Determine the CP composition of the Bs0→J/ψγ decay

Determine the CP composition of the radiative decay Bs0 → J/ψ γ, i.e., whether the final state is CP-even, CP-odd, or a mixture and in what proportion, so that selection efficiencies and lifetime-dependent effects can be modeled without resorting to extreme CP assumptions.

Background

In evaluating systematic uncertainties, the analysis requires an assumption about the CP composition of the Bs0 → J/ψ γ signal because the decay-time efficiency depends on whether the state is CP-even, CP-odd, or a mixture with different effective lifetimes.

Due to the lack of an established CP composition, the authors bracket the efficiency by computing it under two extreme scenarios (pure CP-even and pure CP-odd) with lifetimes taken from external measurements. A direct determination of the CP content would remove this ambiguity and reduce the associated systematic uncertainty.

References

Finally, for the third contribution, since the CP composition of the signal is unknown, the efficiency is evaluated under two extreme scenarios corresponding to purely CP-even and CP-odd states, with lifetimes fixed to 1.429±0.006 ps and 1.622±0.008 ps, respectively.

— Search for the decays $B_{(s)}^0\to J/ψγ$ at LHCb  (2604.02933 - collaboration et al., 3 Apr 2026) in Section 5 (Systematic uncertainties), paragraph on selection efficiencies