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Outline Jet and it’s importance in RHIC
Jets and hard scattering soft vs hard pQCD approach
pp pA AA
Angular correlation some examples Phenix experiment my angular correlation study outlook
Summary
Relativistic Heavy-Ion Collider (RHIC)
Goal Searching for the quark gluon plasma(QGP) exploring the physics of this new state of matter.
Jet quenching as probe
Au Au at
AGeVs 200
Jet quenching: a QGP signature
What is a Jet ? QCD energy loss in deconfined dense
matter Theory prediction dE/dx = 2-4GeV/fm QGP suppresses high pt particles
and angular correlations
b
ac
d
Ref, K
.Geiger
Jet and hard scattering at Jet production rate (K.J.Eskola,hep-ph/9610365)
Hard scattering contribution to particle production is important( )
N p b p b T o t a l g q q
R H I C 1 9 9 1 5 7 2 5 . 7 1 6 . 6
A t = 0 . 1 f m / c , | y | < 0 . 5 , P t > 2 G e V , N os h a d o w , M R S D - ‘ s p a r t o n d i s t r i b u t i o n ,a n d a s s u m e pi
AfAi
f//
AGeVs 200
%20
d/pTdp
T
string modelhydrodynamic model
pQCD
(Hijing,PCM)
pT
soft
Semi-hard
hard
1GeV 5GeV
soft process vs hard process
Jet
Soft/hard boundary?
At SPS ( ) Hydrodynamic models. pQCD(X.N.Wang, hep-ph/9804357) at SPS : both works. Small jet cross-section, measure only to
At RHIC ( ) increase , larger jet cross-section,measure
to high pt ( ). Angular correlation
cGeVpt /35.1
AGeVs 20~
s
AGeVs 200~
cGeV /10
cGeVpt /4
Hydrodynamic Model for SPS
Plot created by Jane Burward Hoy
pQCD calculationX.N.Wang,nucl-th/9812021
Jet production(X.N.Wang,nucl-th/9812021)
pQCD approach
dtd
Aaf /A
a
Abf /B
b
dD
h2
d
2h
cDh1
c
1h
Schematic representation of a high-pt reaction factorized into parton distribution function (f), parton fragmetation function D and a hard-scattering subprocess
parton-parton collision Aaf / cDh
convolution
Cross-section
Cross-section
pp--Initial Kt
Need to take into account intrinsic pt of partons Uncertainty principle high order pQCD process(initial state radiation,etc)
modify parton distribution function
where
)2,(/)2,()2,(/ QaxpafQaTKpgQaxpaf
e pTT kk
Tp QKg22
),( 2
pA--Modification of hard scattering
Assume only one hard parton-parton collision.
Enhancement of high Pt spectra (Cronin effect ) decrease with 1/pt
2 and
A(b) is number of scatteringassume hard sphere distribution
2 is the soft Kt kick, it has following form
)1)()(()()( 222222 bQQkQk AN
TA
T
222
12
3)()( A
ANNANNA Rb
R
Abtb
222
22
)ln(1
)(ln225.0)( cGeV
GeVQ
GeVQQ
Modification of nuclear structure function (Shadowing) assume parton distribution:
)2,(/
)1()2,(/
),(/),2,(/ Qxna
fAZQx
paf
AZbxAaSbQaxAaf
s
Cronin and Shadowing in pA
Tpdydd hppbinaryN
Tpdydd hAB
TpABR2
2)(
Rp
Au
p + Au
AA--Jet quenching If we have QGP, multiple interactions of parton with
the medium lead to loss of energy. Time scale
(h 1/p0 0.1fm/c, p0 2GeV/c, s 1/QCD 1 fm/c)
High pt parton collisions happen in the earliest stage of collision. Then they suffer energy loss in the medium.
Hijing Assume (model dependent): constant energy loss incoherent multiple scattering.
.,
),2,()2,(
ccdxcdElossenergycandcoffunctionischD
mediumindistancetravelaveragetheisLwhere
LQzchDQzchD cc
RA
A(P
T)
Angular correlation At RHIC
Back-to-Back correlation: QGP
(Di-)Jets suppression enhanced acoplanarity.
Study the centrality (impact parameter) dependence From peripheral to central
Some examples
CCOR At ISR pp
7.0||
forward backward
cGeVPTt /0.7
Ref, M.J.Tannenbaum
1)
2()
1(
)2
,1
()
2,
1(
c
X.N.Wang,Phys.Rep.280,287(1997).
Phenix Detector Good Charged particle tracking
high pt resolution, high interaction rate, L=1026~27cm2/s (read out 50Hz)
Phenix detector acceptance default acceptance:
Pt 0.2 GeV/c; 70<<110 or ||<0.35 -33.75<<56.25, 123.75<<213.75
1/2*sin(/2) = 17 of 4 acceptance in azimuthal leads to an intrinsic jet shape
Phenix acceptance : http://skipper.physics.sunysb.edu:80/talks/jjia
)(003.0 / cGeVppp
DC
(degree)
(degree)
-90
270
0 180
0.35
110
-0.35
70
9090
Detector LayoutDetector Acceptance
cGeVtp /2.0
EMCalTECRICH
Studies of pp collisions at
Pythia Generator 100000 pp events at min jet pt = 20GeV/c.
Analysis scheme (as CCOR): study distributions:
back to back correlation of jets ( w/o acceptance) modification with a HIC background (RQMD)
• one Pythia event(two jets) mixed with one RQMD event
effect of Phenix acceptance.
GeVs 200
GeVs 200
Leading Pt>2.0
1<Pt<2
4<Pt<53<Pt<4
2<Pt<3
Outlook RQMD (Hadrons + Strings)
use other models as background (Hijing, Strings + Minijets) Determine methods to correct for and acceptance of Phenix(limited acceptance)
event by event acceptance correction investigate the fiducial region(,,pt)
Study angular correlation function: Rate estimate(1/2000) when we have the data….
Study angular correlation as a function of centrality. )2
,1
( c
Fiducial region
Detector acceptance
Summary Large pt partons or Jets are good probes of the dense matter in ultra-
relativistic heavy-ion collisions. In RHIC, can use pQCD based models to calculate high pt spectra.
Need to combine soft and hard processes together. Study back to back jets angular correlation
if QGP is generated, angular correlation will be affected by jet quenching
Phenix detector have limited acceptance, we can: increase pt and use the fiducial region learn how to correct for and acceptance.
We will further our study on jet angular correlation and look for jet quenching as a probe of QGP formation at RHIC.
References K.J.Eskola,hep-ph/9601365.
Give the parton production rate. Also K.J.Eskola,K.Kajantie,and J.Lindfors Nucl.Phys.B323,37(1989)
it calculate the parton production rate, saying: for RHIC, U + U, have 290 partons Pt>2GeV, and 75 partons Pt>3GeV. For hard Et,SPS 5%, RHIC 50%, Tevatron 80%.
X.N.Wang,nucl-th/9812021. Base of this talk.
X.N.Wang,Phys.Rep.280,287(1997). Base of this talk.
J.F.Owens,Rev.Mod.Phys. 59, 465 (1987). Gives the jet cross section formula.
X.N.Wang,hep-ph/9804357. Calculate the jet quenching under simple assumption.
M.Arneodo,Phys.Rep.240,301(1994) shadowing effect.
K.Geiger. Ultra-Relativistic nuclear collisions in a QCD based space-time description:the parton cascade model
a very good article delving into the history of AA collision, comparing with Hijing, and have a lot of interesting graph.
Nucl.Phys.B480 406. Having UA1 Jet cross section measurement
)(
)2,()2,(
/)2,(
/
)2,()2,(22 2
cdabdtd
z
Qzch
DQ
bx
pbfQaxpa
f
QbT
kPgQaTkpgbT
kdaTkdxbdxadabcdTpdyd
dhpA
c
c
k
PP
pA
)(
)2(),2,(/)2,(/
)2,(),2,(22)(2 2
,
cdabdt
d
z
QzDbQbxAbfQaxpaf
QbTkPgbQaTkAgbTkdaTkdxbdxadbAbabcd
d
Tpdyd
dhpA
c
cch
tk
AA
)(
),2,(|)|,2,(/),2,(/
|)|,2,(),2,(22|)(|)(22 2
cdabdt
d
z
LQzch
DrbQbxBbfrQaxAaf
rbQbTkBgrQaTkAgbTkdaTkdxbdxadrbBtrArtbdabcd
d
Tpdyd
dhpA
c
c
k
Single Inclusive cross section
1<Pt<2
4<Pt<53<Pt<4
2<Pt<3
