Post on 22-Dec-2015
1
Mapping out the Jet correlation landscape: Perspective from PHENIX
Jiangyong Jia for PHENIX CollaborationStony Brook University & BNL
23th WWND Big Sky, MT February 11-18, 2007
2
Trigger and associated pT
Aw
ay jet
I AA
Thermallized gluon radiation
Shock wave or cherenkov? flow, Jet broadening
Punch through jets or tangential contribution?
Correlation landscape in pT1, pT2
T 3T
I II III IV
Rich interactions between jet and medium
Low pT Moderately high pTIntermediate pT high pT
Main goal is to understand: Quenching of the jet by the medium Response of the medium to the jet
3
Evolution with pT1,pT2
Away jet shape: broaden shape -> dip -> broaden shape -> peak
Dip grows
Jet emerges
PHENIX Preliminary
5
Pt,2
Pt,1
Cone
Flat
peak pt,1 pt,2>4
1<pt,1 pt,2<4
Competition between “Head” and “shoulder”.
Head region: Suppression of jetShoulder Region: Response of the medium
6
Location of the “displaced” peaks
D 1, independent of centrality (at Npart>100), collision system and √s.
D D
Independent of pT (when not dominated by head region)
nucl-ex/0611019
7
Relative amplitude of Head/Shoulder: pT dependence
More concave
pT
More concave for increasing pT (in a limited range)
8
Relative amplitude of Head/Shoulder: Centrality
dependence
More concave for increasing Npart
More concave
Npart
peripheralcentral
9
Broad or displaced peak is seen for different energies.
Relative amplitude of Head/Shoulder: √s dependence
nucl-ex/0611019
More concave
√s =17.2 √s =62.4 √s =200
√s
More concave with increasing √s.
11
Peak ~ 0.07, Min ~0.06CM<0.7
Relative amplitude of Head/Shoulder: √s dependence
Peak ~ 0.17, Min ~0.07
Shoulder200 GeV 2.5x Shoulder17.2 GeV
Head200 GeV Head17.2 GeV ||<0.35
Head: Jet dominate! Jet multiplicity at SPS is lower, but less quenching
Shoulder: Weaker medium response at SPS ?
12
A possible picture
Head region: Suppression of jetFragmentation of surviving jet and its radiated gluons
Shoulder Region: Dissipation of the lost energy in mediumCherenkov/Mach Shock/Deflected jet
Increase pt
Cherenkov:wrong pT dependence
Mach Shock + jet
Deflected jet: models need to describe the pT dependence (Hydro wake, Hwa’s MPS model, large angle rad.)
13
Chemistry of the Shoulder/Cone?
Triggering on high pT and identify the associated hadrons Cone shape observed for associated baryons, but away side is flatte
r than mesons.
0-20%2.5-4x1.6-2 GeV/c
Baryon/meson increase with pT and centrality Jet frag.<Bayron/meson< bulk medium.
14
Chemistry of the Shoulder?
ud
uu
d
uud d
u
uud d
u
Bulk medium are boosted by shock wave, which then coalesce into hadrons? => jet frag.<Bayron/meson<Bulk
Cooper-Fryer
15
Quantify the yield: IAA
Integrate the yield in near side: ||</3, away side: ||</2, and make
IAA = YAA/YPP
16
IAA = YAA/YPP
Enhancement at low pT,assoc due to “shoulder” Suppression at large pT,assoc due to “head”
Away side
Away side
17
IAA = YAA/YPP
Strong modification persists to high pT trigger
Away side
Shoulder enhancement
Head suppression
Away side
Competition between enhancement in the Shoulder region and suppression in the Head region. Jet narrows as function of pT,trig, pT,assoc. The fraction of jet fragmentation and gluon radiation ends up in the “Hea
d” region is larger. Jet (“Head”) spectra in pT,assoc is harder than medium (“Shoulder”), shoulder enhancement limited to 4 GeV/c
19
IAA = YAA/YPP
Modifications decrease with increasing trigger pT (flattening)
Near side
Near side
8<pT,t<15GeV/c
zT
STAR
Ridge enhancement
Note: PHENIX ridge yield is smaller than STAR due to smaller range (PHENIX:||<0.35, STAR:||<1)
Modification limited to pT,trig, pT,assoc<4 GeV/c, similar to the range for away side cone.
STAR: This is due to near side ridge
20
Near side width
Trigger pT =
2.5-4 x 2-3 GeV/c
Ridge is also reflected in the broadening of the near side width at intermediate pT
21
Sources of “jet” pairs One usually find only one “jet” pair per event. “Jet” is statistical sum of different types of signals
Near jet
Ridge
Cone
Away jet
L~0
L<R
L~2R
0 <L<2R
Three particle correlation signal
sum of
Different geometrical bias and trigger bias0
22
Sources of “jet” pairs
Near jet
Ridge
Cone
Away jet
L~0
L<R
L~2R
0 <L<2R
Medium response + reco
Jet fragmentation + radiation
0
23
Ridge vs cone: different medium response?
Both important up to 4 GeV/c in pT,trig, pT,assoc. Softer than jet. Both have particle composition close to bulk.
Ridge width in is broader than jet, but no displaced peak.
Same origin: due to different <L>? Ridge is a premature cone (T.Renk). Cone also elongated in (T.Renk), but hidden by swing.
Different origin: Away side should also have a ridge, centered around the “Head” region.
24
Compare the pT1,pT2, PID, charge, √s dependence of the shape and yield for ridge and cone. If ridge is medium response, it’s charge dependence very different from near side jet. Should have less charge ordering effect. √s can tell us how the medium effect turns on and how it competes with the jet quenching. More quenching->stronger medium response.
Distinguish the ridge and cone
Dial the <L> of near and away side jet with multi-par.corr.(T.Renk) Trig on two back-back high pT particle, and correlate with soft particle?
Note: Possible only if the high pT away side have significant punch-though component
Tangential emission
trig1 trig2
assoc
25
Correlation at very low pT
Away “Cone” shape seen for low pt-low pt correlations in central Au+Au (Npart>100) Correlation among soft particles generated or boosted by jets? Why no near side ridge structure?
200 GeV Au+Au, 0-5% Central
PHENIX Preliminary
0.2 < pT,1 < 0.4 GeV/c, 0.2 < pT,2 < 0.4 GeV/c, ||<0.1
Like-Sign Pairs Unlike-Sign
Pairs
26
Comments on flow background subtraction
v2{2}, v2{4}, v2{RP}, v2{v1RP} etc. PHENIX use the v2{RP}, where RP determined in 3<||<4 STAR use the average between v2{RP} and v2{4}.
CF = J() + (1+2<v2tv2
a>cos2)
Two-particle correlation automatically includes all non-flow and e-b-e fluctuations. So v2{2} should be used, except that non-flow due to jet need to be removed since it is the signal.
PHENIX v2{RP} is not affected by jet (nucl-ex/0609009). But it measures in fact:2
2 2v v 2
2 22 2 2
2
1 1.063v
v v vv
v2{4} is too small because it removes the ebe eccentricity fluctuations.
(P. Sorensen QM06 talk). STAR use a smaller v2 in bg subtraction than PHENIX
28
Which v2 should be used?
The non-flow/v2 fluctuation effects (if any) contributes to the flow background. Exception is v2 bias from jets.
CF = J() + (1+2v2tv2
a cos2)
Physical v2 part.
29
2
2 22 2 2
2
1 1.063v
v v vv
physics is driven by the ebe rotated RP: v2{2} should be used (modulo removing jet bias).
Which v2 should be used?
Rajeev,Ollitrault, PLB641:260,2006.
v2{EP} does not include v2 fluctuation
systematically too small.
1/ 422 42{4} {4} 2 part partv
22{2} {2} partv
30
Non-flow/bias effect due to jets
1) HIJING events are randomly assigned a RP direction and particles are weighted according to the experimental measured v2(pT,)
2) Embed pythia di-jet events (trigger >6 GeV/c) into the HIJING with flow
Jet bias should be small at BBC (3<|<4), we confirm it with simulation
Event
nucl-ex/0609009
31
The perturbation in Reaction Plane is correlated with the jet direction. This leads to a fake v2 (non-flow) of the jet at mid-rapidity
This fake v2 depends on the multiplicity and eccentricity.
Large bias
small bias
Distribution of mid-rapidity triggers respective to the RP determined in 0.8<<2.8
Before embedding After embedding
Fake v2 generated!
32
Fake v2 of the high pT triggers Note, the true v2 of trigger is
0.
0.42.8
Central Peripheral
1.02.8
3.04.02.02.8