Astrophysical neutrino flux measurement and search for tau neutrino induced cascades with 11 years of IceCube data

Abstract: IceCube measured the diffuse astrophysical neutrino flux for all flavors up to PeV energies. The high energy (TeV-PeV) IceCube cascade sample is particularly effective at selecting electron and tau neutrinos. We present the results of Single Power Law (SPL) and Broken Power Law (BPL) flux measurements based on 11 years of cascade data. From this cascade sample, we study the identification of high energy (~100 TeV) tau neutrinos by detecting a double cascade signature produced by a charged-current neutrino interaction and the subsequent decay of the tau lepton. A Boosted Decision Tree (BDT) is employed to search for the double cascade signature, achieving a significantly improved signal-to-background ratio of 9:1 compared to previous analyses. The selected sample has a tau-neutrino purity of approximately 90% and a weighted mean reconstruction error on the tau decay length of about 4m. We present sensitivities for a maximum likelihood fit of the flavor composition and constraints on the astrophysical neutrino flavor ratios using this sample in combination with IceCube's northern muon neutrino-induced track sample.