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We search for a dark matter signal in 11 years of Fermi-LAT gamma-ray datafrom 27 Milky Way dwarf spheroidal galaxies with spectroscopically measured$J$-factors. Our analysis includes uncertainties in $J$-factors and backgroundnormalisations and compares results from a Bayesian and a frequentistperspective. We revisit the dwarf spheroidal galaxy Reticulum II, confirmingthat the purported gamma-ray excess seen in Pass 7 data is much weaker in Pass8, independently of the statistical approach adopted. We introduce for thefirst time posterior predictive distributions to quantify the probability of adark matter detection from another dwarf galaxy given a tentative excess. Aglobal analysis including all 27 dwarfs shows no indication for a signal innine annihilation channels. We present stringent new Bayesian and frequentistupper limits on the dark matter cross section as a function of dark mattermass. The best-fit dark matter parameters associated with the Galactic Centreexcess are excluded by at least 95% confidence level/posterior probability inthe frequentist/Bayesian framework in all cases. However, from a Bayesian modelcomparison perspective, dark matter annihilation within the dwarfs is notstrongly disfavoured compared to a background-only model. These resultsconstitute the highest exposure analysis on the most complete sample of dwarfsto date. Posterior samples and likelihood maps from this study are publiclyavailable.

A Global Analysis of Dark Matter Signals from 27 Dwarf Spheroidal Galaxies using 11 Years of Fermi-LAT Observations