The Cross Talk Cut

$apply_xtalk_cut

The cross talk cut is a switch in the TCAL bank which flags cross talk tubes in the data by setting the discard and cross talk bits in KPMT_PF. The parameters of the cut can be found in calibration.dat and the code can be found in cal_xtalk_cut.for:

The cross talk cut by default is not applied to the data. In order to apply the cut, the appropriate bit in TCAL must be set to one.

The cross talk cut flags a tube as cross talk based on three criteria:-

1. Tube is adjacent in crate space to a high charge tube.

2. The adjacent tube has a low charge.

3. The adjacent tube has an ECA time that is late in time to the high charge

   tube.

If all three of these criteria are met, the tube is flagged as a cross talk tube.

The definitions of a high charge tube and an out of time, low charge tube are set by the parameters in TCAL. Generally, the high charge or primary tube has must have a charge of greater than 50 pedestal subracted QHS. This minimum has no real significance and only serves to speed up the processing time. The adjacent tube must have a charge between 10 to -30 pedestal subracted QHS. The lower bound is set so that tubes with bad calibrations are not classified as cross talk tubes. Also, the adjacent tube must be late in time by -8 to -25 nanoseconds with respect to the primary tube. Again, a lower bound is included for badly calibrated tubes. For the timing, ECA times are used for both the primary and adjacent tube. PCA times are not used since the PCA walk incorrectly walks the cross talk tubes. The charge and timing parameters are optimized using low and high rate ${^16}{\rm N}$ data. It is not recommended that the parameters be changed from the defaults set in TCAL unless the user has something very specific in mind while doing this. Lastly, a tube is only considered adjacent to a primary tube if both tubes are on the same motherboard in crate space. Cross talk in the PMT cable bunches is not taken into account in this cut.

Once a tube has been classified as cross talk, the KPF_DIS and the KPF_XT bits in the KPMT_KPF word are set. All fitters ignore tubes that have the discard bit set. RSP ignores tubes that have the cross talk bit set. Any other SNOMAN routine that ignores tubes with the discard bit set will also ignore the cross talk tubes.