1210.1577 (Yinghua Pan et al.)

Baryon Annihilation in Heavy Ion Collisions    [PDF]

Yinghua Pan, Scott Pratt

The role of baryon-antibaryon annihilation during the hadronic stage of a relativistic heavy ion collision is explored by simulating the chemical evolution of a hadron gas. Beginning with a chemically equilibrated gas at an initial temperature of 165 MeV, it is assumed that the gas expands according to the equations of a one-dimensional Bjorken expansion. The evolution includes both annihilation and regeneration of baryons. From an initial time of 5 fm/$c$ until a final time of 20 fm/$c$, the number of baryons drops by approximately half for the case where there is no net baryonic charge. This is consistent with measurements from the ALICE Collaboration at the LHC, where the $p/\pi$ ratio is roughly 50% lower than what comes from hydrodynamic models that ignore baryon annihilation. When the calculations are performed without the inverse process, e.g. $N\pi\rightarrow p\bar{p}$, the loss of baryons was found to be significantly larger. Baryon annihilation is shown to alter the extracted chemical breakup temperature. Assuming that annihilation cross sections are independent of the strangeness and isospin of the annihilating baryon and anti-baryon, the loss of strange baryons from annihilation is found to be similar.

View original: http://arxiv.org/abs/1210.1577