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

Hyperon Production in Cu+Cu Collisions at sNN = 200GeVfrom ExperimentXiaobin Wang(for the STAR Collaboration)Tsinghua University, Beijing, ChinaUniversity of California, Los Angeles, USA Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]

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 / Ratio Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]

Thermalization and chemical equilibration depends on colliding system Cu+Cu Au+Au variationsCanonical suppression increases with increasing strangenessCu+Cu system with intermediate Npart numbers is sensitive to strangeness enhancement and its physics implication Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]+Au@200GeV STARPhys. Rev. Lett. 98, 062301 (2007)

Rcp scaling consistent with constituent quark degree. 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 Au+Au@200GeV STARPhys. Rev. Lett. 98, 062301 (2007) Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]

/ Ratio from Au+Au@200GeV, most central 0-12% / 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

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: [email protected]

Detectors and Data Set ~32.3M minbias events analyzed PID by dE/dx, p // K Hyperon reconstructed through weak decay topology Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] preliminarySTAR preliminary

(anti-) 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: [email protected] preliminary

Strange Hyperon Yield Ratio in Most Central Collisions Most central: (bar)/ = 1.070.14 (bar)/ = 0.800.06 (bar)/ = 0.830.03 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] Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] preliminary

Strange Hyperon Yield in Cu+Cu@200GeV 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 Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] preliminary

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 Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] preliminary

/ 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

Summary Strange hyperon production has been measured from Cu+Cu collisions at RHICW/X = X/L within measured pT(

Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] up

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: [email protected]

Strangeness is enhanced at SPSBaryon and anti-baryons are both enhanced, but by different amount ! No of Wounded Nucleons YieldN-woundWA97/NA57 and NA49 Consistent Results Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]

Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected] [Nucl-ex]: 0705.2511

Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]. Rev. Lett. 99, 112301 (2007).

Xiaobin Wang, QM08 Jaipur India, Feb.4-10, 2008 Email: [email protected]

Cent.0~10%10~20%20~30%30~40%40~60%99.0074.5553.6737.7521.54188.8123.677.6447.6622.724.82+/-0.113.27+/-0.092.13+/-0.071.39+/-0.050.72+/-0.03bar4.00+/-0.102.60+/-0.071.83+/-0.061.18+/-0.040.62+/-0.020.55+/-0.020.38+/-0.020.24+/-0.010.13+/-0.010.072+/-0.004bar0.44+/-0.020.35+/-0.020.22+/-0.010.14+/-0.010.065+/-0.0050.073+/-0.0100.047+/-0.0080.030+/-0.0060.018+/-0.0040.0077+/-0.0013bar0.078+/-0.0100.046+/-0.0070.032+/-0.0060.016+/-0.0040.0060+/-0.0010

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

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