Abstract

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $\Lambda_b^0\to \chi_{c1}(3872)pK^-$ with $\chi_{c1}\to J/\psi\pi^+\pi^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58\pm15)\%$ of the decays proceed via the two-body intermediate state $\chi_{c1}(3872)\Lambda(1520)$. The branching fraction with respect to that of the $\Lambda_b\rightarrow\psi(2S)p K^{-}$ decay mode, where the $\psi(2S)$ meson is reconstructed in the $J/\psi \pi^+\pi^-$ final state, is measured to be: \begin{equation*} \frac{\Lambda_b^0\to\chi_{c1}(3872)pK^-}{\Lambda_b\to\psi(2S)p K^-} \times \frac{\mathcal{B}(\chi_{c1} \to J/\psi \pi^+\pi^-)}{\mathcal{B}(\psi(2S)\to J/\psi \pi^+\pi^-)} = \left(5.4 \pm 1.1 \pm 0.2\right)\times 10^{-2} , \end{equation*} where the first uncertainty is statistical and the second is systematic.

Figures and captions

Projection of the two-dimensional distributions of (left) { $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ $ p $ $ K ^-$ } and (right) { $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ } masses for the (top) $\Lambda ^0_ b \rightarrow \psi {(\rm{2S})} p K ^-$ and (bottom) $\Lambda ^0_ b \rightarrow \chi _{ c 1}\mathrm{(3872)} p K ^- $ candidates.	Fig_1.pdf [191 KiB] HiDef png [494 KiB] Thumbnail [425 KiB] *.C file tex code
Background-subtracted mass distribution for the $ p $ $ K ^-$ system in $\Lambda ^0_ b \rightarrow \chi _{ c 1}(3872) p K ^-$ decays with fit results in the range $1.43 < m_{ p K ^-} < 1.75 \text{ Ge V /}c^2 $ superimposed. The background subtraction is performed using the sPlot technique [63].	Fig_2.pdf [121 KiB] HiDef png [214 KiB] Thumbnail [190 KiB] *.C file tex code
Animated gif made out of all figures.	PAPER-2019-023.gif Thumbnail

Tables and captions

Relative systematic uncertainties for the ratio of branching fractions.

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Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [298 KiB]
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Created on 19 April 2024.