 Solution

The diphoton invariant mass follows by adding the two photon four-momenta: $M^2{c}^4=2E_1{E}_2(1-\cos \theta )$. ThusFor correlated diphoton mass resolution, at fixed angle, $dM/M=(d{E}_1/E_1+d{E}_2/E_2)/2$. If the two quoted fractional errors are independent one-standard-deviation uncertainties,An unknown common energy-scale error would be correlated: with correlation coefficient $\rho$, the fractional variance is $(0.1^2+0.1^2+2\rho 0.1^2)/4$. Fully correlated scale errors give 10%, rather than 7.1%. A mass consistent with a candidate is not by itself evidence establishing its identity.