Legacy analysis of dark matter annihilation from the Milky Way dwarf spheroidal galaxies with 14 years of $\mathrm{Fermi}$-LAT data

The Milky Way dwarf spheroidal satellite galaxies (dSphs) are particularly intriguing targets to search for gamma rays from weakly interacting massive particle dark matter (DM) annihilation or decay. They are nearby, DM-dominated, and lack significant emission from standard astrophysical processes. Previous studies using the Fermi-Large Area Telescope (LAT) of DM-induced emission from dSphs have provided the most robust and stringent constraints on the DM annihilation cross section and mass. We report here an analysis of the Milky Way dSphs using over 14 years of LAT data along with an updated census of dSphs and $J$-factor estimates. While no individual dSphs are significantly detected, we do find slight excesses with respect to background at the $\gtrsim 2\sigma$ local significance level in both tested annihilation channels ($b\overline{b}$, ${\tau }^{+}{\tau }^{-}$) for seven of the dSphs. We do not find a significant DM signal from the combined likelihood analysis of the dSphs ($s_{\text{global}}\sim 0.5\sigma$), yet a marginal local excess relative to background at a $2–3\sigma$ level is observed at a DM mass of $M_{\chi }=150–230\mathrm{GeV}$ ($M_{\chi }=30–50\mathrm{GeV}$) for DM annihilation into $b\overline{b}$ (${\tau }^{+}{\tau }^{-}$). Given the lack of a significant detection, we place updated constraints on the $b\overline{b}$ and ${\tau }^{+}{\tau }^{-}$ annihilation channels that are generally consistent with previous recent results. As in past studies, tension is found with some weakly interacting massive particle DM interpretations of the Galactic Center Excess, though the limits are consistent with other interpretations given the uncertainties of the Galactic DM density profile and Galactic Center Excess systematics. Based on conservative assumptions of improved sensitivity with increased Fermi-LAT exposure time and moderate increases in the sample of Milky Way dSphs, we project that the local $\sim 2\sigma$ signal, if real, could approach the $\sim 4\sigma$ local confidence level with additional $\sim 10\mathrm{years}$ of observation.