Observation of the B+ c → J/ψπ+π 0 decay

Abstract

The first observation of the

B c +

→ J / ψ

π +

π 0

$$ {B}_c^{+}\to J/\psi {\pi}^{+}{\pi}^0 $$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the

B c +

→ J / ψ

π +

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

B

B c +

→ J / ψ

π +

π 0

B

B c +

→ J / ψ

π +

= 2.80 ± 0.15 ± 0.11 ± 0.16 ,

$$ \frac{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}{\pi}^0}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=2.80\pm 0.15\pm 0.11\pm 0.16, $$

where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ → J/ψK*+ and

B c +

→ J / ψ

π +

$$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decays, which are used to determine the π0 detection efficiency. The π+π0 mass spectrum is found to be consistent with the dominance of an intermediate ρ+ contribution in accordance with a model based on QCD factorisation.