Development of the detection of the neutrino magnetic moment using transitoin radiation

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07804018
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 素粒子・核・宇宙線
• Research Institution: National Laboratory for High Energy Physics (KEK)
• Principal Investigator: SAKUDA Makoto KEK,Phys.Dept., Ass.Prof., 物理研究部, 助教授 (40178596)
• Co-Investigator(Kenkyū-buntansha): NAKANO Itsuo Okayama Univ., Faculty of Science Dept., Ass.Prof., 理学部物理, 助教授 (90133024) ; SHIRAI Junpei KEK,Phys.Dept., Res.Asso., 物理研究部, 助手 (90171032)
• Project Period (FY): 1995 – 1996
• Keywords: Transition radiation / Neutrino / neutrino magnetic moment

Research Abstract

In the standard model with the right-handed neutrino singlet (nu_R) the magnetic moment of the neutrino is estimated to be negligibly small : mu_<nu>=(3*10^<-19>m_<nu>)mu_B, where m_<nu> is the neutrino mass in units of eV and mu_B is the electron Bohr magneton. Thus, the existence of a neutrino magnetic moment at an order of 10^<-10> mu_B would require a modification of the standard model of the electro-weak interaction. The existing experimental upper bounds on the neutrino magnetic moment are still weak : mu(nu_e)<10^<-9>mu_B, mu(nu_<mu>)<10^<-9>mu_B, and mu(nu_r)<10^<-6>mu_B at the 90% CL.These experimental searches have been performed using the process of neutrino-electron elastic scattering and the e^+e^-*gammanunu^^- process. One of us recently proposed a new method to measure the neutrino magnetic moment using the transition radiation. Transition radiation is a well established electromagnetic phenomenon. It should also be produced when the neutrino with a magnetic moment cross es the interface between two different media. The probability of the radiation is about 10^<-12> (mu_<nu>/mu_B)^2 per interface and the energy spectrum of the radiation is uniform up to gammaomega_1, where gamma is the Lorentz factor of the neutrino (gamma=E_<nu>/m_<nu>) and omega_1 is the plasma frequency of the medium. It is noted that the energy intensity depends explicitly on the neutrino mass and that the energy emitted is as large as the incident neutrino energy depending on the neutrino mass. The experiment uses the reactor neutrinos with flux of F_<nu>=10^<13>nu^^-_e/cm^2/sec. We propose a detector consisting of a radiator with N Mylar films (area=100m^2, N-5x10^3, omega_1=20eV and thickness l_1=0.1mm) stretched in air (omega_2=0.8eV and spacing l_2=1mm). The produced gamma rays are detected by the 100 sets of scintillator strips. The energy and the direction of the gamma rays are reconstructed by using the multi-Comptom scattering events. The detection efficiency is estimated to be 48%, and the energy resolution and the angular resolution are estimated to be about 14% and 2.5 degrees. The experiment can reach mu_<nu> -5・10^<-9>mu_B after 1 year of data-taking.