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φ -meson Production in Heavy-Ion Collisions at RHIC

φ -meson Production in Heavy-Ion Collisions at RHIC. Jin-Hui Chen Shanghai Institute of Applied Physics (SINAP), CAS. Outline Motivation of studying φ -meson Analysis details and technique Results and discussions Summary and Outlook.

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φ -meson Production in Heavy-Ion Collisions at RHIC

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  1. φ-meson Production in Heavy-Ion Collisions at RHIC Jin-Hui Chen Shanghai Institute of Applied Physics (SINAP), CAS Outline Motivation of studying φ-meson Analysis details and technique Results and discussions Summary and Outlook Thanks to: X.Z. Cai, G.L. Ma, Y.G. Ma (SINAP), J. G. Ma, H.Z. Huang (UCLA), S. Blyth, N. Xu (LBL), H.B. Zhang (BNL) et al. ATHIC (2006), Seoul, June 29 - July 1

  2. Why is φ? • Φ-meson production can be a good probe • small cross section for scattering with non-strange hadrons, relatively long-lived • Information from early time? • Sensitive to early flow? • Production mechanism: • ggg ->  • s sbar ->  • K+K- ->  • May determine whether the grouping of the nuclear modification factor (RCP) is divided by the particle mass or particle type mf~1019 MeV/c2 ; mL~1116 MeV/c2; mKs~498 MeV/c2 • m ~ 1019 MeV/c2 ,  ~ 4.45 MeV/c2,ct ~ 41 fm/c • Vector meson • quark content : s, sbar • Studied decay channel:   K+ K- (49.2%) ATHIC (2006), Seoul, June 29 - July 1

  3. STAR Detector The STAR Experiment • Data-Sets: Au+Au 130GeV; Au+Au 200GeV; Au+Au 62GeV; d+Au 200GeV; p+p 200GeV. • Event-Mixing technique • Select K+ andK- tracks from PID by energy loss in TPC • Combine all pairs from same event  Signal+Background (same event spectra) • Combine pairs from different events Background (mixed event spectra) • Signal = same event spectra – mixed event spectra ATHIC (2006), Seoul, June 29 - July 1

  4. y py px x y z x Elliptic flow v2 • Non-central A+A collisions: azimuthally anisotropic distribution of particles in coordinate-space • Density gradients and interactions between the particles: an asymmetry in momentum-space • Signal is self-quenchingwith time –early time observable! • Measurement: Fourier expansion of the azimuthal angle (φ-Ψ)distributions (mid-rapidity) ATHIC (2006), Seoul, June 29 - July 1

  5. φ-meson production (1) STAR Preliminary ATHIC (2006), Seoul, June 29 - July 1

  6. Ratios of  to π- or K- STAR Preliminary • φ yields increase faster than π-in higher center-of-mass beam energy  onset of strange quark degree of the freedom? • AA>pp: partonic environment favors φ production? • No strong centrality dependence of φ/K- in Au+Au collisions; • RQMD predicts increasing φ/k- vs Npart, and much smaller than the data, • Partonic interactions must play important role in φ production! ATHIC (2006), Seoul, June 29 - July 1

  7. STAR Preliminary φ-meson production (2) Particle groupingbehaviour: • φ follows the same trend as K0but differs from Λ • Confirmation of meson-baryon dependence of RCP rather than mass-type dependence Au+Au 200GeV d+Au 200GeV ATHIC (2006), Seoul, June 29 - July 1

  8. STAR Preliminary STAR Preliminary φ-meson production (3) Comparison with model expectations on particle production can give insight on the constituents of the medium produced in heavy-ion collisions: R. Hwa's recombination model[1]: • φ and Ω (sss) spectra (pT<8GeV/c) mainly due to recombination of thermal quarks (TT) • Seems to match data well • BUT... Ω/φ ratio has similar shape to other baryon/meson measurements • Model matches data for pT < 4 GeV/c [1] R. Hwa & C-B Yang, nucl-th/0602024 ATHIC (2006), Seoul, June 29 - July 1

  9. STAR Preliminary Discrepancy between STAR and PHENIX? D.Pal QM05 ATHIC (2006), Seoul, June 29 - July 1

  10. 1.The integral yield from STAR is a factor of 100% higher than the PHENIX’s? J.Rafelski etc. PRC 72 024905 2.No! (Prof. Rafelski) Discrepancy between STAR and PHENIX? ATHIC (2006), Seoul, June 29 - July 1

  11. STAR Preliminary Elliptic flowof φ-meson at 200GeV φ flows as strong as other meson! Early time information: • For pT<2 GeV/c, φ flows as much as other ID'd particles, consistent with hydro. mass-ordering • For pT>2 GeV/c, φ v2 is more consistent with K0S than Λ (favors NCQ=2) Particle production mechanisms: • Further evidence of species-type dependence of v2 at intermediate pT ATHIC (2006), Seoul, June 29 - July 1

  12. Summary and outlook (1) • Strong suppression of high pT power-law tail ofφ has been observed in central collisions from RHIC, the spectra can be fitted well by exponential function (thermalization). • Observed grouping of RCP at RHIC is a kind of particle type effect but not mass effect. Strange quark DOF ~ u,d quarks • Strong elliptic flow of φ has been observed • φflow favors the NCQ scaling as other hadrons, which indicates the partonic collectivity has been formed at RHIC. ATHIC (2006), Seoul, June 29 - July 1

  13. Summary and outlook (2) • Vector-meson (φ, K*) spin alignment in Au+Au (global ploarized QGP?). Ideals: recombination of q-qbar in polarized QGP; recombination of q(qbar) in polarized QGP with unpolarized qbar(q); fragmentation from polarized q(qbar) see: Liang, Wang, PRL 94(05)102301; PLB629(05)20; EXCHARM Coll, PLB 485 (00) 334 ATHIC (2006), Seoul, June 29 - July 1

  14. Summary and outlook (3) Full TOF MRPC modules construction has been approved by NSF of China. NSFC, CAS and MoST of China will jointly support the project. It will be finished in 2.5 years. φ reconstruction with Full TOF: φ -> K+K- Φ -> e+e- Φ -> +- is there a φ puzzle in RHIC energies, esp. in lower Pt regions? NA50 NA49 Open symbols: φ-> +- Solid symbols: φ -> K+K- Pal, Ko, Lin, NPA707(02)505 ATHIC (2006), Seoul, June 29 - July 1

  15. Welcome to Shanghai ! Nov 14-20, 2006 ATHIC (2006), Seoul, June 29 - July 1

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