Hyperon Production in CuCu Collisions at s NN

Hyperon Production in Cu+Cu Collisions at √s. NN = 200 Ge. V from Experiment Xiaobin Wang (for the STAR Collaboration) Tsinghua University, Beijing, China University of California, Los Angeles, USA Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 1 Outline Ø Motivation Ø Results of Multi-strange Hyperon Production ü Transverse Momentum Spectra ü Strange Hyperon Ratios ü Yield, Compared with Au+Au and p+p ü Nuclear Modification Factor -- Rcp ü Ω/φ Ratio Ø Summary Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Ø Thermalization and chemical equilibration depends on colliding system – Cu+Cu Au+Au variations ØCanonical suppression increases with increasing strangeness ØCu+Cu system with intermediate Npart numbers is sensitive to strangeness enhancement and its physics implication Au+Au@200 Ge. V STAR Phys. Rev. Lett. 98, 062301 (2007) Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov Page 2

Ø Rcp scaling consistent with constituent quark degree. Page 3 Au+Au@200 Ge. V STAR Phys. Rev. Lett. 98, 062301 (2007) l Baryon production follows approximately binary scaling at intermediate p. T l Particle formation may involve dynamics of quark coalescence and surface emission (v 2, see poster 204, by D. Gangadharan) l From Au+Au Cu+Cu --- investigating dependence of these features on parton densities and Npart geometry Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 4 Ø Ω/φ Ratio from Au+Au@200 Ge. V, most central 0 -12% Hwa&Yang p Ω/φ ratio p. T spectra Phys. Rev. C 75, (Phys. Rev. Lett. 99, 112301 (2007). ) p At mid to high p. T range, thermal plus power-law component p Coalescence Model predicts that for p. T<4 Ge. V/c Ω/φ yields dominated by thermal s quarks. What do Cu+Cu data indicate? Xiaobin Wang, QM 08 Jaipur India, 054904 (2007) STAR Data Phys. Rev. Lett. 99, 112301 (2007) Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 5 Ø Collision system size, Cu+Cu (Year 2005 data) compares with p+p and Au+Au published results with the same beam energy u Number of nucleons: 63 (Cu) VS: 197 (Au) u Detected charged particle multiplicities define collision centralities u Glauber Model is applied to calculate equivalent number of nucleons that participate in reaction (Npart) and number of binary collisions (Nbin) Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Detectors and Data Set Page 6 Ø ~32. 3 M minbias events analyzed Ø PID by d. E/dx, p /π/ K Ø Hyperon reconstructed through weak decay topology ry ry a n i m A ST Xiaobin Wang, R li e r p QM 08 Jaipur India, li e r Rp na i m A ST Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

li e r Rp ry a n mi A ST n Λ(anti-Λ) corrected for weak decay feed-downs from other hyperons n p. T distribution fitted by Boltzmann function n power-law component appears significant in peripheral collisions Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov Page 7

Strange Hyperon Yield Ratio in Most Central Collisions l Most central: Ω(bar)/Ω = 1. 07± 0. 14 Ξ(bar)/Ξ = 0. 80± 0. 06 Λ(bar)/Λ = 0. 83± 0. 03 l Ratios of antihyperon to hyperon p. T independent l W/X = X/L, the ratios may be related to s/d(u) ratios within coalescence framework l See poster 158 & ry ar. Xiv: 0801. 2265 [nuclth] R A ST Xiaobin Wang, lim e r p QM 08 Jaipur India, ina Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov Page 8

Strange Hyperon Yield in Cu+Cu@200 Ge. V Page 9 u Hyperon yields per participant are strongly enhanced in central collisions ina ry m R A ST Xiaobin Wang, li e r p QM 08 Jaipur India, Feb. 4 -10, 2008 u Hyperon yield per participant in Cu+Cu is slightly higher than that in Au+Au at the same number of participant Email: wangxb@rcf. rhic. bnl. gov

Page 10 Strange Hyperon Rcp VS: p. T Distribution Ø Stat. error only Ø Hyperon production follows approximately binary scaling at intermediate p. T Ø Constituent quark number scaling ina ØThese features are consistent with what observed previously in Au+Au at intermediate p. T ry m R A ST Xiaobin Wang, li e r p QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 11 Ω/φ Ratio in Cu+Cu & Au+Au ry na mi p Cu+Cu@200 Ge. V data stat. error only R A ST p Same trend as Au+Au measurement p Coalescence model by Hwa and Yang can describe the data p. T<4 Ge. V/c Au+Au@200 Ge. V Cu+Cu@200 Ge. V p The model assumes that most of Ω and φ are formed from bulk s quarks. p φ production see J. H. Chen’s talk, v 2 see Y. Lu’s talk for STAR experiment Xiaobin Wang, QM 08 Jaipur India, li e r p Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Summary Page 12 Ø Strange hyperon production has been measured from Cu+Cu collisions at RHIC ØW/X = X/L within measured p. T(<4 Ge. V/c) range, may reflect the s/d(u) ratios at hadronization ØFor collisions with the same number of participants, strange hyperon production per participant in Cu+Cu is slightly higher than that in Au+Au at the same energy Ø Strange hyperon yields approximately follow binary scaling at intermediate p. T region(1. 5 -4. 0 Ge. V/c). The Λ and Ξ Rcp values are consistent with the constituent quark number scaling previously observed. Ø Ω/φ ratio for p. T<4 Ge. V/c consistent with coalescence model where Ω and φ are formed mostly from bulk s quarks Thanks! Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 14 Back up Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 15 Ø Thermalization and chemical equlibration are sensitive to formation of bulk partonic matter Ø Heavy ion collision system dynamics can be: • Chiral symmetry restored, s quark can be produced via • Hadronic system production, requires much higher energy Ø Energy dependence of strange baryon yields has been measured at RHIC and SPS Ø STAR Au+Au result shows Rcp of strange hyperon is affected by number of constituent quarks but not a mass effect Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Strangeness is ‘enhanced’ at SPS Baryon and anti-baryons are both enhanced, but by different amount ! WA 97/NA 57 and NA 49 Consistent Results Yield N-wound No of Wounded Nucleons Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 17 ar. Xiv [Nucl-ex]: 0705. 2511 Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Page 18 Phys. Rev. Lett. 99, 112301 (2007). Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov

Cent. 0~10% 10~20% 20~30% 30~40% 40~60% <N_ part> 99. 00 74. 55 53. 67 37. 75 21. 54 <N_ bin> 188. 8 123. 6 77. 64 47. 66 22. 72 Λ 4. 82 +/-0. 11 3. 27 +/-0. 09 2. 13 +/-0. 07 1. 39 +/-0. 05 0. 72 +/-0. 03 Λbar 4. 00 +/-0. 10 2. 60 +/-0. 07 1. 83 +/-0. 06 1. 18 +/-0. 04 0. 62 +/-0. 02 Ξ 0. 55 +/-0. 02 0. 38 +/-0. 02 0. 24 +/-0. 01 0. 13 +/-0. 01 0. 072+/-0. 004 Ξbar 0. 44 +/-0. 02 0. 35 +/-0. 02 0. 22 +/-0. 01 0. 14 +/-0. 01 0. 065+/-0. 005 Ω 0. 073+/-0. 010 0. 047+/-0. 008 0. 030+/-0. 006 0. 018+/-0. 004 0. 0077+/-0. 0013 Ωbar 0. 078+/-0. 010 0. 046+/-0. 007 0. 032+/-0. 006 0. 016+/-0. 004 0. 0060+/-0. 0010 Xiaobin Wang, QM 08 Jaipur India, Feb. 4 -10, 2008 Email: wangxb@rcf. rhic. bnl. gov