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Spin alignment of vector mesons ( Φ , K *0 ) in Heavy-Ion Collisions at RHIC

Spin alignment of vector mesons ( Φ , K *0 ) in Heavy-Ion Collisions at RHIC. Jinhui Chen for STAR Collaboration. Outline. Introduction Analysis method and results 1) Spin alignment with respect to reaction plane 2) Spin alignment with respect to production plane Summary and outlook.

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Spin alignment of vector mesons ( Φ , K *0 ) in Heavy-Ion Collisions at RHIC

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  1. Spin alignment of vector mesons (Φ, K*0) in Heavy-Ion Collisions at RHIC Jinhui Chen for STAR Collaboration

  2. Outline • Introduction • Analysis method and results 1) Spin alignment with respect to reaction plane 2) Spin alignment with respect to production plane • Summary and outlook QM06 Nov.14-20 Shanghai China

  3. Introduction • Spin alignment of vector mesons is a unique probe of particle production and dynamics[1,2] 1. Orbital angular momentum  spin? 2. Coalescence/Fragmentation of polarized quarks? 3. Contributions to the significant collective flow observed at RHIC? • Spin alignment of vector mesons is described by • We measure ρ00 through decayed products angular distribution in the rest frame of vector mesons: spin density matrix (s=1)  Deviation of ρ00 from 1/3 manifests the alignment of vector mesons 1. Z.T. Liang and X.N. Wang, PRL 94 102301 (05), PRL 96 039901 (06), PLB 629 (05) 20-26; 2. S.A. Voloshin nucl-th/0410089. QM06 Nov.14-20 Shanghai China

  4. Λpolarization Fermi-lab 1976 G. Bunce et al. PRL 36 (1976) 1113 OPAL Col. PLB 412 (1997) 210 ρ00 J. Duryea et al. PRL 67 (1991) 1193 E896 Col. NPA 698 (2002) 499 PΛ Previous measurements QM06 Nov.14-20 Shanghai China

  5. Features at RHIC: • Formation of bulk partonic matter • Hadronization from bulk partonic matter is different from fragmentation scheme  Constituent quark degree of freedom ? STAR Collaboration, NPA 757 (05) 102 STAR Detector beam • Measurements for: Global hyperon polarization Global vector meson spin alignment x reaction plane y Measurement from RHIC-STAR QM06 Nov.14-20 Shanghai China

  6. 27% Yi-Jin Pei, hep-ph/9703243. beam secondary vertec x y Hyperon polarization vs vector meson spin alignment reaction plane QM06 Nov.14-20 Shanghai China

  7. Using mixed event method to get the raw dN(pT)/dcos(θ*) distribution. Correct thedN(pT)/d(cosθ*) with detector acceptance. Fitting dN(pT)/d(cosθ*) with to get the ρ00obs. Correct ρooobs with “reaction plane resolution” to obtain ρ00. Analysis details (φ-meson) QM06 Nov.14-20 Shanghai China

  8. STAR Preliminary ρ00 vs pT |y|<1.0 With statistical and systematical uncertainties, φand K*0 spin are not aligned w.r.t. reaction plane. QM06 Nov.14-20 Shanghai China

  9. With the data sample, we have not observed global spin alignment for φand K*0 at different centrality. STAR Preliminary Centrality 10-40% ρ00 vs Npart |y|<1.0 QM06 Nov.14-20 Shanghai China

  10. Au+Au @ 200GeV (20-70%) Au+Au @ 62GeV (0-80%) STAR Preliminary (GeV/c) What about Λ global polarization? I. Selyuzhenkov’s talk Section 3.4, Nov. 19 With statistical and systematical uncertainties, we have not observed global spin alignment for φ, K*0and global polarization for Λ at mid-central collisions. QM06 Nov.14-20 Shanghai China

  11. Hyperons H produced in unpolarized p+p  H+X or p+A  H+X are transversely polarized w.r.t. production plane. What about vector mesons? Spin alignment w.r.t. production plane • transversely polarized? • correlated with spin alignment w.r.t. reaction plane? production plane QM06 Nov.14-20 Shanghai China

  12. STAR Preliminary 0.8<pT<1.2GeV/c Φand K*0 spin may be slightly aligned at low pT w.r.t. production plane. ρ00 vs pT |y|<1.0 QM06 Nov.14-20 Shanghai China

  13. STAR Preliminary And p+p collisions ? |y|<1.0 φ-meson spin alignmentin p+p collisions needs more statistics to be conclusive. QM06 Nov.14-20 Shanghai China

  14. STAR Preliminary We are interested in possible difference in φ and K*0 spin alignment between Au+Au and p+p collisions due to different dynamics. In current statistics, the spin alignment ofφ-meson between Au+Au and p+p collisions are similar. Compared with Au+Au QM06 Nov.14-20 Shanghai China

  15. Au+Au 200GeV Au+Au 200GeV (0-80%) (0-80%) STAR Preliminary STAR Preliminary In our current analysis, We used kaons from TPC only. One tray will enhance the S/B ratio by a factor of 3.5 at intermediate pT. Full barrel ~ a factor of 10. J. Wu’s talk Section 1.4, Nov.15 Time of Flight detector upgrade QM06 Nov.14-20 Shanghai China

  16. Reaction plane: within statistics, we have not observed a global polarization forΛand global spin alignments for andK*0. Production plane:  andK*0 spin may be slightly aligned in low pT region. No significant difference in  spin alignments, w.r.t. production plane, between p+p and Au+Au collisions have been observed. STAR Full Barrel Time-of-Flight detector upgrade will significantly enhance our capability for a conclusive measurement in the future. Summary and Outlook Thanks! QM06 Nov.14-20 Shanghai China

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