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First look at positron-annihilation setup

First look at positron-annihilation setup. Geometry updated + more efficient sampling of particles traversing the trigger detector (efficiency 50% now) Compared two setups: one with the direct beam in the detector one with positrons deflected by the magnet

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First look at positron-annihilation setup

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  1. First look at positron-annihilationsetup • Geometry updated + more efficient sampling of particles traversing the trigger detector (efficiency 50% now) • Compared two setups: • one with the direct beam in the detector • one with positrons deflected by the magnet • Triggering on plastic 0 and 1 and vetoing using plastic 2 behind annihilator • In real life, events without veto (downscaled) will be recorded for normalization purpose • 12 cm (4 layers) of annihilator blanket

  2. dump CU magnet magnet Cerenkov 1 Cerenkov 2 Trigger det. veto “Annihilator”

  3. Energy of highest energy gamma-ray Sum of two gamma-ray energies black: positrons red: electrons Important background from bremsstrahlung (2/3 of events): the radiating electron is left with very little energy and is stopped within annihilator or misses the veto.

  4. - magnet on • dump in • condition on position

  5. Energy of highest energy gamma-ray Sum of two gamma-ray energies black: positrons red: electrons 140 events (out of 250 000) pass the cuts: probability: ~ 6 10-4 Possibility of using a thicker “annihilator” slab (Al for instance) Possibility of running at high rate (1-2 kHz), limitation arises from pile-up in CsI pulses We will have to run with and without annihilator to estimate the background.

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