$B^{+}\to K^{+}\hat{I}½\bar{\hat{I}}½$ Excess and DM semi-annihilation

Abstract

In 2023, Belle II collaboration announced the observarion of the $B^{+}\to K^{+}\hat{I}½\bar{\hat{I}}½$ decay channel for the first time. This decay channel provides a clean signal with high precision in theoretical calculation. However, we encounter $2.8\ddot{I}ƒ$ deviation from the Standard Model (SM) prediction. To resolve this excess, we study scalar dark matter (DM) model with local discrete $Z_3$ symmetry. Assuming dark $U(1{)}_X\equiv U(1{)}_{L_{\hat{I}}¼-L_{\ddot{I}}„}$ symmetry, this $U(1{)}_{L_{\hat{I}}¼-L_{\ddot{I}}„}$ symmetry is spontaneously broken into local discrete $Z_3$ by non-zero vacuum expectation value of dark Higgs boson. Considering dark Higgs mass is $2$GeV, we can explain the recent $\mathrm{Br}(B^{+}\to K^{+}\hat{I}½\bar{\hat{I}}½)$ excess reported from Belle II collaboration and relic abundance at the same time.

18 pages, 4 figures