Cross sections and some features of charm photoproduction at γ energies of 20–70 GeV

Abstract

We report some results on charm photoproduction at γ energies ranging from 20 to 70 GeV. 36 events with pairs of charmed particles have been found in emulsions. The computed total cross section is (230±57)nb/nucleon. Frequencies of different production channels and some distributions are presented and compared with the predictions from a photon-gluon fusion model with string fragmentation

Polarization phenomena in open charm photoproduction processes

“…Note that the largest cross section on the neutron target belongs to the process γ + n → Σ being essentially suppressed. Moreover, the D − production is also small in the γp interaction, γ + p → Σ ++ c + D − , in agreement with the experiment [2]. The total cross section as a function of the photon energy, for the reaction Fig.…”

“…The data correspond to the total charm photoproduction cross section from [1] (reverse triangle), [2] (square), [3] (asterisk), [4] (star), [5] (triangles), [6] (circle), following coupling constants:…”

“…A large antiparticle/particle asymmetry, not explainable in terms of pQCD models, has been reported in the literature and numerical estimations of associative charm photoproduction cross sections have been done in Refs. [2,4,6]. The values are reported as open symbols in Fig.…”

“…+ X started about twenty years ago, [1,2], in the energy range E γ = 20 ÷ 70 GeV. Since then, several experiments were devoted to this subject, [3,4,5], but, up to now, the smallest energy where data are available is E γ =20 GeV, [6], which is still relatively far from threshold (for example, E thr = 8.7 GeV for γ + p → Λ + c + D 0 ).…”

Quantitative tests of color evaporation: charmonium production

“…Once ρ ψ has been empirically determined for one initial state, the cross section is predicted without free parameters for the other. We show next that color evaporation passes this test, quantitatively accommodating all measurements, including the high energy Tevatron and HERA data, which have represented a E cm (GeV) [18,19] as a function of the photon energy in the hadron rest frame, W γ . The normalization has been adjusted to show the similar shapes of the data.…”