On the background in the $γp \to ω(π^0γ) p$ reaction and mixed event simulation
In this paper we evaluate sources of background for the $γp \to ωp$, with the $ω$ detected through its $π^0 γ$ decay channel, to compare with the experiment carried out at ELSA. We find background from $γp \to π^0 π^0 p$ followed by decay of a $π^0$ into two $γ$, recombining one $π^0$ and one $γ$, and from the $γp \to π^0 ηp$ reaction with subsequent decay of the $η$ into two photons. This background accounts for the data at $π^0 γ$ invariant masses beyond 700 MeV, but strength is missing at lower invariant masses which was attributed to photon misidentification events, which we simulate to get a good reproduction of the experimental background. Once this is done, we perform an event mixing simulation to reproduce the calculated background and we find that the method provides a good description of the background at low $π^0 γ$ invariant masses but fakes the background at high invariant masses, making background events at low invariant masses, which are due to $γ$ misidentification events, responsible for the background at high invariant masses which is due to the $γp \to π^0 π^0 p$ and $γp \to π^0 ηp$ reactions.