Correlations of the squares of the Riemann zeta on the critical line

We compute the average of a product of two shifted squares of the Riemann zeta on the critical line with shifts up to size $T^{3\mathrm{/}2-\epsilon }$. We give an explicit expression for such an average and derive an approximate spectral expansion for the error term similar to Motohashi’s. As a consequence, we also compute the $(2,2)$-moment of moment of the Riemann zeta, for which we partially verify (and partially refute) a conjecture of Bailey and Keating.