Minutes of the May 18 Meeting

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

1) The expected number of events Eduardo (see talk) is using for the beam test has been confirmed by Gary's calculation. Contrary to what we used to say, the tagger and RECON have high efficiencies. Eduardo presented test matrices for low and high energy photon beams, that will require about 3 and 1 1/2 months runtime, respectively. The caveat is that extra time may be need if we want to apply the correction method used before for the PSF measurement (using different radiators). Also it is not clear from which beam we will get 50 MeV photons. Van der Graaf can do 17 MeV or > hundreds MeV. Hartmut pointed out that is a good idea to have the Van Der Graaf anyway so that we can test every tower if we wish to do so. 

2) Gary checked and agreed with P. Bosted numbers on coherent beam (see calculation) . It is clear that 10 GeV photon energy we would require a factor of 6 less time than that needed for the coherent beam. This factor goes down with the energy of the photon. The caveat is the hardener used for the calculations, one needs to understand systematic effects from generation of particles inside the block of material (hardener). The gain seem not to be that great at 100 MeV and at that energy a tagger may be required. Steve brings out the point that we do not have a similar correction method (using different radiator thickness) as we do in the incoherent beam. A backscattered laser beam may be a good option since the energy is well known (although multiple photons will still be there), but it is  major enterprise.  

3) Tune meets today with Ted Fieguth to discuss a possible channeling beam that gives photons in the range from 25 MeV to 100 MeV.

4) Benoit mentioned that  the CAL group is applying for funds to build a calorimeter model and that will replace the need for the EM. Decision is expected to come this Fall, so we still need to plan for EM as a backup. Tune and Steve pointed out that we need to shoot positrons from the back. The LAT can not tell the difference between events coming from top from those coming from the bottom.

5) There was a discussion about the hadron beam. Some people want to revisit the beam test protons others think is too much work. The main burden is the software needed for that, plus the calorimeter will have to be calibrated for this period of time. Eduardo spoke with Eric Grove after the meeting who estimates that 1 month is sufficient to do the calibration ( and some of the BFEM tools can be used), the problem is that it conflicts with other work.We need to investigate a hadron beam outside SLAC.

6) Eduardo asked people to look at the Requirements list  to check where they can contribute the most (especially those items in green). Timing issues have not been thoroughly discussed yet.

7) We meet again next Friday at 10 am PDT 

Action list after Meeting of May 18