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Future Measurements to Test Recombination

Future Measurements to Test Recombination. Rudolph C. Hwa University of Oregon. Workshop on Future Prospects in QCD at High Energy BNL, July 20, 2006. p T. x F. 1. Outline. Introduction Recombination model Shower partons Hadron production at low p T Hadron production at large 

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Future Measurements to Test Recombination

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  1. Future Measurements to Test Recombination Rudolph C. Hwa University of Oregon Workshop on Future Prospects in QCD at High Energy BNL, July 20, 2006

  2. pT xF 1 Outline • Introduction • Recombination model • Shower partons • Hadron production at low pT • Hadron production at large  • Hadron production at large pT • Summary

  3. probability of finding partons at probability for recombination to form a pion at p I. Introduction What are theproperties ofrecombination that we want to know and test? What partons? Same partons? What is that probability?

  4. number of constituent quarks scaling partons CQ impossible by fragmentation of order 1 or higher Usual strong evidences for recombination What about gluons? Useful to remember in future measurements

  5. Two-particle correlation Where are the partons from? Are they independent? Are they from 1 jet, 2 jets, or thermal medium? Quantitative questions about recombination eventually always become questions about the nature of partons that are to recombine.

  6. Multiparton distributions in terms of the thermal and shower parton distributions

  7. Valons Valons are to the scattering problem what CQs are to the bound-state problem. II. Recombination Model Recombination depends on the wave function of the hadron. Constituent quark model describes the bound-state problem of a static hadron. What good is it to help us to know about the distribution of partons in a hadron (proton)?

  8. We need a model to relate to the wave function of the proton Fq U Valon model p U Hwa, PRD 22, 759 (1981) D valons Deep inelastic scattering e e p Fq

  9. valence quark distr in proton valon distr in proton, independent of Q valance quark distribution in valon, whether in proton or in pion • Basic assumptions • valon distribution is independent of probe • parton distribution in a valon is independent of the host hadron U p U D

  10. Hwa & CB Yang, PRC66(2002) using CTEQ4LQ

  11. Recombination function It is the time-reversed process of the valon distributions U U D recombination function proton pion From  initiated Drell-Yan process valon model U U D valon distribution

  12. _ D Soft gluon radiation --- color mutation without significant change in momentum In a pp or AA collision process U + Is entropy reduced in recombination? The number of degrees of freedom seems to be reduced. The number of degrees of freedom is not reduced.

  13. How do gluons hadronize? Gluon conversion to q-qbar Recombination of with saturated sea gives pion distribution in agreement with data. In a proton the parton distributions are x2u(x) x2g(x) Gluons carry ~1/2 momentum of proton but cannot hadronize directly. x [log] Sea quark dist. Fq ~ c (1-x)7 Saturated sea quark dist. F’q ~ c’ (1-x)7

  14. The black box of fragmentation q p 1 z A QCD process from quark to pion, not calculable in pQCD Momentum fraction z < 1 III. Shower Partons from Fragmentation Functions

  15. shower partons fragmentation recombination can be determined known from data (e+e-, p, … ) Description of fragmentation by recombination hard parton meson

  16. and can be calculated in the RM Meson fragmentation function S(xi) Baryon fragmentationfunction

  17. Hwa & CB Yang, PRC 73, 064904 (2006) Has never been done before in the 30 years of studying FF. This is done in the RM with gluon conversion shower partons  valons  hadrons.

  18. Parton distributions at low Q2 p p H(x) x Hwa, PRD (1980) IV. Hadron production at low pT First studied in pp collision. .

  19. FNAL PL=100 GeV/c (1982) h h’ p    _ K+  + + K Suggested future measurement Better data at higher energy for p  , K, p, Y Hadronic collisionsHwa & CB Yang, PRC 66, 025205 (2002) h + p  h’ +X

  20. Leading (same valence quark) non-leading (sea quark) Asymmetry Hwa, PRD 51, 85 (1995) Suggested future measurement: Leading and non-leading D production

  21. NA49 has good data, but never published. (no target fragmentation, only projectile fragmentation) Shape depends on degradation. Normalization not adjustable. Suggested future measurement: Measure for all x at higher energy Need to know well the momentum degradation effect. Hwa & CB Yang, PRC 65, 034905 (2002) pA collisions h bears the effect of momentum degradation --- “baryon stopping”.

  22. In pB collision the partons that recombine must satisfy p B A B But in AB collision the partons can come from different nucleons Transfragmentation Region (TFR) Theoretically, can hadrons be produced at xF > 1? (TFR) It seems to violate momentum conservation, pL > √s/2. In the recombination model the produced p and  can have smooth distributions across the xF = 1 boundary.

  23. proton pion Suggested future measurement Determine the xF distribution in the TFR • : momentum degradation factor proton-to-pion ratio is very large. Regeneration of soft parton has not been considered. Particles at xF>1 can be produced only by recombination. Hwa & Yang, PRC 73,044913 (2006)

  24. BRAHMS, PRL 93, 242303 (2004) BRAHMS data show that in d+Au collisions there is suppression at larger . Hwa, Yang, Fries, PRC 71, 024902 (2005). No change in physics from =0 to 3.2 In the RM the soft parton density decreases, as is increased (faster for more central coll). Suggested future measurement for  and p V. Large 

  25. AuAu collisions BRAHMS, nucl-ex/0602018

  26. xF = 0.9 xF = 0.8 xF = 1.0 TFR TS ? TTT TT

  27. Hwa & Yang (2006) • Focus on xF>1 region. Suggested future measurement • Determine p/ ratio. • Look for associated particles pT distribution fitted well by recombination of thermal partons No jet => no associated particles

  28. A. Cronin Effect Cronin et al, Phys.Rev.D (1975) for h= both  and p This is an exp’tal phenomenon. Not synonymous to initial-state kT broadening. Suggested future measurement Measure and ratios in d+Au collisions at all , both backward and forward. VI. Hadron production at large pT, small pL In the RM we have shown that final-state recombination alone (without initial-state broadening) is enough to account for CE. We obtained it for both  and p -- impossible by fragmentation.Hwa & Yang, PRL 93, 082302 (2004); PRC 70, 037901 (2004).

  29. If hadrons at high pT are due to initial transverse broadening of parton, then • forward has more transverse broadening • backward has no broadening Suggested future measurement Measure p and  separately at larger range of , and for different centralities. Backward-forward Asymmetry Expects more forward particles at high pT than backward particles RM has B/F>1, since dN/d of soft partons decrease as  increases.

  30. Correlation shapes are the same, yields differ by x2. associated yield in this case Au d x=0.7 x=0.05 is larger than associated yieldin that case Au d x=0.7 x=0.05 Degrading of the d valence q? Soft partons -- less in forward, more in backward RM =>less particles produced forward, more backward STAR(F.Wang, Hard Probes 06)

  31. All in recombination/ coalescence model Measure the ratio to higher pT B. p/ Ratio Success of the recombination model If it disagrees with prediction, it is not a breakdown of the RM. On the contrary the RM can be used to learn about the distributions of partons that recombine.

  32. Hwa & CB Yang, nucl-th/0602024 40% lower Data from STAR nucl-ex/0601042 30% higher 2 4 6 C. Strange particles This is not a breakdown of the RM. We have not taken into account the different hyperon channels in competition for the s quark in the shower.

  33.  production  production 130 GeV small more suppressed

  34. We need to do more work to understand the upbending of . It is significant to note that thermal partons can account for the ratio up to pT=4 GeV/c. We have assumed RFs for  &  that may have to be modified. QGP: s quarks enhanced & are thermalized.

  35. Predict: no associated particles giving riseto peaks in , near-side or away-side. Suggested future measurement Verify or falsify that prediction If  and  are produced mainly by the recombination of thermal s quarks, then no jets are involved. Select events with  or  in the 3<pT<5 region, and treat them as trigger particles. Look for associated particles in the 1<pT<3 region.

  36. 1. Correlation of partons in jets is negative 2. Correlation of pions in jets but not directly measurable Two-particle distribution q1 q2 q3 q4 k Hwa & Tan, PRC 72, 024908 (2005) This can be measured. D. Jet Correlations

  37. Trigger-normalized momentum fraction X.-N. Wang, Phys. Lett. B 595, 165 (2004) J. Adams et al., nucl-ex/0604018 STAR claims universal behavior in D(zT) Focus on this region fragmentation violation of universal behavior due to medium effect ---- thermal-shower recombination Trigger-normalized fragmentation function 3. D(zT)

  38. Suggested future measurement Study zT ~ 0.5 with pT(trigger) ~ 8-10 GeV/c pT(assoc) ~ 4-5 GeV/c Measure p/ ratio of associated particles. My guess: R(p/) >> 0.1 if so, it can only be explained by recombination. Do this for both near and away sides.

  39. Conical Flow vs Deflected Jets near near near Medium Medium Medium away away π away di-jets 0 π 0 deflected jets mach cone 4. Three-particle correlation Ulery’s talk at Hard Probes 06

  40. d+Au Δ2 Au+Au Central 0-12% Triggered Δ1 Δ1 Signal Strengths Δ2 • Evaluate signals by calculating average signals in the boxes. • Near Side, Away Side, Cone, and Deflected.

  41. More studies are needed. • What is the multiplicity distribution (above background) on the away side? • If n=2 is much lower than n=1 events (on away side), then the Mach-cone type of events is not the dominant feature on the away side. • What is the p/ ratio (above background) on the away side? • Evolution with higher trigger momentum should settle the question whether cone events are realistic. • Whatever the mechanism is, hadronization would be by recombination for pT<6 GeV/c.

  42. Factorial moment for 1 event Normalized factorial moment Chiu & Hwa, nucl-th/0605054 Event averaged NFM (a) background only (b) bg + 1jet (c) bg + 2jets Try it out, but it is not a way to test recombination. 5. Using Factorial Moments to suppress statistical background event by event.

  43. 2 hard partons p  1 shower parton from each VII. Two-jet Recombination  and p production at high pT at LHC New feature at LHC: density of hard partons is high. High pT jets may be so dense that neighboring jet cones may overlap. If so, then the shower partons in two nearby jets may recombine.

  44. If (pT)~pT-7, then we get single jet Proton-to-pion ratio at LHC  -- probability of overlap of 2 jet cones Hwa & Yang, PRL (to appear), nucl-th/0603053

  45. But they are part of the background of an ocean of hadrons from other jets. GeV/c That is very different from a super-high pT jet. A jet at 30-40 GeV/c would have lots of observable associated particles. The particle detected has some associated partners. There should be no observable jet structure distinguishable from the background.

  46. Suggested future measurement Verify or falsify these two predictions We predict for 10<pT<20 Gev/c at LHC • Large p/ ratio • NO associated particles above the background

  47. Summary In general, all hadrons produced with pT<6 GeV/c are by recombination. Specifically, many measurements have been suggested. Good signatures: large Rp/ in some regions no particles associated with high pT trigger. After recombination is firmly established, the hadron spectra can be used to probe the distributions of partons that recombine.

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