Post on 21-Dec-2015
transcript
Jet Measurements at RHIC
M.L. Miller, MIT
p p jets p p jets Au Au jets
1. The laboratory2. Expectations3. Measurements4. Missing pieces5. Conclusions
RHIC: A dedicated QCD machineRHIC: A dedicated QCD machine
QCD: ~95% of the bandwidthp+p, d+Au, Au+Au (Cu+Cu next)
Access to perturbative regimeRuns I-4: 19, 63, 130, 200 GeVRun 5: commission 0.5 TeV p+p running
“Mature performance” demonstrated
Run 5 (November?): First “long” polarized p+p run
Expect ~14 pb-1
STAR (SVT+TPC+EMC)0 ≤ Φ ≤ 2π-1 ≤ η ≤ 2
PHENIX (DC+EMC+PID)2 x |Φ| ≤ π/4|η| ≤ 0.3
No hadron calorimetery!
coneRJet interests at RHIC (I): p+p
Fragmentation:
z hadron
parton
p
p
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
5<pT(jet)<25 GeV q+g dominates
:LLA
Expect ~14 pb-1 significant “Δg physics” from p+p at RHIC run5
In QCD Medium Additional kT
Significant energy loss? high pT suppression
Sensitive to color Sensitive to color properties of mediumproperties of medium
coneRJet Interests at RHIC (II): Au+Au
Hard probeearly time Calculable: pQCD Abundant at RHIC, LHC
kT: “Radiative Corrections”
pre- and post-scattering di-jet:
Fragmentation:
z hadron
parton
p
p
Moment Analysis of QCD Matter
dxxxE
dxxk
g
gT
)(
)(2
coneR
I. Vitev, nucl-th/0308028
Induced Gluon Radiation ~collinear gluons in cone “Softened” fragmentation
in je
i j t
t
n e
: increases
z : decreases
chn
Gyulassy et al., nucl-th/0302077
Fragmentation:
z hadron
parton
p
p
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.(p+p, d+Au and peripheral Au+Au)
trigger
“Trigger” = 0
Adler et al., PRL90:082302 (2003), STAR
near-side
away-side
near far
Charged jet evolution at RHIC1STAR: 0.5 , min.biasL dt pb •Thrust axis: direction
of leading “charged” jet
•Study ΣpT, Nch vs. thrust axis
Smooth transition to di-jet topology with increasing jet pT
Agrees well with CDF charged jet study (see red points/curve)
Soft physics of underlying p+p event under study at RHIC (but much to do!)
Foundation for jet studies in Au+Au via leading charged particles
STAR pT>200 MeVCDF pT>500 MeV
MLM, CIPANP03
STAR Preliminary
But first, some jargon…
peripheral (grazing shot)
central (head-on) collision
participants
Centrality: event classes based on mid-rapidity
multiplicity
Preliminary sNN = 200 GeV
Uncorrected
Particle production scales with increasing
“centrality”
Adams et al., Phys. Rev. Let. 91 (2003)Adler et al., PRL90:082302 (2003), STAR
1/N
trig
gerd
N/d
()
Background subtracted
di-hadron
200 GeVNNs
Final state jet quenching p+p
2-jets Peripheral Au+Au2-jets
Central Au+Au 1-jet!
d+Au 2-jets
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
But…But…
Normalization applied potentially sensitive to large kT broadening
awaytoward
syst. error
Stiffer spectrum in cone indicative of jet fragmentation
Similar slope in both systems
Not absolutely normalized
toward
nucl-ex/0404010STAR Preliminary
Towards a frag. function in Au+Au
4 6 GeV/ctrigTp
Study h± pT distributions (pT>150 MeV) in toward, away region.
Compare p+p to Au+Au
Softened spectrum in both systems
Au+Au softer than p+p
Effect largest for most violent collisions
away
hadron
hadron
Δφ
Getting quantitative: Jet profiles
Reconstructed jets
sinhadronT T jet hadj p
-sinjetT T jet jetk p
di-hadron
2 2Fa
TTy Near r
pk
z
sin Nearyj p
Jet “width”
Jet-coplanarity
: of colliding
partons
a b
Ty T Tk p p����������������������������Tk
: of hadron to jet axis
Ty Tj p
Tj
parton
parton
jT, kT from p+p jets, di-jets
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
di-jet
13 jetTE GeV
10.8 L dt pb 2
T
pairTk p
Apanasevich et al.,PRD59, 074007
TPC+EMC reconstructed jets
5 jetTE GeV
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
jT and kT in Au+Au from di-hadrons2 2 2 2
IS nucl FS nuclT T T TAA vack k k k
p+p
d+Au
( ) g x dx
pp <z><|kTy|>
pp <|jTy|>
(2.5pTtrigg4.0)(1.0pTassoc2.5)
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
Perhaps most interpretable di-hadron measure at RHICPerhaps most interpretable di-hadron measure at RHIC
What’s missing? Yieldsd
2 σ /
dM
dy
(nb
GeV
-1)
p+N h± + h ± + X
ECM=38.8 GeV
-0.4<y<0.2
pTpair<2 GeV/c
no
rmal
ized
dσ
/ d
co
s(θ* )
cos(θ*)
p+N h± + h ± + X
ECM=38.8 GeV
-0.25<y<0.1
pTpair<2 GeV/c
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
hep-th/0110036 hep-th/0110036
Conclusions
2-particle correlationsRobust jet probe from p+p to central Au+Au
Partonic energy loss in dense QCD matterEvidence 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 ambiguitiesHigher pT jets access to low-z fragments
Possible with Run4 data on tape
Some added complexity
ΔΦ
Δη
ΔΦ
Δη
Central Au+Au
Periph. Au+Au
Cor
rela
tion
stre
ngth
Cor
rela
tion
stre
ngth
STAR Preliminary
PHENIX preliminary
1/xE -4 to -5
CCOR (ISR) s = 63 GeVNucl Phys B209 (1982)
1/xE -5.3
Fragmentation from p+p di-hadronscos( )
= z TE trigg
parton
px z
p
Simple relation E triggz x z
kT, jT from p+p di-hadrons
J. Rak, Wed.
J. Rak, DNP03
s=200 GeV
di-hadron
Statistical Errors Only
near-side away-side
nearfar
kT, jT from p+p di-hadronsStatistical Errors Only
PHENIX preliminary
|jTy| = 35911 MeV/c
|kTy| = 96449 MeV/c
PHENIX preliminary
|jTy| = 35911 MeV/c
|kTy| = 96449 MeV/c
J. Rak, DNP03
s=200 GeV
Good agreement with previous measurements: PLB97 (1980)163 PRD 59 (1999) 074007
di-hadron
, 200 GeVNNAu Au s
Disappearance of the away-sideDisappearance (at mid-rapidity) is dominated Disappearance (at mid-rapidity) is dominated
by final state effect(s)!by final state effect(s)! Jet Quenching Jet Quenching
Adler et al., PRL90:082302 (2003), STAR
2nd order correlations due to elliptic flow of entire eventcompeting background p+p
2-jets
Peripheral Au+Au2-jets
Central Au+Au 1-jet!
d+Au 2-jets