Quarkonium Production and Polarization in an Improved Color Evaporation Model
An improved version of the color evaporation model (ICEM) has been introduced to describe heavy quarkonium production. In contrast to the traditional color evaporation model, the constraint was imposed that the invariant mass of the intermediate heavy quark-antiquark pair must be larger than the mass of produced quarkonium. A momentum shift between heavy quark-antiquark pair and the quarkonium was also introduced. Calculations show that the model can describe the charmonium yields as well as ratio of $\psi$' over $J$/$\psi$ better than the traditional color evaporation model. The ICEM has been extended to calculate the polarization of prompt $J$/$\psi$ and $Υ$($1S$) production for the first time in the color evaporation approach. The first calculations were made at leading order. The polarization parameter λ$_\vartheta$ was calculated as a function of center of mass energy and rapidity in p + p collisions. The x F dependence of the polarization was also calculated and compred to experimental results in p+Cu and π+W collisions. The next step of calculating the p T dependence of the polarization has been taken, with a calculation in the k T -factorization approach. We compare the unpolarized p T distributions for the $J$/$\psi$ and $\psi$, as well as the $\psi$ to $J$/$\psi$ ratio, in p + p collisions at RHIC and the LHC for several energies. We also present the polarization results and make comparison to polarization data.