Abstract
A modification of the collinear evolution equations as an appropriate approach to improve the behavior of parton distribution functions in the region of small longitudinal momentum fractions, and to find more theoretical arguments to clarify the possible appearence of saturation regime is suggested. It is argued that parton diffusion in the rapidity space at large parton densities along the space-time evolution could result in the emergence of a natural saturation scale on which freezing actually occurs.
Highlights
Nowadays, it is widely recognized the hadron interactions at very high energies are driven by the states with very high densities of partons, in particular, with small longitudinal momentum fractions x
An idea to follow the evolution within the perturbative paradigm and to evaluate the leading contributions at small x for not very large Q2 led to the development of the Balitsky-FadinKuraev-Lipatov (BFKL) approach associated to so-called high-energy factorization
II, we briefly review the principal features of the DGLAP evolution in order to be clear and to introduce the notations
Summary
It is widely recognized the hadron interactions at very high energies are driven by the states with very high densities of partons (quarks and gluons), in particular, with small longitudinal momentum fractions x. The routine theoretical framework for analyzing such systems is essentially grounded on the QCD collinear factorization in which the calculated cross sections are decomposed in the perturbative coefficient functions and nonperturbative parton densities of which evolvement is treated according the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations [1,2,3,4] Already, these linear equations qualitatively capture the traits associated with an increase in the gluon densities at small x with extremely large Q2 values. The interest in physics of the high-density regime of small-x QCD is greatly increasing and dictated by an avalanche of experimental data on collisions of relativistic heavy ions overwhelming this area of research in the last few decades There is another opportunity to address the problem in the framework of well-known DGLAP approach that we would like to draw attention to in this paper.
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