Photons Reaching the PMT Concentrator Bucket

This is another case where part of the data structure may be missing, depending on the level of PMT simulation:-

Black Disk

Any photon reaching the disk terminates; the boundary MCVX is also a sink vertex.

Grey Disk

If the photon is reflected then the boundary MCVX has an outgoing photon. In this simplification the outgoing photon emerges at the entry point.

Clear Disk

In this case the photon is tracked within the concentrator bucket but this tracking is not recorded in the data structure. If the photon reflects back then the exit point will not be the same as the entry point so an additional MCVX bank is needed. If lmctk_in is the link to the incident photon, the following code fragment picks up the outgoing track lmctk_out:-

 
      lmcvx_in  = lq(lmctk_in  - kmctk_mcvx)
      lmctk_con = lq(lmcvx_in  - kmcvx_mctk)
      lmcvx_out = lq(lmctk_con - kmctk_mcvx)
      lmctk_out = lq(lmcvx_out - kmcvx_mctk)

The connecting track lmctk_con is not a straight connection between lmcvx_in and lmcvx_out so has the indirect vertex bit set. By definition the connecting track has the parameters for the track at its end vertex (lmcvx_out). As nothing happens at the end vertex (it just passes from the water in the concentrator bucket to the water in the PMT shell) it follows that the ingoing and outgoing tracks at this vertex have the same direction parameters. So:-

1. If you want to study the relationship between the incident and reflected track angles this can be done just by looking at the incident and outgoing tracks at lmcvx_in. Note that this is exactly the same as for a grey disk.

2. To study the relationship between incident and reflected positions use both lmcvx_in and lmcvx_out. For grey disks this is the identity relationship of course!