high momentum probes nuclear suppression correlations identified particle measurements (for theory...
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High Momentum probesHigh Momentum probes
Nuclear SuppressionNuclear Suppression
CorrelationsCorrelations
Identified particle measurementsIdentified particle measurements
(for theory see lecture 5)(for theory see lecture 5)
hadrons
hadrons
leading particle
Jet: A localized collection of hadrons which come from a fragmenting parton
Parton Distribution Functions
Hard-scattering cross-section
Fragmentation Function
a
b
c
dParton Distribution FunctionsHard-scattering cross-sectionFragmentation Function
c
chbbaa
abcdba
T
hpp
z
Dcdab
td
dQxfQxfdxdxK
pdyd
d
0
/222
)(ˆ
),(),(
High pT (> 2.0 GeV/c) hadron production in pp collisions:
~
Hadronization in QCD (the factorization theorem)
“Collinear factorization”
High-energy parton loses energy by
rescattering in dense, hot medium.q
q
“Jet quenching” = parton energy loss
Described in QCD as medium effect on parton fragmentation:
Medium modifies perturbative fragmentation before final hadronization in vacuo. Roughly equivalent to an effective shift in z:
2 (med) 2 2
1 /( , ) ( , ) ,p h p h p h
E E
zD z Q D z Q D Q
Important for controlled theoretical treatment in pQCD:
Medium effect on fragmentation process must be in perturbative q2 domain.
Induced Gluon Radiation
Induced Gluon Radiation ~collinear gluons in cone “Softened” fragmentation
in je
i j t
t
n e
: increases
z : decreases
chn
Modification according to Gyulassy et al. (nucl-th/0302077) attributable to radiative rather than collisional energy loss
Modification of fragmentation functions (hep-ph/0005044)
STAR, nucl-ex/0305015
energyloss
pQCD + Shadowing + Cronin
pQCD + Shadowing + Cronin + Energy Loss
RAA and high-pT suppression
Deduced initial gluon density at = 0.2 fm/c dNglue/dy ≈ 800-1200
≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA) (e.g. X.N. Wang nucl-th/0307036)
Jet quenching I: hadrons are suppressed, photons are not
FA - QM`04 Strangeness Report 8
nucl-ex/0504001
Energy dependence of RAA
RAA at 4 GeV: smooth evolution with √sNN
Agrees with energy loss models
Two possible mechanisms of radiative e-loss plus collisional e-loss
High energy limit: energy loss by gluon radiation. Two limits:
(a) Thin medium: virtuality q2 controlled by initial hard scattering (LQS, GLV)
(b) Thick medium: virtuality q2 controlled by rescattering in medium (BDMPS)
Trigger on leading hadron (e.g. in RAA) favors case (a).
Low to medium jet energies: Collisional energy loss is competitive!
Especially when the parent parton is a heavy quark (c or b).
q
q
L
q q
g
L
Radiative energy loss in QCD
CS
coherent
LPM Nq
dzd
dI
ldzd
dI ˆHeitlerBethe
2ˆ~ˆ~ LqLqdzd
dIddzE SCS
LPML
med
C
cformation Lt
BDMPS approximation: multiple soft collisions in a medium of static color charges
E independent of parton energy (finite kinematics E~log(E))E L2 due to interference effects (expanding medium E~L)
Medium-induced gluon radiation spectrum:
Total medium-induced energy loss:
2
2
22ˆ
qd
dqqdq mediumTransport coefficient:
Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)
Extracting qhat from hadron suppression data
RAA: qhat~5-15 GeV2/fm
What does qhat measure?q̂
LqxxGN
Nq medium
C
CS ˆ,1
4ˆ
2
2
Equilibrated gluon gas:number density ~T3
energy density ~T4
43
ˆ cq
qhat+modelling energy density
• pQCD result: c~2 (S? quark dof? …)• sQGP (multiplicities+hydro): c~10
R. Baier, Nucl Phys A715, 209c
Hadronic matter
QGP
~RHIC data
Model uncertainties
q-hat at RHIC
Pion gas
QGP
Cold nuclear matter
sQGP? ??
RHIC data
EASW BDMPS sCR
4ˆ q L2
ˆ q 2
L2d
0
L
ˆ q () 2 ˆ q 00
L
/log
1
4
92
3
ELdy
dN
R
C
Eg
Rs
GLV
BDMPS(ASW) vs. GLVBaier, Dokshitzer, Mueller, Peigne, Schiff, Armesto, Salgado, Wiedemann, Gyulassy, Levai, Vitev
1800dy
dN g
ˆ q 10GeV 2
fm
Rough correspondence: (Wiedemann, HP2006) 900
dy
dN g
fm
GeVq
2
5ˆ
BDMPS
GLV
Medium-induced radiation spectrum
Salgado and Wiedemann PRD68 (2003) 014008
2ˆLqC
30-50 x cold matter density
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
RAA for 0: medium density I
C. Loizideshep-ph/0608133v2
I. Vitev
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
Application to Heavy Ion Collisions: Initial Results
Strong suppression in Au+Au collisions, no suppresion in d+Au:Strong suppression in Au+Au collisions, no suppresion in d+Au:Effect is due to interactions between the probe and the mediumEffect is due to interactions between the probe and the medium
Established use as a probe of the density of the mediumEstablished use as a probe of the density of the mediumConclusion (at the time): medium is dense (50-100x nuclear matter density) Conclusion (at the time): medium is dense (50-100x nuclear matter density)
PHENIX: Phys. Rev. Lett. 91 (2003) 072301
STAR: Phys. Rev. Lett. 91 (2003) 072304
PHOBOS: Phys. Rev. Lett. 91 (2003) 072302
BRAHMS: Phys. Rev. Lett. 91 (2003) 072303ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
Binary collision scaling p+p reference
Central RAA Data
Increasing density
The Limitations of RAA: “Fragility”
Surface bias leads effectively to saturation of RSurface bias leads effectively to saturation of RAAAA with density with density
Challenge: Increase sensitivity to the density of the mediumChallenge: Increase sensitivity to the density of the medium
K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511
A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461
What can we learn about Energy Loss?
Fractional effective energy loss: Sloss (MJT)
“Effective” because of surface bias when analyzing single particle spectra
PHENIX 0 SpectrumRenk and Eskola, hep-ph/0610059
8 < pT < 15 GeV/c
PHENIX, nucl-ex/0611007
Calibrated Interaction? Grey Probes
Problem: interaction with Problem: interaction with the medium so strong that the medium so strong that information lost: “Black”information lost: “Black”
Significant differences Significant differences between predicted Rbetween predicted RAAAA, ,
depending on the probedepending on the probe Experimental possibility: Experimental possibility:
recover sensitivity to the recover sensitivity to the properties of the medium properties of the medium by varying the probeby varying the probe
Wicks et al, nucl-ex/0512076
Interpreting Correlations
Geometric biases:Geometric biases:Hadrons: surfaceHadrons: surface
Di-hadrons: tangential, but depending on Eloss can probe deeplyDi-hadrons: tangential, but depending on Eloss can probe deeply
Charm-hadron, and especially Beauty-hadron(B): depends on ElossCharm-hadron, and especially Beauty-hadron(B): depends on Eloss
Note: b and c produced in pairs, B and C decay into multiple hadrons Note: b and c produced in pairs, B and C decay into multiple hadrons
Gamma-hadrons: Precise kinematics, back to surfaceGamma-hadrons: Precise kinematics, back to surface
Beyond reaction of probe to medium, also reaction of medium to probeBeyond reaction of probe to medium, also reaction of medium to probe
T. Renk, nucl-ex/0602045
pedestal and flow subtracted
4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig
Di-Jets through Hadron-Hadron Correlations
““Disappearance of away-side jet” in central Au+Au Disappearance of away-side jet” in central Au+Au collisionscollisions
0-5%
Escaping Jet“Near Side”
Lost Jet“Far Side”
STAR, PRL 90 (2003) 082302
IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)
Evolution of Jet Structure
At higher trigger pT (6 < pT,trig < 10 GeV/c), away-side yield varies with pT,assoc
For lower pT,assoc (1.3 < pT,assoc <1.8 GeV/c), away-side correlation has non-gaussian shape becomes doubly-peaked for lower pT,trig
pedestal and flow subtracted
4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig
M. Horner, QM 2006
“Reappearance of away-side jet”With increasing trigger pT, away-side jet correlation reappears
4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig
STAR, Phys. Rev. Lett. 97 (2006) 162301
Dijets from dihadrons
NOT background subtracted: no ambiguities from background model
At high trigger pT, high associated pT:
clear jet-like peaks seen on near and away side in central Au+Au
8 < pT(trig) < 15 GeV/c
pT(assoc)>6 GeVSTAR PRL 97 (2006) 162301
d+Au
1/N
trig
dN
/d(
)
Au+Au 20-40% Au+Au 0-5%
Surface Bias of Di-Jets?
Renk and Eskola, hep-ph/0610059
8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c
8 < pT,trig< 15 GeV/c
STAR, Phys. Rev. Lett. 97 (2006) 162301
Comparison of IAA to RAA
IAA = Yield(0-5% Au+Au) Yield(d+Au)
In the di-jets where trigger pT is 8-15 GeV/c, the suppression is same as for single particles as a function of pT
= Near-side IAA
= Away-side IAA
8 < pT(trig) < 15 GeV/c
D. Magestro, QM 2005
Modification of Clean SignalsAway-side yield strongly suppressedAway-side yield strongly suppressed
(almost) to level of R(almost) to level of RAAAA
No dependence on zNo dependence on zTT in measured range in measured range
No modification in shape in transverse or No modification in shape in transverse or longitudinal directionlongitudinal direction
The jets you can see cleanly are also in some The jets you can see cleanly are also in some sense the least modifiedsense the least modified
STAR PRL 97 (2006) 162301
Near-side Yields vs. zT
After subracting the Ridge M. Horner, QM 2006
Away-side Yields vs. zTM. Horner, QM 2006
Away-side suppression as a function of pT,trig
M. Horner, QM 2006
Away-side IAA
Away-side suppression reaches a value of 0.2 for trigger pT > 4 GeV/c, similar to single-particle suppression
IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)
Where does the energy go? Lower the associated pLower the associated pTT to search for radiated energy to search for radiated energy Additional energy at low pAdditional energy at low pTT BUT no longer BUT no longer
collimated into jetscollimated into jetsActive area: additional handles on the properties Active area: additional handles on the properties of the medium?of the medium?Mach shocks, Cherenkov cones …Mach shocks, Cherenkov cones …
e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) 011901 011901
PHENIX preliminary
Leadinghadrons
Medium
away
near
M. Horner, QM2006
STAR, Phys. Rev. Lett. 95 (2005) 152301 pT (GeV/c)
AA
/pp
STAR preliminary
0-12% 200 GeV Au+Au
- CorrelationsPhys. Rev. C73 (2006) 064907
mid-central Au+Aupt < 2 GeV
d+Au, 40-100% Au+Au, 0-5%
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)
0.8< pt < 4 GeVSTAR PRC 75(2007) 034901
/√
ref
In Au+Au: broadening of the near-side In Au+Au: broadening of the near-side correlation in correlation in
Seen in multiple analysesSeen in multiple analyses Number correlations at low pNumber correlations at low pTT
PRC73 (2006) 064907PRC73 (2006) 064907 PPTT correlations at low p correlations at low pTT, for , for
multiple energiesmultiple energies Major source of pMajor source of pTT fluctuations fluctuations J. Phys. G 32, L37 (2006)J. Phys. G 32, L37 (2006) J. Phys. G 34, 451 (2007)J. Phys. G 34, 451 (2007)
Number correlations at Number correlations at intermediate pintermediate pTT
PRC 75, 034901 (2007)PRC 75, 034901 (2007) Number correlations with Number correlations with trigger particles up to 8 GeV/ctrigger particles up to 8 GeV/c
D. Magestro, HP2005D. Magestro, HP2005 J. Putschke, QM2006J. Putschke, QM2006
Near-side Correlation
Additional long-range correlation in
Au+Au 20-30%
the “ridge”
Coupling of high pT partons to longitudinal expansion - Armesto et al, PRL 93 (2004)QCD magnetic fields- Majumder et al, hep-ph/0611035In recombination framework: Coupling of shower partons to thermal partons undergoing longitudinal expansion- Chiu & Hwa Phys. Rev. C72:034903,2005Radial flow + trigger bias –S.A. Voloshin, Nucl. Phys. A749, 287 (2005)
J. Putschke, QM 2006Au+Au 0-10%
STAR preliminary
Study near-side yields
Study away-side correlated yields and shapes
Components
near-side jet peak
near-side ridge
v2 modulated background
Strategy:
Subtract from projection: isolate
ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge() Jet()Can also subtract large .
3<pt,trigger<4 GeV
pt,assoc.>2 GeVAu+Au 0-10%
preliminary
Two-Component Ansatz
(J+R)
||<1.7
J = near-side jet-like corrl.
R = “ridge”-like corrl.
v2 modulated bkg. subtracted
(J+R)
||<1.7
flow (v2)corrected
Extracting near-side “jet-like” yields
1
Au+Au 20-30%
2
2
(J+R)- (R)
con
st b
kg.
sub
tra
cte
d
(J
)
||
<0.
7
(J)
no bkg. subtraction
const bkg. subtracted
(J)
||<0.7
J. Putschke, QM 2006
The “Ridge” + “Jet” yield vs Centrality 3<pt,trigger<4 GeV
pt,assoc.>2 GeVAu+Au 0-10%
preliminaryJet+Ridge ()Jet ()Jet)
yie
ld
,
)Npart
““Jet” yield constant with NJet” yield constant with Npartpart
JJöörn Putschke, QM2006rn Putschke, QM2006
Reminder from pReminder from pTT<2 GeV: <2 GeV:
elongated structure already in minbias AuAu elongated structure already in minbias AuAu
elongation in p-p elongation in p-p to to elongation in AuAu. elongation in AuAu.
STAR, PRC 73, 064907 (2006)
/√
ref
STAR preliminary
“Jet” spectrum vs. “Ridge” spectrum
“jet” slope“ridge” slopeinclusive slope
efft Tptt epdpdN //
J. Putschke, QM 2006
STAR preliminary STAR preliminary
Ridge Yield
pt,assoc. > 2 GeV
STAR preliminary
Ridge yield persists up to highest trigger pT and approximately constant yield
J. Putschke, QM 2006
Particle production in jet distinctly different than
in medium
Associated particle production (B/M ratio) similar in ridge and mediumand about a factor 2-3 different than in the jet. Ridge and medium have similar production mechanism ? Recombination ?
/K~1 /K~0.5
Extending the ridge: correlations to =5Trigger: 3<pT
trig<4 GeV/c, A.FTPC: 0.2<pTassoc< 2 GeV/c, A.TPC: 0.2<pT
assoc< 3 GeV/c
Trigger on mid- associated particle high (reverse of FMS)
Near-side correlation: consistent with zero (within large v2 errors)
Away-side correlations are very similar (when scaled)
Energy loss picture is the same for mid- and forward ?
AuAu 0-10%AuAu 0-5%
AuAu 60-80%
STAR Preliminary
2.7<|assoc|<3.9
Levente Molnar, QM2006
STAR Preliminary
STAR preliminary
0-12% 200 GeV Au+Au
How to interpret shape modifications?
Hard-soft: Hard-soft: away-side spectra approaching the bulk. away-side spectra approaching the bulk.
Deflected jets, Mach-cone shock waves, Cherenkov Deflected jets, Mach-cone shock waves, Cherenkov radiation, completely thermalized momentum radiation, completely thermalized momentum conservation, or…?conservation, or…?
Mediumaway
near
deflected jets
away
near
Medium
mach cone
M. Horner, QM2006
STAR Collaboration, PRL 95,152301 (2005)
STAR preliminary
0-12% 200 GeV Au+Au
Hard-soft correlations
Hard-soft: Hard-soft: away-side spectra approaching the bulk. away-side spectra approaching the bulk.
Inclusive in top 5%?Inclusive in top 5%?
Three-particle correlation – N.N. Ajitanand, J. UleryThree-particle correlation – N.N. Ajitanand, J. Ulery
Mediumaway
near
deflected jets
away
near
Medium
mach cone
STAR, PRL 95,152301 (2005)
4 < pT,trig< 6 GeV/c
Three particle correlationsTwo Analysis Approaches:• Cumulant Method
Unambiguous evidence for true three particle correlations.
• Two-component Jet+Flow-Modulated Background Model
Within a model dependent analysis, evidence for conical emission in central Au+Au collisions
pTtrig=3-4 GeV/c
pTassoc=1-2 GeV/c
off-
diag
onal
pro
ject
ion
d+Au
0-12% Au+Au
=(12)/2
Δ2
Δ1 Δ1
0-12% Au+Au: jet v2=0
Δ2
C. Pruneau, QM2006J. Ulery, HP2006 and poster, QM2006
What other handles do we have?
Centrality, trigger and associated pCentrality, trigger and associated pTT,….. ,…..
…….Reaction plane.Reaction plane
In-plane
Out-planeSTAR
4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig
STAR, Phys. Rev. Lett. 93 (2004) 252301
Another handle: -jet
q
Photon-jet measurement is, in principle, sensitive to full medium
Bias to where away-side jet is close to surface?
Together with di-jet measurement for comparison
Another differential observable
Increasing ratio of direct photons to decay photons with centrality due to hadron suppression at high pT
PHENIX, Phys. Rev. Lett. 94, 232301 (2005)
Wang et al., Phys.Rev.Lett. 77 (1996) 231-234
1
/Ntr
igdN
/d
(rad)
Another handle: -jetCurrent Results from Run-4 Current Results from Run-4
Au+Au collisions:Au+Au collisions:
J. Jin, QM 2006T. Dietel, QM 2005
q
Summary Limited information extracted from single-particle pLimited information extracted from single-particle pTT
spectra spectra Effective fractional energy loss reaches 20% for Effective fractional energy loss reaches 20% for
most central collisionsmost central collisions Initial energy density ~ 15 GeV/fmInitial energy density ~ 15 GeV/fm33 from radiative from radiative
energy loss models energy loss models Di-Jets (those that are observed) may have less Di-Jets (those that are observed) may have less
surface biassurface bias Photon-Jet Measurement will complement the di-jet Photon-Jet Measurement will complement the di-jet
for more complete probefor more complete probe Heavy-flavor suppression not consistently described Heavy-flavor suppression not consistently described
by theoretical models with light meson suppression – by theoretical models with light meson suppression – need elastic energy lossneed elastic energy loss
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