GRAMS (Gamma-Ray and AntiMatter Survey) is a novel project that is the first to target both astrophysical observations with MeV gamma-rays and an indirect dark matter search with antimatter, which was recently funded by the NASA Astrophysics Research and Analysis (APRA) Grant (80NSSC23K1661) for the prototype flight scheduled in 2025/2026. The GRAMS instrument is designed with a cost-effective, large-scale LArTPC (Liquid Argon Time Projection Chamber) detector surrounded by plastic scintillators. The astrophysical observations at MeV energies have not yet been well-explored (the so-called ‘MeV-gap’), and GRAMS can open a new window in this energy region.

Astrophysical observations via high-energy gamma-ray (above 20 MeV) and X-ray (up to 80 keV) measurements have been well-explored by the Fermi-LAT (Large Area Telescope on the Fermi Gamma-Ray Space Telescope) and the NuSTAR (Nuclear Spectroscopic Telescope Array) missions, respectively. Spectra of gamma-ray sources in the MeV energy range (MeV gamma rays), however, have not yet been well-explored, leading to the so-called “MeV gap.” COMPTEL (The Imaging COMPton TELescope) produced the first catalog of MeV sources but only with approxi- mately 30 objects [10]. The MeV regime can potentially provide rich information on astrophysical processes. Nuclear lines from the radioactive isotopes are mainly in the MeV range. They are the keys to understanding nucleosynthesis processes and mechanisms of astrophysical phenomena, including relativistic flows generated in stellar-mass black holes, supermassive black holes in active galactic nuclei, and various types of neutron stars such as radio pulsars and magnetars [11]. More- over, MeV gamma rays could be produced in dark matter annihilation/decay and primordial black hole evaporation and association with gravitational waves from neutron-star mergers

GRAMS can improve sensitivity by more than an order of magnitude compared to previous experiments. The GRAMS detector is also optimized for cosmic-ray antimatter surveys to indirectly search for dark matter. In particular, low-energy antideuterons will provide an essentially background-free dark matter signature. With exceptional sensitivity, GRAMS would be able to detect antideuterons from dark matter annihilation or decay, even with a single balloon flight. GRAMS would also be able to investigate and validate possible dark matter signatures suggested by the Fermi Gamma-ray Space Telescope and the Alpha Magnetic Spectrometer.

For more information visit: GRAMS Website