Search for Cosmic Background Neutrino Decay

We present a proposal of an experiment for search for cosmic background neutrino decay. Due to the mass difference between neutrino generations, a heavier neutrino can decay into a lighter neutrino with a photon. Standard model predicts the neutrino lifetime is 10 44 year, while the current experimental lower limit of neutrino lifetime is 3 x10 12 year. However Left-Right symmetric model suggests much shorter neutrino lifetime down to 10 17 year in the shortest. If we assume a mass of the heaviest neutrino is 50 meV/c 2 , the expected photon energy at the neutrino rest frame is 25 meV. The energy spectrum of the photon from the cosmic background neutrino decay has a cutoff at this energy and a low energy tail due to a red shift effect as shown in Fig.1. Thus we propose an experiment to search for the photon emission from the decay of cosmic background neutrino by measuring the photon energy spectrum in the far infrared region with a superconducting tunneling junction (STJ) detector. We plan to perform a rocket experiment with the STJ detector in 2016 in the earliest, aiming at improving the neutrino lifetime limit by two order. We also aim at a 10-hour satellite experiment with 5 sensitivity for the neutrino lifetime of 10 17 year in further future [1]. [1] S. H. Kim, K. Takemasa, Y. Takeuchi and S. Matsuura, J. Phys. Soc. Jpn., 81 (2012) 024101S.