1GeV photons in TOF
In this study 1GeV +/- 0.1 GeV were generated between 1 and 11 degree polar angle and from 0 to 360 degree in phi.
The number of hits per plane as a function of paddle number is shown below for both TOF planes:
Paddle number 41 to 44 are the half length ones locate at the center with only on sided read-out.
At this point no low energy threshold cut is applied. In the following the energy distribution of these hits is shown as seen
on both ends of the paddle. Again for both planes where the first plot shows the more upstream TOF plane.
The black histogram is the left/up PMT the red histogram is the right/down PMT. The plots show paddle 12 to 27 in each plane. What
can easily be identified is the second peak in the second TOF plane originating from the second lepton that is generated in the conversion
of the high energy photon. This second peak is at double the energy of the first prominent peak seen in both planes. At this point no
smearing has been included. Assuming for example a detector resolution of 50% at 1MeV the energy seen by the PMT is smeared with a Gaussion
of a width 0.5*sqrt(E). The resulting smeared energy spectrum is compared to the un-smeared one of Plane1:
The black histogram is the smeared energy seen by the left PMT, while the red histogram is the un-smeared energy seen by the right PMT.
The effect of the smearing is seen more clearly looking at just one paddle. In this example also the large number of hits a very low energy
deposition is visible more clearly which will be subject to a threshold in real life. As a reference the second plot shows the theoretical response of 3GeV muons in the paddle.
The hit multiplicity in the two TOF planes for photons and muons is shown below. In about 35% of the cases a photon does convert and produces
a signal in the TOF however most of these will be at low energy likely below the threshold. While muons are expected to shower in much less than 5%
of the cases.