Parton and Hadron Correlations in Jets

1. Parton and Hadron Correlations in Jets Rudolph C. Hwa University of Oregon RIKEN Workshop on Jet Correlations BNL, March 2005

2. Work done in separate collaborations with Charles Chiu (Univ. of Texas, Austin) Zhiquang Tan (HZNU, Wuhan; UO) Chunbin Yang (HZNU, Wuhan; UO)

3. Outline Hadronization by parton recombination Single particle distributions Two particle distributions Parton correlations Hadron correlations Associated particle distributions Enhanced thermal partons  &  distributions

4. Hadronization by parton recombination At high pT , shower partons can recombine with (a)other shower partons: fragmentation (b) thermal partons in the environment: dominant component at intermediate pT region (c)Thermal partons can recombine with themselves to give the soft component.

5. soft TT TS hard SS thermal Pion distribution (log scale) fragmentation Transverse momentum Some highlights of the successes of this picture

6. fragmentation thermal  production in AuAu central collision at 200 GeV Hwa & CB Yang, PRC70, 024905 (2004)

7. All in recombination/ coalescence model Compilation of Rp/ by R. Seto (UCR)

8. soft-soft No pT broadening by multiple scattering in the initial state. Medium effect is due to thermal (soft)-shower recombination in the final state. d+Au collisions Pions Hwa & CB Yang, PRL 93, 082302 (2004)

9. because 3q  p, 2q   Nuclear Modification Factor

10. Forward production in d+Au collisions BRAHMS data Hwa, Yang, Fries, PRC 71, 024902 (2005) Underlying physics for hadron production is not changed from backward to forward rapidity.

11. Single particle distribution Thermal parton distribution Shower parton distributions Single shower parton Two shower partons in the same jet Fragmentation function

12. Au+Au collisions

13. Thermal partons Shower partons

14. Au+Au collisions TS SS

15. Correlations Calculations done without any other free parameters.

16. Normalized correlation function In-between correlation function Correlation function

17. Correlation of partons in jets A. Two shower partons in a jet in vacuum k Fixed hard parton momentum k (as in e+e- annihilation) x1 x2 The two shower partons are correlated.

18. no correlation

19. B. Two shower partons in a jet in HIC Hard parton momentum k is not fixed. fi(k) fi(k) fi(k) fi(k) is small for 0-10%, smaller for 80-92%

21. trigger associated particle background k q1 4<p1<6 GeV/c must involve S 2<p2<4 GeV/c must also involve S q2 q3 q4 Correlation of pions in jets Two-particle distribution

22. Factorizable terms: Do not contribute to C2(1,2) Non-factorizable terms correlated Correlation function

24. along the diagonal

27. Hwa and Tan (2005)

28. (a) central: (ST)(ST) dominates S-S correlation weakened by separate recombination with uncorrelated (T)(T) (b) peripheral: (SS)(SS) dominates SS correlation strengthened by double fragmentation Physical reasons for the big dip: The dip occurs at low pT because at higher pT power-law suppression of 1(1)1(2) results in C2(1,2) ~ 2(1,2) > 0

29. The foregoing analysis is based on what we can calculate (without free parameters): C2(1,2)K2(1,2)G2(1,2) need data on these No ambiguous subtraction scheme applied. Now, let us compare what we can calculate with what has been measured.

30. STAR has measured: nucl-ex/0501016 Trigger 4 < pT < 6 GeV/c Associated charged hadron distribution in pT Background subtracted  and  distributions

31. Associated particle pT distribution p1 -- trigger p2 -- associated Triggered sample with background subtraction consider only:

32. Reasonable agreement with data

33. P1 pedestal P2 subtraction point no pedestal short-range correlation? long-range correlation?  and  distributions

34. New issues to consider: • Angular distribution (1D -> 3D) shower partons in jet cone • Thermal distribution enhanced due to energy loss of hard parton work done with C. Chiu

35. Longitudinal Transverse t=0 later

36. shower parton q2 hard parton k   z k jet cone Assoc p1 trigger p2 1  z Expt’l cut on trigger: -0.7 < 1 < +0.7

37. Events with jets Thermal medium enhanced due to energy loss of hard parton in the vicinity of the jet new parameter T’- T = T > 0 Thermal partons Events without jets

38. enhanced thermal trigger associated particle peak in  &  Pedestal ForSTSTrecombination Sample with trigger particles and with background subtracted

39. next slide

40. Cone width another parameter ~ 0.22 shower parton Shower parton angular distribution in jet cone k q2 hard parton  z

41. Pedestal in  P1 parton dist 0.15 < p2 < 4 GeV/c, P1 = 0.4 2 < p2 < 4 GeV/c, P2 = 0.04 less reliable P2 more reliable T ’ adjusted to fit pedestal found T ’= 0.329 GeV/c cf. T = 0.317 GeV/c T = 12 MeV/c

42. STAR data Chiu & Hwa (2005)

43. Chiu & Hwa (2005)

44. G2 Porter & Trainor, ISMD2004, APPB36, 353 (2005) ( pp collisions ) STAR Transverse rapidity yt

46. Hwa & Tan (2005)

47. We have not put in any (short- or long-range) correlation by hand. Correlation exists among the shower partons, since they belong to the same jet. The pedestal arises from the enhanced thermal medium. The peaks in  &  arise from the recombination of enhanced thermal partons with the shower partons in jets with angular spread.

48. Is there a hole in ? Conclusion Parton recombination provides a framework to interpret the data on jet correlations. There seems to be no evidence for any exotic correlation outside of shower-shower correlation in a jet. For unbiased study without deciding on bkgd, we suggest the measure, G2(1,2).