Observation of the decay Λ b 0 $$ {\Lambda}_{\mathrm{b}}^0 $$ → χc1pπ−

Abstract

Abstract

The Cabibbo-suppressed decay

Λ b 0

$$ {\Lambda}_{\mathrm{b}}^0 $$ → χc1pπ− is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6 fb−1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV. Evidence for the

Λ b 0

$$ {\Lambda}_{\mathrm{b}}^0 $$ → χc2pπ− decay is also found. Using the

Λ b 0

$$ {\Lambda}_{\mathrm{b}}^0 $$ → χc1pK− decay as normalisation channel, the ratios of branching fractions are measured to be

B

Λ b 0

→

χ

c 1

pπ −

B

Λ b 0

→

χ

c 1

pK −

=

6.59 ± 1.01 ± 0.22

×

10

− 2

,

B

Λ b 0

→

χ

c 2

pπ −

B

Λ b 0

→

χ

c 1

pπ −

= 0.95 ± 0.30 ± 0.04 ± 0.04 ,

B

Λ b 0

→

χ

c 2

pK −

B

Λ b 0

→

χ

c 1

pK −

= 1.06 ± 0.05 ± 0.04 ± 0.04 ,

$$ {\displaystyle \begin{array}{c}\frac{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}{\mathrm{p}\uppi}^{-}\right)}{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}{\mathrm{p}\mathrm{K}}^{-}\right)}=\left(6.59\pm 1.01\pm 0.22\right)\times {10}^{-2},\\ {}\frac{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}2}{\mathrm{p}\uppi}^{-}\right)}{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}{\mathrm{p}\uppi}^{-}\right)}=0.95\pm 0.30\pm 0.04\pm 0.04,\\ {}\frac{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}2}{\mathrm{p}\mathrm{K}}^{-}\right)}{\mathcal{B}\left({\Lambda}_{\mathrm{b}}^0\to {\upchi}_{\mathrm{c}1}{\mathrm{p}\mathrm{K}}^{-}\right)}=1.06\pm 0.05\pm 0.04\pm 0.04,\end{array}} $$

where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of χc1,2 → J/ψγ decays.