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Global polarization

Updated on Fri, 2008-07-11 12:53. Originally created by seluzhen on 2008-07-08 12:03.

Global polarization measurement in Au+Au collisions (paper proposal)

Principal Authors

Ilya Selyuzhenkov and Sergei Voloshin (for the STAR collaboration)

Target Journal

Phys. Rev. C.

Abstract

The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Lambda and Anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt{s_NN}=62 GeV and 200 GeV performed with the STAR detector at RHIC.

The observed global polarization of Lambda and Anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P_{Lambda,Anti-Lambda}| < 0.02, is compared to the theoretical values discussed recently in the literature.

Paper draft

GPC: 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0
Collaboration: 11.0 12.0 13.0 14.0
Referee: 15.0 16.0
As sumbitted to PRC: 01 02

Comments and reports on the paper

God Parent Committee (GPC) comments
comments by the STAR Collaboration
Referee reports

Note: Separate page for the Anti-Lambda hyperon global polarization

Figures

Global polarization

Fig.1 Global polarization of Lambda hyperons as a function of Lambda transverse momentum.

Filled circles show the results for Au+Au collisions at sqrt{s_NN}=200 GeV (centrality region 20-70%) and open squares indicate the results for Au+Au collisions at sqrt{s_NN}=62 GeV (centrality region 0-80%).

 

Global polarization

Fig.2 Global polarization of Lambda hyperons as a function of Lambda pseudorapidity.

Filled circles show the results for Au+Au collisions at sqrt{s_NN}=200 GeV (centrality region 20-70%). A constant line fit to these data points yields P_Lambda = (2.8 +- 9.6)x10^{-3} with chi^2/ndf = 6.5/10. Open squares show the results for Au+Au collisions at sqrt{s_NN}=62 GeV (centrality region 0-80%). A constant line fit gives P_Lambda = (1.9 +- 8.0)x10^{-3} with chi^2/ndf = 14.3/10.

 

Global polarization

Fig.3 Global polarization of Lambda hyperons as a function of centrality given as fraction of the total inelastic hadronic cross section.

Filled circles show the results for Au+Au collisions at sqrt{s_NN}=200 GeV (centrality region 20-70%) and open squares indicate the results for Au+Au collisions at sqrt{s_NN}=62 GeV (centrality region 0-80%).

 

Conclusion

The Lambda and Anti-Lambda hyperon global polarization has been measured in Au+Au collisions at center of mass energies sqrt{s_NN}=62 and 200 GeV with the STAR detector at RHIC.

An upper limit of |P_{Lambda,Anti-Lambda}| < 0.02 for the global polarization of Lambda and Anti-Lambda hyperons within the STAR acceptance is obtained. This upper limit is far below the few tens of percent values discussed in Phys. Rev. Lett. 94, 102301 (2005), but it falls within the predicted region from the more realistic calculations Liang:Xian Workshop (2006) based on the HTL (Hard Thermal Loop) model.

Bibliography

  1. Globally Polarized Quark-Gluon Plasma in Noncentral A + A Collisions

    Z.-T. Liang and X.-N. Wang
    Phys. Rev. Lett. 94, 102301 (2005) [ erratum:Phys. Rev. Lett. 96, 039901 (2006)]

  2. Polarized secondary particles in unpolarized high energy hadron-hadron collisions?

    Sergei A. Voloshin
    nucl-th/0410089

  3. Spin Alignment of Vector Mesons in Non-central A + A Collisions

    Z.-T. Liang and X.-N. Wang
    Phys.Lett.B629:20-26 (2005) [nucl-th/0411101]

  4. Global quark polarization in QGP in non-central AA collisions

    Gao Jian-hua and Z. T. Liang
    Talk on November 24, 2006 (power point file) at Xi'an Workshop (Xi'an, China)

Talks and Publications on the subject

  1. Anti-Lambda hyperon global polarization in Au+Au collisions at RHIC

    Ilya Selyuzhenkov [for the STAR Collaboration]
    International Workshop on "Hadron Physics and Property of High Baryon Density Matter", Xi'an, China (2006)
    arXiv:nucl-ex/0702001 (2007)

  2. Centrality dependence of hyperon global polarization in Au + Au collisions at RHIC

    Ilya Selyuzhenkov [for the STAR Collaboration]
    19th International Conference on "Ultra-Relativistic Nucleus-Nucleus Collisions" (Quark Matter 2006) Shanghai, China, 2006
    arXiv:nucl-ex/0701034 (2007)

  3. Acceptance effects in the hyperons global polarization measurement

    Ilya Selyuzhenkov [for the STAR Collaboration]
    9th Conference on the Intersections of Particle and Nuclear Physics ( CIPANP 2006), Westin Rio Mar Beach, Puerto Rico, 2006
    AIP Conf. Proc. 870, 712 (2006) [arXiv:nucl-ex/0608034]

  4. Global polarization measurement in Au+Au collisions

    Ilya Selyuzhenkov [for the STAR Collaboration]
    International Conference on Strangeness in Quark Matter (SQM 2006), Los Angeles, CA, USA, 2006
    J. Phys. G: Nucl. Part. Phys. 32, S557 (2006) [arXiv:nucl-ex/0605035]

  5. Global polarization and parity violation in Au+Au collisions

    Ilya Selyuzhenkov [for the STAR Collaboration]
    Midwest Critical Mass Workshop (MCM), Toledo OH, USA, 2005
    Download slides

  6. Global polarization and parity violation study in Au+Au collisions

    Ilya Selyuzhenkov [for the STAR Collaboration]
    18th International Conference on "Ultra-Relativistic Nucleus-Nucleus Collisions" (Quark Matter 2005), Budapest, Hungary, 2005
    Rom.Rep.Phys. 58, 049 (2006) [arXiv:nucl-ex/0510069]

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