Measurements using the inelasticity distribution of multi-TeV neutrino interactions in IceCube

Inelasticity, the fraction of a neutrino’s energy transferred to hadrons, is a quantity of interest in the study of astrophysical and atmospheric neutrino interactions at multi-TeV energies with IceCube. In this work, a sample of contained neutrino interactions in IceCube is obtained from five years of data and classified as 2650 tracks and 965 cascades. Tracks arise predominantly from charged-current
ν
μ
interactions, and we demonstrate that we can reconstruct their energy and inelasticity. The inelasticity distribution is found to be consistent with the calculation of Cooper-Sarkar et al. across the energy range from
∼
1
to
∼
100
 
 
TeV
. Along with cascades from neutrinos of all flavors, we also perform a fit over the energy, zenith angle, and inelasticity distribution to characterize the flux of astrophysical and atmospheric neutrinos. The energy spectrum of diffuse astrophysical neutrinos is described well by a power law in both track and cascade samples, and a best-fit index
γ
=
2.62
±
0.07
is found in the energy range from 3.5 TeV to 2.6 PeV. Limits are set on the astrophysical flavor composition and are compatible with a ratio of
(
1
3
∶
1
3
∶
1
3
)
⊕
. Exploiting the distinct inelasticity distribution of
ν
μ
and
¯
ν
μ
interactions, the atmospheric
ν
μ
to
¯
ν
μ
flux ratio in the energy range from 770 GeV to 21 TeV is found to be
0.77
+
0.44
−
0.25
times the calculation by Honda et al. Lastly, the inelasticity distribution is also sensitive to neutrino charged-current charm production. The data are consistent with a leading-order calculation, with zero charm production excluded at 91% confidence level. Future analyses of inelasticity distributions may probe new physics that affects neutrino interactions both in and beyond the Standard Model.