Abstract
Measurements of the net polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons at the Relativistic Heavy Ion Collider (RHIC) have stimulated much interest in how strange quarks might align their spin with the vorticity of the matter created in heavy ion collisions. We calculate the Lagrangian in the rest frame of a fluid element undergoing rotation with angular velocity $\omega$ including photon and gluon fields. There is an additional coupling between the quarks and the gauge fields proportional to $\omega$, but this vertex does not change the spin of the quarks. We also show that the times to equilibrate quark helicity and spin parallel to the vorticity are the same so long as $\omega$ is small compared to the temperature.
Highlights
Polarization of andhyperons was proposed as an observable that provides information on the vorticity of the hot, dense matter created in noncentral heavy ion collisions [1,2]
In these collisions the spins of the andought to couple to the vorticity, resulting in a splitting in energy between particles with spin parallel and antiparallel to the vorticity. The distribution of their decay products can be used to infer their polarizations. Measurements of these polarizations have been made by the STAR Collaboration over the full range of beam energies at the Relativistic Heavy Ion Collider (RHIC) [3,4,5]
In Ref. [9] we considered the Nambu– Jona-Lasinio (NJL) model with the inclusion of the six-quark Kobayashi-Maskawa–’t Hooft interaction which breaks axial U(1) symmetry
Summary
Polarization of andhyperons was proposed as an observable that provides information on the vorticity of the hot, dense matter created in noncentral heavy ion collisions [1,2] In these collisions the spins of the andought to couple to the vorticity, resulting in a splitting in energy between particles with spin parallel and antiparallel to the vorticity. Since helicity is conserved in QCD interactions when the quark is massless, helicity flip can only occur when the quark has a mass Both mechanisms resulted in equilibration times far too long to be relevant to heavy ion collisions. The perturbative QCD calculation treats quarks and gluons as elementary point particles while the NJL calculation treats quarks as dressed quasiparticles Both consider two-body scatterings only, and both calculate the momentum-dependent relaxation time from the relativistic Boltzmann equation. The kinematic vorticity is the one that appears in the tetrad formalism and in the energy eigenvalues of the Dirac equation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
