Long-lived light neutralinos at Belle II

TL;DR

This paper explores the potential of the Belle II experiment to detect light neutralinos around 1 GeV produced via rare tau decays, using displaced vertex signatures to improve sensitivity in RPV supersymmetry models.

Contribution

It demonstrates that Belle II can significantly improve constraints on light neutralinos and RPV couplings through simulation of displaced vertex signatures from tau decays.

Findings

Belle II can probe neutralino parameter space more effectively than current bounds.

Displaced vertex detection with charged pions enhances sensitivity to light neutralinos.

Limits on RPV couplings can be improved by up to two orders of magnitude.

Abstract

We consider light neutralinos of mass about 1 GeV, produced from $\tau$ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of $\tau$ leptons produced at the Belle II experiment, excellent sensitivity to such light neutralinos with the exotic signatures of displaced vertices is expected. We focus on two benchmark scenarios of single RPV operators, $\lambda'_{311} L_3 Q_1 \bar{D}_1$ and $\lambda'_{312} L_3 Q_1 \bar{D}_2$, which induce both the production and decay of the lightest neutralino. For the reconstruction of a displaced vertex, we require at least two charged pions in the final states. We perform Monte-Carlo simulations for both signal and background events, and find that Belle II can explore regions in the parameter space competitive with other probes. In particular, for the $\lambda'_{311}$ scenario, it can put limits up to two orders of magnitude stronger than the current bounds.