Speaker
Description
We study the evolution of the spin alignment of neutral $\rho$ mesons in a pion gas using spin kinetic or Boltzmann equations. The $\rho\pi\pi$ coupling is given by the chiral effective theory. The collision terms at the leading and next-to-leading order in spin Boltzmann equations are derived. The evolution of the spin density matrix of the neutral $\rho$ meson is simulated with different initial conditions. The numerical results show that the interaction of pions and neutral $\rho$ mesons creates very small spin alignment in the central rapidity region if there is no $\rho$ meson in the system at the initial time. Such a small spin alignment in the central rapidity region will decay rapidly toward zero in later time. If there are $\rho$ mesons with a sizable spin alignment at the initial time the spin alignment will also decrease rapidly. We studied the effect on $\rho_{00}$ from the elliptic flow of pions in the blast wave model. With vanishing spin alignment at the initial time, the deviation of $\rho_{00}$ from 1/3 is positive but very small.The effect of tensor polarizations of $\rho$ mesons on $\gamma$ correlator observables for CME has also been investigated.
| Category | Theory |
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