Production cross section of \piz measured in OO collisions at \fivethreesixnn, in pO collisions at \ninesixtwonn and in pp collisions at \fivethirteen, together with the interpolated pp reference at \ninesixtwo used for the \RpO calculation. Vertical bars (boxes) represent the statistical (systematic) uncertainty. Normalization uncertainties (not shown) originating from the luminosity determination are given in the text.