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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 equilibration depends on colliding system – Cu+Cu  Au+Au variations • Canonical suppression increases with increasing strangeness • Cu+Cu system with intermediate Npart numbers is 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 poster 204, by D. Gangadharan) • 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 events analyzed • 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 • power-law component appears significant in peripheral collisions 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 poster 158 & arXiv:0801.2265 [nucl-th] 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 • Constituent quark number scaling • These features are consistent with what 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 & 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) range, may reflect 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 and φ are formed mostly from bulk s quarks Thanks! Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  14. Page 14 Back up Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  15. Page 15 • Thermalization and chemical equlibration are sensitive to formation of bulk partonic matter • Heavy ion collision system dynamics can be: • Energy dependence of strange baryon yields has been measured at RHIC and SPS • STAR Au+Au result shows Rcp of strange hyperon is affected by number of constituent quarks but not a mass effect • Chiral symmetry restored, s quark can be produced via • Hadronic system production, requires much higher energy Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  16. Strangeness is ‘enhanced’ at SPSBaryon and anti-baryons are both enhanced, but by different amount ! WA97/NA57 and NA49 Consistent Results Yield N-wound No of Wounded Nucleons Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  17. Page 17 arXiv [Nucl-ex]: 0705.2511 Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  18. Page 18 Phys. Rev.Lett. 99, 112301 (2007). Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

  19. Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: wangxb@rcf.rhic.bnl.gov

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