Total gluon shadowing due to fluctuation effects Original Research Article

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 A1/3 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/A1/3 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.