Distribution of the test statistics q (equation (5) from Monte Carlo pseudo-datasets). The grey distribution q0 is obtained with no CNO simulated data and includes the systematic uncertainty. The black vertical line represents qdata = 30.05. The corresponding P value of q0 with respect to qdata gives the significance of the CNO discovery (>5.0σ at 99% confidence level). For comparison, in blue is the q0 without the systematics. The red histogram represents the expected test statistics distribution for an injected CNO rate equal to 7.2 cpd per 100 t—that is, our best fit value.