Probing $R$-parity violation in $B$-meson decays to a baryon and a light neutralino

TL;DR

This paper proposes a novel search at Belle II for $B$ meson decays into a baryon and missing energy to detect light neutralinos and $R$-parity violation, providing new sensitivity estimates and recasting existing limits.

Contribution

It introduces a new experimental approach to probe GeV-scale neutralinos with $R$-parity violation in $B$ decays, including detailed theoretical calculations and sensitivity projections.

Findings

Belle II can probe $ ext{lambda}''_{113}/m^2_{ ilde{q}}$ down to 10^{-8} GeV$^{-2}$.

Current limits on $ ext{lambda}''_{123}$ are recast from existing searches.

The analysis techniques and background estimates are detailed for future experimental searches.

Abstract

We propose a search for $B$ meson decays to a baryon plus missing energy at the Belle II experiment to probe supersymmetry with a GeV-scale lightest neutralino ${\tilde{\chi}_1^0}$ and $R$-parity violation (RPV). We perform analytic computations of the signal branching fractions in the framework of effective field theory, with a single nonzero RPV operator $\lambda''_{ij3}\bar{U}_{i}^c\bar{D}_{j}^c\bar{D}_3^c$, where $i,j=1,2$. The hadronic form factors are calculated using an SU(3) phenomenological Lagrangian approach for the proton, as well as several hyperons and charmed baryons. Since the decay of the neutralino is kinematically and CKM suppressed in this theoretical scenario, it decays outside the detector and appears experimentally only as missing energy. We detail the analysis techniques at the experimental level and estimate the background in the ${B^+ \to p {\tilde{\chi}_1^0}}$ search using published results for $B^+\to K^+ \nu\bar\nu$. Our final sensitivity plots are shown for both $\lambda''_{113}$ versus the squark mass $m_{\tilde{q}}$ and $\lambda''_{113}/m^2_{\tilde{q}}$ versus the neutralino mass $m_{{\tilde{\chi}_1^0}}$. We find that the search at Belle II could probe $\lambda''_{113}/m^2_{\tilde{q}}$ down to the order of $10^{-8}$ GeV$^{-2}$ in the kinematically allowed $m_{{\tilde{\chi}_1^0}}$ range. We also obtain current limits on $\lambda''_{123}$ by recasting an existing search interpreted as ${B^0 \to \Lambda^0 {\tilde{\chi}_1^0}}$, and comment about searches for ${B^+ \to \Sigma^+ {\tilde{\chi}_1^0}}$, ${B^0 \to \Sigma^0 {\tilde{\chi}_1^0}}$, ${B^+ \to \Lambda_c^+ {\tilde{\chi}_1^0}}$, and ${B^+ \to \Xi_c^+ {\tilde{\chi}_1^0}}$. In closing, we briefly discuss potential searches at the LHCb and BESIII experiments.