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Measurement of the $B_s^0\to J/\psi K_S^0$ branching fraction

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Abstract

The $B_s^0\to J/\psi K_S^0$ branching fraction is measured in a data sample corresponding to 0.41$fb^{-1}$ of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to the penguin contributions affecting the sin2$\beta$ measurement from $B^0\to J/\psi K_S^0$ The time-integrated branching fraction is measured to be $BF(B_s^0\to J/\psi K_S^0)=(1.83\pm0.28)\times10^{-5}$. This is the most precise measurement to date.

Figures and captions

Decay topologies contributing to the $ B ^0$ $\rightarrow$ $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $ K ^0_{\rm\scriptscriptstyle S}$ and $ B ^0_ s $ $\rightarrow$ $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $ K ^0_{\rm\scriptscriptstyle S}$ channel: tree diagram to the left and penguin diagram to the right.

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Mass distribution of the $ B $ $\rightarrow$ $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $ K ^0_{\rm\scriptscriptstyle S}$ candidates used to determine the PDF. The solid line is the total PDF composed of the $ B ^0$ $\rightarrow$ $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $ K ^0_{\rm\scriptscriptstyle S}$ signal shown in grey and the combinatorial background represented by the dotted line.

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Fit to full sample after the optimal NN cut has been applied with downstream $ K ^0_{\rm\scriptscriptstyle S}$ to the left and long $ K ^0_{\rm\scriptscriptstyle S}$ to the right.

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Animated gif made out of all figures.

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Tables and captions

$ B ^0$ and $ B ^0_ s $ yields. Only statistical errors are quoted. The $ B ^0$ yield is obtained in a fit to one quarter of the events which have not been used in the NN training (normalisation sample) and then scaled to the full sample.

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Summary of corrections and systematic uncertainties on the ratio of branching fractions.

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Created on 27 April 2024.