Precise Neutron Lifetime Measurement with a Gaseous Detector and a Solenoidal Magnet

The neutron lifetime, τ = 880.2 ± 1.0 sec, is an important parameter for particle/nuclear physics and cosmology. There is, however, an 8.4 sec (4.0 σ) deviation between the measured value of the neutron lifetime using two methods. A new method is being implemented at J-PARC / MLF / BL05 using a pulsed cold neutron beam. A Time Projection Chamber records both the electrons from neutron beta decay and protons from the neutron-³He capture reactions in order to estimate the neutron flux. However, electron background signals require the largest correction and are source of uncertainty for this type experiment. It is confirmed by Monte Carlo simulation that an uniform magnetic field along the neutron beam can greatly reduce this background. Hence, we proposed another experiment (LiNA experiment) using a solenoidal magnet. The detector was constructed and operation with neutron beam is carried out soon. We will present the status and future plan of this experiment.