The Color Evaporation Model in Diffractive $J/ψ$ Photoproduction
M. B. Gay Ducati, C. B. Mariotto
TL;DR
The paper tests the Color Evaporation Model (CEM) as a color-dynamics framework for diffractive and elastic photoproduction of heavy quarks, arguing that soft color interactions can replace the Pomeron in elastic channels. By integrating perturbative $c\overline{c}$ production over the appropriate mass range and applying universal fractions $\rho_i$, the authors predict both $J/\psi$ and open-charm yields without relying on Pomeron exchange. Their elastic photoproduction results for $J/\psi$ and $D$ mesons agree with data and support the universality of the nonperturbative parameters, suggesting broader applicability of CEM to other elastic processes. The study also includes LO hadroproduction tests, highlighting the importance of higher-order effects and potential limitations of the approach in those contexts.
Abstract
Our goal is the study of color effects on the $J/ψ$ and $D$ mesons production, as well as the study of their elastic production. We use the Color Evaporation Model (CEM), where a single factor takes into account the probability that the $c\bar{c}$ produced in a color octet state turns into a physical (colorless) quarkonium or continues as a color octet, producing open charm. The main result of this work, besides investigating the range of applicability of the CEM, is to show that this model can be used to describe the elastic processes of $J/ψ$ and open charm photoproduction without the use of a Pomeron.