Searching Saturation in eA Processes

The high density effects should be manifest at small x and/or large nuclei. In this letter we consider the behavior of nuclear structure function F 2 slope in the kinematic region which could be explored in the future eA colliders as a search of these effects. We verify that the high density implies that the maximum value of the slope occurs at large values of the photon virtuality, i. e. in a perturbative regime, and is dependent of the number of nucleons A and energy. Our conclusion is that the measurement of this observable will allow to explicit the saturation. PACS numbers: 11.80.La; 24.95.+p; Key-words: Small x QCD; Unitarity corrections; Nuclear Collisions. E-mail:[email protected] The physics of high-density QCD (hdQCD) has become an increasingly active subject of research, both from experimental and theoretical points of view. Presently, and in the near future, the collider facilities such as the DESY collider HERA (ep, eA), Fermilab Tevatron (pp, pA), BNL Relativistic Heavy Ion Collider (RHIC) (eA, AA), and CERN Large Hadron Collider (LHC) (pp, AA) will be able to probe new regimes of dense quark gluon matter at very small Bjorken x or/and at large A, with rather different dynamical properties. In these experiments, be it because of high energies in ep collisions or because of intrinsically higher numbers of partons in eA and AA collisions, QCD effects are dominated by the large number of gluons involved. The description of these processes is directly associated with a correct gluonic dynamics in this kinematical region. Theoretically, at small x and/or large A we expect the transition of the regime described by the linear dynamics (DGLAP, BFKL) (For a review, see e.g. Ref. [1]), where only the parton emissions are considered, for a new regime where the physical process of recombination of partons become important in the parton cascade and the evolution is given by a nonlinear evolution equation. This regime is characterized by the limitation on the maximum phase-space parton density that can be reached in the hadron wavefunction (parton saturation) and very high values of the QCD field strength Fμν ≈ 1/g [2]. In this case, the number of gluons per unit phase space volume practically saturates and at large densities grows only very slowly (logarithmically) as a function of the energy. At this moment, there are many approaches in the literature that propose distinct evolution equations for the description of the gluon distribution in high density limit [3, 4] [5, 6]. In general these evolution equations resum powers of the function κ(x,Q) ≡ 3π αsA 2Q2 xg(x,Q) πR A , which represents the probability of gluon-gluon interaction inside the parton cascade, matching • the DLA limit of the DGLAP evolution equation in the limit of low parton densities (κ → 0); • the GLR equation and the Glauber-Mueller formula as first terms of the high density effects. The main differences between these approaches occurs in the limit of very large densities, where all powers of κ should be resumed. Although the