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Spin alignment of vector mesons (K* 0 , φ ) in Au+Au and p+p collisions at s - NN = 200 GeV

STAR. Motivations Analysis details Results spin alignment w.r.t. reaction plane spin alignment w.r.t. production plane Conclusions. Spin alignment of vector mesons (K* 0 , φ ) in Au+Au and p+p collisions at s - NN = 200 GeV. Jinhui Chen For STAR Collaboration.

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Spin alignment of vector mesons (K* 0 , φ ) in Au+Au and p+p collisions at s - NN = 200 GeV

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  1. STAR • Motivations • Analysis details • Results • spin alignment w.r.t. reaction plane • spin alignment w.r.t. production plane • Conclusions Spin alignment of vector mesons (K*0,φ) in Au+Au and p+p collisions at s-NN = 200 GeV Jinhui Chen For STAR Collaboration Summer School @ Berkeley

  2. STAR System orbital angular momentum • Spin and polarization phenomena are important part of QCD understanding of hadron structure and particle formation dynamics: e.g., the nucleon spin and the hyperon polarization. The origin of nucleon spin is a mystery: ~25% from quarks[1] (DIS).The gluon helicity distribution and orbital angular momentum are thus essential to the understanding of the nucleon spin. [1] EMC Col. Nucl. Phys. B 328, 1 (1989); B.W.Filippone and X.Ji, Adv. Nucl. Phys. 26, 1 (2001) • Large orbital angular momentum • possessed in non-central Au+Au • collisions[2,3]: • “The local angular momentum for the • two neighboring parton is larger than the • spin of a quark” • A clear b dependence. [3] Z.T. Liang nucl-th/0705.2852 • “Global polarization is essentially a local • manifestation of the global angular momentum of the colliding system through interaction of spin-orbit coupling in QCD” [2] Z.T. Liang and X.N. Wang, Phys. Rev. Lett. 94 (2005) 102301

  3. STAR Global polarization (1) Z.T. Liang nucl-th/0705.2852 At RHIC: • Features of global polarization: • For non-central collisions, it should have a finite value, at small pT in central rapidity; • It should increase with b; • It should vanish in central collisions

  4. STAR or Global polarization (2) • Global spin alignment is sensitive to different hadronization scenarios in different kinematic region[1] • Coalescence (ρ00<1/3) • Fragmentation (ρ00>1/3) [1] Z.T. Liang and X.N. Wang, Phys. Lett. B 629 (2005) 20. • Global vector meson spin alignment and global hyperon polarization • Measured through decay products angular distribution w.r.t. reaction plane

  5. STAR 27% Yi-Jin Pei, hep-ph/9703243. beam secondary vertex x reaction plane y Technically -- vector meson spin alignmentcomplementary to hyperon polarization • Sensitivity: It’s a Pq2 effect for vector meson. • Z.T. Liang nucl-th/0705.2852

  6. STAR Using mixed event method to get the raw dN(pT)/dcos(θ*) distribution. φK+K- Correct thedN(pT)/d(cosθ*) with detector acceptance and tracking efficiency. Fitting dN(pT)/d(cosθ*) with to get the ρ00obs. Correct ρooobs for the “reaction plane resolution” to obtain ρ00. Au+Au (20-60%) w.r.t. reaction plane 0.8<pT<1.2 GeV/c Analysis details (φ-meson)

  7. STAR pT dependence K*0(0.8<pT<5.0 GeV/c): ρ00 = 0.33 +- 0.04 +- 0.12 φ (0.4<pT<5.0 GeV/c):ρ00 = 0.34 +- 0.02 +- 0.03 Within current sensitivity, we cannot probe the proposed pT dependence on different hadronization mechanism as the deviation from ρ00= 1/3 are predicted to be small in the model.

  8. STAR Centrality dependence Within current sensitivity, our measurement exhibits no strong spin alignment for vector meson at all collision centralities, presumably because the spin-orbit coupling for quark polarization is not large enough to be manifested in our measurement.

  9. STAR production plane STAR Col. nucl-ex/0703033 Spin alignment w.r.t. the production plane • Hyperons are transversely polarized • G. Bunce et. al. PRL 36, 1113 (1976); P.T. Cox et. al. PRL 46, 877 (1981); C. Wilkinson et. al. PRL 58, 855 (1987); B.E. Bonner et. al. PRL 62, 1591 (1989); J. Duryea et. al. PRL 67, 1193 (1991)… • It’s related to particle formation dynamics or to intrinsic quark transverse spin distribution • B. Andersson et. al. PLB 85, 417 (1979); J. Szwed PLB 105, 403 (1981); R. Barni et. al. PLB 296, 251 (1992); J. Soffer et. al. PRL 68, 907 (1992) • It may be correlated with the global polarization convoluted with an azimuthal angular anisotropy (v2 ) • S. Voloshin, nucl-th/0410089 • It may be closely related to the AN • Z. Liang and C. Boros PRL 79, 3608(1997); Q.Xu and Z. Liang PRD 68, 034023 (2003).

  10. STAR pT dependence pT<2.0 GeV/c ρ00(K*) = 0.43 +- 0.04 +- 0.08 ; ρ00(φ) = 0.42 +- 0.02 +- 0.04 pT>2.0 Gev/c ρ00(K*) = 0.38 +- 0.04 +- 0.06 ; ρ00(φ) = 0.38 +- 0.03 +- 0.05 In p+p, ρ00(φ) = 0.40 +- 0.04 +- 0.06

  11. STAR K*0 PLB 412 (1997) 210 DELPHI Col. PLB 406 (1997) 271 Comparison between different system PRL 95, 202001 (2005) • At small xp region, ρ00 are consistent with 1/3 from ee, pp, to AuAu collisions • It’s consistent with the null AN observation at central rapidity from RHIC

  12. STAR Conclusions • With respect to the reaction plane, ρ00(pT) are consistent within 1/3 within statistical and systematic uncertainty for vector meson in the measured pT up to 5 GeV/c and are independent of collision centrality and transverse momentum.  Vector meson in the measured kinematic region appear not to be produced with a strong global spin alignment despite the presence of a large orbital angular momentum for the system created in non-central Au+Au collisions. • With respect to the production plane, ρ00(pT) is less than 2 standard deviation above 1/3 and is similar to the results from p+p collisions.  Vector mesons in the measured pT region at mid-rapidity don’t seem to carry a significant polarization through production dynamics. Thanks!

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