サイエンス記事
中性子寿命の謎，解明に向けて
- J-PARCパルス中性子ビームを用いた新手法
2022 年 32 巻 3 号 p. 114-119
詳細
2022 年 32 巻 3 号 p. 114-119
A neutron decays into a proton, an electron, and an antineutrino through the weak interaction. The recent measurements were performed by two different experimental methods. One is a so-called bottle method; the number of the surviving ultra-cold neutrons (UCNs) contained in a storage bottle is measured as a function of the elapsed time, and the lifetime is determined with an exponential decay curve. On the other hand, the beam method determines the neutron lifetime from the decay probability of the neutron obtained from the measured ratio of the decay rate to the incident neutron flux. The averaged neutron lifetimes with the two methods differ by 9.5 s, corresponding to the deviation of 4.6σ using quoted uncertainties. The discrepancy is called the “neutron lifetime puzzle”, and it is still unsettled whether it is due to any unconsidered systematic effect or any new physics. To solve the neutron lifetime puzzle, a new-type of experiment is conducted with pulsed neutron beam at J-PARC MLF.
