Study of $$ {B}_c^{+}\to {\chi}_c{\pi}^{+} $$ decays

Abstract

A study of

B c +

→

χ c

π +

$$ {B}_c^{+}\to {\chi}_c{\pi}^{+} $$ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The decay

B c +

→

χ

c 2

π +

$$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the

B c +

→ J / ψ

π +

$$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decay is measured to be

B

B c +

→

χ

c 2

π +

B

B c +

→ J / ψ

π +

= 0.37 ± 0.06 ± 0.02 ± 0.01 ,

$$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=0.37\pm 0.06\pm 0.02\pm 0.01, $$

where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χc2 → J/ψγ branching fraction. No significant

B c +

→

χ

c 1

π +

$$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ signal is observed and an upper limit for the relative branching fraction for the

B c +

→

χ

c 1

π +

$$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ and

B c +

→

χ

c 2

π +

$$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ decays of

B

B c +

→

χ

c 1

π +

B

B c +

→

χ

c 2

π +

= < 0.49

$$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c1}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}=<0.49 $$

is set at the 90% confidence level.