  The 511 keV gamma-ray emission from the galactic center region may fully or
partially originate from the annihilation of positrons from dark matter
particles with electrons from the interstellar medium. Alternatively, the
positrons could be created by astrophysical sources, involving exclusively
standard model physics. We describe here a new concept for a 511 keV mission
called 511-CAM (511 keV gamma-ray CAmera using Micro-calorimeters) that
combines focusing gamma-ray optics with a stack of Transition Edge Sensor (TES)
microcalorimeter arrays in the focal plane. The 511-CAM detector assembly has a
projected 511 keV energy resolution of 390 eV Full Width Half Maximum (FWHM) or
better, and improves by a factor of at least 11 on the performance of
state-of-the-art Ge-based Compton telescopes. Combining this unprecedented
energy resolution with sub-arcmin angular resolutions afforded by Laue lens or
channeling optics could make substantial contributions to identifying the
origin of the 511 keV emission by discovering and characterizing point sources
and measuring line-of-sight velocities of the emitting plasmas.

Instrumentation and Methods for Astrophysics;High Energy Physics - Experiment