In the beam technique, the lifetime is measured by counting the absolute number of protons within a fiducial volume while continuously monitoring the absolute neutron flux. We completed this experiment in 2003, and the uncertainty in the result was dominated by systematic effects associated with the neutron counting. Since that time, the group has successfully refined the ability to measure absolute neutron fluence at the level of 0.06%, and with this improvement, neutron counting is no longer the limiting systematic effect. In 2013 we published an updated value of (887.7 +/- 2.2) s using the new neutron counting results. We are now working on a new experiment to measure the lifetime with a focus on testing and accounting for possible systematic effects.
The lifetime experiment is currently mounted and running on the NG-C beamline, as shown in Figure 3. It is acquiring production data and working through many of the systematic checks. Operations and data analysis are ongoing.