Observation of the decays 𝐵�0(𝑠�) → Ds1(2536)∓K±

Abstract

Abstract

This paper reports the observation of the decays

B

s

0

$$ {B}_{(s)}^0 $$ → 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 ¯

$$ \overline{D} $$ 0K+K−. The Ds1(2536)− meson is reconstructed in the

D ¯

$$ \overline{D} $$ *(2007)0K− decay channel and the products of branching fractions are measured to be

B

B s 0

→

D

s 1

2536

∓

K ±

× B

D

s 1

2536

−

→

D ¯

∗

2007

0

K −

=

2.49 ± 0.11 ± 0.12 ± 0.25 ± 0.06

×

10

− 5

,

B

B 0

→

D

s 1

2536

∓

K ±

× B

D

s 1

2536

−

→

D ¯

∗

2007

0

K −

=

0.510 ± 0.021 ± 0.036 ± 0.050

×

10

− 5

.

$$ {\displaystyle \begin{array}{c}\mathcal{B}\left({B}_s^0\to {D}_{s1}{(2536)}^{\mp }{K}^{\pm}\right)\times \mathcal{B}\left({D}_{s1}{(2536)}^{-}\to {\overline{D}}^{\ast }{(2007)}^0{K}^{-}\right)\\ {}=\left(2.49\pm 0.11\pm 0.12\pm 0.25\pm 0.06\right)\times {10}^{-5},\\ {}\mathcal{B}\left({B}^0\to {D}_{s1}{(2536)}^{\mp }{K}^{\pm}\right)\times \mathcal{B}\left({D}_{s1}{(2536)}^{-}\to {\overline{D}}^{\ast }{(2007)}^0{K}^{-}\right)\\ {}=\left(0.510\pm 0.021\pm 0.036\pm 0.050\right)\times {10}^{-5}.\end{array}} $$

The first uncertainty is statistical, the second systematic, and the third arises from the uncertainty of the branching fraction of the B0 →

D ¯

$$ \overline{D} $$ 0K+K− normalisation channel. The last uncertainty in the

B s 0

$$ {B}_s^0 $$ result is due to the limited knowledge of the fragmentation fraction ratio, fs/fd. The significance for the

B s 0

$$ {B}_s^0 $$ and B0 signals is larger than 10 σ. The ratio of the helicity amplitudes which governs the angular distribution of the Ds1(2536)− →

D ¯

$$ \overline{D} $$ *(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.