BCAL Readout Segmentation Task group Meeting: May 26, 2011

Meeting Info

Time:

• 11:30 JLab
• 9:30 Regina

Location:

• CC F326-327

Vid-con:

• ESNet 8542553

Agenda

• On Efficiency of BCal Reconstruction (Irina Semenova & Andrei Semenov)
• BCAL Simulation (David L.)

Minutes

Participants

David Lawrence, Elton Smith, Zisis Papandreou, Andrei Semenov, Irina Semenova, Beni Zhilmann

On Efficiency of BCAL Reconstruction (Irina Semenova & Andrei Semenov)

Andrei presented some slides on new efficiency calculations. Some things noted:

Slide 2

• The data set shown was for 90^o photons originating from the center of the target (10k events)
• Previous efficiency calculations done by Andrei and Irina relied on a "primary" flag in the code which is now known to have been defined as something other than "the generated photon". The method they now use has been modified to no longer use this
• Current efficiency calculation uses reconstructed photon with maximum energy
• Reconstructed energy is systematically off (at least for low energies). If cut is placed on Num. σ's from the generated value, the cut is applied asymmetrically to the reconstructed distribution leading to an underestimate of the efficiency.
• Zisis noted that in a recent discussion he had with Blake, that Blake suggested the energy correction function should be re-calibrated due to the fact that other changes have been implemented that could effect the energy distributions.

Slide 3

Some efficiency distributions for various cuts on Num. σ's as a function of energy were shown:

• New efficiency calculations now appear to be much higher than previous ones and are consistent with ones David showed in GlueX-doc-1736 (see fig. 17)

Slide 4

• A typo was found in David's code where the size of the uphits vector was used where the size of the downhits vector should have been
  • This would not have affected any of the previously shown plots since uphits and downhits were filled at the same time and necessarily were the same size.

BCAL Simulation (David L.)

We went over some slides prepared by David starting with a review of action items from the last meeting. Items discussed:

Slide 3

• The 14ns mean time for showers originating from 90^o, center of BCAL photons was confirmed to be fully understood.

Slides 4-5

• The source of the pedestal width being due to the pre-amp or the SiPM tiles was shown to make little difference in the actual threshold setting (<200keV for fine segmentation, <375keV for course segmentation)
• Dave reported having spoken with Fernando about the source . Fernando indicated measurements had been made indicating the width was coming from the SiPM tiles and not the pre-amp. Because of this, the smearing and threshold calculations in mcsmear will be made assuming the entire measured pedestal width is due to the SiPM and so will be scaled by sqrt(16) for the arrays.
• Elton noted that gain differences in the SiPMs would contribute to the pedestal width. This would make the true width for an array wider than what would be otherwise calculated.
  • David will look into this

Slide 6

Some numbers were presented that where used to indicate the number of BCAL "hits" due to dark pulses. This generated some discussion as the motivation and purpose of some of the numbers were not clear to everyone. Some note:

• David proposed changing the fixed parameter used to calculate the thresholds from "120 hits" to "240 values" since the inner cells will have 3 digitized values per hit and the outer 2 digitized values
  • The total event size will depend on how many 3 value hits + 2 value hits per event
• David agreed to write up a short 1-2 page document describing how the cap on event size will be used to determine the thresholds in the BCAL

Slide 7

A table of values to be changed in the calibDB was shown and reviewed

• Zisis reiterated a point he brought up last week that the cross-talk number from Yi/Carl's latest measurements include after pulses which may make it artificially high. This should be checked with Yi/Carl to see if a better estimate if cross-talk + after pulse inside 100ns exists
• The sampling fraction in the calibDB is currently at 15%. The NIM article has it at 12.5%. Zisis noted that there is an even more recent calculation putting it even lower. He will check on it and circulate the latest number so it can be inserted into the calibDB.
  • The main difference is that the newer calculation takes the cladding into account.
  • It was believed that adjusting the mixture of the material used for the active volume in hdgeant was not necessary since the density of the cladding was comparable to that of the fiber core.
  • The actual value may be closer to 10%
• "RELATIVE" was misspelled as "REALTIVE" (will be fixed

Slide 8

A short list of items David will work on over the next week to continue the mission of the task group.

• Elton added that the energy resolutions should be checked using a low threshold.

Action Items

1. Confirm Sampling fraction number for BCAL (Zisis)
2. Check on status of SiPM cross-talk/after pulse separation (David)
3. Investigate addition to pedestal width due to gain variation of SiPMs in an array (David)
4. Update calibDB with most recent values for SiPM and BCAL properties (David)
5. Decide on proper form of energy correction and recalibrate BCAL (Andrei)
6. Write up and distribute document describing how BCAL threshold is calculated based on event size (David)
7. Check widths of energy distributions using low threshold and compare with expected (??)