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Study of swapped PMT signal cables using Reco thetaC data


I generated ntuples to study the correlation between reconstructed thetaC and number of bounces or photon exit angle with high statistics and results on those issues will be posted at a later time. This HN is concerned with an interesting side effect / first application of those ntuples: hunting down more cable errors.

The ntuples were produced for about 1.5Mio DIRC tracks using Elf in release 8.6.1a (with corrected DrcMaxLikel), conditions from recoboot, running on xtc files from post-October-shutdown data. I use the nearest solution algorithm. Quality cuts on the track require the momentum to be between 0.3-9 GeV/c and the number of solutions to be between 15 and 300. The photon quality cuts are |deltaT minus meantime| less than 6nsec and |thetaC(photon) minus thetac(track)| less than 100mrad. That leaves me with about 48Mio hits.

As usual, I fit the thetaC residual (thetaC of tube minus thetaC of track) per tube. The function used here is Gaussian plus a line to allow for asymmetric backgrounds.

The high statistic allows me to plot the sigma of the Gaussian per PMT only for tubes where the PMTs are *not* in the sector opposite the bar box that the track went through: http://www.slac.stanford.edu/~jochen/cableerror/occu_nosec_edi.gif The scale is chosen so that tubes with a sigma of more than 15mrad appear as black dots. One notices immediately a set of 19 neighboring pairs of tubes with large sigma values. The distributions for the tube highlighted in the previous plot can be seen here: http://www.slac.stanford.edu/~jochen/cableerror/sec08105758.gif The top plot shows the thetaC residual for all accepted hits while the other three show the thetaC residual for tracks going through bars in bar box 7, 8, and 9, respectively. It can be seen that the distributions are shifted away from zero when the bar sector is different from the PMT sector with the sign of the shift flipping. This can be understood by visualizing that the Cherenkov ring segment becomes steeper in the sectors one or two bar boxes away from the one that the track passed through, thus giving us some sensitivity to cable swaps within a given row. That sensitivity did not exist in the studies performed previously where the statistics limited us to more horizontal rings in the highest occupancy area.

List of candidates for cable swaps within a row (30 total):

+--------+--------+--------+--------+--------+

|  sec   |  har   |  chan  |  col   |  row   |
+--------+--------+--------+--------+--------+
|   1    |  13    |  12    |  22    |  22    |
|   1    |  13    |  13    |  23    |  22    |
|   5    |   0    |  26    |   0    |  21    |
|   5    |   0    |  27    |   1    |  21    |
|   5    |   8    |  18    |  10    |  12    |
|   5    |   8    |  19    |  11    |  12    |
|   6    |   1    |  12    |   2    |  10    |
|   6    |   1    |  13    |   3    |  10    |
|   6    |   4    |  19    |   5    |  19    |
|   6    |   4    |  20    |   6    |  19    |
|   6    |   4    |  21    |   6    |  20    |
|   6    |   5    |  22    |   7    |  20    |
|   6    |  12    |   2    |  16    |  10    |
|   6    |  12    |   3    |  17    |  10    |
|   8    |  10    |  57    |  20    |  37    |
|   8    |  10    |  58    |  21    |  37    |
|   9    |   0    |   4    |   0    |  10    |
|   9    |   0    |   5    |   1    |  10    |
|   9    |   0    |  24    |   0    |  20    |
|   9    |   0    |  25    |   1    |  20    |
|   9    |   0    |  32    |   0    |  24    |
|   9    |   0    |  33    |   1    |  24    |
|   9    |   4    |  38    |   8    |  29    |
|   9    |   4    |  39    |   9    |  29    |
|   9    |   6    |  52    |  12    |  33    |
|   9    |   6    |  53    |  13    |  33    |
|  11    |   3    |  38    |   5    |  30    |
|  11    |   3    |  39    |   6    |  30    |
|  11    |   6    |  18    |   7    |  15    |
|  11    |   6    |  19    |   8    |  15    |
+--------+--------+--------+--------+--------+

List of swap candidates within a harness, resulting in col&row swaps (8 total):

+--------+--------+--------+--------+--------+

|  sec   |  har   |  chan  |  col   |  row   |
+--------+--------+--------+--------+--------+
|   9    |   5    |   2    |   5    |   2    |
|   9    |   5    |   3    |   4    |   3    |
|  10    |   2    |   4    |   1    |   3    |
|  10    |   2    |   5    |   1    |   4    |
|  10    |   0    |  52    |   1    |  34    |
|  10    |   0    |  53    |   0    |  35    |
|  11    |   1    |  50    |   3    |  35    |
|  11    |   1    |  51    |   1    |  36    |
+--------+--------+--------+--------+--------+

A special case seems to occur in sector 2 where 4 tubes may have been swapped in a more complicated way, resulting in shifts of the thetaC residual mean of up to 30mrad:

+--------+--------+--------+--------+--------+

|  sec   |  har   |  chan  |  col   |  row   |
+--------+--------+--------+--------+--------+
|   2    |   2    |  49    |   4    |  35    |
|   2    |   2    |  50    |   5    |  35    |
|   2    |   3    |  51    |   6    |  35    |
|   2    |   2    |  51    |   6    |  36    |
+--------+--------+--------+--------+--------+

On the next ROD (currently scheduled for April-27) we are going to have the BW doors open to unplug the HV cable of the two light emitting tubes. That should give us a chance to also verify if the 42 candidates listed above are indeed miscabled. If they are, the plan is to leave them in their current state and change the database to correct the cable errors for the entire data set consistently.


Joe


Created: 05/19/2000