Production of $f_0(980)$ meson at the LHC: Color evaporation versus color-singlet gluon-gluon fusion

Abstract

The production of the $f_0(980)$ meson at high energies is not well understood. We investigate two different potential mechanisms for inclusive scalar meson production in the $k_t$-factorization approach: color-singlet gluon-gluon fusion and color evaporation model. The ${\gamma }^{\ast }{\gamma }^{\ast }\to f_0(980)$ form factor(s) can be constraint from the $f_0(980)$ radiative decay width. The $g^{\ast }{g}^{\ast }\to f_0(980)$ form factors are obtained by a replacement of ${\alpha }_{\mathrm{em}}$ electromagnetic coupling constant by ${\alpha }_{\mathrm{s}}$ strong coupling constant and appropriate color factors. The form factors for the two couplings are parametrized with a function motivated by recent results for scalar quarkonia. The differential cross sections are calculated in the $k_t$-factorization approach with modern unintegrated gluon distributions. Unlike for quarkonia it seems rather difficult to describe a preliminary ALICE data for inclusive production of $f_0(980)$ exclusively by the color singlet gluon-gluon fusion mechanism. Two different scenarios for flavor structure of $f_0(980)$ are considered in this context. We consider also mechanism of fusion of quark-antiquark associated with soft gluon emission in a phenomenological color evaporation model (CEM) used sometimes for quarkonium production. Here we use $k_t$-factorization version of CEM to include higher-order contributions. In addition, for comparison we consider also NLO collinear approach with $q\bar{q}q$ and $q\bar{q}g$ color octet partonic final states. Both approaches lead to a similar result. However, very large probabilities are required to describe the preliminary ALICE data. The pomeron-pomeron fusion mechanism is also discussed and results are quantified.

Comments: 20 pages, 12 figures