May 29, 2018 to June 3, 2018
Hyatt Regency Indian Wells Conference Center
US/Pacific timezone

Search for Dark Matter Decay of the Free Neutron from the UCNA Experiment: $n \to \chi+e^+e^-$

May 29, 2018, 2:20 PM
South Foyer | Pinon Room (Hyatt Regency Indian Wells Conference Center)

South Foyer | Pinon Room

Hyatt Regency Indian Wells Conference Center

44600 Indian Wells Lane, Indian Wells, CA 92210, USA
Parallel DM Dark Matter


Dr Christopher Swank (Caltech)


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.
E-mail [email protected]
Collaboration name UCNA Collaboration
Funding source DOE, NSF

Primary author

Dr Christopher Swank (Caltech)

Presentation materials