Complementarity Between Neutrino Neutral and Charged Current Events in the Search for New Physics

TL;DR

This paper explores how neutral-current neutrino events can be used alongside charged-current events in long-baseline experiments to improve constraints on non-standard neutrino interactions with quarks, revealing new physics potential.

Contribution

It demonstrates the first bounds on isovector NSI from long-baseline experiments and shows how combining CC and NC data breaks degeneracies in quark coupling measurements.

Findings

NC events provide sensitivity to flavor-dependent oscillations.

Combining CC and NC data constrains both isoscalar and isovector NSI couplings.

Existing NOvA data and DUNE projections set new bounds on NSI.

Abstract

At long-baseline neutrino experiments, neutral-current (NC) events accumulate in large numbers but are seldom exploited for new physics searches. We demonstrate their potential using non-standard neutrino interactions (NSI) with quarks as a case study. Charged-current (CC) analyses constrain NSI through matter effects on neutrino propagation, which probe almost exclusively the isoscalar combination of up- and down-quark couplings; the orthogonal isovector combination is suppressed by a factor of $\sim$100. Because NSI also modify NC cross sections in a flavor-dependent way, NC events become sensitive to oscillations: the far-to-near detector ratio acquires a dependence on the beam's flavor composition that probes both isoscalar and isovector couplings with comparable weight. Using existing NOvA data and DUNE projections, we derive the first bounded constraints on isovector NSI from a long-baseline experiment and show that combining CC and NC measurements resolves the individual quark couplings, breaking a degeneracy that persists in either analysis alone.