Minutes of the April 12 Meeting

Present: Eduardo do Couto e Silva,  Tune Kamae, Benoit Lott, Bernard Phlips, Steve Ritz, Hartmut Sadrozinski

1) Eduardo and Tune presented a discussion on the time needed for the photon beam, about 6 months. Here are the assumptions:

These numbers are based on the BTEM99/00 performance with an error on PSF 68% of about 10-15 % (BTEM data 400-1000 events/bin)  and an error on PSF 68% of about 6-10 % (BTEM MC 2500 events/bin). Steve commented that the number of L1T was very high in our calculations, but note that that refered to the total number of machine triggers (we were triggering on the beam pulse) so 1/3 of the times we would be getting single photon pulses. 

The group requested to add two more angles (40 and 60 deg) to configurations  8 and 9 .Modularity in teh design indicates we should reject  configurations 2,3, and 4. However testing different towers at 0 degrees is easier and gives us confidence that the design is actually modular.  

2) Hartmut reported on a hodoscope for cosmic ray tests  that is maintained by group B and lives in ESA. Now is going to be used for BABAR tests. The system can handle a rate of 10 Hz and fits the LAT. There is 1 m of Iron to provide a cut off at the order of 1 GeV or so (could it be replaced by steel ?). The main reasons for that would be to test 2 towers or the whole LAT with an external trigger as a cross check to the self triggering scheme . The question of whether this could be used in the clean room building was raised. Hartmut was asked to motivate it better in terms of the parameters we are testing and when in time would it be available. In addition do an assessment of the needs of the DAQ in such a system. 

3)  Hartmut started the Engineering Model discussion. Essentially , the EM is being seeing as a good test for DAQ and software. The next step is to evaluate whether it makes sense to place it in a beam or not. The calorimeter is making a plan to justify the need for the test beam including an evaluation of what kind of tracker they can come up with. The reason is that bring the entire EM together elsewhere (other than SLAC) may be a big burden on DAQ and GSE. This was not a consensus among the group. Bernard clearly stated that a tracker is not a a requirement in the calorimeter tests , but it would be nice to have it. Benoit mentioned that in case on needs to test the calorimeter at GSI and CERN, one should try to accommodate both tests in the same time frame to minimize costs.

4)  ACD , Eduardo reported on emails send by Bob Hartman. Here it goes verbatim

The current baseline is for 14 tiles (covering a corner of the system) in the initial EM configuration. After the initial qualification testing, 10 are to be removed for transfer to the Calibration Unit, with 4 left on the EM for continuing DAQ testing.

 Although we have all seen some of the figures from Alex' backsplash test, including some up to 300 GeV, he has never actually written a full report on that. He knows it is needed and I asked him  to provide at least a rough draft within 2 weeks. (Like JJ and Martin, Alex has too many responsibilities.)  By chance, I learned yesterday that the Free Electron Laser Facility at Duke Univ. has an electron accelerator with which they can generate a Compton back-scattered gamma beam over the range 5-55 MeV. Gottfried Kanbach plans to take a prototype of MEGA (a 0.5-30 MeV Compton telescope) there late this year. I haveno other information, but the facility has a web site at: www.fel.duke.edu

5)  Hadron - Steve mentioned that the hadron background is widespread over the LAT (from all directions) and because of that we do not need top test it up to 105:1 or 106:1 in a beam, because the beam is localized. So, in that smaller region the rejection power needed will certainly be less. Steve suggested 4 (5?) configurations. Top at 0 deg, top incidence off axis,  side incidence onto CAL , back through CAL with some material in the back to simulate spacecraft. The main concern is the "weird" configurations that would be nice to evaluate with teh Monet Carlo especially proton hitting sideways the ACD. In GISMO the low energy protons (below geomagnetic cutoff) are not well rejected mostly because they were not in our background flux when we developed the cuts. This has to be revisited and it would be nice to have it on the beam to validate MC. Bernard mentioned that 250 MeV protons was feasible at CERN. At SLAC we had GeV protons, 0.04% of the sample with 12% e contamination, so if we go down in energy it only tends to get worse. Eduardo will check with Gary whether we could go down to 100 MeV. Clearly PDR will give a big push to get the MC going. The discussion of the beam test came up again. Why did not we analyze the data. There were three main problems: one was the low energy response of CAL 9 according to Eric if one uses the right calibration file this should not be a problem), the other was the efficiency of the ACD, the last one was that the necessary ntuples were not fully available (matching detectors info). Steve has not worried much about pions yet. Eduardo called Bob Hartman after the meeting and suggested he should report on EGRET calibrations for hadrons for next week. 

6) Electrons - It was mentioned that the hardest background for teh ACD is the albedo electrons below geomagnetic cutoff (1-10 GeV). Mainly has to do with flux. Edaurdo pointed out that we shoudl soon move into discussion of electron beam

7) AOB - Next week no meeting, but all should send info to Eduardo to update the web page, 2 weeks from now Tune will call a meeting.  Eduardo is away from April 22 to May 7. He may try to hook up for the VRVS meetings. Meanwhile he will prepare a plan with issues and report on the main meeting on Monday.

Action list after Meeting of April 12