BCAL Readout Segmentation Task group Meeting: Sep 26, 2011

Meeting Info

Time:

• 1:30 JLab
• 11:30 Regina

Location:

• CC F326-327

Vid-con:

• ESNet 8542553

Agenda

New Agenda items

1. BCAL Timing Resolutions (David L.)
2. Photon-Neutron Separation with BCAL (Andrei S. and Irina S.)

Minutes

Participants

David L., Elton S., Andrei S., Zisis P., Irina S., Matt S., Beni Z., Eugene C.

BCAL Timing Resolutions

David gave an update on the BCAL simulation study:

• Electronic noise added to summed signals with 1GHz, 1mV characteristic structure
• Energy calibration corrected
• 244 scheme implemented
• TDC gain changed from 10 to 5
  • Elton noted that there is an additional amplification of the pre-amp board in addition to the "x10" used for the TDC leg. This may or may not be included in the pulse shape used in the simulation. (Dave will look into this.)
• Energy resolutions calculated

The energy resolutions included floor terms in the fits which ranged from 1.4% to 7.1%. The overall resolution of σ/√E at 1 GeV ranged from 10% at 12^o to 6.5% at 90^o. The large floor terms generated a lot of discussion. This included the following points:

• Andrei suggested the low energy (<200MeV) points may not be accurate due to sampling fluctuations being handled incorrectly by the current GEANT-based simulation
• Andrei suggested asymmetric Gaussian fits to derive the points rather than symmetric ones.
• Error bars should be added to the fit values reported. Also, χ² from fits should be reported.

David also noted that the θ angle calculation with up to 4 SiPMs in the radial direction is problematic. Zisis suggested that a Monte Carlo might be needed to give guidance on the correct R-position for any energy deposited in a summed cell. Elton noted that he looked at this with his Toy Monte Carlo study and found that roughly one cell +2cm in was optimal. David will look into it.

Photon-Neutron Separation with BCAL

Andrei showed slides summarizing a Monte Carlo study he and Irina are currently performing to investigate the neutron-photon separation capability of the BCAL. The study uses the ratio of energy deposited in the innermost layer to that deposited in the outermost layer to distinguish showers that are likely neutrons. Results indicate that cutting on this ratio at the edge of the high-efficiency region for photons results in removing all but 30%-40% of the neutrons. The exact value is energy dependent. Other points made during the presentation:

• The 1-2-3-4 scheme appears to have no advantage over the 3-3-4 scheme when using the ratio method.
• The ratio method compliments the TOF method. The TOF method does not work well at higher energies, but the ratio method does.

Andrei suggested that a finer segmentation of the outermost layer might improve the results. Perhaps a 2x2 rather than a 1x4 for the outer region.

Action Items

1. Clarify the total gain of the preamp board and whether or not it is included in the existing simulation
2. Identify source of large floor terms in Energy resolution plots
3. Review Elton's method for choosing a value of R for a summed cell and implement it in current simulation.