41,088 research outputs found
The black-disk limit in high-energy ep and pp scattering
We review a recently proposed framework for studying the approach to the
unitarity limit in small-x processes in ep and pp scattering within the DGLAP
approximation. Our formulation is based on the correspondence between the
standard QCD factorization theorems for hard processes and the dipole picture
of small-x scattering in the leading logarithmic approximation. It allows us to
incorporate information about the transverse spatial distribution of gluons in
the proton (GPD) from exclusive vector meson production at HERA. We show that
the interaction of small-size color singlet configurations with the proton
approaches the "black-disk limit" (BDL) due to the growth of the DGLAP gluon
density at small x. This new dynamical regime is marginally visible in
diffractive DIS at HERA, and will be fully reached in central pp collisions at
LHC.Comment: 6 pages, 3 figures. Uses aipproc.cls. Contributed to proceedings of
PANIC05, Santa Fe, NM, Oct. 24-28, 200
Two-pion light-cone distribution amplitudes from the instanton vacuum
We calculate the two-pion light-cone distribution amplitudes in the effective
low-energy theory based on the instanton vacuum. These generalized distribution
amplitudes describe the soft (non-perturbative) part of the process
in the region where the c.m. energy is much smaller
than the photon virtuality. They can also be used in the analysis of exclusive
processes such as etc.Comment: 13 pages, LaTeX, 4 figures included using eps
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