Observation of the decay \( {\Lambda}_{\mathrm{b}}^0 \) χc1

Abstract

The Cabibbo-suppressed decay \( {\Lambda}_{\mathrm{b}}^0 \) χc1 is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6 fb1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV. Evidence for the \( {\Lambda}_{\mathrm{b}}^0 \) χc2 decay is also found. Using the \( {\Lambda}_{\mathrm{b}}^0 \) χc1pK decay as normalisation channel, the ratios of branching fractions are measured to be

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

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.

A preprint version of the article is available at ArXiv.

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