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Measurement of the ratio of branching fractions of the decays $\Lambda_b^0 \!\to \psi(2S) \Lambda$ and $\Lambda_b^0 \!\to J\!/\!\psi \Lambda$

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Abstract

Using $pp$ collisions corresponding to 3$\,\text{fb}^{-1}$ integrated luminosity, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8$\,\text{TeV}$, the ratio of branching fractions \begin{align*} \mathcal{B}(\Lambda^0_b\!\to\psi(2S) \Lambda )/\mathcal{B}(\Lambda^0_b\!\to J/\psi \Lambda)= 0.513 \pm 0.023\, (\text{stat}) \pm 0.016 \, (\text{syst}) \pm 0.011\, (\mathcal{B}) \end{align*} is determined. The first uncertainty is statistical, the second is systematic and the third is due to the external branching fractions used.

Figures and captions

Interpolated efficiency function for long-track candidates for (a) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (b) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ and for downstream-track candidates for (c) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (d) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ candidates. The distribution of the candidates on data is shown with black dots (each dot refers to one candidate).

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Fits to the (unweighted) invariant-mass distributions of long-track candidates for (a) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (b) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ and for downstream-track candidates for (c) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (d) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ candidates. The signal (blue, dashed), the combinatorial background (green, dotted), the $ B ^0 \!\rightarrow \psi K ^0_{\mathrm{ \scriptscriptstyle S}} $ background (cyan, long-dash-dotted) and the $\Xi ^-_ b \!\rightarrow \psi \Xi ^- $ background (violet, dash-triple-dotted) are indicated.

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Fits to the weighted invariant-mass distributions of long-track candidates for (a) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (b) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ and for downstream-track candidates for (c) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and (d) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ candidates. The signal (blue, dashed), the combinatorial background (green, dotted), the $ B ^0 \!\rightarrow \psi K ^0_{\mathrm{ \scriptscriptstyle S}} $ background (cyan, long-dash-dotted) and the $\Xi ^-_ b \!\rightarrow \psi \Xi ^- $ background (violet, dash-triple-dotted) are indicated.

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Animated gif made out of all figures.

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Tables and captions

Yields from the invariant-mass fits in the range 5350 to 5750 $ {\mathrm{\,MeV\!/}c^2}$ of (top) $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ decays and (bottom) $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ decays for each component.

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Efficiency-corrected yields of $\Lambda ^0_ b \!\rightarrow \psi {(2S)} \Lambda $ and $\Lambda ^0_ b \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ signal decays from the fit to the weighted invariant mass for both track types.

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Relative systematic uncertainties on the ratio of branching fractions.

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Created on 15 February 2019.Citation count from INSPIRE on 21 February 2019.