Speaker
Dr
Christopher Swank
(Caltech)
Description
The neutron lifetime is currently measured by two different types of experiments: "beam" and "bottle". These two measurement techniques have a $4 \sigma$ discrepancy in measured lifetime. It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle ($\chi$) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single $\chi$ along with an $e^+e^-$ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with $\approx4\pi$ acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). The summed kinetic energy ($E_{e^+e^-}$) from such events is used to set limits, as a function of the $\chi$ mass, on the branching fraction for this decay channel. For $\chi$ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at $\approx5\sigma$ level for 100 keV $< E_{e^+e^-} < 644$ keV. If the $\chi+e^+e^-$ final state is not the only one, we set limits on its branching fraction of $< 10^{-4}$ for the above $E_{e^+e^-}$ range at $>90$% confidence level.
| cmswank@caltech.edu | |
| Collaboration name | UCNA Collaboration |
| Funding source | DOE, NSF |
Primary author
Dr
Christopher Swank
(Caltech)
