5 research outputs found
The BFKL Pomeron Calculus in the dipole approach
In this paper we continue to pursue a goal of finding an effective theory for
high energy interaction in QCD based on the colour dipole approach, for which
the BFKL Pomeron Calculus gives a low energy limit. The key problem, that we
try to solve in this paper is the probabilistic interpretation of the BFKL
Pomeron Calculus in terms of the colourless dipoles and their interactions. We
demonstrate that the BFKL Pomeron Calculus has two equivalent descriptions :
(i) one is the generating functional which gives a clear probabilistic
interpretation of the processes of high energy scattering and also provides a
Hamiltonian-like description of the system of interacting dipoles; (ii) the
second is the Langevin equation with a specific noise term which is rather
complicated. We found that at high energies this Langevin equation can be
reduced to the Langevin equation for directed percolation in the momentum space
if the impact parameter is large, namely, , where is the
transverse momentum of a dipole. Unfortunately, this simplified form of
Langevin equation is not applicable for summation of Pomeron loops, where one
integrates over all possible values of impact parameter. We show that the BFKL
Pomeron calculus with two vertices (splitting and merging
of Pomerons) can be interpreted as a system of colourless dipoles with two
processes: the decay of one dipole into two and the merging of two dipoles into
one dipole. However, a number of assumptions we have to make on the way to
simplify the noise term in the Langevin equation and/or to apply the
probabilistic interpretation, therefore, we can consider both of these
approaches in the present form only as the QCD motivated models.Comment: 28 pages, 3 figure
QCD at small x and nucleus-nucleus collisions
At large collision energy sqrt(s) and relatively low momentum transfer Q, one
expects a new regime of Quantum Chromo-Dynamics (QCD) known as "saturation".
This kinematical range is characterized by a very large occupation number for
gluons inside hadrons and nuclei; this is the region where higher twist
contributions are as large as the leading twist contributions incorporated in
collinear factorization. In this talk, I discuss the onset of and dynamics in
the saturation regime, some of its experimental signatures, and its
implications for the early stages of Heavy Ion Collisions.Comment: Plenary talk given at QM2006, Shanghai, November 2006. 8 pages, 8
figure