N. GrauColumbia University 10/17/05
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Jet Correlations at RHIC
Jets from p+p and d+Au collisionsJets in Au+Au collisions
• High-pT jets: higher pT reach over Run-2 (2002)
• Low-pT jets: Exploration of the shape modification
• Cornucopia of other, newer avenues
Is there a consistent picture of jet evolution from two-particle correlations in HIC?
Nathan Grau, Iowa State University
N. GrauColumbia University 10/17/05
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A Baseline for HIC Collisions: p+p
p-pprompt + x
KKP
Kretzer
data vs pQCD
p-p0 + x
Phys. Rev. Lett. 91, 241803 (2003)
NLO pQCD reproduces the measured single 0 production and prompt photons.
Prompt photons – not from hadron decay
N. GrauColumbia University 10/17/05
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A Surprise that pQCD Works?
PHENIX measures at a similar xT ranges as Fermilab and finds good agreement with pQCD.
Implication: no extra kT.
kT: Transverse momentum of partons from confinement, gluon radiation
PHENIX range
J. Owens CTEQ 2004
s
px TT
2 at =0
N. GrauColumbia University 10/17/05
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kT for an Experimentalist
kT: Net pair pT Experimentally determined by
• Drell-Yan• Di-jet acoplanarity• Di-(prompt) photon correlations
Modified by initial and final state gluon radiation• Drell-Yan only initial state• Di-jets initial and final state
L. Apanasevich PRD 59 074007 (1999)
N. GrauColumbia University 10/17/05
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Importance of kT for HIC
Jets good probe of QGP• Strong interaction with final state• Survives hadronization of the QGP• Sensitive to early times of the collision
Useful probe for multiple scattering/Energy Loss• Multiple collisions prior to hard scattering (Cronin
effect)• Energy loss from gluon bremsstrahlung, multiple
scattering, etc.
N. GrauColumbia University 10/17/05
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Jet Measurement by Two-Particle Azimuthal Correlations
ddN
ddNC
d
dN
N mix
realpairs
trig /
/1
Mixed events – corrects pair acceptance
Near-angle = 0, jet
Far-angle , di-jet
Hard scattering Resonance decays
(rad)
Elliptic flowTotal
C(
)
Sum over all events jets measured on a statistical basis
N. GrauColumbia University 10/17/05
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pQCD & Two-Particle Correlations
Inclusive singles distributions described by pQCD• p+p baseline calibrated for single inclusive spectra• Jet rates are well calibrated
Correlations include non-perturbative effects• kT is partly due to confinement
• fragmentation is non-perturbative
No curves overlay p+p correlation functions
N. GrauColumbia University 10/17/05
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Correlations in p+p and d+Au
N. GrauColumbia University 10/17/05
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Strong Broadening at Lower Energies
= 21 GeVsNN
E683
Strong nuclear dependence on kT. A factor of 2 increase between p+p to p+Au at lower energy
+A and +A offset due to an effect from jet reconstruction
All data agree point-to-point when offset taken into account.
A1/3 dependence in the +A and +A.
2Tk
E609
sNN = 27.4 GeV
p+A
N. GrauColumbia University 10/17/05
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Jet Correlations Resultsin p+p and d+Au
Assume an isotropic background and two Gaussian distributions for the jet peaks.
Extract the width of the Gaussian jet peaks.Trigger 5-10 GeV/c
nucl-ex/0510021 PRL 91, 072304 (2003) Trigger 4-6 GeV/c
N. GrauColumbia University 10/17/05
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Jet Acoplanarity Difference Between p+p and d+Au
J. Qiu, I. Vitev PLB 570 161 (2003)
Multiple scattering model not inconsistent with the data.
0 – crosses +/- – circles
N. GrauColumbia University 10/17/05
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Why No Significant Difference Between p+p and d+Au?
“Intrinsic” kT larger than the kT due to multiple scattering.
Could it be recombination (Hwa and Yang)?• Shower (fragmented) partons recombining with the
soft (radiated) background• Initially predicted factor of 2 increase in the near angle
yield (R. Hwa, C.B. Yang: PRC 70,054902 (2004))
N. GrauColumbia University 10/17/05
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Associated Particle Yields
Trigger 5-10 GeV/c
Measured yield in the gaussian near angle jet function
Ra t
i o t
o p
+p
Hwa and Tan, nucl-th/0503060
Data favors no increased yield above p+p, but not inconsistent with reco
N. GrauColumbia University 10/17/05
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Conclusions About Hard Scattering in d+Au Collisions
Two-particle correlations: d+Au like p+p• Lack of acoplanarity increase
Yields and acoplanarity are consistent with multiple scattering picture
And consistent with (modified) recombination picture.
Conclusion: Need more data.
N. GrauColumbia University 10/17/05
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Au+Au Collisions Prior to QM2005
Trigger 4-6 GeV/c Trigger 2.5-4 GeV/c
PRL 90 (2003) 082302 nucl-ex/0507004
N. GrauColumbia University 10/17/05
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Away-side Jet Modificationat High-pT in A+A
N. GrauColumbia University 10/17/05
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Away-Side Jet at High pT
Trigger h 8-15 Associated h > 2
STAR Preliminary
Above 7 GeV/c the (Gaussian?) away-side jet is evident. The beginning of jet tomography…
H. Pei QM2005 poster
D. Magestro QM2005
N. GrauColumbia University 10/17/05
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Away-Side Widths From E-Loss
Red – gluons from energy loss.
Able to fit IAA from STAR.Black – scattering of parent partons
I. Vitev hep-ph/0501255
IAA
IAA
N. GrauColumbia University 10/17/05
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Extracted Away-Side Jet Widths at High pT
8 < pT(trig) < 15 GeV/c
Widths do not change between p+p and Au+Au?!?
Trigger 5-10 GeV/c J. Jin QM2005 poster
N. GrauColumbia University 10/17/05
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Associated Yield Suppression
Yield decrease smoothly with centrality
IAA (with d+Au denominator) suppression!
Factor of 2 peripheral central
8 < pT(trig) < 15 GeV/c
N. GrauColumbia University 10/17/05
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More on Associated Yields
Associated yields multiplied by a factor to put them on the same scale
Suppression stronger at lower pT
Consistent with flat to a factor of two suppression at highest pT
Trigger 5-10 GeV/c
J. Jin QM2005 poster
N. GrauColumbia University 10/17/05
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Picture of High-pT Jets
Are these results reconcilable in E-loss picture? What are the implications for jet tomography?
Very different centrality dependence of these observables.
N. GrauColumbia University 10/17/05
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Non-Gaussian Away-side Shape at Lower pT
N. GrauColumbia University 10/17/05
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Extracting Jet Correlations in A+A (I)
Assumptions:• Two source model
Elliptic flow Di-jets
• v2 from reaction plane measurements
• <v2trigv2assoc> = <v2trig><v2assoc>
• Similar assumptions between PHENIX and STAR
JvvBC assoctrig 2cos21)( 22
N. GrauColumbia University 10/17/05
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Extracting Jet Correlations in A+A (II)
Extraction of the background level• Absolute normalization• Parameter in the fit of C()• Assume Zero Yield from jets At the Minimum of the
C() (ZYAM) Similar to STAR from disappearance paper.
• Typically 1-2% difference between results but jet S/B few % at low and intermediate pT
Large yield uncertainties, less effect on the shape
N. GrauColumbia University 10/17/05
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Au+Au Correlations from High to Low pT
Most peripheral collisions: Jet is seen for all pT
Onset of away-side jet modification in semi-peripheral collisions.
Flattening and dip structure at low pT and at high centrality.
h-h
J. Jia QM2005 Poster
ZYAM subtracted, green/blue lines indicate subtraction uncertainty.
N. GrauColumbia University 10/17/05
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Formation of a Local Minimum
h-h
C() strength ~ S/B. Flat correlation where a harmonic is present.
J. Jia QM2005 Poster
PHENIX preliminary
N. GrauColumbia University 10/17/05
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Evidence of Mach Cones
1cos M
sc
csQGP= 31
+/-1.23=1.91,4.37
J. Casalderrey-Solana, E. Shuryak and D. Teaney hep-ph/0411315
STAR Preliminary
N. GrauColumbia University 10/17/05
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Or Cerenkov Radiation
Requires colored bound states (mass m) in medium (temperature T).
Strong p-dependence of cone angle
Koch, Majumder, Wang nucl-th/0507063
N. GrauColumbia University 10/17/05
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Testing the Splitting
Parameterize the away-side shape as a double Gaussian that are offset symmetrically around = by fit parameter D.
trigg
assoc
D
Dassoc
Could be a “bent” jet or a mach/ Cherenkov cone – no physics assumption made
N. GrauColumbia University 10/17/05
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Parameterize the Away-Side Shape
Smooth increase splitting with centrality
Plateau at most central Lowest pT correlations
systematically above the higher pT correlations.• Possible indication of
Cerenkov-like radiation?
P. Constantin QM2005 Poster
PHENIX Preliminary
N. GrauColumbia University 10/17/05
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System Size and Energy Systematics of Away-Side Shape
D is independent of system and energy.
Is this reconcilable with Mach or Cerenkov cones?
Au+Au @ 62.4 GeVh-h 2.5-4 x 1-2.5 GeV/c
PHENIX Preliminary
J. Frantz QM2005 poster
N. GrauColumbia University 10/17/05
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Dip Persists at SPS
CERES data at much lower root-s but similar trigger and associated pT ranges • higher xT – quark jet
dominated
Background by ZYAM Correlation is flat at far
angles – dip present at SPS at a smaller level!
M. Ploskon QM2005 Poster
N. GrauColumbia University 10/17/05
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Near Side Broadening
Systematic trend of broadening as a function of centrality.
First observation of medium effect on the near side.
PHENIX Preliminary A. Kravitz QM2005 Poster
N. GrauColumbia University 10/17/05
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Other New/Upcoming/Interesting Jet Correlations
N. GrauColumbia University 10/17/05
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Three-particle Correlations: Mach/Cerenkov Cone
Trigger 2.5-4 GeV/c
Two associated particles 1-2.5 GeV/c
Choose specific reaction plane bin such that v2trig = 0
Contains correlations between the associated particles
Flow+Jet
PHENIX Preliminary Mach cone
Mach cone
Sim
ulat
ion
Sim
ulat
ion
N. GrauColumbia University 10/17/05
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Reaction Plane Dependence: Path Length Dependence
Red – 6 Green – 5 Blue – 4 Light Blue – 2 Pink – 1 Black - Integral
Require the trigger particle within a given RP orientation Flow varies in a particular way
J. Bielcikova et al Phys. Rev. C69:021901, 2004
J. Jia QM2005 Poster
N. GrauColumbia University 10/17/05
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Electron Triggered Correlations:Heavy Quark Energy Loss
Use jet correlations to further understand heavy quark energy loss.
1-4 GeV/c
F. Matathias QM2005 Poster
N. GrauColumbia University 10/17/05
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Direct- Triggered Correlations: Holy Grail of Energy Loss
Studies
Hadrons
gqq
Direct photons not suppressed in the medium.
PRL 94 232301 (2005)
N. GrauColumbia University 10/17/05
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Inclusive-h Correlations in Au+Au
J. Jin QM2005 Poster
C
(
C(
: 5-10 GeV/ch: 1-2 GeV/c
Comparison with 0 triggered data necessary to extract direct photon correlations.
: 5-10 GeV/ch: 3-5 GeV/c
N. GrauColumbia University 10/17/05
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Conclusions
d+Au jets look like p+p jets.• Multiple scattering small
Jets at high pT in Au+Au collisions • Show no away-side width broadening• Show suppression of away-side yields
Jets at low pT Au+Au: strong shape modifications• Due to a medium? Effect at lower root-s and different systems.• What properties can we extract? cs, n, etc.
More results to come• Three-particle correlations, reaction plane dependence, heavy
flavor tagging• Prompt--jet correlations!
N. GrauColumbia University 10/17/05
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Backup Slides
N. GrauColumbia University 10/17/05
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Cronin Effect in Single Inclusive Particle Production in d+Au
Enhancement at mid-pT
Meson-Baryon differenceLook for jet acoplanarity in d+Au vs p+p
PRL 91, 072303 (2003) PRL 91, 072304 (2003)
N. GrauColumbia University 10/17/05
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Jet Acoplanarity in p+p and d+Au
Independent Fragmentation Model:
Triggers 0 +/-
Open: p+p, Closed: d+Au
N. GrauColumbia University 10/17/05
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Fragmentation Functions
Scaled z at high trigger pT.
)(1
assoctrigassoctrig
trig
Etrig
zDzdz
dN
N
z
dx
dN
N
N. GrauColumbia University 10/17/05
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dN/dxE Scaling
PHENIX Preliminary
d+Au
p+p
PHENIX Preliminary
p+p and d+Au are similar
N. GrauColumbia University 10/17/05
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Unchanging Jet Widths: Possible Implications
Away-side jet fragments in vacuum and parent parton unaffected by medium?
Tangential jets?• Suppressed production
area/volume of the colliding region
• Inconsistent with inclusive RAA
Punch throughs• Little E-loss/multiple
scattering
c
L1 L2
a
L1 L2
b
L1 L2
A. Dainese et al, EJPC 38 (2005) 461
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Lack of Near Side Broadening at High pT
At higher pT, no increase with centrality
Consistent with the picture of production at the corona.
N. GrauColumbia University 10/17/05
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Reaction Plane Dependence at Higher pT
High trigger pT
High associated pT
N. GrauColumbia University 10/17/05
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RP Dependence of Near Angle Widths
Near angle widths are flat as a function of reaction plane – still consistent with production at the corona
N. GrauColumbia University 10/17/05
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Comparison of and 0 Triggers
Near-side widths are consistent between -triggered and 0-triggered.
N. GrauColumbia University 10/17/05
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-h Near Side Yields
PRL 94 232301 (2005)
~50% direct photons above 5 GeV/c in the most central.
Also seen in -triggered near side yield ratio to 0 -triggered yield.
Trigger 5-10 GeV/c
h 5-10 GeV/c
J. Jin (#76)