Observation of the decays B0(s) → Ds1(2536)∓K±

Abstract

[Abstract] This paper reports the observation of the decays B0(s) → Ds1(2536)∓K± using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The branching fractions of these decays are measured relative to the normalisation channel B0 → D 0 K+K−. The Ds1(2536)− meson is reconstructed in the D∗(2007)0K− decay channel and the products of branching fractions are measured to be

B(B0s→ Ds1(2536)∓K±) × B(Ds1(2536)−→ D∗(2007)0K−) = (2.49 ± 0.11 ± 0.12 ± 0.25 ± 0.06) × 10−5, B(B0→ Ds1(2536)∓K±) × B(Ds1(2536)−→ D∗(2007)0K−) = (0.510 ± 0.021 ± 0.036 ± 0.050) × 10−5.

The first uncertainty is statistical, the second systematic, and the third arises from the uncertainty of the branching fraction of the B0 → D0K+K− normalisation channel. The last uncertainty in the B0s result is due to the limited knowledge of the fragmentation fraction ratio, fs/fd. The significance for the B0 s and B0 signals is larger than 10 σ. The ratio of the helicity amplitudes which governs the angular distribution of the Ds1(2536)− → D∗(2007)0K− decay is determined from the data. The ratio of the S- and D-wave amplitudes is found to be 1.11±0.15±0.06 and the phase difference between them 0.70 ± 0.09 ± 0.04 rad, where the first uncertainty is statistical and the second systematic.