Angular momentum of glasma

Abstract

The earliest phase of an ultrarelativistic heavy ion collision can be described as a highly populated system of gluons called glasma. We study some glasma characteristics related to the system's angular momentum. The first one is the global angular momentum perpendicular to the reaction plane, which is spanned by the beam axis and impact parameter vector. We show that only a small fraction of the enormous initial angular momentum of the colliding ultrarelativistic nuclei is transferred to the glasma. Our main focus is the glasma angular momentum directed along the beam axis. This quantity has a local character and results from the inhomogeneous velocity field generated in the glasma. We calculate the vorticity and local angular momentum which show noticeably different behaviour. The results are analyzed in detail and discussed in the context of existing experimental data. We argue that neither vorticity nor thermal vorticity but instead the local angular momentum controls the polarization of final-state hadrons.