# Properties of excited $B_c$ states in QCD

## TL;DR

This paper calculates the masses and decay constants of excited B_c meson states using QCD sum rules, aligning well with experimental data and providing predictions for future experimental verification.

## Contribution

It introduces a detailed QCD sum rule analysis of excited B_c states, incorporating multiple approaches and fitting methods to improve accuracy of mass and decay constant predictions.

## Key findings

- Mass of B_c(2S) state: 6.88 ± 0.03 GeV
- Mass of B_c* (2S) state: 6.94 ± 0.03 GeV
- Predicted decay constants: 0.42 ± 0.02 GeV and 0.46 ± 0.01 GeV

## Abstract

The mass and leptonic decay constants of recently observed two new excited $B_c$ states at LHC are studied within the QCD sum rules. Considering the contributions of the ground and radially excited states, the mass and residues of the excited states of pseudoscalar and vector mesons are calculated in the framework of two different approaches of the QCD sum rules, namely, linear combinations of the corresponding sum rules and its derivatives as well as QCD sum rules with the incorporation of the least square fitting method. The obtained results on mass $m_{B_c^+}(2S) = 6.88 \pm 0.03~\rm{GeV} $ and $m_{B_c^{*+}}(2S) = 6.94 \pm 0.03~\rm{GeV} $ are in good agreement with the experimental data. Our predictions for the decay constants of these states are: $f_{B_c^+}(2S) = 0.42 \pm 0.02~\rm{GeV} $ and $f_{B_c^{*+}}(2S) = 0.46 \pm 0.01~\rm{GeV}$, which can be checked at future experiments to be conducted at the LHC. Comparison of our results with the predictions of the other approaches on mass and residues is also presented.