Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies

TL;DR

This paper calculates differential distributions for exclusive c production in high-energy proton collisions, analyzing uncertainties, off-shell effects, and comparing diffractive and photon-photon fusion mechanisms across Tevatron, RHIC, and LHC energies.

Contribution

It provides a detailed calculation of c production using unintegrated gluon distributions and discusses the impact of off-shell effects and different models on cross sections and distributions.

Findings

Off-shell effects reduce cross sections by a factor of 2-5.

Diffractive production dominates over photon-photon fusion.

Results vary significantly with different UGDF models.

Abstract

We calculate several differential distributions for exclusive double diffractive $\chi_c(0^{++})$ production in proton-antiproton collisions at the Tevatron and in proton-proton collisions at RHIC and LHC in terms of unintegrated gluon distributions (UGDFs) within the $k_t$-factorisation approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed in detail. The $g^* g^* \to \chi_c(0^{++})$ transition vertex is calculated as a function of gluon virtualities applying the standard pNRQCD technique. The off-shell effects are discussed and quantified. They lead to a reduction of the cross section by a factor 2--5, depending on the position in the phase space and UGDFs. Different models of UGDFs are used and the results are shown and discussed. The cross section for diffractive component depends strongly on UGDFs. We calculate also the differential distributions for the $\gamma^* \gamma^* \to \chi_c(0^{++})$ fusion mechanism. The integrated cross section for photon-photon fusion is much smaller than that of diffractive origin. The two components have very different dependence on momentum transfers $t_1, t_2$ in the nucleon lines as well as azimuthal-angle correlations between both outgoing nucleons.