Evidence Of Sterile Neutrino From Endpoint Analysis Of Beta-Spectrum

An anomaly has been observed around the endpoint of the measured beta spectrum of second unique forbidden transition of La-138(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 3 sigma 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.