Hyperon Production in Cu+Cu Collisions at √sNN = 200GeV from Experiment Xiaobin Wang (for the STAR Collaboration) Tsinghua University, Beijing, China University of California, Los Angeles, USA Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Outline Motivation Results of Multi-strange Hyperon Production Summary Page 1 Outline Motivation Results of Multi-strange Hyperon Production Summary Transverse Momentum Spectra Strange Hyperon Ratios Yield, Compared with Au+Au and p+p Nuclear Modification Factor -- Rcp Ω/φ Ratio Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Page 2 Thermalization and chemical equlibration depends on colliding system – Cu+Cu  Au+Au variations Cu+Cu system with intermediate Npart numbers sensitive to Strangeness enhancement and its physics implication Au+Au@200GeV STAR Phys. Rev. Lett. 98, 062301 (2007) Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Rcp scaling consistent with constituent quark degree. Page 3 Au+Au@200GeV STAR Phys. Rev. Lett. 98, 062301 (2007) Baryon production follows approximately binary scaling at intermediate pT Particle formation may involve dynamics of quark coalescence and surface emission (v2, see Dhevan Gangadharan’s poster) From Au+Au  Cu+Cu --- investigating dependence of these features on parton densities and Npart geometry Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Ω/φ Ratio from Au+Au@200GeV, most central 0-12% Page 4 Ω/φ Ratio from Au+Au@200GeV, most central 0-12% Hwa&Yang Phys.Rev.C 75, 054904 (2007) Ω/φ ratio pT spectra (Phys. Rev. Lett. 99, 112301 (2007).) At mid to high pT range, thermal plus power-law component Coalescence Model predicts that for pT<4 GeV/c Ω/φ yields dominated by thermal s quarks. What do Cu+Cu data indicate? STAR Data Phys.Rev.Lett. 99, 112301 (2007) Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Page 5 Collision system size, Cu+Cu (Year 2005 data) compares with p+p and Au+Au published results with the same beam energy Number of nucleons: 63 (Cu) VS: 197 (Au) Detected charged particle multiplicities define collision centralities Glauber Model is applied to calculate equivalent number of nucleons that participate in reaction (Npart) and number of binary collisions (Nbin) Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Detectors and Data Set ~32.3M minbias collisions Page 6 ~32.3M minbias collisions Primary vertex, global track Good track: Nhits>15 PID by dE/dx, p /π/ K Hyperon reconstructed through weak decay topology STAR preliminary STAR preliminary Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Λ(anti-Λ) corrected for weak decay feed-downs from other hyperons Page 7 STAR preliminary Λ(anti-Λ) corrected for weak decay feed-downs from other hyperons pT distribution fitted by Boltzmann function Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Strange Hyperon Yield Ratio in Most Central Collisions Page 8 Strange Hyperon Yield Ratio in Most Central Collisions Most central: Ω(bar)/Ω = 1.07±0.14 Ξ(bar)/Ξ = 0.80±0.06 Λ(bar)/Λ = 0.83±0.03 Ratios of anti-hyperon to hyperon pT independent W/X = X/L, the ratios may be related to s/d(u) ratios within coalescence framework See arXiv:0801.2265 [nucl-th], ratios in Au+Au@200GeV model STAR preliminary Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Strange Hyperon Yield in Cu+Cu@200GeV Page 9 Hyperon yields per participant are strongly enhanced in central collisions Hyperon yield per participant in Cu+Cu is slightly higher than that in Au+Au at the same number of participant STAR preliminary Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Strange Hyperon Rcp VS: pT Distribution Page 10 Strange Hyperon Rcp VS: pT Distribution Stat. error only Hyperon production follows approximately binary scaling at intermediate pT Consistent with constituent quark number scaling observed previously in Au+Au at intermediate pT STAR preliminary Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Ω/φ Ratio in Cu+Cu VS: Au+Au Page 11 Ω/φ Ratio in Cu+Cu VS: Au+Au Cu+Cu@200GeV data stat. error only Same trend as Au+Au measurement Coalescence model by Hwa and Yang can describe the data pT<4 GeV/c The model assumes that most of Ω and φ are formed from bulk s quarks. φproduction see J.H. Chen’s talk, v2 see Y. Lu’s talk for STAR experiment STAR preliminary Au+Au@200GeV Cu+Cu@200GeV Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

Summary Page 12 Strange hyperon production has been measured from Cu+Cu collisions at RHIC W/X = X/L within measured pT<4 GeV/c, may indicate the s/d(u) ratios at hadronization For 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 Strange hyperon yields approximately follow binary scaling at intermediate pT region(1.5-4.0GeV/c). The Λ and Ξ Rcp values are consistent with the constituent quark number scaling previously observed. Ω/φ ratio for pT<4 GeV/c consistent with coalescence model where Ω/φ are formed mostly from bulk s quarks Thanks! Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov