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Hyperon Production in Cu+Cu Collisions at √ s NN = 200GeV from Experiment

Hyperon Production in Cu+Cu Collisions at √ s NN = 200GeV from Experiment. Xiaobin Wang (for the STAR Collaboration) Tsinghua University, Beijing, China University of California, Los Angeles, USA.

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Hyperon Production in Cu+Cu Collisions at √ s NN = 200GeV from Experiment

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  1. Hyperon Production in Cu+Cu Collisions at √sNN = 200GeVfrom 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

  2. Page 1 Outline • Motivation • Resultsof 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Detectors and Data Set 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

  8. 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

  9. 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

  10. Strange Hyperon Yield in Cu+Cu@200GeV Page 9 • Hyperon yields per participant are strongly enhanced in central collisions • Hyperon yield per participantin 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

  11. 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

  12. 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

  13. 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

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