December 1, 2018
Lawrence Berkeley National Lab
US/Pacific timezone

The GAmmas from Nuclear Decays Hiding from Investigators (GANDHI) Experiment

Dec 1, 2018, 11:45 AM
Building 50 Auditorium (Lawrence Berkeley National Lab)

Building 50 Auditorium

Lawrence Berkeley National Lab


Harikrishnan Ramani


We propose a high statistics experiment to search for invisible decay modes in nuclear gamma
cascades. A radioactive source (such as 60Co or 24Na) that triggers gamma cascades is placed
in the middle of a large, hermetically sealed scintillation detector, enabling photon identification
with high accuracy. Invisible modes are identified by establishing the absence of a photon in a wellidentified
gamma cascade. We propose the use of fast scintillators with nanosecond timing resolution,
permitting event rates as high as 107 Hz. Our analysis of the feasibility of this setup indicates that
branching fractions as small as 1E−12 − 1E−14 can be probed. This experimental protocol benefits
from the fact that a search for invisible modes is penalized for weak coupling only in the production
of the new particle. If successfully implemented, this experiment is an exquisite probe of particles
with mass below ∼4 MeV that lie in the poorly constrained supernova “trapping window” that
exists between 100 keV - 30 MeV. Such particles have been invoked as mediators between dark
matter and nucleons, explain the proton radius and (g − 2)µ anomalies and potentially power the
shock wave in type II supernovae. The hadronic axion could also be probed with modifications to
the proposed setup.

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