Searching for beyond-standard-model solar neutrino interactions using directional detectors

Micropattern gaseous detectors (MPGDs) are a class of technologies that enable the full three-dimensional spatial reconstruction of ionization tracks from nuclear and electron recoils in gas. Anticipating near-future <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>30</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:msup> <a:mrow> <a:mi mathvariant="normal">m</a:mi> </a:mrow> <a:mrow> <a:mn>3</a:mn> </a:mrow> </a:msup> </a:mrow> </a:math> -scale time projection chambers with MPGD-based readout, we forecast the sensitivity of such directionally sensitive low-energy recoil detectors to neutrino interactions beyond the standard model. We work in the framework of neutrino nonstandard interactions (NSIs), and calculate the combined recoil energy-angle distributions of the electron recoil signal generated by solar neutrinos in atmospheric-pressure <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mrow> <d:mi>He</d:mi> <d:mo>:</d:mo> <d:msub> <d:mrow> <d:mi>CF</d:mi> </d:mrow> <d:mrow> <d:mn>4</d:mn> </d:mrow> </d:msub> </d:mrow> </d:math> gas. We estimate the expected exclusion limits that such an experiment could place on various NSI parameters, as well as the mass and coupling of a new light mediator that interacts with electrons and neutrinos. We find that with an achievable background reduction of around a factor of ten from current estimates for a <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mrow> <f:mn>30</f:mn> <f:mtext> </f:mtext> <f:mtext> </f:mtext> <f:msup> <f:mrow> <f:mi mathvariant="normal">m</f:mi> </f:mrow> <f:mrow> <f:mn>3</f:mn> </f:mrow> </f:msup> </f:mrow> </f:math> optical-readout detector using this gas mixture, sensitivity to NSI parameters would already approach Borexino’s sensitivity. Directionality also allows for event-by-event neutrino energy reconstruction, which would provide a means to resolve some parameter degeneracies present in the modified neutrino cross section in this formalism. Our results strongly motivate the development of small-scale directionally sensitive gas detectors for neutrino physics.