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David Winter

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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David Winter

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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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 p± p± PHENIX Preliminary David Winter Jets and High-pt Azimuthal Correlations in PHENIX 11

  12. 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

  13. Backup Slides David Winter Jets and High-pt Azimuthal Correlations in PHENIX 13

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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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