Minutes of the March 29 Meeting
Present: Eduardo do Couto e Silva, Gary Godfrey, Bob Hartman, Bernard Phlips, Steve Ritz, Hartmut Sadrozinski
1) Bob presented a discussion on the EGRET knowledge of various parameters. We agreed to set the following goals:
Effective area ( > 100 MeV) - 10%
Effective area ( < 100 MeV) - 10% (although after some studies we may find out that 20% may be more realistic)
Energy _resolution - 10%
We need to add to the table normalization and absolute energy scale and the knowledge on that. Bernard pointed out that relative knowledge may still be useful even if we do not have absolute knowledge on the energy. However, it seems that in practice, both are very hard to know.
Knowledge on Beam parameters
Beam flux < 10% (since we need to have max 10% for effective area- see above)
multiple photon contamination < 10% for the same reason as above.
angle of incidence - need to revisit. Gary indicated we had 1 degree for beam test and that may be adequate. EGRET had 0.1 degree knowledge on their direction. It was also pointed out the need for stability and reproducibility. Table will be updated (see action list)
2) Eduardo reported on discrepancies on the PSF measurements especially for the ratio PSF95/PSF68 , which is required to be <3. Together with Hartmut they are setting up a study group to prepare us for PDR and maybe fed information into the Calibration Committee. He also confirmed that beam divergence was not a major source of error for the BTEM analysis.
3) Bernard discussed about measurements at 300 GeV. It seems that we can live with extrapolations to 300 GeV. Going to CERN for 200 GeV test will require some work in setting up the beam and maybe worth it for the calorimeter resolution and ACD backsplash. For the backsplash maybe a beam with 6 particles of 50 GeV will simulate a 300 GeV beam. If this happens then one must think about the possibility of including the tracker and maybe this will be the test for the Engineering Model (Hartmut). Investigation will proceed (see action list).
4) Gary reported on the possibility of using a Van der Graaf for low energy photons. That could be calibrated with CsI crystal, but not clear how photons will be tagged. He also started making phone calls to find out about operational plans for SLAC 2003/2004. Steve requested that investigations about a better hadron beam be included in the plan. There was a concern about the logistics to move into a beam that can only do low energy.
5) Eduardo reported on a meeting with Peter Bosted. Essentially one could use the monochromatic beam to get up to 10-15 GeV, but not obvious how much work is needed for 20 MeV. Peter Bosted insists that a tagger will not give us a knowledge on multiple photon contamination but rather the knowledge on the absolute energy. He is running a MC with some analytical calculations to produce some spectra for low and high energies so that we can look at.
Transparencies on the coherent beam
Notes from a meeting with peter Bosted
6) Steve reported that 1x4 configuration seem more appropriate than 2 x 2 due to the following reasons: 1 GeV photons at 55 degrees will probably cross at least 3 towers before we get an energy measurement and provides more radiation lengths for calorimetry. 2 x 2 is more adequate for 0 degree (inclination) studies (understanding contribution from tower walls) and azimuth angles but note that most of the events are NOT at 0 degrees (inclination) anyway (the effective area at 55 degrees corresponds to 1/2 of our on-axis effective area).
7) Background rejection. Steve explained that there is no obvious choice for 1 x 4 over 2 x 2 as far as background is concerned. We need to define better the goal of rejection and what kind of distributions we need to reconstruct. It is certainly better to do rejection with full flight LAT since events are more spread among 16 towers than they are over 4. Need absolute rejection in the beam, Gary reported that we had 0.004 protons per pulse in the SLAC beam tests 99/00.