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Production of Strange Particles at Intermediate p T at RHIC

Production of Strange Particles at Intermediate p T at RHIC. Rudolph C. Hwa University of Oregon. Strangeness in Collisions BNL/RIKEN Workshop February 2006. Work done in collaboration with Chunbin Yang Central China Normal University Wuhan, China.

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Production of Strange Particles at Intermediate p T at RHIC

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  1. Production of Strange Particles at Intermediate pT at RHIC Rudolph C. Hwa University of Oregon Strangeness in Collisions BNL/RIKEN Workshop February 2006

  2. Work done in collaboration with Chunbin Yang Central China Normal University Wuhan, China

  3. Production of by recombination Outline • What’s interesting about the problem • Quick review of recombination • New results on shower partons • Implications of the results

  4. Preamble s quarks are enhanced in bulk medium --- low pT. Strange particles are suppressed in fragmentation functions --- high pT. At intermediate pT strange particle production is sensitive to both properties. We find features not present in the non-strange sector, some quite unusual. That’s why it is interesting.

  5. # of or 1 2 1 3 There is competition among various channels # of or 1 0 2 0 Formation depends on the densities of all species. with q w/o q meson baryon

  6. on strangeness no pT depen-dence Greco, Ko, Levai, PRL90, 202302 (03); PRC 68, 034904 (03). Fries, Muller, Nonaka, Bass, PRL90, 202302 (03); PRC 68, 044902 (03). Das, Hwa, PLB 68, 459 (77); Hwa PRD22, 1593(80). Hwa, Yang, PRC 67, 034902 (03). in the following Recombination/Coalescence (ReCo) Many groups have worked on Recombination/Coalescence. Bialas “linear model” [PLB 442, 449 (98)] Biro et al. (ALCOR) “nonlinear model” [95,97,00] Hwa & Yang --- parton model [PRC 66, 064903(02)]

  7. One-dimensional description of invariant distribution of meson Partons and meson are all collinear. invariant distribution non-invariant wave function in terms of constituents (valons) A quick review of recombination

  8. Pion: (from ) a=b=0 u 1 Kaon: (from ) a=1, b=2 1 phi: (from phi being a loosely bound state of ) Meson wave function

  9. shower thermal suppression factor 0.07 hard scattering in AuAu: pdf, shadowing, a+b->i+i’(LO) SPD: i->q,s Two-quark distribution

  10. Fragmentation functions into , K theoretical output Shower parton distributions Parton recombination experimental input experimental input Fragmentation functions into p,  in agreement with data Shower partons in heavy-ion collisions pQCD Hard parton scattering Heavy-ion collisions Parton recombination compare with data Soft partons medium effect on jets pT distributions Logical connections and experimental relevance

  11. Fragmentation functions into , K theoretical output Shower parton distributions Parton recombination experimental input Shower partons The shower partons are so important in heavy-ion collisions to account for the medium effect on jets, we review the essence here, and add some new findings.

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

  13. Shower parton distributions valence u d s sea u d L L DSeaKNS L  DVG G  DGL Ls  DKSeaG Gs  DKG s R g 5 SPDs are determined from5 FFs. RK

  14. Suppressed Shower Parton Distributions Hwa & CB Yang, PRC 70, 024904 (04)

  15. Fragmentation functions into , K theoretical output Shower parton distributions Parton recombination experimental input Fragmentation functions into p,  in agreement with data The inter-relationships between meson FFs and baryon FFs have never been explored before. Shower partons pQCD has focused on the evolution of FFs with Q2. We study the hadronization processes into M and B.

  16. Gluon  proton Gluon  pion Using the same G(xi) we can calculate the FF to proton That takes care of the momentum constraint of the 3 quarks. But there must be also an antiproton in the gluon jet.

  17. Joint p-pbar fragmentation function Similarly, for FF into.

  18. Gluon fragmentation function into proton No adjustable parameters Hwa & CB Yang, nucl-th/0601033

  19. Fragmentation function of gluon into  also no adjustable parameters Hwa & CB Yang, nucl-th/0601033

  20. Fragmentation functions into , K theoretical output Shower parton distributions Parton recombination experimental input experimental input Fragmentation functions into p,  in agreement with data Shower partons in heavy-ion collisions pQCD Hard parton scattering Heavy-ion collisions Parton recombination compare with data Soft partons medium effect on jets pT distributions Logical connections and experimental relevance

  21. production Cq = 23.2 GeV-1, Tq=0.317 GeV, from  Cs = 15.5 GeV-1, Ts=0.323 GeV to fit K0 If i=u,d,g,…, Sis is small. If i=s,sbar, fi(k) is small. (comments later) Central Au+Au collisions

  22. mostly TsSq Lines from Hwa & CB Yang, nucl-th/0602024 Data from STAR nucl-ex/0601042

  23. small smaller very small i=q: Sqq can be (a) sea, or (b) valence u uval K  ? usea  K  production

  24. Data from STAR nucl-ex/0601042 sea only Hwa & CB Yang, nucl-th/0602024 valence also

  25. 40% lower 30% higher 2 4 6 Ratio R/K Having determined their pT distributions, we can take their ratio.

  26. small Shower partons make negligible contribution Recombination function g = 0.3 Suppression of formation in the presence of light quark medium Hwa & CB Yang, nucl-th/0602024 STAR, Phys.Lett.B612,181(2005)  production Ts = 0.382 GeV

  27. Ts = 0.382 GeV even more suppressed as before for  Shape of pT distribution well reproduced. 130 GeV Supports the finding that no other component is important besides Recombination of sss in the presence of u,d,… is highly suppressed. STAR, PRL 92, 182301 (2004); PHENIX also (05)  production g = 0.008

  28. i a b Hard parton distributions Shower parton distributions Nonstrange soft parton distribution Strange soft parton distribution important for pT > 4 Gev/c , , important for pT < 4 Gev/c suppressed throughout , dominant throughout , • What cannot be changed. • What can be adjusted.

  29. Bending over of RB/M is a sign of the contribution of the TS component. We expect Rnot to bend. The dominant term is made up from Can the parton momentum be extrapolated to from 1 to 4 GeV/c? We need data on  and  up to 8 GeV/c.

  30. Predict: no associated particles giving rise to peaks in , near-side or away-side. A prediction that can be checked now! Since shower partons make insignificant contribution to  production for pT<8 GeV/c, no jets are involved. Select events with  or  in the 3<pT<6 region, and treat them as trigger particles. Thermal partons are uncorrelated, so all associated particles are in the background. If there are no peaks, there is no need to make background subtraction.

  31. Associated particle distribution (PHENIX)

  32. p+p Jet-like structures Signal (1/Ntrig) dN/d(Df) Au+Au top 5%  trigger (pT>3 GeV/c) in Au+Au ? background Df charged hadrons

  33.  Normalization factors in the recombination functions g = 0.3, g = 0.008 The rate of recombination is suppressed by the medium environment of light quarks.

  34. , p Cq = 23.2 GeV-1, Tq = 0.317 GeV K,  Cs = 15.5 GeV-1, Ts = 0.323 GeV ,  Cs = 15.5 GeV-1, Ts = 0.382 GeV ~18% higher Can it be because  and  hadronize earlier before s & s become too diffuse by expansion? Thermal partons enhanced, but still low compared to q ~ Tq (2%)

  35. Conclusion • K,  well described by thermal-thermal, and thermal-shower recombination. But R/Kis not well reproduced. Need some fine-tuning. • ,  are due mainly to TsTs, TsTsTs recombination. Rate of recombination is suppressed due to light quark environment. Inverse slope is higher. • s quark shower partons have no effect in the production of , for pT<8 GeV/c. Jets are not involved. No peaks in associated particle distribution.

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