20.500.12556/RUL-178835 Measurement of the $D^0 \to K^-\pi^+e^+e^-$ branching fraction and search for $D^0 \to \pi^+\pi^-e^+e^-$ and $D^0 \to K^+K^-e^+e^-$ decays at Belle We present a study of the rare charm meson decays $D^0 \to K^+K^-e^+e^-, \pi^+\pi^-e^+e^-$, and $K^-\pi^+e^+e^-$ using a 942 fb$^{-1}$ dataset collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We identify $D^0$ candidates via the charge of the pion from $D^{\ast +} \to D^0\pi^+$ decays and normalize the branching fractions to $D^0 \to K^-\pi^+\pi^-\pi^+$ decays. The branching fraction for decay $D^0 \to K^-\pi^+e^+e^-$ is measured to be (39.6 $\pm$ 4.5 (stat) $\pm$ 2.9 (syst))×10$^{-7}$, with the dielectron mass in the $\rho/\omega$ mass region 675 < $m_{ee}$ < 875  MeV/c$^2$. We also search for $D^0 \to h^-h^{(\prime)+}e^+e^-(h^{(\prime)}=K, \pi)$ decays with the dielectron mass near the $\eta$ and $\phi$ resonances, and away from these resonances for the $K^+K^-e^+e^-$ and $\pi^+\pi^-e^+e^-$ modes. For these modes, we find no significant signals and set 90% confidence level upper limits on their branching fractions at the $\mathcal{O}⁡(10^{-7})$ level. physics of elementary particles experimental physics meson decays fizika osnovnih delcev eksperimentalna fizika razpadi mezonov true false true Angleški jezik Slovenski jezik Članek v reviji 2026-01-30 11:10:28 2026-01-30 11:10:28 2026-03-13 11:52:15 0000-00-00 00:00:00 2025 0 0 Str. L071101-1-L071101-8 iss. 7 Vol. 112 Oct. 2025 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 539.1 2470-0010 10.1103/mkx8-cl23 266652931 mkx8-cl23_(1).pdf mkx8-cl23_(1).pdf 1 A9CEE83A6BE63282D3E0392E94DB89B4 c48734d42f91ee4ff20ebf0c3296a4f05af069b9d273bd62aa99ecab15597bf7 031e6ec1-fdc4-11f0-a1ba-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=226844 https://journals.aps.org/prd/abstract/10.1103/mkx8-cl23 0 09a5cf7b-fdc4-11f0-a1ba-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=226845 Fakulteta za matematiko in fiziko 0 0 0