Observation of the Decay Λ0b→Λ+cτ−¯ντ

Physical Review Letters. 2022. Vol. 128. No. 19. Article 191803.

Aaij R., Abdelmotteleb A. S., Abellán Beteta C., Abudinén F., Ackernley T., Adeva B., Adinolfi M., Arzymatov K., Boldyrev A., Belavin V., Borisyak M., Derkach D., Hushchyn M., Karpov M., Maevskiy A., Mokhnenko S., A. Philippov, Popov S., Ratnikov F., Ryzhikov A., Ustyuzhanin A.

The first observation of the semileptonic b-baryon decay Λ0b→Λ+cτ−¯ντ, with a significance of 6.1σ, is reported using a data sample corresponding to 3  fb−1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ− lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λ0b→Λ+cτ−¯ντ)/B(Λ0b→Λ+cπ−π+π−) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λ0b→Λ+cτ−¯ντ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λ0b→Λ+cπ−π+π−. The ratio of semileptonic branching fractions R(Λ+c)≡B(Λ0b→Λ+cτ−¯ντ)/B(Λ0b→Λ+cμ−¯νμ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λ0b→Λ+cμ−¯νμ contributes to the last term. This result is in agreement with the standard model prediction.

Keywords: анализ данных, data analysis, high energy physics, физика высоких энергий, baryons, leptonic decays, semileptonic decays, radiative decays, Hadron colliders, flavor symmetries

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 (2022)