BCAL Beam Tests 2012

Objectives

The possibility to carry out a BCAL beam test in the spring of 2012 has been discussed within the Calorimetry Working Group (CWG). Below, information is being gathered to agree upon the goals for this test before proceeding further and requesting parasitic time in Hall-B.

The central objective is to fully instrument a BCAL module with SiPMs, complete with their board electronics, cooling and mechanical assembly, coupled to Flash ADCs and readout by the planned Hall-D DAQ system. This would afford a comprehensive tryout of all aspects connected with the BCAL readout in a realistic beam environment and expose any issues that would require corrections or adjustments, before instrumenting the BCAL modules in the solenoid.

In no particular order, below are possible goals, for discussion.

1. Instrument a module with 80 SiPMs, 40 per side. If possible, these should be instrumented as planned for the physics runs, with
   1. final lightguides
   2. pre-amplifier boards
   3. full cooling
   4. mechanical assemblies
   5. cabling,
   6. Flash ADCs and F1 TDCs
   7. the Hall-D DAQ system
   8. Data runs will be converted for analysis by ROOT.
2. Such a test will allow verification of operation in a beam environment, and would give us valuable information in validating our MC studies on SiPM noise, thresholds, etc.
3. If possible, a broad energy range should be used, from at least 500 MeV to 2 GeV. This would extend the range acquired during the 2006 beam tests, and would allow us to get a better handle on the floor term in the energy resolution, by going to higher energies.
4. The module should be oriented to allow both 90 degree and shallow angle (>20 degrees) measurements. These would then be compared to the 2006 data and show the difference in behaviour between SiPMs and PMTs.
5. To achieve a large energy range, the module may have to be placed at a location behind the tagger, where a full-length module would not fit. If this is the case, a shorter module can be used out of an existing prototype piece, or especially constructed in Regina following the completion of the 49 modules (48 plus the spare). Calculations would have to be carried out to determine the appropriate length so as not to clip the showers for the shallow angle measurements.
6. If available by that time, Athens LEDs should be installed at least on two opposing BCAL cells, located centrally and surrounded by other cells so as to investigate operation as well as optical cross talk.

Coordination

The coordinators for this effort are Zisis and Elton. Information from mechanical (Tim) and electronics/readout (Fernando) will be coordinated through Elton. Eugene, Elton and Sascha will interact with Hall B folks to ensure a smooth procedure from hall access request to installation and running.

Documentation

At the appropriate times, a request will be submitted to the Hall B Manager, followed by all other necessary documentation for running and safety. See the 2006 runs for reference.

Logistics

Following a conference call between IU and UR on October 17, the IU summary follows, with additional information added from feedback by Matt and Elton on October 19.

1. Test station: Optimal location for our study appears to be the Tagger Alcove, under the upstream end of the tagger magnet. The available volume between the floor and the Tagger ranges from 2-3m down to 0m where the Tagger contacts the floor. The allowable width for any setup is about 1m wide. For this reasons and the fact that there is no crane access there, a small baby-cal, around 50cm will work, allowing for space to mount the readout. Elton notes that In the alcove, you only get about 5-15% of the incident beam energy. For higher energies, one needs to locate the detector down

onto the Hall B floor where we may reach 30% of the energy. The space there is somewhat more crowded -- although it is being cleaned -- but should allow room for the BabyCal.

1. Energy: The FCAL beam test will be planned to allow a scanning of a 20x20cm² area of the device. IU expects the electron energy range of 5-40% of beam energy to strike the FCAL. This would also be handy for the BCAL, namely a scan would allow better extraction of the energy resolution floor term.
2. Running mode: IU plans to use their own tagging scintillators to run entirely independent of the tagger, i.e. parasitically. UR will do the same.
3. Gain Balancing: The IU group plans to centre their own tagged beam in each crystal for gain balancing. UR will do this using cosmics.
4. Count Rate: The Tagger MOR runs at 20 MHz. IU expects 1-10 kHz in each of their 4"x4" blocks. This is manageable for the BCAL as well.
5. Orientation: It may be advantageous to orient the BabyCal perpendicular to the Hall B beam line so as to intercept only a slice of the tagger rate, that over the width (~8-12cm) of the BabyCal. The beam envelope is expected to be ~2cm. We need to ensure that we do not clip the showers for small angles of incidence. We may consider adding veto counters to cover certain parts of the BabyCal. This requires further thinking and discussion.