1. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 1/6 PS Positron Simulations Stefan Funk June 6, 2006

2. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 2/6 Updated geometry –Included two cherenkov detectors (5 and 3 m) with mylar windows and CO2 filling –Included two plastic scintillators upstream of magnet –Included annihilator blanket (3cm) –Removed dump –Included third plastic scintillator as veto between annihilator and CU –Recording of energy in each detector Cherenkov volumes Plastic 0 and 1 Magnet = 0 Annihilator Plastic 2

3. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 3/6 Comparison electrons positrons –Simulated 500,000 positrons and electrons –Beam energy 1 GeV –Require trigger in plastic scintillators 0 and 1 –Veto in plastic scintillator 2 to selected annihilated positrons –To increase efficiency in the Monte Carlo, select only events that hit plastic 0 by sampling from the area covered by plastic0 and extrapolating the start of the event back to the beam position –Annihilation probability: ca 1e-3 (for cm blanket) Plastic 0 and 1 Annihilator Plastic 2

4. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 4/6 Comparison electrons positrons All Events - Electrons - Positrons EnergyEnergy sum No Positrons and two gammas in Event at Reporting plane Positrons in Event at Reporting plane Distance of two gammas Energy vs Distance from center

5. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 5/6 Comparison electrons positrons Cut on plastic0&1 & veto in plastic2 - Electrons - Positrons Still some charged particles miss the veto detector Some numbers: Nparticles: 500,000 Trigger Plastic0: 25600 Veto Plastic2: 870 Veto Plastic2 above 900 GeV: 86

6. GLAST LAT Project Test Beam Meeting, June 6, 2006 S. Funk 6/6 Summary –Updated geometry and gave code to Francesco –Positron runs are technically working –Next step: See how we can distinguish annihilation events Mass production Think about how to best perform the positron runs to optimise the background studies …