Towards a beta spectrum shape measurements at WISArD

by Simon Vanlangendonck (KU Leuven)

Wednesday 3 Jul 2019, 14:15 → 15:00 Europe/Zurich

In our research group at KU Leuven (Belgium), we perform precision studies, mainly experimental, of the weak interaction. There exists a broad range of possible experiments, e.g. the measurement of beta-neutrino correlation coefficients, determining the Ft-value of the β-decay, probing the shape of the beta energy spectrum … of which the latter is the subject of this talk.
When talking about precision experiments we mean experiments that reach a precision close to 10-3. When probing beyond standard model (BSM) physics these kinds of experiments are complementary to high-energy physics experiments, i.e. LHC, when interpreted in an effective field theory.

During the long shutdown at CERN we will adapt the existing WISArD set-up at CERN. With the objective to measure the beta-spectrum shape of  114In, a pure Gamow-Teller decay, and look for the QCD influence on the β-decay of which the weak-magnetism term is the major contribution. The interest in this influence is motivated by the reactor neutrino anomaly. This is the observation that the measured number of antineutrinos emerging from reactor fission fragments inside a reactor is at close distance lower than theoretically predicted. The deficit is approximately -6 % and is a 3σ effect. Moreover, there is an additional anomaly between theory and prediction in the energy spectrum, the so-called shoulder or bump in the spectrum at about 5 MeV. Besides the possibility of new physics, i.e. sterile neutrinos, another explanation might be the uncertainties and approximations present in the theoretical calculations. Especially the occurrence of the shoulder is said to have a nuclear physics origin. Therefore, calculations would benefit from additional experimental information. One of the uncertainties now is the value of weak-magnetism in the mass range of the reactor fission fragments.

A direct measurement of the weak-magnetism contribution from the beta-spectrum shape would be the first of its kind in this mass range.