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. Here I present IceCube’s High-Energy Starting Event sample and the new results obtained with a livetime of about 7.5 years. I will focus on the new measurement of the flavor composition performed using this sample. IceCube is directly sensitive to each neutrino flavor via the single cascade, track and double cascade event topologies, the latter being the topology produced in tauneutrino interactions above an energy threshold of ~100 TeV. A measurement of the flavor ratio on Earth can provide important constraints on sources and production mechanisms within the standard model, and also constrain various beyond-standard-model processes.
Highlights
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 IceCube collaboration [1] has reported the observation of a diffuse flux of astrophysical neutrinos using the High-Energy Starting Events (HESE) selection [2]
The HESE selection has been applied to more data collected since with the last update having a livetime of 6 years [3]
Summary
Most previous flavor composition measurements did not distinguish between single and double cascades, leading to a large degeneracy between the νe and ντ flavors. In this analysis we identify the first two double cascades, on an expectation of ∼ 2 (1.4 signal and 0.7 background) events. TeV reconstructed deposited energy we classify the 60 events into 42 single cascades, 16 tracks, and 2 double cascades. Note that not all systematic uncertainties have been taken into account yet in this work in progress This analysis yields νe : νμ : ντ = 0.29 : 0.50 : 0.21 as the best fit flavor composition. OM(17, 6):O9M8.(917p,e6): 98.9 pe OM(17, 7):O3M77(.197,pe7): 377.9 pe OM(17, 8):O1M25(31.79, p8e): 1253.9 pe OM(20, 22)O: M76(.280,pe22): 76.8 pe OM(20, 23)O: M12(2.05, p2e3): 122.5 pe Charge [pe]
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