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- meson and strange quark dynamics at RHIC

- meson and strange quark dynamics at RHIC. Yu-Gang Ma Shanghai Institute of Applied Physics, Chinese Academy of Sciences International Workshop Heavy Ion Physics at LHC Also dedicate to whom died in the 5/12 Wen-Chuan Earthquake. Outline. Motivation

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- meson and strange quark dynamics at RHIC

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  1. -meson and strange quark dynamics at RHIC Yu-Gang Ma Shanghai Institute of Applied Physics, Chinese Academy of Sciences International Workshop Heavy Ion Physics at LHC Also dedicate to whom died in the 5/12 Wen-Chuan Earthquake

  2. Outline • Motivation • -meson production and s-quark at RHIC • f-meson production and elliptic flow, partonic (s-quark) collectivity • W/f ratio, s-quark transverse momentum dis. • f-meson spin alignment, s-quark polarization • f-meson enhancement, s-quark enhancement • Summary/outlook

  3. RHIC puzzle: large p/p Unexpected large p/p ratio in central Au+Au collisions: behavior different from elementary collisions!

  4. STAR PHENIX RHIC puzzle: v2 saturation & grouping • At intermediate pT region (2<pT<5 GeV/c) • v2 saturated andshown a constituent quark number scaling behavior.

  5. [yield/N-N]central RCP= [yield/N-N]peripheral • At intermediate pT region: • RCP shown an baryon-meson grouping behavior! RHIC puzzle: RCP grouping RCP

  6. What can we learn from those puzzle? • At RHIC intriguing experimental features: • enhanced baryon over meson production • strong elliptic flow • grouping behavior of v2 and RCP for identified particles • Hadronization of bulk dense matter created at RHIC should be different from e+e- collisions! • Quark Coalescence/Recombination? • Evidence for Deconfinement? • Possible for mass-effect rather than B/M type? f mesons are particularly important probes for these issues!

  7. K- K+ K+ Thef-meson is a clean probefrom early time: K- • Smallsfor interactions with non-strange particles[1] • Relatively long-lived (41 fm/c) →decays outside the fireball • Previous measurements have ruled outK+K- coalescence asfproduction mechanism[2] φ φ QGP φ The f can provide info on particle production mechanisms/medium constituents: K- • The f is a meson but as heavy asL,p baryons (mass vs. particle type?) K+ Why f-meson ? [1] A. Shor, Phys. Rev. Lett. 54 (1985) 1122 [2] J. Adams et al., Phys. Lett. B 612 (2005) 181

  8. STAR TPC used to identify KaonviadE/dx in TPC gas STAR Detector • We used the high-statistics 200 GeV and 62.4 GeV Cu+Cu data to measure the -meson production at STAR: • ~10.6M 200 GeV events (0-54%); • ~8.8M 62.4 GeV events (0-60%). The STAR experiment • Event-mixing method used to estimate combinatorial background from uncorrelated K+K- pairs; • Final subtracted minv distribution fitted with Breit-Wigner + straight line.

  9. <pT> f/K- 1. Evolution in the centrality dependence; 2. <pT>, -meson decoupled early; 3. N()/N(K), ruled out the K+K-coalescence. STAR Col. Phys. Lett. B 612, (2005) 181, Phys. Rev. Lett. 99, (2007) 112301. -meson production at RHIC

  10. f-meson RCP RCP • referred to mid-central collisions: • RCP of f meson is more consistent with that of K0 rather than L, supporting the baryon/meson grouping behavior. • The observable favors the prediction based on quark Coa/Recom model. • referred to peripheral collisions: • The binary scaled f production is very similar to that in p+p and d+Au collisions where strangeness production may be canonically suppressed. • Therefore a baryon-meson scaling behavior of RCP is not expected. SINAP & LBL et al. (for STAR), PRL 99 (2007)112301

  11. At intermediate pT,W(sss)and f(ss)should be dominated by bulk thermal quark coalescence – no jet contribution (Hwa and Yang PRC 75, 054904 (2007)) It appears that thermal quark coalescences dominate the particle production below pT~4 GeV/c in centralAu+Aucollisions f’sare mostly from bulk thermal s quarks SINAP & LBL et al. (for STAR), PRL 99 (2007)112301

  12. Bulk s quarks show collective elliptic flow The f-meson shows sizeable v2 and its magnitude appears to follow the same trend as K’s, supporting the B/M species grouping. SINAP & LBL et al. (for STAR), PRL 99 (2007)112301

  13. Parton PT distributions at Hadronization Can we extract the strange quark pT distribution from multi-strange hadron data? If baryons at pT are mostly formed from coalescence of partons at pT/3 and mesons at pT are mostly formed from coalescence of partons at pT/2, then we could extract quark information: • and f particles have no decay feed-down contribution! These particles will freeze-out earlier from the system and have small hadronic rescattering cross sections.

  14. Strange and down quark distribution arXiv:0801.2265 Strange quark distributions are flatter than light quarks! J.H. Chen, F. Jin (SINAP-UCLA) et al., arXiv:0801.2265

  15. Test on s/d ratio at hadronization s/d quark ratios = W/X = X/L Yes! but with large uncertainties due to decay feed-down corrections in L. J.H. Chen, F. Jin et al., arXiv:0801.2265

  16. The original AMPT spectra is too soft Input our s,d spectra in AMPT model we can get a satisfied momentum spectra for hyperon and phi Test on hyperon and phi spectra with AMPT J.H. Chen, F. Jin et al., arXiv:0801.2265

  17. -Ly in unit of 105 b/RA Strange quark polarized at RHIC? Huge orbital angular momentum of the collisions system Z.T. Liang et al., PRL 94 (2005) 102301; PLB 629 (2005) 20; arXiv0710.2943; B. Betz et al., PRC 76 (2007) 044901; F. Becattini et al., PRC 77 (2008) 024906. Observable correlated with reaction plane? Well-develop flow technique

  18. x z impact parameter Global polarization effect • gradient in pz-distribution along the x-direction • local orbital angular momentum of the created parton • quark polarized via spin-orbit? • final state hadron polarization? • hyperon polarization • vector meson spin alignment

  19. Vector meson spin alignment-pT dependence Reconstruction: ->K++K-, K*0  +- + K -+ Deviation of ρ00 from 1/3 manifests the alignment of vector mesons The data are consistent with the unpolarized expectation of 1/3 and thus provide no evidence for global spin alignment despite the large OAM in non-central Au+Au collisions at RHIC. J.H. Chen et al (SINAP-USTC for STAR) Phys Rev C (Rap Comm.) (in press), 0801.1927(nucl-ex)

  20. Vector meson spin alignment-Npart dependence No evidence is found for the transfer of the orbital angular momentum of the colliding system to the vector meson spins. PRC(R)(in press),0801.1927(nucl-ex)

  21. Strangeness enhancement ? We do observe strangeness enhancement: yield relative to p+p BUT -meson enhancement: -- Enhancement between Strangeness = 1 (L, K) and 2 (X) particles -- 200 GeV data > 62.4 GeV -- could not be solely due to the canonical suppression, there could be dynamics effect. -- possible Core-corona superposition (Becattini et al)

  22. Since  mesons are made via coalescence of seemingly thermalized s quarks in central Au+Au collisions, the observations imply hot and dense matter with partonic collectivity has been formed at RHIC. Summary • N(f)/N(K) vs. Npart rules out the Kaon coalescence as a dominant channel for f production at RHIC; • N(W)/N(f) vs. pT favors the model prediction that fs are made via thermalied s-quarks coalescence at RHIC; • N(W)/N(f) and N(X)/N(f) vs. pT/nq indicate that strange quarks seem to develop a stronger radial flow than the light quarks prior to hadronization at RHIC; • v2(f) vs. pT concludes that the partonic collectivity has been formed at RHIC; • The disappearance of the polarization signal might imply that the system created at RHIC is isotropic to the extent that, locally, there is no longer a preferred direction. Again, favors the QGP scenario.

  23. Five “final item” trays in place and in STAR data stream now • PID information for > 95% of kaons and protons in the STAR acceptance • Clean e± ID down to 0.2 GeV/c Collaboration plan 120 trays of MRPC modules which leverage MRPC development at CERN (Crispin Williams et al) Development of HPTDC Chip MRPC tech transfer and construction (contributed) in China Fully complete in time for run 10 (fall 2009)‏ Phi reconstruction from e+e- • /K separation to 1.6 GeV/c • 0.7 for TPC alone • (+K)/p to p = 3 GeV/c • 1.2 for TPC alone TOF+TPC : one kaon from φ identified by TPC, the other by TOF TPC+TPC : the 2 kaons from φ identified using only TPC

  24. Ultimately the focus of such studies in the future: Beam Energy Scan & QCD critical point search LQCD predicts a rapid transition from a hadron resonance gas to a quark-gluon plasma. The location of the QCD Critical Point,if it exists, remains a matter for experiment STAR Collaboration is planning for initial beam energy scan in Run 10 (fall 2009) Primary tool: search for anomalously large particle identified fluctuations with comprehensive particle identification for charged particles provided by TPC + TOF

  25. Many Thanks for STAR collaborators, especially for Jinhui Chen, Guoliang Ma, Xiangzhou Cai, Huanzhong Huang, Nu Xu et al.

  26. STAR Preliminary dN/dy and <pT> • The dN/dy and <pT> are similar for Cu+Cu and Au+Au at similar Npart bin for the same collisions energy. • f yields from Au+Au and Cu+Cu collisions depend on the number of participant nucleons only, unlike Kaon and hyperons. see STAR Xiaobin Wang – parallel session VII [1] NA49 Col. Phys. Rev. Lett. 96, 052301 (2005); [2] E-802 Col. Phys. Rev. C 60, 044904 (1999).

  27. Nuclear Modification factor STAR Preliminary Comparing central Au+Au and central Cu+Cu with peripheral Au+Au Collisions— 1) the yield and pT shape depend on number of participants only 2) in terms of number of binary collisons the Cu+Cu data is higher indicating given the same top 10% centrality Cu+Cu has less number of collisions per participant

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