Electron events from the scattering with solar neutrinos in the search of keV scale sterile neutrino dark matter

摘要

In a previous work we showed that keV scale sterile neutrino dark matter$\nu_s$ is possible to be detected in $\beta$ decay experiment usingradioactive sources such as $^3$T or $^{106}$Ru. The signals of this darkmatter candidate are mono-energetic electrons produced in neutrino captureprocess $\nu_s + N' \to N +e^-$. These electrons have energy greater than themaximum energy of the electrons produced in the associated decay process $N'\to N +e^- + {\bar \nu}_e$. Hence, signal electron events are well beyond theend point of the $\beta$ decay spectrum and are not polluted by the $\beta$decay process. Another possible background, which is a potential threat to thedetection of $\nu_s$ dark matter, is the electron event produced by thescattering of solar neutrinos with electrons in target matter. In this articlewe study in detail this possible background and discuss its implication to thedetection of keV scale sterile neutrino dark matter. In particular, bound statefeatures of electrons in Ru atom are considered with care in the scatteringprocess when the kinetic energy of the final electron is the same order ofmagnitude of the binding energy.