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This commit updates the find peaks algorithm with several improvements which
together drastically improve its ability to find Cerenkov rings:
- when computing the Hough transform, instead of charge we weight each PMT hit
by the probability that it is a multi-photon PMT hit
- we don't subtract off previously found rings (this makes the code simpler and
I don't think it previously had a huge effect)
- ignore PMT hits who are within approximately 5 degrees of any previously
found ring (previously we ignored all hits within the center of previously
found rings)
- ignore PMT hits which have a time residual of more than 10 nanoseconds to
hopefully ignore more reflected and/or scattered light
- switch from weighting the Hough transform by exp(-fabs(cos(theta)-1/n)/0.1)
-> exp(-pow(cos(theta)-1/n,2)/0.01). I'm still not sure if this has a huge
effect, but the reason I switched is that the PDF for Cerenkov light looks
closer to the second form.
- switch to calling quad with f = 1.0 in test-find-peaks (I still need to add
this update to fit.c but will do that in a later commit).
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This commit updates find_peaks() to only return peaks which are at least a
certain number of degrees apart from each other. This is because I found that
for many events the first few peaks would all be essentially the same direction
and so the fit was taking a lot of time fitting essentially the same seed
points. Since I now have to only try 3 peaks in order to get my grid jobs to
run for less than a few hours it's necessary to make sure we aren't just
fitting the same three directions for the "quick" minimization.
I also updated the fit to only use a maximum of 3 seed directions.
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Previously, the algorithm used to find peaks was to search for all peaks in the
Hough transform above some constant fraction of the highest peak. This
algorithm could have issues finding smaller peaks away from the highest peak.
The new algorithm instead finds the highest peak in the Hough transform and
then recomputes the Hough transform ignoring all PMT hits within the Cerenkov
cone of the first peak. The next peak is found from this transform and the
process is iteratively repeated until a certain number of peaks are found.
One disadvantage of this new system is that it will *always* find the same
number of peaks and this will usually be greater than the actual number of
rings in the event. This is not a problem though since when fitting the event
we loop over all possible peaks and do a quick fit to determine the starting
point and so false positives are OK because the real peaks will fit better
during this quick fit.
Another potential issue with this new method is that by rejecting all PMT hits
within the Cerenkov cone of the first peak we could miss a second peak very
close to the first peak. This is partially mitigated by the fact that when we
loop over all possible combinations of the particle ids and directions we allow
each peak to be used more than once. For example, when fitting for the
hypothesis that an event is caused by two electrons and one muon and given two
possible directions 1 and 2, we will fit for the following possible direction
combinations:
1 1 1
1 1 2
1 2 1
1 2 2
2 2 1
2 2 2
Therefore if there is a second ring close to the first it is possible to fit it
correctly since we will seed the quick fit with two particles pointing in the
same direction.
This commit also adds a few tests for new functions and changes the energy step
size during the quick fit to 10% of the starting energy value.
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