Measurement of the diffuse astrophysical neutrino flux over six seasons using cascade events from the Baikal-GVD expanding telescope

We present an updated measurement of the diffuse astrophysical neutrino flux using Baikal-GVD cascade data collected between April 2018 to March 2024. In this period, the detector grew from 15% to 55% of its baseline cubic kilometer configuration. The diffuse astrophysical neutrino flux is detected with a statistical significance of 5.1 $\sigma$. Assuming a single power law model of the astrophysical neutrino flux with identical contribution from each neutrino flavor, the following best-fit parameter values are found: the spectral index ${\gamma }_{astro}$ = 2.64${}_{-0.11}^{+0.09}$ and the flux normalization ${\phi }_{astro}$ = 4.42${}_{-1.29}^{+2.31}\times {10}^{-18}{\text{GeV}}^{-1}{\text{cm}}^{-2}{\text{s}}^{-1}{\text{sr}}^{-1}$ per one flavor at 100 TeV. These results are broadly consistent with IceCube measurements.