Total gluon shadowing due to fluctuation effects

Abstract

We show a new physical phenomenon expected for the ratio RpA of the unintegrated gluon distribution of a nucleus over the unintegrated gluon distribution of a proton scaled up by the atomic factor A 1/3 in the fluctuation-dominated (diffusive scaling) region at high energy. We calculate the dependence of RpA on the atomic number A, the rapidity Y and the transverse gluon momentum k ⊥ . We find that RpA exhibits an increasing gluon shadowing with growing rapidity, approaching 1/A 1/3 at asymptotic rapidities which means total gluon shadowing, due to the effect of gluon number fluctuations or Pomeron loops. The increase of RpA with rising gluon momentum decreases as the rapidity grows. In contrast, in the geometric scaling region where the effect of fluctuations is negligible, the ratio RpA shows only partial gluon shadowing in the fixed-coupling case, basically independent on the rapidity and the gluon momentum.

Quantum chromodynamics at high energy and statistical physics

“…The ratio of the gluon distribution in a nucleus to the same quantity in a proton was computed in Ref. [131].…”

On possible implications of gluon number fluctuations in DIS data

“…). At high energy, such that σ 2 ≫ 1, it has been shown that fluctuations do strongly modify measurable quantities [13,14]. (A more detailed presentation of the recent theoretical progress is given in Refs.…”

Recent Developments in Small-x Physics

“…(12) A solution to the evolution equations, which is not yet available because of their complexity, would have helped to better understand the subasymptotics. However, using the methods outlined in the previous subsections, phenomenological consequences of fluctuations in the fixed coupling case have been studied, for example for DIS and diffractive cross sections [9], forward gluon production in hadron-hadron collisions [10] and for the nuclear modification factor R p A [8], in case fluctuations become important in the range of LHC energies.…”

“…New evolution equations [5,6,7], which describe Pomeron loops, have been proposed to account for the above effects. Very recently possible effects of Pomeron loops on various observables [8,9,10] have been studied in case they become important in the range of collider energies.…”