Eur. Phys. J. C (2025) 85: 66
https://doi.org/10.1140/epjc/s10052-025-13745-6

Regular Article - Theoretical Physics

The decay $B\to K+\nu +\overline{\nu }$ at Belle II and a massless bino in R-parity-violating supersymmetry

¹ School of Physics, Hefei University of Technology, 230601, Hefei, China
² Physikalisches Institut der Universität Bonn, Bethe Center for Theoretical Physics, Nußallee 12, 53115, Bonn, Germany

^a wzs@mx.nthu.edu.tw

Received: 20 September 2024
Accepted: 2 January 2025
Published online: 24 January 2025

Abstract

Recently, Belle II announced evidence for the decay $B^{+}\to K^{+}+\nu +\overline{\nu }$ at the $3.5\sigma$ significance, and measured the corresponding decay branching ratio to be $2.7\sigma$ above the Standard Model prediction. Here, we provide a theoretical explanation based on a massless bino in R-parity-violating (RPV) supersymmetry. With a single non-vanishing RPV coupling ${\lambda }_{i23/i32}^{\prime }$, ${\lambda }_{i13/i33}^{\prime }$, or ${\lambda }_{i12/i22}^{\prime }$, where $i=1,2,3$, the decay $B^{+}\to K^{+}+\stackrel{(-)}{{\nu }_i}+{\tilde{\chi }}_1^0$ can be induced, which would lead to the same signature as $B^{+}\to K^{+}+\nu +\overline{\nu }$. Taking into account both theoretical and experimental uncertainties, we derive the regions of the parameter space spanned by the RPV couplings and sfermion masses that could accommodate the new measurement at various significance levels and obey the existing bounds simultaneously.