Aug 25 – 31, 2019
The Grand Hotel Daegu
Asia/Seoul timezone

A search for Majoranality of neutrinos in muon decay using a positron polarimeter

Aug 30, 2019, 4:25 PM
Maple Hall (LL/B1F) (The Grand Hotel Daegu)

Maple Hall (LL/B1F)

The Grand Hotel Daegu

Oral Presentation Working Group 4


Dr Sohtaro Kanda (RIKEN)


It is an unsolved problem of prime importance whether the neutrinos are Dirac or Majorana paricles. The Majoranality of neutrinos is predicted in the presence of V+A interactions. It appeares as a time-reversal (T) symmetry breaking term in the general form of the differential decay rate of muons [1]. Positrons from muon decays are mostly polarized in the longitudinal direction. However, the T-violating term results in the transverse polarization of the positron which is perpendicular to both the muon spin and the positron momentum. It gives a clear evidence of the Majoranality of neutrinos without contributions from the standard model background. The polarization of positrons can be analyzed via the spin dependence of the annihilation-in-flight with electrons [2]. Towards a search for the T-violating effect, we propose a new experiment to measure the decay positron's polarization with a magnetized foil, a segmented calorimeter, and high-intensity pusled muon beam at J-PARC. A positron polarimeter for the experiment is designed using GEANT4-based Monte-Carlo simulation. In this presentation, a measurement method and details of the polarimeter will be discussed.

[1] M. Doi, T. Kotani, H. Nishiura, K. Okuda, and E. Takasugi, Progress of Theoretical Physics 67, 281 (1982).
[2] N. Danneberg et al., Phys. Rev. Lett. 94, 021802 (2005).

Working Group WG4 : Muon Physics

Primary authors

Dr Sohtaro Kanda (RIKEN) Prof. Takeshi Fukuyama (RCNP, Osaka Univ.) Dr Daisuke Nomura (KEK) Prof. Koichiro Shimomura (KEK)

Presentation materials