φ-meson production and partonic collectivity at RHIC Jin-hui Chen for the STAR Collaboration Shanghai Institute of Applied Physics (SINAP), CHINA Outline Motivation & introduction Dataset & analysis method φ-meson production (spectra & RCP) Elliptic flow v2 of φ-meson from RHIC Conclusion & outlook Thanks to: J. G. Ma, H.Z. Huang (UCLA), S. Blyth, N. Xu (LBL), X.Z. Cai, G.L. Ma, Y.G. Ma(SINAP), H.B. Zhang (BNL) et al. J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Importance of  The medium produced in HI collisions is very short-lived → we need probes which carry information from the early stage to find out about the medium constituents: K+ K- φ QGP The φ-meson (ss) is a clean probe from early time: Small σ for interactions with non-strange particles[1] Relatively long-lived (41 fm/c) →decays outside the fireball Previous measurements have ruled out K+ + K- coalescence as φ production mechanism[2] → info not “diluted” by hadronic phase The φ can provide info on particle production mechanism : The φ is a meson but as heavy as Λ,p baryons Differentiate between mass-type or meson/baryon- type dependencies in the RHIC measurement of grouping RCP and v2 [3] [1] A. Shor, Phys. Rev. Lett. 54 (1985) 11 [2] J. Adams et al., Phys. Lett. B 612 (2005) 181 [3] J. Adams et al. Phys. Rev. Lett. 92 (2004) 052302 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Dataset and analysis method We used the high-statistics 200 GeV Au+Au data to measure the φ observables at STAR: ~14.2 M minbias (0-80%) events ~13 M central triggered (0-12%) events Measured decay channel: φ → K++K- (BR = 49.1%) STAR TPC used to identify K via dE/dx in TPC gas STAR Detector Event-mixing method used to estimate background from uncorrelated K+K- pairs Final subtracted minv distribution fitted with Breit-Wigner + straight line J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Methods to extracted φ-meson v2 Standard event plane method[1,2] 1)In each pT bin, extract φ yield in each (Ф-Ψ2) bin. 2)Fitted φ yield(pT) vs. (Ф-Ψ2) to obtain v2obs(pT). 3)Corrected the v2obs (pT) with reaction plane resolution Invariant mass method[3] v2=v2obs/res [1]A.M. Poskanzar and S.A. Voloshin Phys. Rev. C 58 (1998) 1671 [2]J.Adams et al. Phys.Rev.Lett 95 (2005) 122301 [3]Borghini et al. nucl-th/0407041 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

φ-meson production (1) STAR Preliminary The shape of the φ pT spectra provide info on the mechanisms of particle production: φ pT spectra show a systematic centrality-dependent evolution in shape For peripheral collisions, a pQCD power-law tail is evident Peripheral spectra favor a Levy function description For central collisions, exponential and Levy functions fit spectra equally well The power-law tail is suppressed by the medium produced in central collisions J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

φ-meson production (2) STAR Preliminary For both centrality groupings, nuclear modification factor RCP of φ < 1 : φ yield suppressed in central compared to peripheral collisions: Particle grouping behaviour: φ follows the same trend as K0S in RCP Confirmation of meson-baryon dependence of RCP rather than mass-type dependence Described by recombination/ coalescence models[1] [1]R. J. Fries et al., Phys. Rev. C 68 (2003) 044902 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

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 STAR Preliminary STAR Preliminary [1] R. Hwa & C-B Yang, nucl-th/0602024 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Elliptic flow v2 The φ experiences significant elliptic flow! (result is mean of 2 different, but consistent methods): STAR Preliminary 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[1] =2) Consistent with v2 of other multi-strange hadrons (Ξ, Ω)[2] i.e. s-quarks flow! Particle production mechanisms: Further evidence of species-type dependence of v2 at intermediate pT (described by recombination/ coalescence models[3]) [1] X. Dong et al., Phys. Lett. B, 597 (2004) 328 [2] STAR Collab. Phys. Rev. Lett. 95 (2005) 122301 [3] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Elliptic flow v2 The φ experiences significant elliptic flow! (result is mean of 2 different, but consistent methods): 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[1] =2) Consistent with v2 of other multi-strange hadrons (Ξ, Ω)[2] i.e. s-quarks flow! STAR Preliminary Particle production mechanisms: Further evidence of species-type dependence of v2 at intermediate pT (described by recombination/ coalescence models[3]) [1] X. Dong et al., Phys. Lett. B, 597 (2004) 328 [2] STAR Collab. Phys. Rev. Lett. 95 (2005) 122301 [3] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Elliptic flow v2 The φ experiences significant elliptic flow! (result is mean of 2 different, but consistent methods): 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] =2) Consistent with v2 of other multi-strange hadrons (Ξ, Ω)[2] i.e. s-quarks flow! STAR Preliminary Particle production mechanisms: Further evidence of species-type dependence of v2 at intermediate pT (described by recombination/ coalescence models[3]) [1] X. Dong et al., Phys. Lett. B, 597 (2004) 328 [2] STAR Collab. Phys. Rev. Lett. 95 (2005) 122301 [3] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Conclusions Large elliptic flow (despite small σ) at low pT STAR Preliminary Large elliptic flow (despite small σ) at low pT NCQ-scaling of v2 for pT > 2 GeV/c (similar to Ω (sss) ) Reco. models describe data well[1] RCP critical confirmation of baryon-meson dependence of RHIC observables Scaling described by reco. models Central data well-described (intermediate pT) by reco. model[2] pQCD power-law tails suppressed in central compared to peripheral spectra Central Ω/φ ratio well-described by thermal quark reco. model up to pT~4 GeV/c[2] [1] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 [2] R. Hwa & C-B Yang, nucl-th/0602024 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

PARTONIC COLLECTIVITY & DECONFINEMENT Conclusions STAR Preliminary Large elliptic flow (despite small σ) at low pT NCQ-scaling of v2 for pT > 2 GeV/c (similar to Ω (sss) ) Reco. models describe data well[1] PARTONIC COLLECTIVITY & DECONFINEMENT RCP critical confirmation of baryon-meson dependence of RHIC observables Scaling described by reco. models Central data well-described (intermediate pT) by reco. model[2] pQCD power-law tails suppressed in central compared to peripheral spectra Central Ω/φ ratio well-described by thermal quark reco. model up to pT~4 GeV/c[2] [1] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 [2] R. Hwa & C-B Yang, nucl-th/0602024 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

PARTONIC COLLECTIVITY & DECONFINEMENT ...hints of THERMALIZATION? Conclusions Large elliptic flow (despite small σ) at low pT NCQ-scaling of v2 for pT > 2 GeV/c (similar to Ω (sss) ) Reco. models describe data well[1] STAR Preliminary PARTONIC COLLECTIVITY & DECONFINEMENT RCP critical confirmation of baryon-meson dependence of RHIC observables Scaling described by reco. models Central data well-described (intermediate pT) by reco. model[2] pQCD power-law tails suppressed in central compared to peripheral spectra Central Ω/φ ratio well-described by thermal quark reco. model up to pT~4 GeV/c[2] ...hints of THERMALIZATION? [1] C. Nonaka et al., Phys. Lett. B 583 (2004) 73 [2] R. Hwa & C-B Yang, nucl-th/0602024 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai

Outlook : φ puzzle? With Full TOF 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 region as NA49 and NA50 shows? NA50 NA49 Open symbols: φ -> ++- Solid symbols: φ -> K++K- Pal, Ko, Lin, NPA707(02)505 J.H. Chen 6th China-Japan Joint Nuclear Physics Symposium, May 16-20, 2006, Shanghai