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Observation of the decay<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Υ</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>4</mml:mn><mml:mi>S</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:mo>→</mml:mo><mml:mi>Υ</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mi>S</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math>
We study transitions between $\ensuremath{\Upsilon}$ states with the emission of charged pions using $477\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The measured product branching fraction $\mathcal{B}(\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(1S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})\ifmmode\times\else\texttimes\fi{}\mathcal{B}(\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})=(4.42\ifmmode\pm\else\textpm\fi{}0.81(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.56(\mathrm{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. When the PDG value for $\mathcal{B}(\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$ is used, this corresponds to $\mathcal{B}(\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(1S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})=(1.78\ifmmode\pm\else\textpm\fi{}0.33(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and a partial …