Energy Loss Cut

Download a postscript version of this plot here.

Along the y axis, we have the measurable quantity E_loss-cal, which is simply the apparent photon energy (E_silicon - E_resh) minus the energy that appears in the MCAL and BCAL.

Along the x axis, we have the immeasurable quantity E_loss-MC, which is determined by the beam monte carlo and is the apparent photon energy minus the lead photon energy minus the energy the beam monte carlo puts into the BCAL EM (all other photons plus all pairs that make it to our target). In other words, E_loss-MC is the energy we lose to extra photons and pairs that are absorbed or swept out somewhere upstream of our target.

As is clearly evident, the two losses are very highly correlated. We recommend a cut on E_loss-cal of 60 GeV. This will remove the small set of events (four percent on a particular sample of data, for example) in which we simply mismeasure the energy of the interacting photon badly.