Abstract

The Cabibbo-suppressed decay $\Lambda_b^0\rightarrow\chi_{c1}p\pi^-$ is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6fb$^{-1}$, collected with the LHCb detector at a centre-of-mass energy of 13TeV. Evidence for the $\Lambda_b^0\rightarrow\chi_{c2}p\pi^-$ decay is also found. Using the $\Lambda_b^0\rightarrow\chi_{c1}pK^-$ decay as normalisation channel, the ratios of branching fractions are measured to be $$\begin{array}{rcl} \frac{ \mathcal{B} (\Lambda_b^0\rightarrow\chi_{c1}p\pi^-)}{\mathcal{B} (\Lambda_b^0\rightarrow\chi_{c1}pK^-)} & = & (6.59 \pm 1.01 \pm 0.22 ) \times 10^{-2} , \frac{\mathcal{B} (\Lambda_b^0\rightarrow\chi_{c2}p\pi^-)}{\mathcal{B} (\Lambda_b^0\rightarrow\chi_{c1}p\pi^-)} & = & 0.95 \pm 0.30 \pm 0.04 \pm 0.04 , \frac{\mathcal{B} (\Lambda_b^0\rightarrow\chi_{c2}pK^-)}{\mathcal{B} (\Lambda_b^0\rightarrow\chi_{c1}pK^-)} & = & 1.06 \pm 0.05 \pm 0.04 \pm 0.04 ,\end{array}$$ where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of $\chi_{c1,2}\rightarrow J/\psi\gamma$ decays.

Figures and captions

Mass distribution for selected $\Lambda ^0_ b \rightarrow \chi _{ c J } p \pi ^- $ candidates. A fit, described in the text, is overlaid.	Fig_1.pdf [151 KiB] HiDef png [295 KiB] Thumbnail [244 KiB] *.C file tex code
Mass distribution for selected $\Lambda ^0_ b \rightarrow \chi _{ c J } p K ^- $ candidates. A fit, described in the text, is overlaid.	Fig_2.pdf [158 KiB] HiDef png [362 KiB] Thumbnail [257 KiB] *.C file tex code
Background-subtracted mass distributions of the (left) $\chi _{ c 1} p $ , (centre) $\chi _{ c 1} \pi ^- $ and (right) $ p \pi ^- $ combinations in the $\Lambda ^0_ b \rightarrow \chi _{ c 1} p \pi ^- $ decay. Expectations from a phase space simulation are overlaid.	Fig_3.pdf [140 KiB] HiDef png [148 KiB] Thumbnail [142 KiB] *.C file tex code
Animated gif made out of all figures.	PAPER-2021-003.gif Thumbnail

Tables and captions

Signal yields, $N$, from the fits described in the text. The uncertainties are statistical only.	Table_1.pdf [66 KiB] HiDef png [94 KiB] Thumbnail [39 KiB] tex code
Relative systematic uncertainties (in %) in the ratios of branching fractions. The total uncertainty is obtained as the sum of individual components in quadrature. Empty cells correspond to cases where no uncertainty is applicable.	Table_2.pdf [72 KiB] HiDef png [84 KiB] Thumbnail [39 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [232 KiB]
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Created on 19 April 2024.