Constraining The Neutrino-Nucleon Cross Section with the Ultrahigh-Energy KM3NeT Event

Abstract

KM3NeT's detection of a muon track produced by a $\sim 220 \, {\rm PeV}$ neutrino provides an opportunity to probe physics at center-of-momentum energies greater than those probed by the Large Hadron Collider or other existing particle accelerators. In this study, we use this single event to place an upper limit on the neutrino-nucleon cross section of $σ_{νN} < 40 \, σ_{νN}^{\rm SM}$ at $E_{\rm CM} \sim 20 \, {\rm TeV}$. This result can be used to constrain a variety of scenarios beyond the Standard Model. With future very large volume neutrino telescopes, constraints on the neutrino-nucleon scattering cross section are expected to become substantially more stringent and, in some scenarios, could become competitive with accelerator probes of new physics.

Figures (4)

• Figure 1: Measurements of the total high-energy neutrino-nucleus cross section compared to the Standard Model prediction Bertone:2018dse. In gray, we show the measurements from IceCube showers Bustamante:2017xuyIceCube:2020rnc and tracks IceCube:2017roe. For measurements of the charged-current cross section, we have rescaled the results by $(\sigma^{\rm CC}_{\nu N}+\sigma^{\rm NC}_{\nu N})/\sigma^{\rm CC}_{\nu N}$, as predicted by the Standard Model. The vertical dashed line denotes the center-of-momentum energy of proton-proton collisions at the Large Hadron Collider. In black, we show the measurement of the total neutrino cross section as derived in this analysis from the KM3NeT event. For the first time, neutrino telescopes allow for a measurement of this cross section beyond the energy range of particle accelerators.
• Figure 2: The angular distribution of $>$10 PeV muons tracks predicted at KM3NeT from the charged-current interactions of an isotropic flux of $\sim 220 \, {\rm PeV}$ neutrinos. Results are shown for the Standard Model cross section (filled green), and for a total cross section that is larger by a factor of 10 (orange) or 50 (blue). The vertical dashed line denotes the zenith angle of the 220 PeV KM3NeT event, $\theta_{\rm obs} = 90.6^\circ$, which is only slightly above the horizon. The horizontal direction of this track is compatible with the angular distribution predicted for the Standard Model cross section, but such events would have been more likely to be downgoing if the cross section were larger.
• Figure 3: The change in the log-likelihood as a function of the total neutrino-nucleon cross section at $E_{\nu} = 220 \, {\rm PeV}$. The dots represent points computed in the Markov Chain Monte Carlo chain and the solid line interpolates between them. The likelihood is maximized near the Standard Model value of the total cross section and the KM3NeT event allows us to constrain $\sigma_{\nu N} < 40 \, \sigma^{\rm SM}_{\nu N}$ at the 95% confidence level.
• Figure 4: The change in the log-likelihood as a function of the total neutrino-nucleon cross section at $E_{\nu} =220 \, {\rm PeV}$, as projected from the observation of 10 or 100 neutrino-induced muon track events with IceCube-Gen2. A measurement of 10 such events is projected to result in a constraint of $\sigma_{\nu N}/\sigma_{\nu N}^{\rm SM} \mathrel{\hbox{$<$$\sim$}} 7.7$ at the 95% confidence level. With 100 events, this constraint is projected to improve to $\sigma_{\nu N}/\sigma_{\nu N}^{\rm SM} \lesssim 1.6$.