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Jets and High-p T (Di-hadron) Correlations in PHENIX Lake Louise Winter Institute 2005 Lake Louise, Alberta CA. David Winter. Outline. RHIC and PHENIX The nuclear medium and jet modifications Correlation Functions Hard scattering Near (Same)-side and Away-side (di-jet) correlations

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Jets and High-pT (Di-hadron) Correlations in PHENIXLake Louise Winter Institute 2005Lake Louise, Alberta CA

David Winter


Outline
Outline

  • RHIC and PHENIX

  • The nuclear medium and jet modifications

    • Correlation Functions

    • Hard scattering

    • Near (Same)-side and Away-side (di-jet) correlations

  • Jet modifications in Heavy-Ion Collisions

  • Future measurement technique

  • Summary

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 2


Rhic and phenix

Event characterization detectors in center

Two central arms for measuring hadrons, photons and electrons

Two forward arms for measuring muons

RHIC and PHENIX

  • Brookhaven National Laboratory

    • 70 mi from Manhattan

  • Two rings / 3.83 km circumference

  • Capable of colliding ~ any nuclear species on ~ any other species

  • Energy:

    • 500 GeV for p-p

    • 200 GeV for Au-Au (per N-N collision)

  • Luminosity

    • Au-Au: 2 x 1026 cm-2 s-1

    • p-p : 2 x 1032 cm-2 s-1 (polarized)

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 3


The nuclear medium

d+Au

p0

x4-5

suppression

Au+Au

The Nuclear Medium

  • Nuclear modification factor

  • Multiple scattering in the medium results in kT broadening

  • Thought to be source of Cronin Enhancement

  • Nuclear modification factor

  • Medium-induced energy loss?

Let’s go beyond single-particle observables -- What can study of jet observables tell us?

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 4


Correlation functions

Same-event pairs

3.0<pT<6.0

Mixed-event pairs

Correct for limited h acceptance and single-particle efficiency

Observed yield per trigger

Real yield per trigger particle

Correlation Functions

  • Azimuthal correlations are an alternative approach to jet studies where full reconstruction is impractical

  • Df is f between leading and associated particles

  • Correlation functions typically defined as :

p+p h± Correlation Function

Fit with: 2 Gaussians + Constant Bg term

  • Conditional Yields can be extracted from correlation when properly normalized and corrected for acceptance and efficiency:

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 5


Hard scattering

jet

Hard-scattering

  • Partons scatter with large Q2

  • Outgoing partons fragment into cone of hadrons

  • Parameters of interest

    • Spread of particles around jet axis (jT)

    • Acoplanarity of back-to-back jets (kT)

    • Hadronic spectrum (Frag. Func. D(z))

Leading hadron

Transverse plane:

jT

Partons have intrinsic transverse momentum kT:

jT = hadron’s momentum transverse to the jet axis

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 6


Near side correlation
Near-side Correlation

  • Leading (highest pT) “Trigger” particle used as estimator for jet axis

  • “Near-Side”: particles from same jet will be correlated in a peak around Df ~ 0

  • Simple relations can be derived (assume pT,trig >> jTy):

Projection onto transverse plane

ftjtrigger-parton

fajassociated-parton

Assume angles are statistically independent

Near-side peak

Note there are corrections to these expressions, but they are small

See J. Jia, nucl-ex/0409024 for further details

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 7


Away side correlation
Away-side Correlation

  • “Away-Side”: particles from (nearly) back-back jets form a peak at Df ~ p

  • Average di-jet acoplanarity kT can be extracted from angles btn hadrons:

Projection onto transverse plane

ftjtrigger-parton

fajassociated-parton

fjj parton-parton

Assume angles are statistically independent

Away-side peak

Again, there are small corrections…

cf. nucl-ex/0409024

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 8


Jet modifications
Jet Modifications

  • One of the most exciting results at RHIC has been the behavior of the away-side peak in azimuthal correlations

PHENIX Preliminary

Courtesy W.Holzmann, 21st WWND

There is little if any difference between p+p, d+Au away-side peak (esp. at high pT), but the broadening of away-side peak in Au+Au is striking!

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 9


K t comparison

p+p

p+A

A+A

kT comparison

  • Comparison of p+p/d+Au/Au+Au allows separation of medium effects

  • We see little, if any, difference between kT of p+p & d+Au

    • Disappearance of away-side in Au+Au complicates this comparison...

PHENIX Preliminary

p0

PHENIX Preliminary

PHENIX Preliminary

1d RMS kTztrig product using p0 and p± as triggers

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 10


Future measurements
Future Measurements

  • Correlation method requires rough binning in pT

    • Observables extracted as averages within these rough bins

    • Corresponding bin widths also need to be “extracted”

  • Alternatively, statistical weighting can be used to extract distributions directly

  • Example:

    • Away-side dN/dxE sensitive to the fragmentation function (e.g.. at high-pT, slopes of dN/dxE and D(z) are related)

  • See upcoming d+Au Correlations paper, to be submitted to PRC

PHENIX Preliminary

PHENIX Preliminary

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 11


Summary
Summary

  • Traditional jet-finding methods are unpractical in RHIC collisions. Azimuthal Correlations make jet studies possible this high multiplicity environment

  • Study of the jet structure (jT, kT) allows us to distinguish between vacuum, initial-state, and final-state effects

  • Evolution of jet structure from pp to AuAu collisions

    • No difference btn pp & dAu, but broadening of di-jet peak in AuAu

  • Look for upcoming publications

    • (nucl-ex/0410003) “Formation of dense partonic matter in relativistic heavy-ion nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration”

    • (nucl-ex/0408007) “Jet Structure of Baryon Excess in Au+Au collisions at sNN = 200 GeV”

    • (nucl-ex/0404024) J. Jia, HotQuarks04 proceedings

    • Jets and correlations: p+p, d+Au, and Au+Au

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 12


Backup Slides

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 13


Relative gluon quark contrib

qg+gq

qq

Fraction of produced p0s

gg

pT (GeV/c)

Relative Gluon/Quark Contrib.

  • In current measurement, p0s mainly produced by gg and qg scattering

Kretzler,

hep-ph/0410219

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 14


Is it hard scattering

Au+Au p0 + X (peripheral)

Peripheral spectra agree well with p+p

(data & pQCD) scaled by Ncoll

Is It Hard-scattering?

  • Single-particle spectrum and QCD predictions

Au+Au p0 + X (central)

PHENIX Collab.

PRL91, 241803

hep-ex/0304038

Strong suppression

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 15


Correlations example
Correlations Example

d+Au s=200 GeV

5<pT,trig<10 GeV/c

2<pT,assoc<3 GeV/c

Same-event

Mixed-event

Mimics acceptance

Same / Mixed

Fully-corrected

Acceptance divides out

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 16


Comparison with pythia

Red: data

Blue: pythia

5<pT,trig<6

Comparison with Pythia

p+p s=200 GeV (Run3)

Pythia results agree within ~20%

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 17


How high is high multiplicity
How high is high (multiplicity)?

  • Central events: Npart ~ 300

  • dNch/dh ~ 450

  • Most particles are p’s

    dN/dh ~ 670

David Winter

Jets and High-pt Azimuthal Correlations in PHENIX 18


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