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

Abstract

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 ¼ 2.62 AE 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 ð 1 3 ∶ 1 3 ∶ 1 3 Þ ⊕. Exploiting the distinct inelasticity distribution of ν μ andν μ interactions, the atmospheric ν μ toν μ flux ratio in the energy range from 770 GeV to 21 TeV is found to be 0.77 þ0.44 −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.

On the relevance of prompt neutrinos for the interpretation of the IceCube signals

“…In [7,8,32] the spectral difference between the HESE and the through-going muons spectra is labelled as an anomaly, and it has been already addressed in [33,34]. In fact, if we compare the astrophysical neutrino fits to the cascade and starting track samples, which together constitute the HESE dataset, from [31] to that from the through-going muons analysis [2] there is an evident difference, as can be appreciated from 2.13 ± 0.13 Table 3. The flux normalizations, in units of 10 −18 GeV −1 cm −2 s −1 sr −1 , and slopes deriving from the astrophysical best fits to the cascade (C) and starting tracks (ST) samples from [31], to the 6-years HESE sample from [35] and to the through-going muons (TM) sample from [2].…”

“…It follows that the cascade sample is the one with the smallest relative contribution of muon neutrinos, which, as already seen in figure 2, are very prompt-neutrino poor. Another reason to focus on the cascade subset of the HESE dataset is that the track-like subset is compatible with being due to background events (atmospheric muons and atmospheric muon neutrinos) only [8,31]. The contributors to the cascade dataset are:…”

Sterile neutrinos in astrophysical neutrino flavor

“…The astrophysical neutrino flavor composition is a powerful observable for studying both astrophysical neutrino production mechanisms and oscillation parameters [56]. The current uncertainty in this observable does not allow us to differentiate between astrophysical neutrino flavor compositions [41][42][43]45] at their source. However, it has been pointed out that the astrophysical neutrino flavor composition can explore new physics despite this situation, because the unitary evolution of the flavor structure is predictable and the flavor ratio on Earth can take only certain values even with new physics [49,57].…”

W -boson and trident production in TeV–PeV neutrino observatories

“…For those W -boson production events that are analyzed as CCDIS events with tracks, the non-track energy comes primarily from the W -boson decay, and this is typically much larger than the energy going to the track, in contrast to CCDIS. Therefore, W -boson production events should be included in theoretical expections of attempts to better measure the ν µ toν µ flux ratio and neutrino chargedcurrent charm production [99]. This may also provide a way to detect W -boson production.…”