BCAL Readout Segmentation Task group Meeting: Jun 30, 2011

Meeting Info

Time:

• 11:30 JLab
• 9:30 Regina

Location:

• CC F326-327

Vid-con:

• ESNet 8542553

Agenda

Review action items from previous meeting

• Reproduce Nshower plots but with dark hits disabled (Irina / Andrei)
• Send calibration scripts with instructions to David (Andrei: In progress but not finished yet)
• Check on step size in X-Y plane and total step size to verify steps don't jump cells (David)

  See today's slides

• Check proton and neutron contribution to BCAL showers (David)

  See today's slides

• Continue signal timing distribution studies (David)

  See Today's slides

New Agenda items

• BCAL Signal Timing Distributions (David L.)

Minutes

Participants

Andrei S., Zisis P., David L., Elton S.

Review action items from previous meeting

• Andrei showed plots of the number of reconstructed showers for both the fine and course segmentation schemes with the dark hits turned on and off.
  • The plots showed that there was basic agreement between the two segmentation schemes when dark hits were off, but that the course had significantly more reconstructed showers when the dark hits are turned on.
  • Some discussion was had as to the exact mechanism, but it is likely related to the fact that the course segmentation has a lower threshold relative to the fine.

• Other action items were addressed in Dave's slides which are discussed below

BCAL Signal Timing Distributions

Dave showed some slides updating the status of the signal timing distribution study:

Slide 2

Plots of the distribution of particle types for GEANT steps taken inside the BCAL were shown indicating only a few steps from hadrons relative to leptons and photons (10^-3). This addressed an action item from last week.

Slide 3

Plots showing the radial step size taken by GEANT were shown. These indicated that GEANT is stepping up to the boundaries of of cells (in R) and not over complete cells. This addressed an action item that came up at the last meeting.

Slide 4

An SiPM pulse shape was obtained from Fernando and used to define a functional form that could be used to better represent the pulse shape convoluted with the signal distributions when looking at the BCAL timing.

• It was remarked that the pre-pulse was an anomaly of this particular pulse shape due to cross-talk from the led trigger and will exist in the production signals.

Slide 5

Numbers used to calculate the conversion between pulse amplitude and energy deposited were shown. Some comments made:

• The numbers don't appear to include a factor of 0.5 due to the light guides
  • Zisis or Andrei will look over this and verify that the factor is missing (see action items)
• After the meeting Elton also noted that the gain used to obtain the 61.67 number was larger than what will be used in production (turns out it's 20 times larger!)

Slide 6

Calculating thresholds in mV based on previous calculations of the thresholds in MeV. Only the "near" one is relevant. Note that with the factor of 20 (not discussed at the meeting, but mentioned above), the thresholds would be down around 2mV.

Slide 7

Plots indicating thresholds relative to signal sizes. The 4 plots in each row represent 4 different events. The two rows use different functional forms for the pulse shape. Note that the bottom plots are zoomed in quite a bit for the signal amplitudes (plotted against the right-hand axis).

These plots indicate that the pre-pulse is at exactly the wrong height for us. Elton mentioned that the pre-pulse was due to cross-talk from the LED trigger and would not be present in real data.

Slide 8

Plots of the time at which the signal crossed threshold for various layers in both the fine and course segmentation schemes. These simply indicate the level of timewalk correction that will be needed.

Slide 9

Summary of tasks still needed in order to complete the current studies. There was some discussion and clarification on what the deadlines are (were). Elton explained that the decision on the segmentation is already about 6 months behind schedule and further delays for more detailed studies are not an option. We need to make a decision by mid to late July so as not to affect the electronics board design an procurement further.

Action Items

• E-mail proposal for a plan of work that can be completed by 3rd week of July so decision on BCAL segmentation can be made (Zisis, Andrei)
• Verify number of 0.668 for MeV/PE (Zisis)
• Check on gain difference between SiPM test configuration and production configuration (Elton)
• Implement timewalk corrections and continue timing resolution study (David)