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

Backup Slides

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