Jet Correlations at RHIC

N. GrauColumbia University 10/17/05

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Jet Correlations at RHIC

Jets from p+p and d+Au collisionsJets in Au+Au collisions

• High-pT jets: higher pT reach over Run-2 (2002)

• Low-pT jets: Exploration of the shape modification

• Cornucopia of other, newer avenues

Is there a consistent picture of jet evolution from two-particle correlations in HIC?

Nathan Grau, Iowa State University


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A Baseline for HIC Collisions: p+p

p-pprompt + x

KKP

Kretzer

data vs pQCD

p-p0 + x

Phys. Rev. Lett. 91, 241803 (2003)

NLO pQCD reproduces the measured single 0 production and prompt photons.

Prompt photons – not from hadron decay


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A Surprise that pQCD Works?

PHENIX measures at a similar xT ranges as Fermilab and finds good agreement with pQCD.

Implication: no extra kT.

kT: Transverse momentum of partons from confinement, gluon radiation

PHENIX range

J. Owens CTEQ 2004

s

px TT

2 at =0


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kT for an Experimentalist

kT: Net pair pT Experimentally determined by

• Drell-Yan• Di-jet acoplanarity• Di-(prompt) photon correlations

Modified by initial and final state gluon radiation• Drell-Yan only initial state• Di-jets initial and final state

L. Apanasevich PRD 59 074007 (1999)


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Importance of kT for HIC

Jets good probe of QGP• Strong interaction with final state• Survives hadronization of the QGP• Sensitive to early times of the collision

Useful probe for multiple scattering/Energy Loss• Multiple collisions prior to hard scattering (Cronin

effect)• Energy loss from gluon bremsstrahlung, multiple

scattering, etc.


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Jet Measurement by Two-Particle Azimuthal Correlations

ddN

ddNC

d

dN

N mix

realpairs

trig /

/1

Mixed events – corrects pair acceptance

Near-angle = 0, jet

Far-angle , di-jet

Hard scattering Resonance decays

(rad)

Elliptic flowTotal

C(

)

Sum over all events jets measured on a statistical basis


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pQCD & Two-Particle Correlations

Inclusive singles distributions described by pQCD• p+p baseline calibrated for single inclusive spectra• Jet rates are well calibrated

Correlations include non-perturbative effects• kT is partly due to confinement

• fragmentation is non-perturbative

No curves overlay p+p correlation functions


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Correlations in p+p and d+Au


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Strong Broadening at Lower Energies

= 21 GeVsNN

E683

Strong nuclear dependence on kT. A factor of 2 increase between p+p to p+Au at lower energy

+A and +A offset due to an effect from jet reconstruction

All data agree point-to-point when offset taken into account.

A1/3 dependence in the +A and +A.

2Tk

E609

sNN = 27.4 GeV

p+A


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Jet Correlations Resultsin p+p and d+Au

Assume an isotropic background and two Gaussian distributions for the jet peaks.

Extract the width of the Gaussian jet peaks.Trigger 5-10 GeV/c

nucl-ex/0510021 PRL 91, 072304 (2003) Trigger 4-6 GeV/c


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Jet Acoplanarity Difference Between p+p and d+Au

J. Qiu, I. Vitev PLB 570 161 (2003)

Multiple scattering model not inconsistent with the data.

0 – crosses +/- – circles


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Why No Significant Difference Between p+p and d+Au?

“Intrinsic” kT larger than the kT due to multiple scattering.

Could it be recombination (Hwa and Yang)?• Shower (fragmented) partons recombining with the

soft (radiated) background• Initially predicted factor of 2 increase in the near angle

yield (R. Hwa, C.B. Yang: PRC 70,054902 (2004))


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Associated Particle Yields

Trigger 5-10 GeV/c

Measured yield in the gaussian near angle jet function

Ra t

i o t

o p

+p

Hwa and Tan, nucl-th/0503060

Data favors no increased yield above p+p, but not inconsistent with reco


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Conclusions About Hard Scattering in d+Au Collisions

Two-particle correlations: d+Au like p+p• Lack of acoplanarity increase

Yields and acoplanarity are consistent with multiple scattering picture

And consistent with (modified) recombination picture.

Conclusion: Need more data.


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Au+Au Collisions Prior to QM2005

Trigger 4-6 GeV/c Trigger 2.5-4 GeV/c

PRL 90 (2003) 082302 nucl-ex/0507004


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Away-side Jet Modificationat High-pT in A+A


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Away-Side Jet at High pT

Trigger h 8-15 Associated h > 2

STAR Preliminary

Above 7 GeV/c the (Gaussian?) away-side jet is evident. The beginning of jet tomography…

H. Pei QM2005 poster

D. Magestro QM2005


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Away-Side Widths From E-Loss

Red – gluons from energy loss.

Able to fit IAA from STAR.Black – scattering of parent partons

I. Vitev hep-ph/0501255

IAA

IAA


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Extracted Away-Side Jet Widths at High pT

8 < pT(trig) < 15 GeV/c

Widths do not change between p+p and Au+Au?!?

Trigger 5-10 GeV/c J. Jin QM2005 poster


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Associated Yield Suppression

Yield decrease smoothly with centrality

IAA (with d+Au denominator) suppression!

Factor of 2 peripheral central

8 < pT(trig) < 15 GeV/c


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More on Associated Yields

Associated yields multiplied by a factor to put them on the same scale

Suppression stronger at lower pT

Consistent with flat to a factor of two suppression at highest pT

Trigger 5-10 GeV/c

J. Jin QM2005 poster


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Picture of High-pT Jets

Are these results reconcilable in E-loss picture? What are the implications for jet tomography?

Very different centrality dependence of these observables.


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Non-Gaussian Away-side Shape at Lower pT


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Extracting Jet Correlations in A+A (I)

Assumptions:• Two source model

Elliptic flow Di-jets

• v2 from reaction plane measurements

• <v2trigv2assoc> = <v2trig><v2assoc>

• Similar assumptions between PHENIX and STAR

JvvBC assoctrig 2cos21)( 22


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Extracting Jet Correlations in A+A (II)

Extraction of the background level• Absolute normalization• Parameter in the fit of C()• Assume Zero Yield from jets At the Minimum of the

C() (ZYAM) Similar to STAR from disappearance paper.

• Typically 1-2% difference between results but jet S/B few % at low and intermediate pT

Large yield uncertainties, less effect on the shape


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Au+Au Correlations from High to Low pT

Most peripheral collisions: Jet is seen for all pT

Onset of away-side jet modification in semi-peripheral collisions.

Flattening and dip structure at low pT and at high centrality.

h-h

J. Jia QM2005 Poster

ZYAM subtracted, green/blue lines indicate subtraction uncertainty.


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Formation of a Local Minimum

h-h

C() strength ~ S/B. Flat correlation where a harmonic is present.


PHENIX preliminary


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Evidence of Mach Cones

1cos M

sc

csQGP= 31

+/-1.23=1.91,4.37

J. Casalderrey-Solana, E. Shuryak and D. Teaney hep-ph/0411315

STAR Preliminary


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Or Cerenkov Radiation

Requires colored bound states (mass m) in medium (temperature T).

Strong p-dependence of cone angle

Koch, Majumder, Wang nucl-th/0507063


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Testing the Splitting

Parameterize the away-side shape as a double Gaussian that are offset symmetrically around = by fit parameter D.

trigg

assoc

D

Dassoc

Could be a “bent” jet or a mach/ Cherenkov cone – no physics assumption made


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Parameterize the Away-Side Shape

Smooth increase splitting with centrality

Plateau at most central Lowest pT correlations

systematically above the higher pT correlations.• Possible indication of

Cerenkov-like radiation?

P. Constantin QM2005 Poster

PHENIX Preliminary


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System Size and Energy Systematics of Away-Side Shape

D is independent of system and energy.

Is this reconcilable with Mach or Cerenkov cones?

Au+Au @ 62.4 GeVh-h 2.5-4 x 1-2.5 GeV/c

PHENIX Preliminary

J. Frantz QM2005 poster


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Dip Persists at SPS

CERES data at much lower root-s but similar trigger and associated pT ranges • higher xT – quark jet

dominated

Background by ZYAM Correlation is flat at far

angles – dip present at SPS at a smaller level!

M. Ploskon QM2005 Poster


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Near Side Broadening

Systematic trend of broadening as a function of centrality.

First observation of medium effect on the near side.

PHENIX Preliminary A. Kravitz QM2005 Poster


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Other New/Upcoming/Interesting Jet Correlations


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Three-particle Correlations: Mach/Cerenkov Cone

Trigger 2.5-4 GeV/c

Two associated particles 1-2.5 GeV/c

Choose specific reaction plane bin such that v2trig = 0

Contains correlations between the associated particles

Flow+Jet

PHENIX Preliminary Mach cone

Mach cone

Sim

ulat

ion

Sim

ulat

ion


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Reaction Plane Dependence: Path Length Dependence

Red – 6 Green – 5 Blue – 4 Light Blue – 2 Pink – 1 Black - Integral

Require the trigger particle within a given RP orientation Flow varies in a particular way

J. Bielcikova et al Phys. Rev. C69:021901, 2004



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Electron Triggered Correlations:Heavy Quark Energy Loss

Use jet correlations to further understand heavy quark energy loss.

1-4 GeV/c

F. Matathias QM2005 Poster


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Direct- Triggered Correlations: Holy Grail of Energy Loss

Studies

Hadrons

gqq

Direct photons not suppressed in the medium.

PRL 94 232301 (2005)


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Inclusive-h Correlations in Au+Au

J. Jin QM2005 Poster

C

(

C(

: 5-10 GeV/ch: 1-2 GeV/c

Comparison with 0 triggered data necessary to extract direct photon correlations.

: 5-10 GeV/ch: 3-5 GeV/c


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Conclusions

d+Au jets look like p+p jets.• Multiple scattering small

Jets at high pT in Au+Au collisions • Show no away-side width broadening• Show suppression of away-side yields

Jets at low pT Au+Au: strong shape modifications• Due to a medium? Effect at lower root-s and different systems.• What properties can we extract? cs, n, etc.

More results to come• Three-particle correlations, reaction plane dependence, heavy

flavor tagging• Prompt--jet correlations!


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Backup Slides


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Cronin Effect in Single Inclusive Particle Production in d+Au

Enhancement at mid-pT

Meson-Baryon differenceLook for jet acoplanarity in d+Au vs p+p

PRL 91, 072303 (2003) PRL 91, 072304 (2003)


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Jet Acoplanarity in p+p and d+Au

Independent Fragmentation Model:

Triggers 0 +/-

Open: p+p, Closed: d+Au


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Fragmentation Functions

Scaled z at high trigger pT.

)(1

assoctrigassoctrig

trig

Etrig

zDzdz

dN

N

z

dx

dN

N


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dN/dxE Scaling

PHENIX Preliminary

d+Au

p+p

PHENIX Preliminary

p+p and d+Au are similar


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Unchanging Jet Widths: Possible Implications

Away-side jet fragments in vacuum and parent parton unaffected by medium?

Tangential jets?• Suppressed production

area/volume of the colliding region

• Inconsistent with inclusive RAA

Punch throughs• Little E-loss/multiple

scattering

c

L1 L2

a

L1 L2

b

L1 L2

A. Dainese et al, EJPC 38 (2005) 461


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Lack of Near Side Broadening at High pT

At higher pT, no increase with centrality

Consistent with the picture of production at the corona.


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Reaction Plane Dependence at Higher pT

High trigger pT

High associated pT


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RP Dependence of Near Angle Widths

Near angle widths are flat as a function of reaction plane – still consistent with production at the corona


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Comparison of and 0 Triggers

Near-side widths are consistent between -triggered and 0-triggered.


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-h Near Side Yields

PRL 94 232301 (2005)

~50% direct photons above 5 GeV/c in the most central.

Also seen in -triggered near side yield ratio to 0 -triggered yield.

Trigger 5-10 GeV/c

h 5-10 GeV/c

J. Jin (#76)

Documents

Jet Correlations at RHIC