Probing proton fluctuations with asymmetric rapidity correlations

Abstract: Intrinsic fluctuations of the proton saturation momentum generate asymmetric rapidity distributions on an event-by-event basis. We argue that the asymmetric component, $\left<a_1^2\right>$, of the orthogonal polynomial decomposition of the two-particle rapidity correlation function is a sensitive probe to this distribution of fluctuations. We present a simple model connecting the experimentally measured $\left<a_1^2\right>$ to the variance, $\sigma$, of the distribution of the logarithm of the proton saturation scale. We find that $\sigma\approx 0. 5-1$ describes the asymmetric component of the rapidity correlations recently measured by the ATLAS collaboration.