# 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. Fig1a.pdf [11 KiB] HiDef png [115 KiB] Thumbnail [103 KiB] *.C file Fig1b.pdf [13 KiB] HiDef png [136 KiB] Thumbnail [119 KiB] *.C file 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. Fig2.pdf [26 KiB] HiDef png [212 KiB] Thumbnail [217 KiB] *.C file 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. Fig3a.pdf [22 KiB] HiDef png [278 KiB] Thumbnail [268 KiB] *.C file Fig3b.pdf [21 KiB] HiDef png [267 KiB] Thumbnail [264 KiB] *.C file Animated gif made out of all figures. PAPER-2011-041.gif Thumbnail

## 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. Table_1.pdf [53 KiB] HiDef png [40 KiB] Thumbnail [16 KiB] tex code Summary of corrections and systematic uncertainties on the ratio of branching fractions. Table_2.pdf [47 KiB] HiDef png [102 KiB] Thumbnail [49 KiB] tex code

Created on 21 October 2019.