Speaker
Description
Neutron invisible decay is a baryon-number-violating process in which
one or two neutrons decay into neutral particles without accompanying
charged particles. Invisible neutron decay into only Standard Model particles is strongly constrained, while new light neutral particles beyond the Standard Model can open additional decay channels with rates potentially within experimental reach. When a bound neutron disappears from a nucleus, the
residual nucleus is left in an excited state, and its de-excitation can
produce experimentally observable signals. In liquid scintillator
detectors, in particular, it is known that such nuclear de-excitation
and the subsequent beta decay of the daughter nucleus can form a triple
time- and space-correlated signal, enabling highly sensitive searches
with strong background suppression.
We are conducting a search for neutron invisible decay using KamLAND,
which contains 1 kt of liquid scintillator. In this search, the nuclear
de-excitation signal model is an essential input that directly affects
the signal efficiency and lifetime sensitivity. However, the
conventional signal model is subject to model dependence in its
calculation, including the omission of light-ion emission channels such
as deuterons, tritons, and helium-3.
We are therefore re-evaluating the de-excitation reactions using modern
nuclear de-excitation codes, GEMINI++4νand TALYS. In this presentation,
we report the results obtained so far from the re-evaluation of the signal model and discuss its impact on the KamLAND full-data search for
neutron invisible decay.