Increase with energy of parton transverse momenta in the fragmentation region in DIS and related phenomena

TL;DR

This paper demonstrates that in deep inelastic scattering, parton transverse momenta increase with energy, affecting cross sections and the shape of fast projectiles, with implications for high-energy collider experiments.

Contribution

It combines dipole and DGLAP approximations with $k_t$ factorization to reveal energy-dependent growth of parton transverse momenta in the fragmentation region, a novel insight in pQCD.

Findings

Transverse momenta of quarks increase as x decreases at fixed Q^2.

The ratio of DVCS to DIS amplitudes approaches one at high energies.

A rapid projectile exhibits a biconcave shape, contrary to preQCD expectations.

Abstract

The dipole and the DGLAP approximations are combined with the $k_t$ factorization theorem to demonstrate the fundamental property of pQCD: smaller is the size of the colorless quark-gluon configurations in the fragmentation region, more rapid is the increase of its interaction with the target as a function of energy. First, we show that the transverse momenta of the quark(antiquark) within the $q\bar{q}$ pair, produced in the fragmentation region by the strongly virtual photon, increase with the decrease of x for fixed $Q^2$. As practical consequence of these effects we show that the cross sections of DIS and DVCS. We predict that the ratio of DVCS to DIS amplitudes should very slowly approach one from above at very large collision energies. Second, we study a closely related phenomenon of the increase of the transverse momenta with the energy of the characteristic transverse momenta of the gluon/quark configurations responsible for the transition to the black disk regime. We discuss the impact of this phenomenona on the slowing of the dependence on the initial energy of the coherence length. We demonstrate that a rapid projectile has the biconcave shape, which is different from the expectations of the preQCD parton model where a fast hadron has a pancake shape. We show that the increase of the transverse momenta leads to a new expression for the total cross section of a DIS scattering at very large energies, relevant to LHeC and LHC. We discuss the impact of the discovered phenomena on the hard processes in pp collisions, and on the dominance ofdifferent phases of chiral and conformal symmetries in the central and peripheral pp, pA, and AA collisions.