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2M. van Leeuwen, High-pT and jets
MotivationA reminder
Use jets and high-pT particles to probe the medium
Initial production at high-pT is calculable in perturbative QCD and can be calibrated by reference measurements
Goal: measure medium properties• Density, temperature
Number of degrees of freedom• Dynamical properties
e.g. viscosity
However, we still need to calibrate our probe:• Fragmentation, hadronisation in the vacuum• … and in the medium• Calibrate/constrain energy loss mechanism• Check initial production rates
3M. van Leeuwen, High-pT and jets
Direct at high-pT
T. Isobe
p+p year-5
RHIC is accumulating p+p stats
0-10% Au+Au
Nuclear effects + E-loss (frag )
Quark- in-medium conversions
No enhancement in Au+AuAgrees with NLO pQCD
4M. van Leeuwen, High-pT and jets
0 in p+p, d+AuM. Russcher
2005 p+p
STAR gearing up , 0 in p+p, d+Au
Good agreement with NLO pQCD and PHENIX
PHENIX, B. Sahlmüller
RdA centrality dependence
Measures Cronin, initial state effects
nucl-ex/0610036
5M. van Leeuwen, High-pT and jets
RAA for 0: medium density I
C. Loizideshep-ph/0608133v2
I. Vitev
PHENIX, B. Sahlmüller
W. HorowitzUse RAA to extract medium density:
I. Vitev: 1000 < dNg/dy < 2000
W. Horowitz: 600 < dNg/dy < 1600
C. Loizides: 6 < < 24 GeV2/fmq̂
Statistical analysis to make optimal use of dataCaveat: RAA folds geometry, energy loss and fragmentation
6M. van Leeuwen, High-pT and jets
What do we learn from RAA?
~15 GeV
E=15 GeV
Energy loss distributions very different for BDMPS and GLV formalisms
But RAA similar!
Renk, Eskola, hep-ph/0610059
Wicks et al, nucl-th/0512076v2
BDMPS formalismGLV formalism
Need more differential probes
7M. van Leeuwen, High-pT and jets
L-dependence I: azimuthal asymmetryPQM: Dainese, Loizides, Paic, Eur Phys J C38, 461 RAA, Sloss vs azimuthal angle
L(2) scaling sets in pT > 6-8 GeVv2 only described by models above pT> 6 GeV
nucl-ex/0611007
In Plane
Out of Plane
L
Au+Au 200GeV
0-10%
50-60%
V. Pantuev, D. Winter
New scaling parameter L
No significant loss for L < 2 fm Formation time effect? V. Pantuev hep-ph/0506095
Describes RAA vs angle down to lower pT
8M. van Leeuwen, High-pT and jets
Quark vs gluon from quark energy loss
90% of p from gluons40% of from gluons
X.N. Wang and X.F. Guo, NPA 696, 788 (2001)W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047
Medium modifications to FF?
STAR, L. Ruan
PRL 97, 152301 (2006)
Curves: X-N. Wang et al PRC70(2004) 031901
No sign of stronger gluon energy loss in p/ or p/p ratios
Need new calculations, with better baryon FF (AKK)
pT (GeV/c)
p/STAR, B. Mohanty
9M. van Leeuwen, High-pT and jets
Energy dependence of RAA
preliminaryp+C reference
0-12.7% most central Pb+Pb
K. Reygers
Broad agreement between experiments
Lower √sNN, steeper initial spectra• More pronounced ‘Cronin’ effect• Stronger suppression
(same RAA for more dilute medium)
NA49 preliminary
Central Pb+Pb/Au+Au
NA49
PHENIX
(+ + -)/2 -0.3 < y < 0.7B. Sahlmüller
B. Mohanty
C. Blume
10M. van Leeuwen, High-pT and jets
nucl-ex/0504001
Energy dependence of RAA
RAA at 4 GeV: smooth evolution with √sNN
J. Velkovska
Agrees with energy loss models
11M. van Leeuwen, High-pT and jets
Single particle measurements
• Energy dependenceSPS to RHIC 200 GeV
• System size dependence– p+p and d+Au references
– RAA vs Npart
– RAA vs reaction plane, v2
• Particle type dependence
Large set of systematics becoming available
Comparisons to theory ongoing
Warrants revisiting some areas of theory?(e.g. baryon fragmentation, path length dependence)
12M. van Leeuwen, High-pT and jets
Fragmentation and energy loss I: near-side
• What is it ? ‘something’ coupling to long flow ? Can this quantify E-loss ?
• How to deal with it?Need to subtract for near-side studies?
Components
Near-side jet peak
Near-side ridge
Away-side (and v2)
3 < pt,trigger < 4 GeV
pt,assoc. > 2 GeVAu+Au 0-10%
preliminary
Two distinct questions:
Lesson: The near-side jet does interact with the medium
M. Calderon, J. Putschke
associated
trigger
Di-hadron correlations
13M. van Leeuwen, High-pT and jets
Ridge phenomenology
nucl-ex/0611016
Jet
Ridge observed for all trigger particle types
After subtraction: jet-yield independent of centrality
Jet + Ridge
PHENIX, A. SicklesJ. Bielcikova
Jet + Ridge
PHENIX: drop in baryon-triggered yield for most central events
14M. van Leeuwen, High-pT and jets
Subtracting the ridge IISTAR, M. Horner
C. Zhang
C. Zhang
Near side increase at low pT,assoc seen by STAR and PHENIX
Subtraction of -independent ‘ridge-yield’ recovers centrality-independent jet yield
Vacuum fragmentation after energy loss? Or non-trivial effect hidden by exponential spectra?
1
1zT = pT,assoc/pT,trig
15M. van Leeuwen, High-pT and jets
pT-dependence of ridge
Ridge pT-spectra are ‘bulk-like’
Ridge independent of pT,trigger
STAR, J. Putschke
Jet spectra
Yie
ld (
pt,
as
so
c >
pt,
as
so
c,c
ut)
Ridge spectra
Yie
ld (
pt,
as
so
c >
pt,
as
so
c,c
ut)
pt,assoc,cutpt,assoc,cut
16M. van Leeuwen, High-pT and jets
What is the ridge?
A. Majumder, B. Muller, S. Bass
3 < pt,trigger < 4, pt,assoc. > 2 GeV
STAR, J. Putschke
dN/d
hep
-ph/0611135
Proposed explanations so far:
Ridge shape
• Radiated gluons, broadened by– Longitudinal flow, Armesto et al, PRL 93 (2004) – QCD magnetic fields, Majumder et al, hep-ph/0611035
• Medium heating + recombination,Chiu & Hwa PRC72, 034903
• Radial flow + trigger bias, Voloshin nucl-th/0312065, Nucl. Phys. A749, 287
More differential measurements possible?Jury still out Detailed predictions welcome!
17M. van Leeuwen, High-pT and jets
Energy content of RidgeSTAR, Phys. Rev. Lett. 95 (2005) 15230
0.15 < pt,assoc < 4 GeV
4 < pt,trigger < 6 GeV
6 < pt,trigger < 10 GeV
“Ridge energy”
“Ridge energy”
}
}
Near-side modification in published results also due to ridge
J. Putschke talk
Energy content of ridge: few GeV
18M. van Leeuwen, High-pT and jets
Away-side yields and energy lossC. Zhang M. Horner
|| > /2
Clear evolution of away-side suppression with pT,trig, pT,assoc
Low pT,trig, pT,assoc: enhancement
Increase Q2 for same pT,trig due to energy loss?
Caveat: shapes change non-trivially
8< pTtrig < 15 GeV, PRL 95, 152301
Preliminary
|| > 0.9
19M. van Leeuwen, High-pT and jets
Di-hadrons: away-side shape
Preliminary2.5 < p
T,trig < 4.0 GeV/c
1.0 < pT,assoc < 2.5 GeV/c
Clear evolution peripheral → central: Widening, flattening and ‘dip at ’
nucl-ex/0611019
0-12%
40-60%
0-12%
PHENIX: C. Zhang, N. Grau, J. Jia, E. Vazquez
STAR, M. Horner
High statistics Run IV data
20M. van Leeuwen, High-pT and jets
Away-side shape: energy dependence
PHENIX, C. Zhang
0-5% 10-20%
CERES, S. Kniege
Similar trends seen at lower √s=62.4 GeV
at RHIC
nucl-ex/0611019
2.5 < pT,trig
< 4.0 GeV/c
1.0 < pT,assoc < 2.5 GeV/c
And at SPS
Is this still jet-fragmentation?
Compare p+p?
21M. van Leeuwen, High-pT and jets
Away-side shape: pT,trig
dependence
0-12%
4.0 < pT
trig < 6.0 GeV/c 6.0 < pT
trig < 10.0 GeV/c3.0 < pT
trig < 4.0 GeV/c
Preliminary
0-12%
1.3 < pT
assoc < 1.8 GeV/cSTAR, M. Horner
Away-side flatter for larger pT,trigger
But broadening at low pT,assoc persist
22M. van Leeuwen, High-pT and jets
Summary of shape evolution
Cu+Cu follows trend vs Npart
awayhump
dashed=PHENIX, solid=STAR*0.35
PHENIX, C. Zhang, A. Sickles
F. Wang
224
2
/
)(
kurtosis
rms
nn
Shape change due to yield increase away from =
System size dependence
Npart1/3
23M. van Leeuwen, High-pT and jets
Interpretations of away-side broadening
Mach Cone/Shock wave
T. Renk, J. Ruppert
Stöcker, Casseldery-Solana et al
Cherenkov radiation Gluon rad+Sudakov
A. Polosa, C. Salgado
V. Koch, A. Majumder, X-N. Wang
Many explanations possible, need more input to conclude
Or large kT from radial flow or energy loss Fries, Armesto et al, Hwa
Also: Vitev, Phys. Lett. B630 (2005)
24M. van Leeuwen, High-pT and jets
3-particle correlations
1
3
12
0
13
12
0
Event by event deflection of jets
Cone like structure in each event
3-particle - probes away-side structure:Distinguish event-by-event deflection vs conical (Mercedes) emission pattern
However: Large backgrounds, background shapes not simple
25M. van Leeuwen, High-pT and jets
3-particle results
Au+Au 0-12%
(12-13)/2
(12+13)/2-
PHENIX Preliminary
C. Pruneau, J. Ulery
C. Zhang, N. Ajitanand
13
Cumulant analysis:Model-independentNon-zero 3-particle structure
Jet+background analysis:Model-dependent, more sensitiveOff-diagonal peaks consistent with conical emission
Different co-ordinates:No ‘deflected-jet peak’ consistent with conical emission
12
Tantalising results! Discussion/comparison of methods between experiments needed
3 < pT,trig
< 4 GeV/c
1 < pT,assoc < 2 GeV/c
26M. van Leeuwen, High-pT and jets
3-particle correlations at SPSLike sign Unlike sign
CERES, S. Kniege
ti tj
All chargebackground subtracted
0-5% central
Strong charge-dependence seen in raw signal
Baryon density effect?
Off-diagonal peaks seen after background subtraction
Indicative of conical emission
Mach cones at SPS? Some other mechanism?
2.5 < pT,trig
< 4.0 GeV/c
1.0 < pT,assoc < 2.5 GeV/c
Raw signal Raw signal
27M. van Leeuwen, High-pT and jets
Origin of p/ enhancement: PID correlations
Preliminary Preliminary
Near side Away side
Bar
yon
/mes
on
ass
oc
Bar
yon
/mes
on
ass
oc
B/M singles
Trigger h±: 2.5 < pT < 4.0GeV/c
A. Sickles
Near side: increase with centralityMeasure particle composition of ridge?
Away-side B/M increases strongly with centrality
Need comparisons to theory for interpretation
Extended pT -range desirable
28M. van Leeuwen, High-pT and jets
J. Bielcikova
R. C. Hwa et al., nucl-th/0602024
-h correlation
Near-side yield similar for , , triggered correlations
Initial expectation: dominantly from TTT recombination, no associated yield
Revisited (at QM06): possible large contribution from reheated mediumExperimental tests pending
29M. van Leeuwen, High-pT and jets
Away-side suppression at high pT
NLO
Theory talk, H. Z. Zhang
J. Jin, N. Grau, J. Jia, H. Pei
Data
: ST
AR
PR
L 95, 152
301
T. Renk and Eskola, hep-ph/0610059
Di-hadron suppression: smaller surface bias, potentially better
differential probe
Comparison to theory ongoing
New data: RAA IAA also in Cu+Cu
Emission pointsHydro profile
30M. van Leeuwen, High-pT and jets
-jet measurementsJ. Jin, M. Nguyen S. Chattopadhyay, F. Benedosso
First results in p+p
Promising results: statistical errors can be reduced in coming runs
Consistent with expectations from PythiaConsistent between experiments
31M. van Leeuwen, High-pT and jets
-jet in Au+Au
J. Jin, M. Nguyen
distribution Yields
First results in Au+Au: consistent with suppression
Upcoming RHIC run will improve statistics for this measurement
But large statistical uncertainties
Monochromatic source: differential measurement of jet-quenching
Goal: Measure -jet suppression in A+A
X.-N. Wang, Z. Huang, PRC 55:3047, F. Arleo et al JEHP 0411, 009, T. Renk, PRC 71, 034906
32M. van Leeuwen, High-pT and jets
Summary/outlook
• Impressive amount of new data– Extending pT-reach for inclusives– System size, energy dependence mapped out– Detailed shapes/yields at low, intermediate pT
Some open questions:1) Intermediate pT: origin of ridge and away-side broadening2) Role of baryon fragmentation vs coalescence
(quark/gluon energy loss)
Will this constrain energy loss models?
Expect developments in near future:Baryon/meson fragmentation at higher pT
Improve on -jet measurements
33M. van Leeuwen, High-pT and jets
Future directions-jet rates
RAA at LHC
S. Wicks, W. Horowitz
T. Renk
Slower rise in BDMPS than GLV
… and much more!
Need plot
RAA at LHC not independent of pT:more sensitive to energy loss distribution
B. Jacak, W. Vogelsang
-jet at RHIC-II and LHC