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Andr é Mischke for the STAR Collaboration

Amsterdam. Recent STAR results on hard probes. Andr é Mischke for the STAR Collaboration. Rencontres de Moriond, La Thuile, Italy, March 18-25, 2006. modified. hadronic. partonic. ?. q. modified. Probing QCD matter with jets. Parton scattering in the early stage

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Andr é Mischke for the STAR Collaboration

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  1. Amsterdam Recent STAR results on hard probes André Mischke for the STAR Collaboration Rencontres de Moriond, La Thuile, Italy, March 18-25, 2006

  2. modified hadronic partonic ? q modified Probing QCD matter with jets • Parton scattering in the early stage • of the collision • Traverse through the medium and • interact strongly • In-medium fragmentation • Model expectations: • - Collisional energy loss (small effect ?!) • - Partonic energy loss via medium induced gluon • Bremsstrahlung (jet-quenching) • - Jet broadening due to parton rescattering • - Modification of the FF (softening) • Energy loss sensitive to the medium density q q q q Andre Mischke (Utrecht)

  3. BRAHMS PHOBOS RHIC PHENIX STAR The RHIC accelerator at BNL STAR detector • Two concentric rings • 3.8 km circumference • Counter-rotating ion • beams • 4 experiments • Au+Au @ sNN = 19.6, 62.4, 130, 200 GeV • Cu+Cu @ sNN = 200 GeV • - d+Au @ sNN = 200 GeV • - polarized p+p @ s = 200 GeV Andre Mischke (Utrecht)

  4. RHIC performance Ldt = 241 b-1 Most 200 GeV Au+Au results are from the FY04 run Andre Mischke (Utrecht)

  5. 8.2m 7.9m 20.7m The STAR detector Solenoidal Tracker at RHIC Large acceptance magnetic spectrometer • Particle identification and tracking (TPC, ToF, SVT) • Energy measurement (EMC) Andre Mischke (Utrecht)

  6. Au+Au  ??? ? Jet measurements in Au+Au sNN = 200 GeV, STAR-TPC profile p+p  jet+jet • Jet-like correlation • Statistical reconstruction using angular correlations Andre Mischke (Utrecht)

  7. Nucl. Phys. A757, 102 (2005) Results so far Inclusive hadron spectra di-hadron correlation factor 4-5 4 < pTtrig < 6 GeV/c pTasso > 2 GeV/c Nuclear modification factor: • Strong high-pT particle suppression • Disappearance of the away-side jet •  Jet quenching is a final state effect •  Initial medium density is high Andre Mischke (Utrecht)

  8. Outline • Inclusive identified particle spectra (particle ratio) • - modification of jet fragmentation • Low-pT recoil and three particle correlation • (Mach-like cones ?) • - jet-medium interplay • Di-hadron correlation at higher pT • - reappearance of the away-side jet Andre Mischke (Utrecht)

  9. Au+Au 0-10% Au+Au 0-10% p+p p+p Identified particle ratios vacuum fragmentation • Significant baryon enhancement in central Au+Au collisions with a maximum around 2-3 GeV/c • Additional effects besides jet fragmentation • Vacuum fragmentation approach at pT > ~6 GeV/c L/K0s Au+Au 0-5% p+p Andre Mischke (Utrecht)

  10. cos(Df) Where does the deposited energy go? 4 < pTtrig < 6 GeV/c pTasso > 2 GeV/c pTasso > 0.15 GeV/c • Suppression of high-pT hadrons  enhancement of low-pT hadrons • Broadening and softening of the recoil distribution momentum • balance shape (cos) Andre Mischke (Utrecht)

  11. Mean-pT of away-side asso. hadrons • Softening of the associate hadrons in the cone opposite to leading trigger hadron • Indication for thermal • equilibration with the bulk medium central Au+Au 4 < pTtrig < 6 GeV/c pTasso > 0.15 GeV/c Andre Mischke (Utrecht)

  12. near Medium away Conical flow near Medium away Deflected jets Indication for Mach-like cones ? • Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315 • Stoecker, Nucl. Phys A750, 121 (2005) • Ruppert and Muller, PLB 618, 123 (2005) Df2 • Does a shock wave form? • Three-particle correlations, two scenarios: • - Conical flow: associated particles may appear on opposite sides of Δφ = π • - Deflected jets: associated particles on the same side of Δφ = π Df1 Df2 Df1 Andre Mischke (Utrecht)

  13. pTtrig = 3-4 GeV/c, pTasso = 1-2 GeV/c 2-particle corr., bg, v2 subtracted near d+Au min-bias Dφ2=φ2-φtrig Medium away Conical flow Au+Au 10% near Dφ2=φ2-φtrig dN2/dΔφ1dΔφ2/Ntrig Medium away Deflected jets Dφ1=φ1-φtrig Three-particle correlations • Elongated along diagonal: kT effect? deflected jets? • Distinctive features of conical flow are not seen in present data within these pT windows. Andre Mischke (Utrecht)

  14. Di-hadron azimuthal correlation at higher pT Large year-4 Au+Au dataset • Correlation peak visible at near- and away-side • Away-side peak is • - finite suppressed • - not broadened • Limits on parton energy loss 8 < pTtrig < 15 GeV/c Andre Mischke (Utrecht)

  15. Width of the away-side peak 8 < pTtrig < 15 GeV/c • Away-side widths similar for central and peripheral collisions • Fragmentation similar as in the vacuum? Andre Mischke (Utrecht)

  16. Away-side yields • Away-side suppression similar to RAA measurement • No zT dependence Andre Mischke (Utrecht)

  17. X-N Wang, PLB 595, 165 (2004)  STAR preliminary Comparison to model prediction • Model (recoil fragmentation) with modified di-hadron fragmentation function • Suppression factor shows no zT dependence • Qualitative but not quantitative agreement with measurement Andre Mischke (Utrecht)

  18. Conclusion • Inclusive hadron spectra and di-hadron correlations • - strong suppression in central Au+Au • - final state modification of jets • Baryon enhancement • - non-perturbative effects dominates at intermediate pT • Low-pT recoil • - away-side correlation widely dispersed • - strong coupling effects of jets to bulk matter • Three particle correlation using intermediate trigger-pT particle • - Mach-cone like patterns not observed in present data •  correlations at higher pT • - reappearance of the away-side jet • - no modification of the fragmentation distribution (width and slope) • - stringent constraints for model descriptions Andre Mischke (Utrecht)

  19. Back-up slides Andre Mischke (Utrecht)

  20. The STAR collaboration 50 institutes from 13 countries, 545 participants Andre Mischke (Utrecht)

  21. Experimental and theoretical challenges in the search for the QGP • Strong evidence for a dense, opaque, non-viscous, pre-hadronic liquid state of matter at RHIC • Open question: do the quarks and gluon reach thermal equilibration with each other in this matter before confinement The STAR collaboration's critical assessment of the evidence from RHIC collisions, Nucl. Phys. A757, 102 (2005) Andre Mischke (Utrecht)

  22. Identified particle RCP • Φ follows mesons at intermediate pT  no mass dependence • All particles consistent for pT larger than ~5 GeV/c • Coalescence of valence quarks? Andre Mischke (Utrecht)

  23. out-of-plane in-plane Azimuthal correlations wrt. to the reaction plane • Parton energy loss depends on the path length traversed • Qualitatively consistent with jet-quenching picture: 4 < pTtrig < 6 GeV/c 2 GeV/c < pTasso < pTtrig Andre Mischke (Utrecht)

  24. Recombination models In vacuofragmentation of a high momentum quark to producehadrons competes with the in mediumrecombinationof lower momentum quarks to produce hadrons Example: • Fragmentation: Dq→h(z) produces • a 6 GeV/c proton from a 10 GeV/c quark • Recombination: • produces a 6 GeV/c proton from two 3 GeV/c quarks • produces a 6 GeV/c proton from three 2 GeV/c quarks Andre Mischke (Utrecht)

  25. STAR preliminary , |h|<1 5-10% 0-5% 20-40% 10-20% 40-60% 60-80% Conical flow pTtrig = 2.5-4.0 GeV/c pTasso = 1.0-2.5 GeV/c Andre Mischke (Utrecht)

  26. syst. error away pT spectra of associate hadrons Andre Mischke (Utrecht)

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