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Collision Geometry and Suppression What is happening at high pT?

High pT. @. Collision Geometry and Suppression What is happening at high pT?. Jiangyong Jia. State University of NewYork at StonyBrook. Outline. Introduction Jet tomography of Quark Matter Quick overview of high pT results from 200GeV

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Collision Geometry and Suppression What is happening at high pT?

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  1. High pT @ Collision Geometry and SuppressionWhat is happening at high pT? Jiangyong Jia State University of NewYork at StonyBrook

  2. Outline • Introduction • Jet tomography of Quark Matter • Quick overview of high pT results from 200GeV • Jet-like angular correlation and spectra shape at high pt • High pT suppression continues to highest pT measured • Large v2 at high pT • Mysterious scaling behavior for baryon at high pt • Comparison with simple geometrical model calculation. • Consistent with high pT yield and di-jet suppression • Insufficient to describe v2 and baryon yield • Conclusion Jiangyong Jia

  3. e+ e- q e+ q e- DELPHI RHIC Jets — a Unique Observable for Heavy Ion Physics • jet example: e+e- annihilation into two ~50 GeV jets • jet cross section can be calculated in pQCD for nucleon-nucleon collisions • jets are “calibrated” probe for dense nuclear matter created at RHIC Jiangyong Jia

  4. schematic view of jet production jet production in quark matter jet production in quark matter hadrons hadrons hadrons leading particle leading particle leading particle q q q q q q hadrons hadrons leading particle leading particle Positron Emission Tomography of the Brain Jets—New Penetrating Probe at RHIC • jets are important particle production mechanism at RHIC energies • hard to observe directly in A-A collisions • indirect measurements through • high pT leading particles • azimuthal correlation • in colored “quark matter” partons expected to lose significant energy via gluon bremsstrahlung • attenuation or absorption of jets “jet quenching” • suppression of high pT hadrons • modification of angular correlation • changes of particle composition jet tomography of quark matter Jiangyong Jia

  5. raw differential yields 2-4 GeV PHENIX Preliminary  20-40% Pair distribution Subtracted distribution Mixed distribution Direct evidence of jets • Leading particle + angular correlation Both STAR and PHENIX identify the jet signal • jet like near angle correlation for p+p and Au+Au • Similar width(STAR,PHENIX) • Similar +/- ratio(STAR) • jet fragmentation not modified much? STAR Preliminary Au+Au @ 200 GeV/c 4<pT(trig)<6 GeV/c 2<pT(assoc.)<pT(trig) Jiangyong Jia

  6. ? The yield per trigger • Compare the yield per trigger for f ~0 and f ~p • (Au+Au – flow) / p+p per trigger. • Near angle ~ 1, pT>4 GeV/c, large fraction come from jet. • Back angle correlation decrease with centrality Disappearance of away side jet. • Away side jet are absorbed or mono-jet production? Jiangyong Jia

  7. Preliminary sNN = 200 GeV Preliminary sNN = 200 GeV Charged Hadron Spectra 200 GeV results from all experiments Jiangyong Jia

  8. Charge spectra shape at high pT • Inverse slope increase with pT • Spectra is more power law • <pTtrunc> = pT - pTmin as function of centrality • Nearly flat at high pT Slope~constant at high pT Low pT ‘flow’ pattern Jiangyong Jia

  9. 3 1 Preliminary sNN = 200 GeV Charge spectra shape at high pT • Inverse slope increase with pT • Spectra is more power law • <pTtrunc> = pT - pTmin as function of centrality • Nearly flat at high pT • AuAu Yield 200GeV/130GeV • Compare UA1(200)/Extrap(130) for || < 0.5(blue lines) • Consistent with pQCD calculation? • pT>4 ~5 GeV/c are jet like Jiangyong Jia

  10. Centrality dependence of high pT suppression • But when we compare with pp, jet production are strongly suppressed • Suppression continues decrease as function of centrality • Charged : factor ~3.5 from peripheral to central • p0 : factor ~5 from peripheral to central • Interesting to see STAR data on Ks and L Nuclear Modification Factor as a function of Npart Binary-scaled yield as a function of Npart PHENIX Preliminary 4 < pT < 6 GeV/c h+ + h- p0 5 3.5 Jiangyong Jia

  11. High pt particles have strong anisotropical flow! • Both STAR and PHENIX showed v2 saturates finite value at high pT • Hydro : v2 created by pressure, only applicable to low pt (<3GeV/c) • Saturation : insufficient to produce v2 • To produce v2, jets have to be strongly influenced by geometry. This qualitatively goes in the direction of jet quenching • Different energy loss along different path—jet tomography • But current models in market are not enough to produce observed v2 • Decrease at high pT • Sensitive to geometrical profile STAR preliminary M. Gyulassy, I. Vitev and X.N. Wang PRL 86 (2001) 2537 Cylindrical Woods-Saxon Jiangyong Jia

  12. At medium pt, particle compositions are very different from elementary collisions • p/p ratio for AuAu at pT>2GeV/c • ~ 1 in central collisions • ~ 0.4 in peripheral collisions • ~ 20% lower for anti-proton • Above gluon jet value Not normal fragmentation Jiangyong Jia

  13. STAR h++h- p p0 k p+pbar PHENIX Identified particle suppression • Suppression behaviors are very different at medium pt • If suppressions merge at high pt, particle composition will be similar to peripheral collision— like pp • What mechanism affects 2-5GeV/c region? Flow? Baryon transport? Jet Suppression + Quark recombination? Note that there are difference in centrality selection PHENIX curve just show the trend and can have large uncertainty at high pt Jiangyong Jia

  14. Jet Suppression + Quark recombination? • Fragmentation : minijet partons combine with q,qbar from vacuum to form hadron • Recombination: minijet partons combine with q,qbar from QGP soup • Pt<4GeV/c dominated by recombination — p/p anomaly. • Pt>6GeV/c dominated by fragmentation — particle composition like pp Fragmentation Recombination By B.Muller. et al. nucl-th/0301087 V.Creco. et al. nucl-th/0301093 Jiangyong Jia

  15. however • Flow, baryon transport, or recombination are not jets! • STAR’s correlation measurement is in favor of jets even in 3-4GeV/c region • Need to better quantify how much contribution are from jets in these pt range and study PID dependence of the angular correlation Jiangyong Jia

  16. ? What do we learn? • High pt particle production are really hard — jets • Strong centrality dependence of suppression, v2, away side jets at high pT • Suggestive of “surface emission” of jets or mono-jet production? • In qualitative agreement with jet quenching model • Saturation model is insufficient to produce large v2 • Anomalous proton/L yield at medium pt 2-4GeV/c • Soft or hard or in between? • Back to back correlation using identified leading particle should be able to tell us whether they are from jets. • At pt>5 GeV/c particle composition might approach composition for pp • Jet suppression + quark recombination Inspired by E. Shuryak Phys.Rev. C66 (2002) 027902 • Which effect can be explained by jet absorption and collision geometry? • Consistent with high pT yield and di-jet suppression. • Insufficient to describe v2 Jiangyong Jia

  17. Simple Toy Geometrical Model for Jet absorption • Jets are absorbed in overlap region according to • Density of matter in transverse plane determined by participant density • Azimuth isotropic di-jets production according to binary collision profile • Hadron spectra are related to jet distribution via parton-hadron duality r~ rNpart rNcoll Jiangyong Jia

  18. 0-5% 75-80% Density distribution calculated from glauber model Woods-saxon nuclear density profile rNpart rNcoll Jiangyong Jia

  19. Model Assumptions to Compare with Data • Model is simplistic and can only describes main features of geometry • Assume all particles above 4 GeV/c from jets • Assume jets are back-to-back • Ignore the fragmentation • Contains no pT and s and flavor dependence • Try different kind of absorption : •  is the only free parameter • Adjust absorption strength k to reproduce suppression factor of 3.5(charged) and 5(p0) in most central collisions. • Predict centrality dependence of yield suppression • Predict centrality dependence of di-jet suppression • Predict centrality dependence of v2 Normal nuclear absorption Energy loss style absorption Absorption + expansion, l0 ~ 0.2 fm Jiangyong Jia

  20. Scaling behavior of the yields • Qualitatively describe the centrality dependence of the yield • Not sensitive to the absorption pattern Ncoll Npart/2 • h, 4-8 GeV/c • p0, 4.5-5 GeV/c Solid line factor 3.5, dash line factor 5 Jiangyong Jia

  21. Centrality dependence of back-back jets • Compare STAR back-back jet measurement for 4 <pT<6 GeV/c • By construction, same side jet will always be 1 • Qualitatively describe the centrality dependence of the away side Jiangyong Jia

  22. Centrality dependence of v2 • NB: in these models,v2 are purely geometrical origin, does not consider detailed modification of momentum distribution • Geometrical anisotropy is insufficient to produce observed v2 by jet absorption • V2 is sensitive to absorption model, smallest for longitudinal expanding source • V2 will increase using hard sphere or cylindrical nuclear profile, but unphysical Jiangyong Jia

  23. Suppression factor for 0-5% centrality • V2 for 50-55% centrality Away side jet for 0-5% centrality Varying  ws profile • Maximum v2 produce by surface. • Different geometrical profile have different geometrical limit. • v2 is below geometrical limit at experimental observed suppression value • Geometrical limit for WS profile is less than observed v2 hard sphere profile cylindrical profile For sphere, surface volume is S. Voloshin Jiangyong Jia

  24. Conclusion • Exciting high pT results from 200GeV AuAu • Direct observation of jets • Strong high pT suppression and suppression of away side jet • Qualitatively consistent with jet quenching and saturation model • Puzzle1 : Large v2 at high pT • Puzzle2: High pT proton and L • Binary scaling between 2-4GeV/c • Mysterious particle composition at same pt range. • Jet suppression + quark recombination • Jet absorption gives characteristic centrality dependence of observables • Consistent with high pT yield and di-jets suppression • Insufficient to describe v2 and proton yield Jiangyong Jia

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