Large Rapidity Gaps in proton-nucleus interaction

We analyse the cross-section of events with Large Rapidity Gaps observed in proton-lead collisions by the CMS collaboration. The role of the transverse size of elementary $pN$ amplitude is discussed. We emphasize that the cross-section of incoming proton dissociation caused by the photon radiated off the lead ion is close to the value of $d\sigma \mathrm{/}d\mathrm{\Delta }{\eta }^F$ measured by the CMS, and it is not clear why there is no room in the data for the Pomeron-induced contribution