nov 2001 craig ogilvie 1 angular correlations at high pt: craig ogilvie for the phenix collaboration...

Nov 2001 Craig Ogilvie 1

Angular Correlations at High pt:Craig Ogilvie for the Phenix Collaboration

Energy-loss:increased medium-induced

gluon-radiation

hadron distributionsoftened, broadened?

hard-scatteredparton during Au+Au

hard-scatteredparton from e.g. p+p

gluon radiation

cone of hadrons

p p

Nov 2001 Craig Ogilvie 2

Correlations

2-particle angular correlation functions

Medium-induced gluon emission within QGP – predicted to be broad angles (>10 deg shown later in talk)– fragmentation angular-width may be broader – correlations at small may be broadened

study correlations from peripheral => central reactions– complementary to single-particle pt spectra and +hadron

back-to-back correlations.

)(N

)(N)C(

events mixed

real

21

Nov 2001 Craig Ogilvie 3

Outline

Examples of angular correlation data from p+p, e+p Angle correlations from Au+Au at s1/2 = 130 AGeV

– pt dependence – centrality dependence

Simulations of possible sources of angular correlations – work in progress

Measurements for this year-2 Which observable makes a link between experiment and theory

Nov 2001 Craig Ogilvie 4

ISR Data p+p s1/2 = 62 GeV

CCOR Collaboration (M. J. Tannenbaum) Trigger particle (neutral) with pt > 7.0 GeV/c

– azimuthal distribution of charged particles– strong back-to-back and near-side emission

back-to-backnear-side

Nov 2001 Craig Ogilvie 5

Transverse Momentum Within Jet

jT transverse momentum with respect to “jet” axis

Trigger PTjTJetJet

PT jT

PoutkT

<| jT|> = 400 MeV/c, use as one check for what we observe in HI

CCOR CollaborationPhys. Lett. 97B, 163 (1980))

Nov 2001 Craig Ogilvie 6

HERA e+p Angular Distribution Within a Jet

Within a jet Yield of two particles

separated by angle 12

Transformed to

)/)sin(ln()/ln( 12

coneAngleP

coneAngle

Yield peaked atsmall 12 ,

More complicated variablechosen to match expt. with what can be calculated.

Nov 2001 Craig Ogilvie 7

Au+Au s1/2 = 130 AGeV

1.5M events, summer 2000 Phenix data -20 < collision vertex < 20 cm Central arm tracks

– momenta from drift chamber tracks– 1 < pt < 2.5 GeV/c

Centrality cuts expressed as a % of int=7.2b

– (zero degree energy) vs (charge in beam counters) Correlation functions

– mixed events from similar beam-vertex, centrality– 2-track acceptance cuts on both real, mixed pairs

Nov 2001 Craig Ogilvie 8

Correlations Presented Today

Both hadrons between 1< pt < 2.5 GeV/c Two correlations formed

– both hadrons in west arm of PHENIX– one hadron in east, west arm of PHENIX

Studied as a function of pt, centrality

)(N

)(N)C(

events mixed

real

21

Nov 2001 Craig Ogilvie 9

Possible Causes of Angular Correlation

Elliptic flow, jet fragmentation produce azimuthal correlations Analysis challenge to extract both

– jet fragmentation extends to narrow angles» near-side ~ 0-30 deg

– flow extends over full range with a harmonic oscillation

Nov 2001 Craig Ogilvie 10

40-92% Centrality, 1.0 < pt < 2.5 GeV/c

Near-angle correlation fallsmore steeply than back-to-back correlation

Add correlations by ensuringsymmetry near 90o

Both hadrons in west arm

One hadron in west arm,other in east arm

Nov 2001 Craig Ogilvie 11

1<pt<2.5 GeV/c (40-92%)

offset)2cos(a

2)/(2

1

widtheC

offset)2cos(a Csymmetric (elliptic flow) fit (poor)

stronger near-anglecorrelation than back-to-back

phenix preliminary

phenix preliminary

Nov 2001 Craig Ogilvie 12

Centrality Dependence

40 to 92%

0 to 5%

1) near-angle correlation in central reactions: broader, smaller amplitude

2) elliptic flow v.small in central reactions

phenix preliminary

phenix preliminary

1< pt < 2.5 GeV/c

Nov 2001 Craig Ogilvie 13

Au+Au Centrality Dependence

offset)2cos(a2)/(

2

1

width

eC

npart

width of correlation broadensfor more central reactions

systematic errors: how fit changes for different normalization criteria

1< pt < 2.5 GeV/cphenix preliminary

Nov 2001 Craig Ogilvie 14

First-Order Comparison to p+p

npart

GeV/c 34.0

GeV/c 4.1)2

20sin(||

)2

sin(||

0

T

Thadron

T

j

pangleWidth

j

for peripheral data, on average both hadrons comparable pt

pp running this year impt.

phenix preliminary

Nov 2001 Craig Ogilvie 15

Pt Dependence of Correlation

Fit to full function, display only offset)2cos(osc

near-anglecorrelation strongestfor high-pt

1.0 < pt < 2.5 GeV/c

0.5 < pt < 1.0 GeV/c

0.2 < pt < 0.5 GeV/c

central 40 –92%

Nov 2001 Craig Ogilvie 16

Feasible Causes of Near-Angle Correlation(next slides)

Resonance decay leading to correlated particles

Decay of K0s (in progress, not shown today)

Fragmentation of high-pt parton Other….?

Nov 2001 Craig Ogilvie 17

1) UrQMD Au+Au2) tag all resonances3) decay, apply pt cut

correlation strength 0.001due to decay of resonances5-10 times smaller than data

Resonance Study

1.0 < pt < 2.5 GeV/c|| <0.35

Nov 2001 Craig Ogilvie 18

PYTHIA 6p+p at s1/2 = 130 GeV

Hard-Processes

1.0 < pt < 2.5 GeV/c, || <0.35

C

C

near-angle correlation strongerthan back-to-back

small acceptance reducesback-to-back acceptance fordifferent x1, x2

width of 0.35 rad = 20 degcomparable to periph. Au+Au<pt> scattered parton ~ 3GeV/c

Nov 2001 Craig Ogilvie 19

Possible Reach With Year-2 Data

p+p baseline data 30-100 times more Au+Au statistics Higher-pt reach, pt > 5 GeV/c Asymmetric pt cuts, pt1 > 5 GeV/c, pt2 > 2 GeV/c

– better match to transverse momentum within jet Tag PID of leading hadron, correlate with all others

– 0 correlated with others» heading towards correlated with others

– leading p or p» speculative possible sensitivity to gluon vs quark jets

Nov 2001 Craig Ogilvie 20

Making Connection With E-Loss Theory

Recent calculations, e.g. Baier, Schiff, Zakharov, calculate how much energy is radiated to outside a given cone angle

250 GeV jet1/3 of E is radiated > 20o

Can this formalism calc C()?Do we need new observablethat expt and theory can both use

Ann. Rev. Nucl. Sci 2000, 50, p37

Nov 2001 Craig Ogilvie 21

Summary

High-pt near-angle correlations slightly stronger than back-angle correlations – well reproduced by Gaussian superimposed on oscillation– width of correlation broadens for more central reactions

Possible causes of near-angle correlation– decay of resonances

» factor of 5-10 smaller than observed signal

– weak decay of K0s , in progress

– fragmenting hard-physics» needs higher pt reach to be convincing» in this scenario, increasing width, broader fragmentation» open question: medium-induced gluon emission?