Single Photon Finding Study

The effectiveness of the V1 peak finder and a square peak finder for sparse photon events are compared below. The square peak finder finds pixels above a specific threshold which are contained within a 2x2 area allowing for 1, 2, 3 or 4 pixel photons then the rest of the remaining square is included which contributes the most to the photon energy. This makes the assumption that photon create square peaks on detectors.

The data from experiment xcs06016 and run 37 were used in this analysis. Only sparse events were used so multiple photon peaks or pixels shared by multiple photons are extremely rare; events with less than 3000 peaks found by each peak finder were used. A total of 13 events were used.

Energy Distribution

The distribution of events for each peak finder is shown below. In the lower plot, the square peak finder distribution is manually shifted by -4.8 to compare the shapes of the distribution which appear to be very similar.

One can see that the peaks roughly follow a Gaussian distribution but on the higher end, there is a very noticeable shoulder. At first, it appears to be a result of dense photons, a situation that was avoided. With the use of sparse events. A Gaussian curve was fitted to both distributions but to ignore the effects of the shoulder, only the data between 120 and 150 ADU was used. The result from this was the V1 peak finder having a mean of 141.93 ± 0.06 and a standard deviation of 8.37 and the square peak finder having a mean of 146.68 ± 0.060 and a standard deviation of 8.20 where the errors were obtained by σ/√N.

Just to confirm the suspicions, the sparsest event, event 634, was looked at separately. The V1 and square peak finders found only 545 and 584 peaks, respectively. It can be seen in the energy distribution of the peaks for event 634 that the high energy shoulder is still present so it cannot be due to multiple photon complications. Furthermore, by manually checking peaks, it can be seen that the high energy peaks do not neighbor other peaks and are merely just higher energy peaks.

One possible explanation is how the peaks are chosen. For the square peak finder, since the 2x2 region with the highest energy is chosen to complete the square for 1 and 2 pixel photons, it is possible that this includes noise that is higher than average thus shifting the total energy above the mean. Likewise for the V1 peak finder, large noise has a greater chance of being included since it may surpass the lower threshold again shifting the total energy of the peak above the mean.

Pixel Size Effect on Energy

Since the square peak finder only find 4 pixel peaks, only the data for the V1 peak finder is shown below.  This data consists of 29,342 peaks found from the 13 different events.