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Research: Toward solving the neutron lifetime puzzle: Launch of the third method


A group of researchers, including scientists from Nagoya University, the High Energy Accelerator Research Organization (KEK), the University of Tokyo, Kyoto University, Kyushu University, Osaka Electro-Communication University, Tsukuba University, and Osaka University, reported the first result of neutron lifetime measurement by adopting a new experimental technique.

Neutrons are one of the particles that constitute the nuclei of atoms. Neutron decay is related to the mechanism of synthesis of elements in the early universe and particle physics. This result paves a new way to improve the accuracy of neutron lifetime to study the evolution of the universe.

Learn more about the result at Press Release (Nagoya University website, Japanese).

Associate Prof. Masaaki Kitaguchi, KMI, is actively involved in the project.


Neutrons are not only common but also important to study the evolution of our universe and new physics of elementary particles. KMI, Nagoya University, has been playing a central role in various neutron physics experiments worldwide. The Neutron Optics and Physics (NOP) collaboration, of which KMI is one of the members, has already started to improve the measurement. Please stay tuned. (Associate Prof. Masaaki Kitaguchi )



Two types of neutron lifetime measurements.
(Left) Beam method counts emitted particles from neutron decay.
(Right) Bottle method counts survived neutrons after storage.
Fig 2. Series of published values of neutron lifetime.
There is a discrepancy between the values using the two methods.
Fig.3 Measurement procedure adopted in this work. The electrons emitted from neutron decay were counted only when the neutron bunch was completely in the detector to suppress the background signals.

Press Release

Nagoya University webpage (PDF, Japanese)

Paper Information

Hirota et al., “Neutron lifetime measurement with pulsed cold neutrons”, Progress of Theoretical and Experimental Physics (online, January 8, 2021)