1 Jiangyong Jia, ISMD Aug 4-9 2007 Probe the QGP via dihadron corr elations: Jet quenching and Med ium-response Jiangyong Jia Stony Brook University Medium Jet ?
Jan 01, 2016
1Jiangyong Jia, ISMD Aug 4-9 2007
Probe the QGP via dihadron correlations: Jet quenching and Medium-response
Jiangyong Jia Stony Brook University
Medium
Jet
?
2Jiangyong Jia, ISMD Aug 4-9 2007
Particle production mechanisms
53
RAA=A+A/p+p
pT
1
Jet
Flow+Recombination
Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination
0.2
High pT: surface emission
factor of 5
3Jiangyong Jia, ISMD Aug 4-9 2007
Particle production mechanisms
53
RAA=A+A/p+p
pT
1
Jet
Flow+Recombination
Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination
0.2
High pT: surface emission Low pT: bulk emissionLocally thermalized QGP -> flow -> recombination
TTthermal+m<v>2
factor of 5
4Jiangyong Jia, ISMD Aug 4-9 2007
Jet contribution via dihadron correlation
53
RAA=A+A/p+p
pT
1
Jet
Flow+Recombination
0.2
High pT: Jet quenching and Jet tomography. Low pT: Dissipation of lost energy to medium
How the energy of the 80% jet redistributed to low pT? pT scan: Evolution of jet fragmentation and medium
response
5Jiangyong Jia, ISMD Aug 4-9 2007
Azimuth correlation at high pT
d+Au Au+Au 0-5%
8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV
Per
-trig
ger
yiel
d
Observed jet are those “do not” suffer energy loss. Near-side: surface emission Away-side: tangential emission
(factor of 5 suppression)
6Jiangyong Jia, ISMD Aug 4-9 2007
Azimuth correlation at high pT
d+Au Au+Au 0-5%
8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV
Per
-trig
ger
yiel
d
Observed jet are those “do not” suffer energy loss. Near-side: surface emission Away-side: tangential emission
(factor of 5 suppression)
IAA 0.2 RAA, Why??
STAR, Phys. Rev. Lett. 97 (2006) 162301
I AA
0.2
Direct proof that high pT hadrons are from vacuum fragmentation.
But they do not directly constrains the energy loss processes. Calculations model dependent:
qhat 1~10 GeV2/fm
7Jiangyong Jia, ISMD Aug 4-9 2007
Average energy loss vs. absorption?
pT
Yield
RAA alone can’t distinguish the two cases. But,
Case I: Suppression factor depends on the spectra shape, Flatter spectra -> larger shift.
Case II: Suppression factor almost independent of the spectra shape
Shift to left
0( )E E
Case I
p+p
A+A
AbsorptionDownward shift
Case II
(1 ) ( ) ( )A E A E E
8Jiangyong Jia, ISMD Aug 4-9 2007
PRC.71:034909,2005
Due to longer pathlength for away-side jet, it always leads to IAA<RAA. Need shift term!
Consider only absorption term
pT
Yield
9Jiangyong Jia, ISMD Aug 4-9 2007
Single spectra n= 8.1 in dn/ptdpt
n=4.8 in dn/dpt for 5-10 GeV/c trigger
Per-trigger spectra
Consider only Energy shift
Away spectra flatter than single spectra
10Jiangyong Jia, ISMD Aug 4-9 2007
2( )
( ) 1n
TAA T
T
E pR p
p
8.1 2
1( )1 ( ) 0.23T
AA TT
E pR p
p
4.8 1
1( )1 ( ) 0.35T
AA TT
E pI p
p
• Flatter spectra and longer pathlength) compensated by bigger fractional energy loss --> IAA ~ RAA
• For -jet, pure absorption: IAA=RAA pure energy shift: IAA>RAA.• By combing IAA and RAA, one gain some sensitivity on energy loss
nucl-ex/0410003
50% bigger
Consider only Energy shift
Single spectra n= 8.1 in dn/ptdpt
n=4.8 in dn/dpt for 5-10 GeV/c trigger
Per-trigger spectra
Away spectra flatter than single spectra
11Jiangyong Jia, ISMD Aug 4-9 2007
Low pT: medium response to jet Near-side: elongated structure in , enhancement in yield.
Jet + medium-induced component (ridge) Away-side: strongly modified shape and yield
Suppressed jet (head region) + medium-induced component (Shoulder region)
STAR PHENIX
12Jiangyong Jia, ISMD Aug 4-9 2007
Away-side particle composition
Similar shape for asso Baryon and asso Meson
0-20%2.5-4x1.6-2 GeV/c
Jet frag.<Bayron/meson< bulk medium.
W.Holtzmann
Recombine into correlated pairs?
13Jiangyong Jia, ISMD Aug 4-9 2007
Away-side energy dependence
p+p
CM<0.7
Same pT cut, similar window
Head200 GeV Head17.2 GeV Shoulder200 GeV 2.5x Shoulder17.2 GeV
At SPS Smaller jet quenching -> Less suppressed Head Smaller medium component -> Smaller Shoulder
||<0.35
14Jiangyong Jia, ISMD Aug 4-9 2007
pT Scan: Competition between Jet and medium
Suppression in HR, enhancement in SR. Jet shape become similar between pp and AuAu at high pT.
Dip grows
Jet emerges
arXiv:0705.3238 [nucl-ex]
15Jiangyong Jia, ISMD Aug 4-9 2007
Head region: Upper limit of jet fragmentationShoulder Region: Response of the medium
pTA
pTB
Many possible routes! A single number summarizing the shape:
RHS
Dip: RHS<1; Peak: RHS>1; flat: RHS=1
Away-side modification pattern vs pT
jet
medium
16Jiangyong Jia, ISMD Aug 4-9 2007
Cone
Flat
Peak
1<pTA,B < 4 -> RHS<1 -> Shoulder region dominant!
pTA or B >5 -> RHS>1 -> Head region dominant!
pTA or B < 1 -> RHS~1
arXiv:0705.3238 [nucl-ex]
pt,1 pt,2>5
1<pt,1 pt,2<4
Competition between “Head” and “shoulder”.Suppression and enhancement
pT Scan: Competition between Jet and medium
17Jiangyong Jia, ISMD Aug 4-9 2007
Jet spectra slope at low pT
Near-side: flat with Npart (>100), increase with pTA.
Dominated by jet fragmentation
arXiv:0705.3238 [nucl-ex]
2<pTA<3
3<pTA<4
4<pTA<5
Mean-pT at intermediate pT (1<pTB< 5)
Shoulder region: flat with Npart (>100), independent of pTA !
Dominated by medium. Universal slope ~0.44 GeV/c, reflects property of the medium?
18Jiangyong Jia, ISMD Aug 4-9 2007
Low trigger pT, decrease with Npart Onset of jet quenching, soft contribution dominates (feed in from shoulder)
High trigger pT, flat with Npart Soft contribution dies out, Jet dominate.
STAR Preliminary
||<0.4
dn/d
Fuqiang
Jet spectra slope at head region
Jet and medium dominates different pT
19Jiangyong Jia, ISMD Aug 4-9 2007
Parton-medium interaction
1) Radiative energy loss -> High pT suppression
Collective mode
Deflected jet
Punch-through jet
Large angle radiation/Cerenkov
Propagation mode
2) Radiated energy converted into flow -> Low pT enhancement
4) Or propagating partons get deflected
3) Radiated energy propagate -> Gluon feedback at low pT
20Jiangyong Jia, ISMD Aug 4-9 2007
Radiation contribution
A. Polosa, C. Salgado, hep-ph/0607295, sudokov splitting
C. Salgado, U. Wiedemann, hep-ph/0310079
I. Vitev, gluon feedback
Can be large angle => But for hard jets, radiation almost collinear
Can explain multiplicity
21Jiangyong Jia, ISMD Aug 4-9 2007
Modifications decrease with increasing trigger pT (flattening) Modification limited to pT
A,B 4 GeV/c, similar to the away-side Shoulder.
STAR: This is due to the Ridge.
Near-side yield modification: IAA
Jet
Ridge
Dilution effects due to soft triggers
J. Putschke
22Jiangyong Jia, ISMD Aug 4-9 2007
Low pT : dilution effect
per-jet yield IAA at low pT is complicated sinc
e the trigger jet is modified.
per-trig yield
IAA reflects modification on Pairs √ and Triggers x
JetPairsper-trig yield=
TrigsAA
pp
per-trig yieldI =
per-trig yieldAA
Jetpairs
Jetpairs AA AA AA AA
A A B BAAAA
coll pp
J R I R IN
AAAA
AA
JI
R
We define pair suppression JAA
23Jiangyong Jia, ISMD Aug 4-9 2007
Are low pT particles from jets? Near-side jet pairs with one particle in 5-10 GeV/c.
Most of these pairs comes from jet fragmentation. When normalized by 5-10 GeV/c trigger, Iaa ~1. But when normalized by low pT triggers, Iaa <1.
Origins:1) low pT triggers from soft processes such as Thermal-T recombination.2) low pT triggers are jet-induced but don’t have high pT partners:
fragmentation of radiated partons
24Jiangyong Jia, ISMD Aug 4-9 2007
Near side JAA
At high pT, both hadrons comes from same jet! JAA represent the suppression on the jet (>pt1+pt2). Since Jet suppression is constant at h
igh pT, JAA should approach the constant RAA level at high pT! Low pT Jaa is factor of 4-5 of the high pT limit? (almost no suppression)
These pairs are remnants of quenched jets (not from surface!)
Leading hadron suppressionJet pair suppression
=
25Jiangyong Jia, ISMD Aug 4-9 2007
Both important at pT<4, softer than jet, similar PID chemistry (see Jana, Anne’s talk).
Mechanisms for Ridge and cone should play a role on both sides. They do not suffer surface bias.
Ridge
Cone
Near jet
Away jet
0
Sources of pairs• Fragmentation contribution from survived jets• Medium-induced contribution from quenched jets
high pT pairs are rare
Connection between Ridge and Cone
26Jiangyong Jia, ISMD Aug 4-9 2007
Summary
Jet correlation @ high pT provide constraints on the jet quenching and geometrical bias
Jet correlation @ low pT shows complex evolution due to competition between Jet quenching and medium response on both near- and away-side.
Models should describe the full pT dependence (shape and yield).
27Jiangyong Jia, ISMD Aug 4-9 2007
Backup
28Jiangyong Jia, ISMD Aug 4-9 2007
ud
uu
d
uud d
u
uud d
u
Medium are boosted by shock wave, which then recombine into hadrons? => jet frag<Bayron/meson
Cooper-Fryer
Recombination is important
29Jiangyong Jia, ISMD Aug 4-9 2007
Outline
Single particle production mechanisms
High pT: jet fragmentation and surface bias.
Low pT: medium response Away-side properties. Away-side Jet and medium competition Near-side properties. Near-side Pair suppression Connection between near- and away-side medium respo
nse Summary
30Jiangyong Jia, ISMD Aug 4-9 2007
Should I worry about non-flow in correlation?
PHENIX: event plane measured at 3<|<4, tracks in ||<0.35Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets
•HIJING event is weighed with measured v2(pt,,b)•PYTHIA has 10 GeV dijet•Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. •Use away-side pp jet to approximate the ridge
Near jet
Away jetΦ
η
Ridge
Hijing+flow
31Jiangyong Jia, ISMD Aug 4-9 2007
Should I worry about non-flow in correlation?
PHENIX: event plane measured at 3<|<4, tracks in ||<0.35Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets
•HIJING event is weighed with measured v2(pt,,b)•PYTHIA has 10 GeV dijet•Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. •Use away-side pp jet to approximate the ridge
3.04.00.42.8Fake v2
nucl-ex/0609009
Near jet
Away jetΦ
η
Ridge
Hijing+flow
32Jiangyong Jia, ISMD Aug 4-9 2007
What v2 to use in correlation?
C() = (1+2<v2tv2
a>cos2) + J()
Non-flow due to jet is small with BBC Event plane
Other Non-flow and v2 fluctuations contribute to C(), so should be included in the two source model.
If minijets are important, then it should be much longer range in , or many minijets emitted in a correlated way?