Impact of Wave Packet Separation in Low-Energy Sterile Neutrino Searches

Abstract

Light sterile neutrinos have been motivated by anomalies observed in short-baseline neutrino experiments. Among them, radioactive-source and reactor experiments have provided evidence and constraints, respectively, for electron-neutrino disappearance compatible with an eV-scale neutrino. These seemingly conflicting results have been derived under the approximation that the neutrino wave package can be approximated as a plane wave. This letter demonstrates that when the neutrino wave package is taken into account, the tension between the different electron-flavor observations and constraints are resolved. Based on this study, in the future all results should be presented with zero and maximal wavepacket effects, since the true value must lie in between.

White Paper on Light Sterile Neutrino Searches and Related Phenomenology

“…In this section, we follow the discussion given in Ref. [111] and point out that when interpreting experimental data in the context of 3+1 this possibility has been overlooked. This fact could partially or completely resolve the existing tension between appearance and disappearance data sets.…”

“…Notice that this value is far from some first-order estimations of the wave packet in various contexts [118,120,122,123]; however, Ref. [111] decided to be agnostic and use an experimental result that should be robust even in more exotic scenarios. The global analysis performed in Ref.…”

“…However, as pointed out in Ref. [111], due to the lack of detailed calculations of the neutrino production and detection mechanism, or from additional BSM effects, this is not guaranteed. In this section, we follow the discussion given in Ref.…”

“…To show the impact of the wave packet separation [111] chooses the smallest value allowed by oscillation experiments for the wave packet size, σ x = 2.1 × 10 −4 nm [129,131], and performs analyses searching for sterile neutrinos with and without the PW approximation. Notice that this value is far from some first-order estimations of the wave packet in various contexts [118,120,122,123]; however, Ref.…”

“…The global analysis performed in Ref. [111] considers the null results from Daya Bay [132,133], NEOS [134], and PROSPECT [135,136] and the anomalous results observed from radioactive sources by BEST [137].…”