Neutron lifetime measurements with the big gravitational trap for ultracold neutrons

Understand

Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory.

• There remains the unsolved problem of a 3.9{\sigma} discrepancy between measurements of this lifetime using neutrons in beams and those with stored neutrons (UCN).
• In our experiment we measure the lifetime of neutrons trapped by Earth's gravity in an open-topped vessel.
• Two configurations of the trap geometry are used to change the mean frequency of UCN collisions with the surfaces - this is achieved by plunging an additional surface into the trap without breaking the vacuum.