Toward the discovery of novel Bc states: Radiative and hadronic transitions

The properties of the B-c-meson family (cb over bar) are still not well determined experimentally because the specific mechanisms of formation and decay remain poorly understood. Unlike heavy quarkonia, i.e., the hidden heavy quark-antiquark sectors of charmonium (cc over bar) and bottomonium (bb over bar), the B-c mesons cannot annihilate into gluons and they are, consequently, more stable. The excited Bc states, lying below the lowest strong-decay BD threshold, can only undergo radiative decays and hadronic transitions to the B-c ground state, which then decays weakly. As a result of this, a rich spectrum of narrow excited states below the BD threshold appear, whose total widths are 2 orders of magnitude smaller than those of the excited levels of charmonium and bottomonium. In a different article, we determined bottom-charmed meson masses using a nonrelativistic constituent quark model which has been applied to a wide range of hadron physical observables, and thus the model parameters are completely constrained. Herein, continuing to our study of the B-c sector, we calculate the relevant radiative decay widths and hadronic transition rates between cb over bar states which are below the BD threshold. This shall provide the most promising signals for discovering excited B-c states that are below the lowest strong-decay BD threshold. Finally, our results are compared with other models to measure the reliability of the predictions and point out differences.

Automated summary

The properties of the B-c meson family are still uncertain due to the lack of understanding of their formation and decay mechanisms. Unlike other heavy quarkonia, the B-c mesons are more stable because they cannot annihilate into gluons. In this study, we use a well-established quark model to calculate the radiative decay widths and hadronic transition rates of cb over bar states below the BD threshold, providing potential signals for the discovery of excited B-c states.