ALICE-USA Collaboration Meeting

Xin-Nian WangLawrence Berkeley National Laboratory

Jet Quenching: From RHIC to LHC

pQCD Analysis of Jet Quenching

2 2 2 2 21 2 1 22

( ) ( )ABA B a a b b

abcdT

dK d b d rd r t r t r dx d k dx d k

dyd p

/ // 1 2( , , ) ( , , )1

( )aa A a a

b ch

db b cb B c

c

f x k r f xdt z

k zd

Dr

Parton distr. in nuclei & pT broadening Modified Frag. Fun.

0

320( )(

2ln)a

R

A s

EE C C d

2 122

40

( , ) ( , )2

h

Q

S hq h h L q h

z

zd dzD z Q z x D

z z

Hard vs soft radiation

202

Fdyn S

dE CQ

dx

Dynamic “string tension”:

qQ2 >kT

2>Q02 kT

2<Q02

perturbative non-perturbative

2

2 (1 )f

T

Ez z

k

22 hadr h

T h

EE r

k Hadronization time: <kT>~1/rh

D meson can be formed very early

Modified Fragmentation

12 2

/ /

0

1( , ) ,

1 1( )med vac

h q h qz

D z Q d D QP

0 2

20

0

1(1 ) 2

2 2 2 2 2 20 0

1 2 (1 ) 3

2 ln ( / )

zz z Q g

DGLAP TQg T Tz

dNEz z Edz dk

N k dzdk Q Q Q

DGLAP time:

?2 1

22

( , ),

ln( ,

2)

h

q h h S h

z

g q h

D z Q zdzD Q

Q z zz

Sensitivity of RAA

•Cronin effect

•Slope of the jetspectra

•E-dependence ofthe energy loss

Effect of non-Abelian energy loss

Eg=Eq

Eg=2Eq

Q. Wang & XNW nucl-th/0410079

pT=6 GeV

q=0.9 0.1

EskolaHonkanenSalgadoWiedemann

Back-2-back Dihadron Correlations

Pedestal&flow subtracted

/( )

/

( ) ( )

( )

asso trigtrig T T

AA T T trigT

trig assoT T

TT T T

trigT

TT T

d dp dpD z p

d dp

d p pdE D D

dE E E

d pdE D

dE E

ET

= STAR preliminaryMajestero

XNW, PLB595(04)165.

Hadron Trigger Bias

Trigger hadron

Trigger hadron

No apparent reason why IAA(pT) should be similar to RAA(pT)

Photon Trigger

trigger

trigger

associated hadron

associated hadron

IAA should behavior like RAA, take into account underlying jet spectra

Photon-tagged jets

• No-trigger bias– Initial energy– Surface emission– Correlation

background due to v2

XNW, Huang & Sarcevic,PRL77(96)231-jet Events

assoc hadron

Hadron versus photon trigger

= STAR preliminaryMajestero

Dependence on pTtrig

Some practical remarks

• Same-side correlation

• Correlation with reaction plane

• Mixing direct and jets0

Background, background and background