No abstract

Screening of initial parton production due to the presence of on-shell partons in high-energy heavy-ion collisions is discussed. It is shown that the divergent cross sections in the calculation of parton production can be regulated self-consistently without an ad hoc cut-off, and that the resultant parton production and transverse energy production rate are finite. Consequences on the energy density estimates are discussed.PACS numbers:12.38. Mh,25.75+r,12.38.Bx Typeset using REVT E X 1 Hard and semihard parton scatterings have been shown to play an important role in both high energy pp(p) and ultrarelativistic heavy ion collisions. In pp(p) collisions they are believed to be responsible for the rapid growth of the inelastic and total cross sections [1,2], and in AA collisions they are expected to produce a large amount of transverse energy in the central rapidity region [3][4][5][6]. Because the dominant QCD parton cross sections are singular in the soft scattering limit, most model calculations of minijet production via perturbative QCD (pQCD) have introduced an infrared cut-off, p 0 , corresponding to the smallest permissible transverse momentum transfer in a 2 → 2 parton scattering, to which perturbative QCD can still be applied. This cut-off is used in most of the models to separate perturbative hard processes from nonperturbative soft interactions which can be modeled, e.g., by strings or flux tubes. Since there is no distinct boundary between soft and hard physics, both the hard and soft part of the interaction in this scheme are very sensitive to the cut-off p 0 .Heavy ion collisions differ from pp collisions in that minijets are produced in large number, so that a medium of minijets is formed. In the space-time evolution of a heavy-ion collision soft particle production will be completed after semihard and hard processes. Therefore, the soft interactions are expected to be screened by interactions with the semihard quanta (minijets). We here take a step further by proposing that the perturbative semihard particle production should also be screened by the processes which have happened even earlier, i.e., by the harder processes. In this paper we will study the influence of the final-state interactions among minijets. We will investigate to what extent minijet production is screened and whether the screening effect can provide an effective self-consistent regularization of the infrared behavior of minijet production.Consider an example of two hard processes as illustrated in Fig. 1. Let us assume jets from the first hard scattering are produced in the 90 degree direction and have a large transverse momentum p T 1 . Because of this large transverse momentum, the interaction point is well localized in the transverse direction to a distance of 1/p T 1 . As these two jets travel in the transverse direction, they will experience secondary interactions. These secondary interactions can give rise to many nuclear effects of hard scatterings, i.e., energy loss and Cronin effects. Since we are interested...

No abstract