相对论重离子碰撞中f介子的产生

1、1相对论重离子碰撞中相对论重离子碰撞中f f介子的产生介子的产生陈金辉陈金辉中国科学院上海应用物理研究所中国科学院上海应用物理研究所QCD相变与重离子碰撞物理国际暨相变与重离子碰撞物理国际暨第七届全国研讨会第七届全国研讨会USTC2008年年7月月10号号-12号号Many thanks to: X. Cai, S. Blyth, F. Jin, H. Huang, G. Ma, J. Ma, B. Mohanty, N. Xu 2Outlinel Introduction What we have learnt from RHICl Motivation Why we focus on f-

2、meson?l Results f-meson elliptic flow measurement f-meson spectra measurement W/f and X/f ratiol Conclusion and Outlook3pT Scales and Physical ProcessesRCPThree PT Regions:- Fragmentation (high pT jet energy loss) - multi-parton dynamics (recombination or coalescence or ) - Hydrodynamics (constituen

3、t quarks ? parton dynamics from gluons to constituent quarks? )4High pT suppressionl Very dense matter has been created in central Au+Au collisionsl The dense matter is responsible for the suppression of high pT particles and the disappearance of back-to-back correlation5The Suppression is the Same

4、for p0 and h Parton level effectNo suppression photons dont participate!6High pT phenomena at RHICl Very dense matter has been created in central Au+Au collisions!l This dense matter is responsible for the suppression of high pT particles and the disappearance of back-to-back correlation!l The energ

5、y loss observed at RHIC is in parton level, but the mechanism for parton energy loss is yet to be understood! Wont elaborate in this talk.7Intermediate pT, large p/p ratiol Unexpected large p/p p ratio in central Au+Au collisions The hadronization scheme should be different from e+e- !8Intermediate

6、pT, v2 and RCP groupingSTARPHENIXBaryonMesonl V2 and RCP for PID measurement shown a B/M grouping behavior partonic degree of freedom?9What can we learn from those phenomena?At RHIC intriguing experimental features: enhanced baryon over meson production strong elliptic flow grouping behavior of v2 a

7、nd RCP for PID ? 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 typef are particularly important probes for these issues!10Why f-meson ?1 A. Shor, P

8、hys. Rev. Lett. 54 (1985) 1122K+K-K-K+K+K-QGP The f-meson is a clean probe from early time:Small s s for interactions with non-strange particles1Relatively long-lived (41 fm/c) decays outside the fireball The f-meson can provide info on particle production mechanisms /medium constituents:The f is a

9、meson but as heavy as L, p baryons (mass vs. particle type?) An interesting probe to understand the strangeness dynamics:No net strangeness in the initial colliding nuclei11f-meson measurement, v2 and RCPl For v2 and RCP measurement, f-meson follows the trend observed in the Ks,p mesons rather than

10、in the L, p baryons clear signature for the Coa./Reco. hadronization mechanism.STAR Col. Phys. Rev. Lett. 99, (2007) 112301.12f-meson production at RHICf f/K-STAR Col. Phys. Lett. B 612, (2005) 181, Phys. Rev. Lett. 99, (2007) 112301.1. Evolution in the centrality dependence;2. , f-meson may decoupl

11、e early;3. N(f)/N(K), ruled out the K-coalescence.13 fs are mostly from bulk s quarksl N(W)/N(f) vs. pT is consistent with a model based on the recombination of thermal s quarks up to pT 4.0 GeV/c, but disagrees at higher pT.l v2(f) shows similar behavior as PIDs, positive signature for partonic col

12、lectivity at RHIC.STAR Col. Phys. Rev. Lett. 99, (2007) 112301.14Parton pT distributions at Hadronization?)2/()3/()2/()3/(TTTTppdppsffXWCan we extract the strange quark pT distribution from multi-strange hadron data? If baryons of pT are mostly formed from coalescence of partons at pT/3 and mesons o

13、f pT are mostly formed from coalescence of partons at pT/2W and f f particles have no decay feed-down contribution!These particles will freeze-out earlier from the system and have small hadronic rescattering cross sections1,2.1 A. Shor, PRL 54 (1985) 1122;2 H. Van Hecke et al., PRL 81 (1998) 5764.15

14、 Strange and down quark distributionStrange quark distributions are flatter than light quarks! arXiv:0801.226516Test on s/d ratio at hadronizations/d quark ratios= W/XW/X= X/LX/LYes! but with large uncertainties due to decay feed-down corrections in L.L.arXiv:0801.2265X. Wang17Summary and Conclusion

15、l N(f)/N(K) vs. Npart rules out the Kaon coalescence as a dominant channel for f production at RHIC;l N(W)/N(f) vs. pT favors the model prediction that fs are made via thermalied s-quarks coalescence at RHIC;l v2(f) vs. pT conclude that the partonic collectivity has been formed at RHIC;l N(W)/N(f) a

16、nd N(X)/N(f) vs. pT/nq indicate that strange quarks may have developed a stronger collective radial flow than the light quarks during the initial parton evolution at RHIC; Since f f mesons are made via coalescence of seemingly thermalized s quarks in central Au+Au collisions, the observations imply

17、hot and dense matter with partonic collectivity has been formed at RHIC.18Outlook: Extend PID CapabilityToF detector updated: 5 trays of ToF system installed in Run 8, commissioned, and used for physics. 90 (of 120) ToF trays to be installed for Run 9 and will be completed before Run 10. l p/K separatio