Diurnal Modulations of the Neutron Lifetime from the UCNtau Experiment

The UCNtau experiment has measured the most precise value of the neutron lifetime. It also opens an opportunity to search for new physics. One possibility is that the measured neutron lifetime could vary with the motion of Earth. Neutrons coupled to galactic dark matter or Lorentz-violating couplings yield diurnal modulation. To investigate this possibility, a sinusoidal function C+A*sin(w*t+phi) was fit to neutron lifetime values from 2017 to 2022. A wide scan of frequencies from diurnal to sidereal oscillations was then performed. Results show a significant peak in amplitude of lifetime variation as large as 1.34 +/- 0.28 seconds when the frequency is 1.312 sidereal days.

This result may provide evidence for a number of mysteries in physics. One of the possibilities is dark matter scattering. It is possible that dark matter in our galaxy scatters neutrons, lowering the number of neutrons in the UCNtau trap. In particular, the theoretical model "dark blob"(PhysRevD 103, 035014, 2021) suggests a mechanism to provide compatible number density for UCNtau's sensitivity. On the other hand, because the experiment is temperature sensitive, the difference in temperature from night and day might have caused the fluctuation in lifetime. Future work would require more experimental control and continued theoretical considerations on potential dark matter scattering and investigating the diurnal modulation as a solution to the neutron bottle anomaly.