Suggestions to 2006 LAT prototype beam test plan Alex Moiseev, NASA/GSFC

1. Suggestions to 2006 LAT prototype beam test planAlex Moiseev, NASA/GSFC 10/10/2005 Alex Moiseev 2006 LAT Beam test

2. LAT Science Topics supported by proposed tests: • High Energy Electrons Topic: Search for nearby cosmic ray sources which would reveal in sharp cutoff in cosmic ray electrons energy spectrum in the area somewhere above a few TeV Subject of the study: HE flux spectrum measurement for electron energies from 100 GeV to as high as possible, desirably to 10 TeV Expected number of electrons detected with 0.1 m2sr instrument for 1 year of observation: Already published/presented on this subject by GLAST team: • A. Moiseev and J.F.Ormes, Studies of TeV Electrons with GLAST Calorimeter, GLAST Collaboration Meeting, SLAC, 1997 • J.F.Ormes et al. Detection of High Energy Electrons by GLAST, XXV ICRC, Durban, 1997 • I. Grenier, ~ same title, GLAST Collaboration Meeting, 2002 (?) • J. Norris et al. Hodoscopic CsI calorimeter for GLAST, XXV ICRC, Durban, 1997 • Anything else? Up to now One event only! 10/10/2005 Alex Moiseev 2006 LAT Beam test

3. All these things have already been addressed by us; we need just to revisit them 10/10/2005 Alex Moiseev 2006 LAT Beam test

4. LAT Geometric Factor for electrons 156 cm top entry event ACD side entry event 20cm calorimeter 8.5 X0 ACD Height Here is a result of our crude simulations of possible geometric factor assuming using a part of ACD. Backsplash effect is taken into account, but for the old data – overestimated by a factor of ~2. If we do not use bottom long ACD tile, the ACD height would be ~55 cm, so the effective geometric factor could be ~0.1 m2sr for the paths in a calorimeter >30X0. Not much but still promising! 10/10/2005 Alex Moiseev 2006 LAT Beam test

5. Gamma-ray contamination in the electron flux • I estimate that for 1 TeV gamma-events ~15% of them will be accompanied by backsplash signals in 3-rd row tile (450 cm2 of the area) if we select the trajectories longer than 30X0 in a calorimeter. These events can be misindentified as electrons • This plot uses Sreekumar et al., 1998, high latitude gamma ray flux extrapolated to high energy. This certainly is not the best data to compare; at low latitude diffuse gamma-ray flux is much higher. So, at few-TeV energy range gamma-contamination can be a very serious problem. • Needs to be clarified: • gamma-background conditions for high energy electrons measurements at Galactic plane • Backsplash issue – accurately measure in beam test and after that simulate for the real instrument 10/10/2005 Alex Moiseev 2006 LAT Beam test

6. Cosmic Ray contamination in the electron flux • In our 1997 work (Ormes et al., ICRC in Durban) we studied electron-proton separation power by a calorimeter and found that for long paths (> 50X0) it can be excellent – 105 or better. But this approach does not work in current LAT design without ACD segmentation in the bottom part. Also, crystals saturation probably makes it impossible to use trajectories along the crystals • To be done: Study proton-electron separation powerby LAT. Needs to be 104 and better. Calorimeter pattern recognition is very much needed – ACD does not help here.Beam test and simulations 10/10/2005 Alex Moiseev 2006 LAT Beam test

7. Dark Matter – gamma-ray spectrum features at high energy (above 100-200 GeV) • gamma-ray lines • “bump”, or excess in the energy spectrum • Improved to 2-3% energy resolution and energy range extension to 1 TeV or higher increase the chance of discovery! • Similar approach as for high energy electrons – long paths in a calorimeter • Backslpash issue is slightly easier – it only reduces sensitivity (due to removed good events due to backsplash) • Proton separation – ACD works; but calorimeter still be helpful in proton removal • Calorimeter crystal saturation – more serious problem than for electrons: here we need better energy resolution, but saturated crystals will make it worse. Needs to be studied. • See also a paper A. Moiseev et al. Detection of Galactic Dark Matter by GLAST, XXVI ICRC, Salt Lake City, 1999 10/10/2005 Alex Moiseev 2006 LAT Beam test

8. What can be done during LAT Beam test at CERN to support this work? • Two main things: • Include ACD to confirm backsplash measurements with real LAT detectors and materials. • Study the power of the calorimeter to separate hadron from electromagnetic events • Scheme of beam setup to cover both these issues: • Bent ACD tile • top ACD tile (not necessary) Crown ACD tile • beam • 2-nd row tile • 3-rd row tile T T C C C C 10/10/2005 Alex Moiseev 2006 LAT Beam test

9. What is needed for proposed experiment: • ACD Hardware: • There is a very low chance that ACD flight spare tiles will be needed after the time of beam test (summer 2006), but still we will try to minimize the use of flight spares. - bent and crown tiles. That ones which were sent to SLAC for EU can be used after some refurbishing and tests by ACD team. Second option – just take flight spares. - 2-nd and 3-rd row tiles. That ones which were sent to SLAC along with flight ACD for software tests can be used. They are left over flight spare and meet all specs. - PMT – we have many of them at Goddard (potted ones) which are not flight spares, but meet all specs except low temperature, - PMT chassi and FREE boards – there are two sets of them, exactly flight design, at SLAC. Any of them can be used • ACD tiles mounting frame. - requires some simple, but work. It can be angle-shaped frame to hold tiles, made of say 2mm thick aluminum, with stand-offs to mount the tiles. PMT chassi can be mounted to the bottom of this frame - I think it would be better to have this mounting frame to be stand-alone to allow easier and flexible configuration with the tracker and calorimeter towers 10/10/2005 Alex Moiseev 2006 LAT Beam test

10. Beam setup • Beam setup for backsplash measurements: • electron beam, 3-4 energies (50, 100, 200 GeV and highest possible) and 2-3 angles. Collect 50K events in each run (takes approximately 5 hours with ~500 electrons per spill) • 3 up-stream scintillating detectors tagging the beam (can be provided by ACD team) • Down-stream scintillating detector to remove hadrons (can be provided by ACD team). • PMT’s for all these detectors can be installed in ACD PMT chassi and can be used for triggering by “ACD trigger”. • No special critical requirements to the beam • 2. Beam setup for electron-proton separation • This is more challenging: electron acceptance criteria will be developed from the electron run data. After that, with proton (more likely pion) beam data, we will check how many hadrons passed electron selection criteria. This means that the electron contamination in hadron beam should be better than the required hadron rejection power (104 minimum) • Hadron beam itself is rather free of electrons – probably at the level of 10-2 or better – CHECK! Anyway ancillary detector is needed to efficiently (at least 99%) detect electrons and remove them from the analysis • This detector shall be installed upstream the LAT. TRD would be the best choice. Check with the Italian group in Bari (Paolo Spinelli) if something can be available. I will also check with ATLAS TRD group at CERN where I have good friends 10/10/2005 Alex Moiseev 2006 LAT Beam test

11. Preliminary simulations • Simulate expected performance of beam setup to optimize beam run setup • 2. All mentioned above simulations to justify the efforts to be spent on high energy electrons and dark matter search studies 10/10/2005 Alex Moiseev 2006 LAT Beam test