Precise Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mi>s</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math> Lifetime at Belle II

We measure the lifetime of the ${D}_{s}^{+}$ meson using a data sample of $207\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the Belle II experiment running at the SuperKEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The lifetime is determined by fitting the decay-time distribution of a sample of $116\ifmmode\times\else\texttimes\fi{}{10}^{3}$ ${D}_{s}^{+}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\pi}}^{+}$ decays. Our result is ${\ensuremath{\tau}}_{{D}_{s}^{+}}=(499.5\ifmmode\pm\else\textpm\fi{}1.7\ifmmode\pm\else\textpm\fi{}0.9)\text{ }\text{ }\mathrm{fs}$, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.

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