Phantom Jets: the  puzzle and v 2 without hydrodynamics

1. Phantom Jets: the  puzzle and v2without hydrodynamics Rudolph C. Hwa University of Oregon Early Time Dynamics in Heavy Ion Collisions Montreal, July2007

2. Conventional jet structure Phantom jet ? Jets

3. Bielcikova (STAR) 0701047 pT distribution is exponential; thus no contribution from jets  puzzle Blyth (STAR) SQM 06  distribution of associated particles shows what seems like jet structure.

4. The specific problem Phantom jet How phantom jets solve the  puzzle The more general problem v2 without hydrodynamics Do not assume fast thermalization. There is no need to conjecture sQGP; no basis for concluding perfect liquid.

5. J+R     Jet structure R J Putschke, QM06

6. Jet Ridge 3 - 4 Putschke, QM06 Dependence on pT(trig) and pT(assoc)

7.     Bielcikova, QM06 Dependence on particle species

8. Phantom Jet Thus we have a ridge without any significant peak on top. The ridge would not be there without a hard scattering,but it does not appear as a usual jet. is formed bythe s quarks in the ridge, since s quark in the shower is suppressed. Triggering on  is the experimental way to select events to exhibit the properties of phantom jets. But phantom jets of intermediate pT are there with or without  trigger.

9. peak ridge It generatesshower partons outside. The peak is due to thermal-shower recombination in both  and  Recombination of enhanced thermal partons gives rise to the ridge, elongated along  J bg R pT Chiu & Hwa, PRC 72, 034903 (2005) In the case of usual jets,a hard- scattered parton near the surface loses energy to the medium. Power-law behavior is a sign of TS recombination

10.    puzzle can thus be resolved.  and  spectra Exponential  thermal Phantom jets  ridges   has associated particles above background.

11. Hadronization by recombination Hwa&Yang,PRC(2004)

12. Hwa & Yang , PRC(2007) nucl-th/0602024

13.  trigger (thermal s quarks in ridge) T’=0.33 GeV Associated particles (thermal q quarks in ridge)  dist. 6.9 yield H0 our only free parameter.

14. All ridge ! <1% variation (a) H0=0.795 (b) H0=0.790 STAR data nucl-ex/0701047 2.5<pTtrig<4.5 1.5<pTassoc<pTtrig Chiu & Hwa, 0704.2616 The  problem is not a puzzle any more. It leads to 20% change in dN/d and yield.

15. Implications • Even for pT up to 6 GeV/c, one should not think of  as a product of fragmentation of hard partons. Predictions • Ridge height: dNR/d~0.06 • p/ ratio >1 in the ridge for pT>2 GeV/c • similar behavior for -triggered events • Phantom jets and ridges are present, irrespective of  trigger, so long as there are semi-hard partons near the surface to generate enhanced thermal partons.

16. It is an assumption. What if it is regarded as unacceptable? hydrodynamical results high pressure gradient sQGP leads to momentum space asymmetry: v2>0 perfect liquid Azimuthal Anisotropy Conventional approach: hydrodynamical flow requires fast thermalization. 0=0.6 fm/c

17. Relevant physics must be sensitive to the initial configuration (a) Soft physics --- hydrodynamics No commonly accepted mechanism for fast development of pressure gradient (b) Hard physics --- high-pT jet quenching Process too rare at high pT (c) Medium hard physics --- semi-hard scattering Soft enough to have frequent occurrences, hard enough to create intermediate-pT jets at early times.

18. At any given    on average, jet direction is normal to the surface. || <  = cos-1(b/2R) Phantom jets --- ridges Each scattering sends semi-hard partons in random directions If the phantom jets are soft enough, there are many of them, all restricted to || < .

19. pions Hwa&Yang,PRC(2004) Bulk+Ridge partons pions Bulk partons

20. v2 Small pT region

21. “jet” slope ridge slope inclusive slope STAR preliminary Ridge Jet T “Jet”/ridge yield vs. pt,assoc. in central Au+Au STAR preliminary preliminary Au+Au 0-10% preliminary Ridge/Jet yield Putschke HP06 ridge spectrum harder than inclusive h+,- (~ 40-50 MeV in slope parameter)

22. PHENIX 40-50% T=0.28 GeV At small pT The first time that a connection is made between ridge and v2. Use T=45 MeV Get T”=2.12 GeV Max of sin2(b) at =/4 b=√2 R=10 fm centrality 50%

23. 40-50% 30-40% 20-30% 10-20% 5-10% STAR

24. 40-50% 30-40% 20-30% 10-20% 5-10% STAR

25. v2 pT=0.5 GeV/c sin2(b) b v2 v2 % centrality Npart Centrality dependence

26. 40-50% at small pT Proton

27. In peripheral collisions there are some complications. It is harder to produce protons in the bulk because of lower density of soft partons.(remember pp collisions)Thermal parton distributions in Fuud are not factorizable. T in B(pT) is lower. Thus phantom jets are relatively more effective in enhancing the thermal partons. So B(pT)/R(pT) for proton is smaller than in pion Hence, v2(pT,b) continues to increase for (b) smaller than /4.

28. For pT>1.5 GeV/c, shower partons must be considered for both  and p spectra. Jet dominance (>3GeV/c) will saturate v2. For pT<1.5 GeV/c, the analysis is simple, and the result can be expressed in analytic form. No part of it suggests that the medium behaves like a perfect fluid.

29. Conclusion • Phantom jets produced by semi-hard parton scattering create ridges that are important in low and intermediate pT physics. •  up to 6 GeV/c is produced by thermal partons in the ridge and can have associated particles. • Azimuthal anisotropy is mainly a ridge effect. No fast thermalization or hydrodynamical flow are needed. Calling v2 “elliptic flow” may be misleading.