Diffractive Dijet Production and Nuclear Shadowing in pA Interactions

Recently, measurements of diffractive jet rates in p̄p interactions at the Tevatron were observed to be significantly lower than the theoretical expectations (for a review see [1]). The expectations were obtained using parameterizations of diffractive parton distribution functions extracted from ep interactions at HERA. The discrepancy between the data and the calculations revealed the breakdown of factorization or the onset of absorptive corrections in p̄p diffractive events[2]. The physical reason for the breakdown of factorization is likely to be related to the different color structure of the probes in p̄p and ep reactions. In ep, the compact, color singlet q̄q pair produced by the virtual photon has a smaller probability of interacting with the external color fields and therefore has a larger rapidity gap survival probability. In p̄p, the color octet gluon at comparable virtualities still interacts strongly with the external color fields, reducing its rapidity gap survival probability. The implications of the breakdown of factorization are now studied in nuclear shadowing and dijet production. Nuclear shadowing is defined as the ratio of the pA to the pp total cross section, R = σpA/Aσpp. The total cross section for pA interactions can be written as the sum of two terms σpA ≃ AσpN − δσpA, (1)