CERN Accelerating science

Cartoon of the $D^0$ meson semileptonic decay, with the definition of the momentum component $p_T'(\nu)$. The red and green dots represent the origin and decay vertex of the $D^0$, respectively, the arrowed black lines represent the momentum components of the final state particles, the purple line indicates the initial flight direction of the $D^0$, and the red and blue dashed lines represent the component of the momentum $p_T'$ perpendicular to the $D^0$ flight direction.

Fit to the visible difference in mass $m(K\mu\pi)-m(K\mu)$ of the decay $D^0\to K\mu\nu$. The points correspond to the sample of $D^0\to K\mu\nu$ decays in the 2012 magnet down dataset lying in the mass range $1600 \leq m(K\mu)<1700$ MeV/$c^2$. The total fit is shown in magenta, with the signal component shown in dashed blue, and the combinatorial background in dashed red.

Comparison of the ratio of measured branching fractions for $D^0\to h^- e^+\nu$ and $D^0\to h^-\mu^+\nu$. The term $h$ denotes the hadron in question, either $K^-$, $\pi^-$ or $K^{*-}(892)$. Each point represents the ratio from the measurements reported in \cite{Olive:2016xmw} compared to the standard mode prediction (red dashed line) and its error(green band) provided by S. Fajfer using~\cite{Koponen:2013tua}. The central values of each point lie systematically to one side of the standard model prediction.