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Jet Correlations

Jet Correlations. Mike Miller (Yale University). Why Jets?. k T : “Radiative Corrections” pre- and post-scattering di-jet: . In QCD Medium Additional k T Significant energy loss? high p T suppression Sensitive to color properties of medium. “So, why jets?”.

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Jet Correlations

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  1. Jet Correlations Mike Miller (Yale University)

  2. Why Jets? • kT: “Radiative Corrections” • pre- and post-scattering • di-jet:  • In QCD Medium • Additional kT • Significant energy loss? high pT suppression • Sensitive to color properties of medium “So, why jets?” • Hard probeearly time • Calculable: pQCD • Abundant at RHIC, LHC

  3. Moment Analysis of QCD Matter I. Vitev, nucl-th/0308028 Induced Gluon Radiation • ~collinear gluons in cone • “Softened” fragmentation Gyulassy et al., nucl-th/0302077

  4. Partonic vs. Hadronic Mechanisms Hottest Questions: • Fragment inside/outside of medium? • Partonic vs. hadronic model of Final State interaction? A Better Question: • To what degree do partonic and hadronic interactions contribute to quenching? • Discussion only recently started!

  5. 4 Ways to “Skin a Cat Jet” “Trigger”  = 0 Adler et al., PRL90:082302 (2003), STAR away-side trigger near-side • 1) Integral Distributions: • <pT>, <Nch> • 2) Single Particle Spectra: • d/dpT  RAA, RdA • 3) 2-Particle Correlations: • dN/d() • 4) Jet Reconstruction: • d/dET, Frag. Func.

  6. Disappearance of the away-side Adams et al., Phys. Rev. Let. 91 (2003) • d+Au • 2-jets ppdAuAuAu Near side jet “identical” Disappearance (at mid-rapidity) is dominated by final state effect(s)! Jet Quenching 2nd order correlations due to elliptic flow of entire event competing background Adler et al., PRL90:082302 (2003), STAR • p+p • 2-jets 1/NtriggerdN/d() • Peripheral Au+Au • 2-jets di-hadron • Central Au+Au • 1-jet! Background subtracted

  7. Initial state effects? What should 2-particle correlation look like? Partonic/nuclear kT jT Measurable at SPS? Final state energy loss? Baryons vs. Mesons? PID? Background subtraction? Jets correlated with reaction plane? And many more… Questions Raised at QM02 Discussed in parallel This talk

  8. Path Length Dependence Measured Reflected Suppression larger out-of-plane Background Subtracted See J. Bielcikova et al., (nucl-ex/0311007) for background derivation di-hadron, 20-60% Central STAR Preliminary Out-of-plane In-plane K. Filimonov DNP03

  9. Path Length Dependence Background Subtracted See J. Bielcikova et al., (nucl-ex/0311007) for background derivation di-hadron, 20-40% Central Out-of-plane In-plane Quenching: Consistent with path length Dependence

  10. Jet Fragmentation: “Shape” hadron hadron di-hadron Reconstructed jets Jet “width” Jet-coplanarity parton parton

  11. kT, jTat RHIC from p+p Data Statistical Errors Only di-hadron J. Rak, Wed. J. Rak, DNP03 PHENIX preliminary Df near-side away-side

  12. kT, jTat RHIC from p+p Data STAR Preliminary p+p d+Au T. Henry, Fri. p 2p 0 Statistical Errors Only PHENIX preliminary |jTy| = 35911 MeV/c |kTy| = 96449 MeV/c di-hadron Good agreement with previous measurements: PLB97 (1980)163 PRD 59 (1999) 074007 J. Rak, DNP03 PHENIX preliminary kT, jT from p+p, d+Au, Au+Au from “0”-hadron, di-hadron, jet, di-jet Friday:Completing the reference measurements!

  13. Au+Au near-side: Jet-like at all centralities? di-hadron correlations -near <|jTy|>=400 MeV PHENIX PRELIMINARY Follows fragmentation prediction: Yes, but… widens in  (see c07)

  14. Quenching at SPS? No, but… Broadening at RHIC! width yield Away side correlations: • Present at all centralities • Width broadens with centrality Near angle correlations: • Present at all centralities • Consistent with fragmentation + WA98 Spectra: RAA>1 See p36 charged-pion pairs mid-central central pT>1.2 GeV/c Accepted by PRL, nucl-ex/0303014, CERES

  15. Quenching at SPS? Where is the enhancement at RHIC?

  16. Di-Hadrons at “all” pT See F. Wang, Fri. QM04 di-hadron correlations • + mixed event background subtraction • + elliptic flow background subtraction • Study “fragmentation” in p+p, Au+Au • Full range in pT • Transport from high-pT to low-pT? • Change in jet “size”? Study pT distribution in near- and away-side jet cones

  17. Di-Hadrons at “all” pT p+p 40-80% Au+Au 0-5% Au+Au di-hadron correlations Near-Side Away-Side F. Wang, DNP03 STAR Preliminary See F. Wang Friday

  18. pT Distribution in Near-Side Jet p+p 40-80% Au+Au 0-5% Au+Au Near-Side 0-5% / pp  2 40-80% / pp  1.2 “enhancement” di-hadron correlations Near-Side F. Wang, DNP03 STAR Preliminary ratio AuAu/pp See F. Wang Friday

  19. pT Distribution in Away-Side Jet enhanced p+p 40-80% Au+Au 0-5% Au+Au Near-Side 0-5% / pp  2 40-80% / pp  1.2 “enhancement” suppressed Away-Side (pT>2) AuAu/pp <1 “Disappearance” Away-Side (pT<2) AuAu/pp >1 “Enhancement!” di-hadron correlations Near-Side Away-Side F. Wang, DNP03 STAR Preliminary ratio ratio AuAu/pp See F. Wang Friday

  20. Is The Away-Side Jet-Like? STAR Preliminary p+p Au+Au 0-5% (1/Ntrig) dN/d(Df) Background subtracted Background subtracted Df Df Away-side looks jet-like in p+p, not central Au+Au! So what’s going on? See F. Wang Friday

  21. Is The Away-Side Jet-Like? free fit Borghini et al., nucl-th/0004026 Momentum conservation: stat. mom. conserv. stat. mom.conserv. STAR Preliminary Fit to near side: const. + gaussian + Borghini-cos(fixed) p+p Au+Au 0-5% (1/Ntrig) dN/d(Df) Background subtracted Background subtracted Df Df Amplitude: -Depends on pT “window” -Can be tested -Work in progress (see ) See F. Wang Friday

  22. What could this mean? free fit stat. mom. conserv. stat. mom.conserv. Away-side energy re-distributed over many particles, broad in angle, but it is still there! STAR Preliminary Fit to near side: const. + gaussian + Borghini-cos(fixed) p+p Au+Au 0-5% (1/Ntrig) dN/d(Df) Background subtracted Background subtracted Df Df Optimist: Maybe the most exciting result yet! Pessimist: A fundamentally boring result…Another background See F. Wang Friday

  23. Conclusions • 2-particle correlations • Successful measure of hard-scattering, fragmentation • Away-side quenching in central Au+Au • Indicative of strong final state interactions • In/out-of plane consistent with path length dependence • Semi-hard scattering at SPS • Present at all centralities • Large away-side broadening • Near-side correlations in Au+Au • Consistent with fragmentation at all centralities • pT distribution in near- and away-side jet cones • Consistent with modified fragmentation?

  24. The Real Conclusions • 2-particle correlations • Robust jet probe from p+p to central Au+Au • QM02Disappearance of away-side jet • QM04Finding the “lost-energy” on the away-side • Qualitative consistency between PHENIX and STAR • “Transport” from high pT low pT • But… away-side has lost jet-like shape!

  25. Future Directions at RHIC • Minimize ambiguities, sensitivities • Higher trigger pT  only jet production • higher trigger pT  smaller kT effects • Higher statistics test of path length dependence • Away-side pT “transport” • d+Au? • Trigger-pT dependence? • Punch through above momentum conservation? • Calibrate the jet-energy scale: photon-jet • Mass effect: heavy quarks vs. light quarks E • Color charge: quark vs. gluon jets?

  26. Old…

  27. Back side correlations between charged hadrons: 3.7 GeV < PT trigger <4.5 GeV 5.4 GeV < PT trigger <6.5 GeV 2.5 GeV < PT associated <3.7 GeV 2.5 GeV < PT associated <3.7 GeV Trigger PT Fig. 12 Same side and back side as function of Trigger PT 1/Ntrigger*dN/d(∆Φ) 1/Ntrigger*dN/d(∆Φ) same side is calculated by integrating the Gaussian component and the back side is calculated by integrated the cosine component. Notices that there is a back side signal for the higher PTcorrelation ∆Φ (radians) ∆Φ (radians) 4.5 GeV < PT trigger <5.4 GeV 6.5 GeV < PT trigger <10 GeV 2.5 GeV < PT associated <3.7 GeV 2.5 GeV < PT associated <3.7 GeV 1/Ntrigger*dN/d(∆Φ) 1/Ntrigger*dN/d(∆Φ) Fig. 13 Trigger PT ∆Φ (radians) ∆Φ (radians) In Fig.13. The fitting Ccos is compared to estimation due to the momentum conservation[6]. Fig. 11 Charged Hadrons correlations for different trigger PTrange Fitting Function:

  28. Path Length Dependence Out-of-plane In-plane Measured Reflected Suppression larger out-of-plane Background Subtracted See J. Bielcikova et al., (nucl-ex/0311007) for background derivation di-hadron, 20-60% Central STAR Preliminary K. Filimonov DNP03 Quenching: Consistent with path length Dependence!

  29. Path Length Dependence Out-of-plane Measured Reflected Suppression larger out-of-plane Background Subtracted See J. Bielcikova et al., (nucl-ex/0311007) for background derivation di-hadron, 20-60% Central STAR Preliminary In-plane K. Filimonov DNP03 Quenching: Consistent with path length Dependence!

  30. Away-Side Quenching (2002) • p+p • 2-jets • Peripheral Au+Au • 2-jets 2nd order correlations due to elliptic flow of entire event competing background Adler et al., PRL90:082302 (2003), STAR 1/NtriggerdN/d() di-hadron • Central Au+Au • 1-jet! Background subtracted

  31. Away-Side Quenching (2002) • p+p • 2-jets • Peripheral Au+Au • 2-jets 2nd order correlations due to elliptic flow of entire event competing background Adler et al., PRL90:082302 (2003), STAR 1/NtriggerdN/d() di-hadron • Central Au+Au • 1-jet! Background subtracted

  32. Conclusions • 2-particle correlations • Successful measure of hard-scattering, fragmentation • Jet-like correlations at all centralities in Au+Au • Away-side correlations • pT distribution in near- and away-side jet cones • Consistent with modified fragmentation?

  33. Unraveling final state mechanisms at RHIC • Minimize ambiguities, sensitivities • Higher trigger pT  only jet production • higher trigger pT  smaller kT effects • Higher statistics test of path length dependence • Away-side pT “transport” • d+Au? • Trigger-pT dependence? • Punch through above momentum conservation? • Calibrate the jet-energy scale: photon-jet • Mass effect: heavy quarks vs. light quarks E • Color charge: quark vs. gluon jets?

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