Evidence of sterile neutrino from endpoint analysis of β-spectrum

Abstract

An anomaly has been observed around the endpoint of the measured β spectrum of second unique forbidden transition of 138La(5+). The data has been analyzed in the light of Fermi–Kurie plot and an extra component around the endpoint energy has been observed at a 3σ level of statistical significance. The probability of observing that extra component with respect to the beta events are same (⩽0.01%) in a number of repeated experiments and the fitted parameters of the extra strength with Gaussian shape around endpoint energy are within the error of 99.7% confidence limit. All possible tentative explanation in the light of atomic, nuclear and neutrino physics have been discussed. A favorable tentative explanation could be existence of the sterile neutrino. The present data analysis provides mass limit, 15 ± 9 ± 4 (sys.) ⩽ m 4 (keV) ⩽ 45 ± 27 ± 4 (sys.) for active-sterile mixing ratio 0.3 ⩾ |U e4|2 ⩾ 0.03.