Fig. 5.

Left local p values for the background-only hypothesis as a result of a resonance search with respect to the production of a new vector gauge boson $Z^{\prime }$ as a function of $m_{Z^{\prime }}$, determined via a search for local excesses in the $m_{3\mathit{\gamma }}$ spectrum, using a narrow-width approximation to the $Z^{\prime }$ resonance width. The smallest local p value is found to be 0.0003 ($3.4\mathit{\sigma }$) which corresponds to a global p value of 0.087 ($1.4\mathit{\sigma }$). Right upper limits, at the 95 % CL, on ${\mathit{\sigma }}_{Z^{\prime }}\times \text{BR}(Z^{\prime }\to a+\mathit{\gamma })\times \text{BR}(a\to \mathit{\gamma }\mathit{\gamma })$. Also shown are the $\pm 1$ and $2\mathit{\sigma }$ uncertainty bands resulting from the resonance search hypothesis tests, taking into account the statistical and systematic uncertainties from simulated signal samples which are used to determine signal efficiency and Gaussian resonance width due to detector resolution for each mass hypothesis