Precise Measurement of Reactor Antineutrino Spectra from Joint Analyses of PROSPECT, STEREO, and Daya Bay*

The PROSPECT, Daya Bay, and STEREO reactor antineutrino experiments have made world-leading measurements of the $^{235}$U antineutrino spectra from fission reactors using high-performance liquid scintillator detectors.

PROSPECT and STEREO have made modern measurements of antineutrinos at highly enriched uranium (HEU) research reactors where over 99\% of the antineutrino flux comes from $^{235}$U, while the Daya Bay experiment has studied antineutrino emission at commercial power reactors which use a mixture of fissile isotopes.

Recently PROSPECT has performed joint analyses with Daya Bay and STEREO yielding the most precise determination of the measured $^{235}$U reactor antineutrino spectrum. 

The work with STEREO directly combines the two pure $^{235}$U measurements and jointly unfolds the spectra to provide and improved result in antineutrino energy, independent of assumptions regarding other isotopes' contributions.

PROSPECT's combination with the high-statistics measurement from Daya Bay improves the deconvolution of the power reactor spectrum to obtain a more precise unfolded $^{235}$U antineutrino spectrum.

In this talk, I will present the results of both analyses.