Search for double cascade tau neutrinos with 13 years of IceCube data

The IceCube Neutrino Observatory has made measurements of diffuse astrophysical neutrino flux up to PeV scales. It is challenging to distinguish between tau and other neutrino flavor charged current interactions at ~ 1 TeV energy due to the limitation of IceCube digital optical module spacing. This analysis targets high energy (~ 100 TeV) tau neutrinos by identifying a double cascade signature produced by a charged current neutrino-nucleon interaction and a hadronic (electromagnetic) decay of the tau lepton. We use a machine learning technique to search for the double cascade signature from IceCube 13 years of cascade data. We obtain double cascade tau neutrino sample with high purity (~ 90%) and good reconstruction quality. A flavor composition measurement is performed using a maximum likelihood fit with this double cascade sample combined with a cascade and a muon track samples.