Transcript Jet Measurements at RHIC p  p  jets p  p  jets M.L.

Jet Measurements at RHIC
p  p  jets
p  p  jets
M.L. Miller, MIT
A u  A u  jets
1.
2.
3.
4.
5.
The laboratory
Expectations
Measurements
Missing pieces
Conclusions
RHIC: A dedicated QCD machine
QCD: ~95% of the bandwidth
p+p, d+Au, Au+Au (Cu+Cu
next)
Access to perturbative regime
Runs I-4: 19, 63, 130, 200 GeV
Run 5: commission 0.5 TeV p+p
running
“Mature performance”
demonstrated
STAR (SVT+TPC+EMC)
Run 5 (November?): First “long”
polarized p+p run
0 ≤ Φ ≤ 2π
-1 ≤ η ≤ 2
PHENIX (DC+EMC+PID)
2 x |Φ| ≤ π/4
|η| ≤ 0.3
No hadron calorimetery!
Expect ~14 pb-1
Jet interests at RHIC (I): p+p
R cone
F rag m en tatio n :
z
p h a d ro n
p p a rto n

PHENIX
– Well calibrated for leading π0

STAR
–
–
–
–
Tevatron RunII jet algorithms
Ellis/Soper kT cluster
Midpoint cone with split/merge
20-30% jet energy resolution,
calibration in progress
AL L :
5<pT(jet)<25 GeV
q+g dominates
Expect ~14 pb-1 
significant “Δg
physics” from
p+p at RHIC run5
Jet Interests at RHIC (II): Au+Au
R cone  Hard probeearly time
F rag m en tatio n :
z
p h a d ro n
p p a rto n


Calculable: pQCD
Abundant at RHIC, LHC
kT: “Radiative Corrections”
 pre- and post-scattering
 di-jet: 



In QCD Medium
Additional kT
Significant energy loss?
high pT suppression
Sensitive to color
properties of medium
Moment Analysis of QCD Matter
R cone
 kT 
2
F rag m en tatio n :
z
E 
p h a d ro n

 x
g
( x ) dx
g
( x ) dx
I. Vitev, nucl-th/0308028
p p a rto n
Induced Gluon Radiation
~collinear gluons in cone
“Softened” fragmentation


Gyulassy et al., nucl-th/0302077
in je t
n ch
z
: increases
in je t
: decreases
Jets and jet surrogates
1) Integral Distributions:
<pT>, <Nch>
2) Single Particle Spectra:
d/dpT  RAA, RdA
3) di-hadron correlations:
dN/d()
4) Jet reconstruction:
d/dET, Frag. Func.
“Trigger”
=0
Adler et al., PRL90:082302 (2003), STAR
 near

(p+p, d+Au and peripheral Au+Au)
trigger
near-side
away-side
fa r
Charged jet evolution at RHIC
•Thrust axis: direction
of leading “charged” jet
STAR:
 L  dt  0.5 pb
1
, m in.bias
•Study ΣpT, Nch vs.
thrust axis
STAR Preliminary
MLM, CIPANP03
STAR pT>200 MeV
CDF pT>500 MeV
Smooth transition to di-jet topology Soft physics of underlying p+p event
under study at RHIC (but much to do!)
with increasing jet pT
Agrees well with CDF charged jet
study (see red points/curve)
Foundation for jet studies in Au+Au
via leading charged particles
But first, some jargon…
Particle production scales with
increasing “centrality”
Preliminary sNN = 200 GeV
peripheral (grazing shot)
participants
Uncorrected
Centrality: event classes based
on mid-rapidity multiplicity
central (head-on) collision
Final state jet quenching
Adams et al., Phys. Rev. Let. 91 (2003)
Adler et al., PRL90:082302 (2003), STAR
 2-jets
 Peripheral Au+Au
 2-jets
 Central Au+Au
 1-jet!
 d+Au
1/NtriggerdN/d()
 p+p
 2-jets
But…
Biased towards high-z hadron pairs
 not a sensitive measure of
modified fragmentation
2nd order correlations due to elliptic
flow of entire event  competing
background
s N N  200 GeV
di-hadron
Background subtracted
Normalization applied potentially
sensitive to large kT broadening
Towards a frag. function in Au+Au
Study h± pT distributions (pT>150 MeV)
in toward, away region.
STAR Preliminary
nucl-ex/0404010
Compare p+p to Au+Au
4  pT
trig
syst. error
 6 G eV /c
toward
Stiffer spectrum in cone indicative of jet
fragmentation
Similar slope in both systems
Not absolutely normalized
away
Softened spectrum in both systems
Au+Au softer than p+p
Effect largest for most violent collisions
toward
away
Getting quantitative: Jet profiles
parton
kT
a
Δφ
jT
hadron
kTy
:
b
pT  pT
of colliding
partons
hadron
parton
jTy
:
pT
of hadron 
to jet axis
di-hadron
j y
kTy
 p sin

pT
z
Jet “width”
 Near

jT  pT
hadron

2
Far

Reconstructed jets
2
Near
Jet-coplanarity
sin  jet  had 
kT  pT sin   jet - jet 
jet
jT, kT from p+p jets, di-jets
TPC+EMC reconstructed jets
jet
ET
 5 G eV
Good agreement between data and
Pythia/Lund+Geant
Mean value depends on pT of hadron
pT>2 GeV/c, STAR di-jet <jT>=515±50 MeV/c
pT>1 GeV/c PHENIX di-h± <jT>= 510±10 MeV/c
nucl-ex/0403031
STAR di-jet <kT>=2.3 ±1.1 GeV/c
PHENIX di-h± <kT>= 1.92 ± 0.1 GeV/c
Reasonable agreement with previous di-jet
measures
Apanasevich et al.,PRD59, 074007
jet
ET
 13 G eV
 L  dt  0.8 pb

1
di-jet  
2

kT
 pT
pair
jT and kT in Au+Au from di-hadrons
2
 kT
2
kT
AA
 kT
2
vac
 kT
2
IS nucl
FS nucl
(2.5pTtrigg4.0)(1.0pTassoc2.5)
p+p
d+Au

g
( x ) dx
jT constant with centrality, consistent
with p+p value
kT increases ~30% from p+p to
peripheral Au+Au  consistent with
PHENIX d+Au measure
Strong centrality dependent kT
broadening  large final state radiation
pp <z><|kTy|>
pp <|jTy|>
Perhaps most interpretable di-hadron measure at RHIC
hep-th/0110036
p+N  h± + h ± + X
ECM=38.8 GeV
-0.4<y<0.2
pTpair<2 GeV/c
normalized dσ / d cos(θ*)
d2σ / dM dy (nb GeV-1)
What’s missing? Yields
hep-th/0110036
p+N  h± + h ± + X
ECM=38.8 GeV
-0.25<y<0.1
pTpair<2 GeV/c
cos(θ*)
Lower energy di-hadron invariant mass
spectra: NLO re-summation critical
Strong scale dependence
Do we understand the yields?
di-jet/di-hadron MInv and cos(θ*) are
critical next measures at RHIC
Conclusions
2-particle correlations
Robust jet probe from p+p to central Au+Au
Partonic energy loss in dense QCD matter
Evidence of softened fragmentation, increased multiplicity in
jet in central Au+Au
Large, centrality dependent kT
Need to measure, compare di-jet, di-hadron
yields to NLO QCD
Reduce ambiguities
Higher pT jets  access to low-z fragments
Possible with Run4 data on tape
Backup Slides
Correlation strength
Correlation strength
Some added complexity
Periph. Au+Au
ΔΦ
STAR Preliminary
Δη
Central Au+Au
ΔΦ
Δη
Fragmentation from p+p di-hadrons
x E z trigg 
p T cos(   )
= z
p parton
 Simple relation
 z    x E  z trigg 
1/xE  -4 to -5
1/xE  -5.3
PHENIX preliminary
CCOR (ISR) s = 63 GeV
Nucl Phys B209 (1982)
kT, jT from p+p di-hadrons
Statistical Errors Only
di-hadron
J. Rak, Wed.
J. Rak, DNP03
 near
s =200 G eV

fa r

near-side
away-side
kT, jT from p+p di-hadrons
Statistical Errors Only
di-hadron
J. Rak, DNP03
PHENIX preliminary
|jTy| = 35911 MeV/c
|kTy| = 96449 MeV/c
Good agreement with previous
measurements: PLB97 (1980)163
PRD 59 (1999) 074007
s =200 G eV
Disappearance (at mid-rapidity) is dominated
Disappearance
of the
away-side
by final state effect(s)!
Jet Quenching
2nd order correlations due to
elliptic flow of entire event
competing background
 p+p
 2-jets
 Peripheral Au+Au
 2-jets
 Central Au+Au
 1-jet!
 d+Au
 2-jets
Au  Au ,
s N N  200 GeV
Adler et al., PRL90:082302 (2003), STAR