Central and diffractive components of charm production

Abstract

To $\mathrm{O}\left({{\alpha }_s}^2\right)$ in perturbative QCD one can identify two separate components in the production of heavy flavors such as charm: central $q\overline{q}\to c\overline{c}$, $\mathrm{gg}\to c\overline{c}$ and diffractive $\mathrm{qc}\to \mathrm{qc}$, $\mathrm{gc}\to \mathrm{gc}$. For diffractive production, QCD evolution is the source of charm quarks inside the colliding hadrons. With an estimated 0.5% charm momentum fraction at $Q^2\simeq 4{m_c}^2$ from QCD evolution, a hard $x$ distribution of charm, and a resolution cutoff on gluonexchange contributions, the diffractive component reproduces the ${\Lambda }_c^{+}$ and $D$ cross sections observed at intermediate to large longitudinal $x$, both at Fermilab and at CERN ISR energies. The diffractive component also contributes to charm production near $x_L=0\mathrm{}$. This explains the failures of previous analyses, based on annihilation diagrams alone, to account for the observed charm cross sections in the central region. Estimates are made of cross sections and $x_L$ dependences of $b$- and $t$-quark production up to $\overline{\mathrm{pp}}$ collider energies.