On the Possibility of Separating Coherent and Incoherent (Anti)neutrino Scattering on Nuclei

V A Bednyakov,D V Naumov,I V Titkova

doi:10.1134/s1063778821030066

Abstract

The discovery of coherent neutrino–nucleus scattering in the COHERENT experiment opened a source of new information for fundamental investigations in the realms of neutrino and nuclear physics, as well as in the realms of searches for new physics beyond the Standard Model. Owing to substantial momentum transfers, a feature peculiar to the kinematical region of this experiment is that the effect of coherence is mixed with a sizable incoherent contribution rather than being seen in a pure form. On one hand, this leads to additional systematic uncertainties in studying the neutrino component of the coherence effect as such. On the other hand, this makes it possible to study a dynamical transition between the coherent and incoherent scattering modes and, in principle, to separate them experimentally. In our opinion, a consistent measurement of the coherent and incoherent cross sections for (anti)neutrino scattering on a nucleus in the same experiment seems a unique possibility, and its implementation would of course provide new data for neutrino physics, as well as for nuclear and new physics. In the present study, it is shown that this possibility is implementable not only in experiments that explore coherent neutrino and antineutrino scattering on various nuclei at accelerators, where the neutrino energy reaches several hundred MeV units but also in reactor experiments, where antineutrino energies do not exceed 10 MeV. The respective estimation is based on the approach that controls qualitatively a ‘‘smooth transition’’ of the cross section for (anti)neutrino–nucleus scattering from a coherent (or elastic) to an incoherent (inelastic) mode. In the former case, the target nucleus remains in the initial quantum state, while, in the latter case, its quantum state changes. Observation of a specific number of photons that have rather high energies and which remove the excitation of the nucleus after its inelastic interaction with (anti)neutrinos is proposed to be used as a signal from such an inelastic process. An upper limit on the number of such photons is obtained in this study.

Highlights

Coherent neutrino scattering on nuclei was discussed by Freedman in [1] and by Freedman and his coauthors in [2] on the basis of the general quantum-mechanical rule for the addition of the probability amplitudes for indistinguishable processes leading to the same final state
By considering the example of target nuclei used and proposed for use in lowthreshold measurements—in particular, for detecting and studying coherent neutrino–nucleus scattering in the COHERENT experiment and at ESS—we will discuss, in the following, the theoretical results obtained above and will estimate numerically the contributions of coherent and incoherent processes to the total cross section forneutrino scattering on these nuclei
The differential cross sections for this detector are calculated at theneutrino energy of 50 MeV, while the total cross sections are calculated for the interval of possibleneutrino-flux energies between 1 and 50 MeV

Summary

Introduction

Coherent neutrino scattering on nuclei was discussed by Freedman in [1] and by Freedman and his coauthors in [2] on the basis of the general quantum-mechanical rule for the addition of the probability amplitudes for indistinguishable processes leading to the same final state. It seems possible to detect experimentally (perform estimations of respective cross sections) coherent and inelastic [9, 10] neutrino–nucleus interactions (CIνNS—abbreviation proposed by Yu. Efremenko) by measuring, for example, the flux of photons from the removal of nuclear excitations caused by this interaction.

Results

Conclusion