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
25m
Maple Hall (LL/B1F) (The Grand Hotel Daegu)

Maple Hall (LL/B1F)

The Grand Hotel Daegu

Oral Presentation Working Group 4

Speaker

Dr Sohtaro Kanda (RIKEN)

Description

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