Impact of Valence Quark Distributions in $AA$-Collisions

K. Itakura (RIKEN BNL), Y. Kovchegov and L. McLerran (BNL)

Together with Kazunori Itakura (RIKEN BNL), Larry McLerran (BNL) and Derek Teaney (BNL) we have investigated nuclear valence quark distribution in relation to baryon stopping observed at RHIC. Baryon stopping is the name given to the observed non-zero baryon number in the central rapidity region in heavy ion collisions. In an asymptotically high energy collision the valence quarks in the nuclei should just pass through each other leaving no valence quarks behind. However in the experiments at RHIC studying the baryons and anti-baryons at mid-rapidity one observes a small amount of net baryon number left behind. Arguing that a possible QGP formation can not significantly modify the rapidity distribution of the baryon number (that would be acausal) we concluded that the produced net baryon number is a result of initial state interactions. To understand how much baryon number would be generated by the initial state interactions we have constructed an equation deriving the valence quark distribution functions of the colliding nuclei. The equation is nonlinear and includes the effects of parton saturation/ high field strengths in the colliding nuclei. We have solved the equation and demonstrated that the observes net baryon number distribution is consistent with the solution of this equation. We are currently in the process of finishing up the paper on the subject.