# Conference on Neutrino and Nuclear Physics (CNNP2020) Arabella Hotel and Spa, South Africa, 24-28 February 2020

23-28 February 2020
Africa/Johannesburg timezone

## Implications of new theoretical calculations on reactor antineutrino and gallium anomalies

28 Feb 2020, 09:20
20m
Parallel Venue

### Speaker

Joel Kostensalo (University of Jyvaskyla, Finland)

### Description

The reactor antineutrino and gallium anomalies have been long unexplained. Possible explanations for both of these anomalies include new physics, such as the existence of one or more eV-scale sterile neutrino [Ga15]. However, the previous theoretical calculations, which do not replicate the experimental results, rely on many simplifying approximations [Ba97,Ha19].

In the reactor-antineutrino analysis the beta decays contributing to the cumulative electron spectrum are usually assumed to have allowed spectral shapes. However, many of these decays are actually first-forbidden. Moreover, these decays dominate the experimentally observable region. In some cases, like in the case of the ground-state-to-ground-state decay of $^{140}\rm Cs$ (see figure), this is found to be a rather poor approximation. Based on the recent results, the use of this allowed approximation can at least partially explain the so called reactor antineurtino anomaly.

Our new large-scale shell model calculations regarding the neutrino-nucleus scattering cross section off $^{71}\rm Ga$ shows no statistical difference to the experimental results of GALLEX and SAGE experiments. Conflict between charge-exchange BGTs and the neutrino-nucleus cross sections can to some extent be explained by destructive interference between Gamow-Teller and tensor contributions. A Bayesian approach to estimating the significance of the gallium anomaly is discussed.

[Ga15] S. Gariazzo, C. Giunti, M. Laveder, Y. F. Li, and
E. M. Zavanin, J. Phys. G: Nucl. Part. Phys. 43, 033001
(2015).

[Ba97] J. N. Bahcall Phys. Rev. C 56, 3391 (1997).

[Ha19] L. Hayen, J. Kostensalo, N. Severijns, and J. Suhonen
Phys. Rev. C 99, 031301(R) (2019).

### Primary authors

Joel Kostensalo (University of Jyvaskyla, Finland) Jouni Suhonen (University of Jyväskylä) Dr Leendert Hayen (KU Leuven)