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June 25, 2015 Drift Chamber meeting


  1. Instructions for Bluejeans meeting connection
  2. Meeting ID: 290664653
  3. To join via a Web Browser, go to the page [1] https://bluejeans.com/290664653.


  1. CDC analysis update (Mike, Simon)
  2. FDC analysis update (Lubomir)
  3. Electronics (Fernando, Chris, Nick)
  4. Engineering
  5. Other


Participants: Mike, Naomi(CMU), Sean(NU), Eugene, Luke, Chris, Nick, Simon, Beni, and Lubomir (JLab).

CDC update

- Mike showed his latest CDC alignment results using Millepede linked above . The scale varies +/-200 microns, some "structures" in the offsets are visible. After applying the offsets, the chi2 of the track fits improves; Mike will show more results next meeting. Simon's results are different in scale (+/-600microns). Mike will compare the two results channel by channel to see if there's some systematics.

- Beni looked at the pedestals in the CDC varying different parameters: number of samples used, integer vs real number averaging, position of the pedestal window - all this explained in the above link. The main discussion was about the fact that Beni sees some slope (increase), when averaging over all the events, in the region before the real detector signal comes in case the signals are late. Mike suggested this may come from cross-talk from the other channels, but Beni has looked at this. Late signals can happen in cosmic showers (Eugene). Beni will do more studies when the computers are back.

FDC update

- Lubomir showed some plots demonstrating his studies of the effect of the centroid reconstruction. First plot shows the rhombus defined by two crossing strips and the wire position w.r.t. middle of the rhombus. If the wire is in the middle, the corrections for the reconstructed wire position cancel out at each point. If the wire is half-way distance from the middle the corrections are maximal, still on average along the wire, they should cancel if everything is symmetrical. Second plot shows the variations of the residuals, on top of them the red curve is the distance of the wire to the middle of the rhombus - we have minimum when the wire is in the middle and maximum when it's half-way from the middle. Obviously there's correlation.

- The next plots show how different the variations of some quantities can be depending on whether the wire is in the middle or half-way from the middle. It turned out the wire picked up for the measurements in the Hall with 5Fe source was half-way from the middle, and the wire for the measurements with the spare package in EEL126 was in almost in the middle. One sees strong variations of the reconstructed wire position or up/down charge ratio for the measurements in the Hall, while there are no such variations with the spare package.

- We looked once more at the corrections (discussed at the last meeting) using different methods. Eugene is concerned for some of the methods the corrections change sign depending on the shape of the signal. He suggested adding also the simplest calculation - just using the middle of the strip.


- All the electronics will be turned on on Monday. Before that Chris and Nick are going to clean the filters from the crates in the tagger; they are dirty. Eugene suggested consulting with the RadCon before duing this due to possible contamination.