a Measurement of the Beta Spectrum of NEON-19 to Search for Heavy Neutrino Mixing and to Test the Conserved Vector Current Hypothesis
I report on a measurement of the beta decay spectrum of ('19)Ne. A precise determination of the spectral shape can set new limits on the extent of neutrino mass mixing and the correlated mass(es) of the heavy component(s) that may appear in the electron neutrino: these would produce distinctive kinks in the observed spectral shape. The ('19)Ne spectrum (T(,0) = 2216 KeV) is sensitive to heavy neutrino components with masses below (TURN)2 MeV. Shot noise in a one-week experiment limits the observable mass range to above (TURN)50 KeV, and limits the observable branching ratio of a heavy component in the electron neutrino to above B (DBLTURN) 0.008. the corresponding mixing angle limit is (THETA) (DBLTURN) arcsin(SQRT.(B)) (DBLTURN) 5(DEGREES). The principal theoretical uncertainty of the predicted spectral shape is in the calculation of the nuclear matrix element. The distortion is due mainly to the weak magnetic form factor; this can be related to a comparable measured electromagnetic matrix element in the daughter ('19)F if the conserved vector current hypothesis holds. Since the resultant nuclear matrix element has a smooth energy dependence of (TURN) -0.4% per MeV in the spectral shape, the CVC hypothesis can be tested simultaneously. Instrumental distortions introduced a systematic energy dependence into our measured spectrum five times larger than the expected weak magnetic effect. Related random noise, five times larger than the shot noise, prevented the observation of any heavy neutrino kink. Thus, no conclusion on either effect can be deduced from the present data. Improvements needed for a successful measurement are discussed.
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- Physics: Nuclear