Prospects for a new cold neutron beam measurement of the neutron lifetime

In the most accurate cold neutron beam determination of the neutron lifetime based on the absolute counting of decay protons, the largest uncertainty was attributed to the absolute determination of the capture flux of the cold neutron beam. Currently an experimental effort is underway at the National Institute of Standards and Technology (NIST) that will significantly reduce this contribution to the uncertainty in the lifetime determination. The next largest source of uncertainty is the determination of the absolute count rate of decay protons, which contributes to the experimental uncertainty approximately at the 1 s level. Experience with the recent neutron radiative decay experiment, which used the neutron lifetime apparatus, has provided valuable insights into ways to reduce other uncertainties. In addition, the cold neutron fluence rate at NIST is presently 1.5 times greater than in the 2003 measurement, and there is the prospect for a significantly higher rate with the new guide hall expansion. This paper discusses an approach for achieving a determination of the neutron lifetime with an accuracy of approximately 1 s.