# First Double Cascade Tau Neutrino Candidates in IceCube and a New Measurement of the Flavor Composition

## TL;DR

This paper reports the first identification of double cascade tau neutrino candidates in IceCube and presents a new measurement of the astrophysical neutrino flavor composition, providing insights into neutrino sources and fundamental physics.

## Contribution

It introduces the first double cascade tau neutrino candidates in IceCube and provides a novel measurement of the flavor composition of astrophysical neutrinos on Earth.

## Key findings

- First two tau neutrino double cascade candidates identified.
- Measured flavor composition consistent with 1:1:1 ratio.
- Results constrain neutrino source models and beyond-standard-model physics.

## Abstract

The IceCube Neutrino Observatory at the South Pole, which detects Cherenkov light from charged particles produced in neutrino interactions, firmly established the existence of an astrophysical high-energy neutrino component. The expected neutrino flavor composition on Earth is $\nu_e:\nu_{\mu}:\nu_{\tau}$ of about 1:1:1 for neutrinos produced in astrophysical sources through pion decay. A measurement of the flavor composition on Earth can provide important constraints on sources and production mechanisms within the standard model, and can also constrain various beyond-standard-model processes. Here the measurement of the flavor composition performed on IceCube's High-Energy Starting Events sample with a livetime of about 7.5 years is presented. IceCube is directly sensitive to each neutrino flavor via the single cascade, track and double cascade event topologies. In IceCube, $\nu_{\tau}$-CC interactions above $\sim$ 100 TeV can produce resolvable double cascades, breaking the degeneracy between $\nu_e$ and $\nu_{\tau}$ present at lower energies. IceCube's first two identified double cascades are presented and the properties of the two $\nu_{\tau}$ candidates are discussed.