English

Geometric Scaling above the Saturation Scale

High Energy Physics - Phenomenology 2014-11-17 v1

Abstract

We show that the evolution equations in QCD predict geometric scaling for quark and gluon distribution functions in a large kinematical window, which extends above the saturation scale up to momenta Q2Q^2 of order 100GeV2100 {\rm GeV}^2. For Q2<Qs2Q^2 < Q^2_s, with QsQ_s the saturation momentum, this is the scaling predicted by the Colour Glass Condensate and by phenomenological saturation models. For 1\simleln(Q2/Qs2)ln(Qs2/ΛQCD2)1 \simle \ln(Q^2/Q_s^2) \ll \ln(Q_s^2/\Lambda^2_{\rm QCD}), we show that the solution to the BFKL equation shows approximate scaling, with the scale set by QsQ_s. At larger Q2Q^2, this solution does not scale any longer. We argue that for the intermediate values of Q2Q^2 where we find scaling, the BFKL rather than the double logarithmic approximation to the DGLAP equation properly describes the dynamics. We consider both fixed and running couplings, with the scale for running set by the saturation momentum. The anomalous dimension which characterizes the approach of the gluon distribution function towards saturation is found to be close to, but lower than, one half.

Keywords

Cite

@article{arxiv.hep-ph/0203137,
  title  = {Geometric Scaling above the Saturation Scale},
  author = {E. Iancu and K. Itakura and L. McLerran},
  journal= {arXiv preprint arXiv:hep-ph/0203137},
  year   = {2014}
}

Comments

24 pages

R2 v1 2026-07-22T13:39:53.066Z