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

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: [email protected]

Page Page 11

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


Page Page 22 Thermalization and chemical equlibration depends on col

liding system – Cu+Cu Au+Au variations

Cu+Cu system with intermediate Npart numbers sensitive to Strangeness enhancement and its physics implication


Au+Au@200GeV STARPhys. Rev. Lett. 98, 062301 (2007)

Page Page 33

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 Dhevan Gangadharan’s poster)

From Au+Au Cu+Cu --- investigating dependence of these features on parton densities and Npart geometry

Au+Au@200GeV STAR

Phys. Rev. Lett. 98, 062301 (2007)


Page Page 44

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

Ω/φ ratio pT spectra (Phy

s. 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)

Hwa&Yang

Phys.Rev.C 75,

054904 (2007)


Page Page 55 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)


Page Page 66

Detectors and Data Set

~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

Page Page 77

Λ(anti-Λ) corrected for weak decay feed-downs from other hyperons

pT distribution fitted by Boltzmann function


STAR preliminary

Page Page 88Strange 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

=, 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

Page Page 99

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


STAR preliminary

Page Page 1010Strange Hyperon Rcp VS: pT Distribution

Stat. error only

Hyperon production follows approximately binary scaling at intermediate p

T

Consistent with constituent quark number scaling observed previously in Au+Au at intermediate pT


STAR preliminary

Page Page 1111Ω/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

Cu+Cu@200GeVCu+Cu@200GeV

Au+Au@200GeV


STAR preliminary

Page Page 1212Summary

Strange hyperon production has been measured from Cu+Cu collisions at RHIC

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!

Documents

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