Screening and antiscreening effects in J/ψ production on nuclei

Abstract

Nuclear effects in J/ψ hadro-and electroproduction on nuclei are considered in framework of reggeon approach. It is shown that screening regime which holds for electroproduction at x F 0.7 and for hadroproduction at x F −(0.3 ÷ 0.4) is changed with anti-screening regime for smaller x F values.Heavy-quark production on nuclei provides an important information on strong-interaction mechanisms and is intensively discussed (see e.g. refs [1, 2, 3] for review of experimental data, discussion of some phenomenological models and more references). In this note we will discuss a phenomenon of changing screening regime to anti-screening one in J/ψ hadro-and electroproduction when x ψ ≡ x F decreases in the framework of the BCKT model [4,5] based on the reggeon approach. For

Kinematic distributions and nuclear effects of J/ψ production in 920 GeV fixed-target proton-nucleus collisions

“…Ultimately, the observed J /ψ mesons are pro-jected out of the energy-depleted colorless state. The measurements of HERA-B are qualitatively compatible with the calculations described in BK [12].…”

“…Another theoretical model by Boreskov and Kaidalov [12], formulated in the framework of reggeon phenomenology, predicts an anti-screening effect in the region of negative x F . An important ingredient of their model is the assumption that a colorless state containing c andc quarks which has some probability of projecting into a charmonium state is produced and propagates through the nucleus.…”

“…Interpretations of the existing proton-nucleus data at positive x F rely on a delicate balance of several processes: nuclear absorption, shadowing of parton densities, energy loss, interactions with co-movers, hadronization of intrinsic cc components of the scattering nucleons, and so on. Ad hoc combinations of such elementary mechanisms, considered within various theoretical frameworks [10][11][12] are able to qualitatively reproduce the observed strong increase of J /ψ suppression as x F approaches unity [7].…”

J/ψ production in p-A and A-A collisions at fixed target experiments

“…It is, therefore, clear that the interpretation of the kinematical dependence of the cold nuclear matter effects is extremely complicated since there are many competing mechanisms affecting the J/ψ production and propagation into the nuclei. A theoretical description of the cold nuclear matter effects over the full kinematic range is extremely complex and not yet available [15,16,17].…”

Quarkonium production in high energy proton-proton and proton-nucleus collisions

“…At the other extreme of the explored x F region (negative values), one observes a slight tendency towards enhancement of the J/ψ production (α > 1). In this region a model [96] formulated in the framework of reggeon phenomenology, indeed predicts an anti-screening effect, which cannot be reproduced by more conventional approaches based on the commonly used shadowing parameterizations. At midrapidity, several experiments have studied J/ψ production.…”