Darmstadt 2008 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 49: Theorie

HK 49.6: Talk

Friday, March 14, 2008, 15:15–15:30, 2F

Polarized photon production in non-central heavy ion collisions — •Andreas Ipp, Antonino Di Piazza, Jörg Evers, and Christoph H. Keitel — MPI für Kernphysik, Heidelberg

The strong angular momentum in non-central heavy-ion collisions can lead to global quark polarization in a quark gluon plasma (QGP) through spin-orbit coupling [1]. The global quark polarization can be transfered to a polarization of massive secondary particles like the Λ-hyperon. So far only an upper bound for the Λ-hyperon polarization |P_Λ,Λ|≤0.02 has been found, but its result is affected by all stages of the collision to an unknown degree. Photons on the other hand are likely to leave the QGP without further interaction and thus provide a primary probe for thermodynamic properties of the QGP [2].

In this work we study the possibility to detect global quark polarization using photons emitted from the QGP through Compton scattering of quarks (antiquarks) and gluons, qg→ qγ (qg→qγ), and annihilation of quarks and antiquarks, qq→ gγ [3]. We calculate the visibility of the photon polarization for various degrees of momentum anisotropy of the QGP that naturally arise due to the anisotropic expansion of the QGP itself. We find that especially for anisotropies compressed along the beam axis and higher photon energies, global quark polarization is transfered efficiently to circular polarization of photons.

[1] Z.-T. Liang and X.-N. Wang, Phys. Rev. Lett. 94, 102301 (2005)
[2] A. Ipp, K. Kajantie, A. Rebhan and A. Vuorinen, Phys. Rev. D 74, 045016 (2006)
[3] A. Ipp, A. Di Piazza, J. Evers, and C. H. Keitel, arXiv:0710.5700