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


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


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


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


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))


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.


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


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


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


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


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


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


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


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


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%


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….?


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


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


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


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


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?

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

Documents

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