Speaker
Hidetoshi Otono
(Kyushu University (JP))
Description
According to the PDG, the neutron lifetime is reported as $880.3\pm1.1~\rm{s}$ in 2015. Although the neutron lifetime is a crucial parameter for the unitarity in the CKM matrix, there is a 1% discrepancy, i.e., $8.4\pm2.2$ s, between two methods: counting surviving ultra-cold neutrons after storing ($879.6\pm0.8~\rm{s}$) and counting trapped protons from the neutron decay ($888.0\pm2.1~\rm{s}$).
A experiment at J-PARC employs an electron-counting method, based on a experiment at ILL by R. Kossakowski et al; Pulsed neutron beams pass through a time projection chamber (TPC) which detects electrons from the neutron decay, and also measures the neutron flux with mixed ${\rm{^{3}He}}$ via the $\rm{^3He(n,p)^3H}$ reaction. The performance of the TPC was recently published -- Nucl. Instr. and Meth. A 799, 187-196 (2015).
A new TPC housed in a solenoid coil is also considered. The TPC is divided into three regions by anode and cathode wires. The main systematic uncertainties on the experiment at ILL and J-PARC are related to the subtraction of background events against electrons from the neutron decay, and the separation between the neutron decay and the $\rm{^3He(n,p)^3H}$ reaction. The newly introduced magnetic and electric fields for the TPC reduce these uncertainties, which would reach a 0.1% accuracy and offer a clue to help resolve the 1% discrepancy among the neutron lifetime measurements. In this talk, our current status and prospect will be presented.
Primary author
Hidetoshi Otono
(Kyushu University (JP))
