Oak Ridge National Laboratory

Physics Division

Physics Division Seminars

Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,

Alfredo Galindo-Uribarri
Tel (Office): (865) 574-6124  (FAX): (865) 574-1268

Thu., October 27, 2016, at 3:00 PM - 4:00 PM (refreshments served at 2:40 PM)

The upgrade of the ultracold neutron source at the Los Alamos Neutron Science Center and status of the UCNτ experiment

Robert W. Pattie, Jr., Los Alamos National Laboratory, Los Alamos, NM 87545
ORNL, Bldg. 6008 Large Conference Room

The spallation-driven solid deutrium-based ultracold neutron (UCN) source at Los Alamos Neutron Science Center (LANSCE) has provided a facility for precision measurements of fundamental symmetriesvia the decay observables from neutron beta-decay for nearly a decade. To improve the statistical sensitivity of all experiments using the source an upgrade has been underway for the last two years. This upgrade includes redesign of the cold neutron moderator and UCN converter geometries, improved coupling and coating of the UCN transport system through the biological shielding, optimization of beam timing structure, and increase of the proton beam current. During the spring and summer of 2016 the redesigned source was installed.

One experiment that will benefit from the source upgrade is UCNτ. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime. This design eliminates a major systematic of previous bottle experiments related to the loss of UCN on material trap walls and with unloading neutrons from the storage vessel. UCNτ is designed to achieve a ∼1 s precision measurement of τn with complementary systematics to previous bottle experiments. A result at 1 s precision should help shed light on the current 4σ discrepancy between measurements of the neutron lifetime performed using cold neutron beams and those performed with ultracold neutron (UCN) storage vessels. A new in situ detection system was used in the 2015-2016 run that was able to measure the population of surviving UCN at different heights in the trap, providing important information on spectral evolution. Understanding the behavior of quasi-bound UCN in a bottle experiment is essential to achieving a subsecond precision measurement of τn.

Alfredo Galindo-Uribarri, (865) 574-6124