a “golden probe” of parton energy loss in the medium
•precise measurement of the in-medium modification of fragmentation function
See talk by A. Hamed
Jana Bielcikova 234th workshop "High-pT at LHC", Prague
STAR preliminary
A. H
am
ed
(ST
AR
),QM
20
08
A. H
am
ed
(ST
AR
),Ha
rd P
rob
es 2
00
8
RHIC upgrade, stochastic cooling
Projected performance for-hadron measurement
TOF (Run 10): PID, clean e± μ± ID down
to low pT
DAQ1000 complete (Run 9):3x improvement in sampled luminosity for rare probes(e.g. jets in p+p)
Heavy Flavor Tracker (Run 13):direct measuruments of charm/bottom
STAR and RHIC upgrades
Jana Bielcikova 244th workshop "High-pT at LHC", Prague
Jana Bielcikova 4th workshop "High-pT at LHC", Prague 25
Summary• Constraining medium density using combined fits to RAA and IAA
large d+Au data sample will help to reduce exp. uncertainties
• Strong modification of correlation patterns in central A+A collisions at RHIC:
• broadening of away-side peak with angular substructurepossible evidence for conical emission
• medium responds through “ridge” formation in pseudo-rapidity bulk-like properties (spectra, particle composition) medium density/path length effects (dominated in the event plane)
• THE future measurements: -jets and full jet reconstruction are emerging
Stay tuned for new results coming from Run7 and Run8 + future STAR upgrades
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