Note from Eric Grove - May 24, 2001

1) Energy resolution (< 100 MeV) - we have assumed < 50% so far

I don't see how we can give an honest answer to this. Since we've never had a properly tagged photon beam, we've never known what the photon energy is, so we've never been able to measure the resolution.

2) Agreements with simulations

Based on Sacha Chekhtman's experience with ATLAS, there are "noticeable" discrepancies between observed and simulated (G3) longitudinal and transverse shower profiles at energies ~100 GeV. By "noticeable" I mean greater than order 1%, and less than order factor-of-two, so say, 10s of percent.

3) Beam tests

What the CAL really needs is tagged photons over the full energy range, protons, and relativistic heavy ions. These are the major issues for beam tests of CAL modules. To the extent that CERN can provide these beams, it's the right place to go, but it should be with full towers and multiple modules. Profiling at high energies is a side topic, and should not be a driver for scheduling of testing of GLAST modules.

3) Positron beam

It's not at all obvious to me that the CAL group is the driver for leptons rather than photons, but I haven't been part of the discussion. To calibrate gains and light output, what we really need is protons and relativistic heavy ions. EM showers are terrible calibrators. Such a calibration could be entirely on axis, at a large number of positions over the face of CAL towers.

4) High energy showers

A typical 200 GeV shower has an entirely different profile than the sum of ten 20 GeV showers. A 200 GeV shower reaches its maximum at just less than 10 RL, while a 20 GeV shower -- or ten simultaneous 20 GeV showers -- reaches max at about 7 RL. After 10 RL, 200 GeV showers deposit on average~35% of their energy, or 70 GeV. In contrast, after 10 RL, ten simultaneous 20 GeV showers deposit on average ~60% of their energy, or 120 GeV.