Angular analysis of 𝐵0→𝐷∗−𝐷∗+𝑠 with 𝐷∗+𝑠→𝐷+𝑠𝛾 decays

Journal of High Energy Physics. 2021. Article 177.

Aaij R., Beteta C. A., Ackernley T., Adeva B., Arzymatov K., Belavin V., Boldyrev A., Borisyak M., Derkach D., Hushchyn M., Maevskiy A., Попов С. А., Ratnikov F., Ryzhikov A., Ustyuzhanin A.

The first full angular analysis of the 𝐵0→𝐷∗−𝐷∗+𝑠B0→D∗−Ds∗+ decay is performed using 6 fb−1 of pp collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The 𝐷∗+𝑠→𝐷+𝑠𝛾Ds∗+→Ds+γ and D*− → 𝐷⎯⎯⎯⎯⎯0𝜋−D¯0π− vector meson decays are used with the subsequent 𝐷+𝑠Ds+ → K+K−π+ and 𝐷⎯⎯⎯⎯⎯0D¯0 → K+π− decays. All helicity amplitudes and phases are measured, and the longitudinal polarisation fraction is determined to be fL = 0.578 ± 0.010 ± 0.011 with world-best precision, where the first uncertainty is statistical and the second is systematic. The pattern of helicity amplitude magnitudes is found to align with expectations from quark-helicity conservation in B decays. The ratio of branching fractions [ℬ(𝐵0→𝐷∗−𝐷∗+𝑠B0→D∗−Ds∗+) × ℬ(𝐷∗+𝑠→𝐷+𝑠𝛾Ds∗+→Ds+γ)]/ℬ(B0 → D*−𝐷+𝑠Ds+) is measured to be 2.045 ± 0.022 ± 0.071 with world-best precision. In addition, the first observation of the Cabibbo-suppressed Bs → D*−𝐷+𝑠Ds+ decay is made with a significance of seven standard deviations. The branching fraction ratio ℬ(Bs → D*−𝐷+𝑠Ds+)/ℬ(B0 → D*−𝐷+𝑠Ds+) is measured to be 0.049 ± 0.006 ± 0.003 ± 0.002, where the third uncertainty is due to limited knowledge of the ratio of fragmentation fractions.

Keywords: HEP LHC Standard Model, стандартная модель, БАК, тяжелые кварки

Publication based on the results of: Machine learning to check and improve the quality of data collected at the Large Hadron Collider and other particle physics experiments (2021)