Constraints on neutrino-nucleon interactions at energies of 1 EeV with the IceCube Neutrino Observatory

A search for extremely high energy cosmic neutrinos has been carried out with the IceCube Neutrino Observatory. The main signals in the search are neutrino-induced energetic charged leptons and their rate depends on the neutrino-nucleon cross section. The upper limit on the neutrino flux has implications for possible new physics beyond the standard model such as the extra space-time dimension scenarios which lead to a cross section much higher than the standard particle physics prediction. In this study we constrain the neutrino-nucleon cross section at energies beyond ${10}^9\mathrm{GeV}$ with the IceCube observation. The constraints are obtained as a function of the extraterrestrial neutrino flux in the relevant energy range, which accounts for the astrophysical uncertainty of neutrino production models.

Figure 1

Integral fluxes of the muon and taus above 10 PeV ($={10}^7\mathrm{GeV}$) at IceCube depth ($\sim 1450\mathrm{m}$) for GZK cosmogenic neutrinos [17]. The solid lines represent muons while the dashed lines represent taus. Numbers on each of the curves are the multiplication factors ($N_{\mathrm{scale}}$) that enhance the standard $\nu N$ cross section [19] in the relevant calculations.

Figure 2

Constraints on the all-flavor sum of cosmic neutrino flux and the charged current $\nu N$ cross section based on the null detection of neutrino signals by the IceCube 2007 observation. The right upper region is excluded by the present analysis. The horizontal lines provide references of the expected GZK cosmogenic neutrino fluxes [20] and the vertical lines correspond to the SM cross section [19].

Figure 3

Constraints on the all-flavor sum of cosmic neutrino flux and the neutral current $\nu N$ cross section for the scenario that only the neutral current reaction is enhanced by a new physics beyond the standard model. The right upper region is excluded by the present analysis. The horizontal lines provide references of the expected GZK cosmogenic neutrino fluxes [20] and the vertical lines correspond to the SM cross section [19].

Figure 4

(Left) integral fluxes of the muon and taus above 10 PeV ($={10}^7\mathrm{GeV}$) at IceCube depth ($\sim 1450\mathrm{m}$) of the GZK cosmogenic neutrinos [17] in case of the microscopic black hole creation scenario [5] for $(M_D,x_{\min })=(1\mathrm{TeV},1)$ (solid line), (1 TeV,3) (dotted-dashed line). The dashed line corresponds to the intensities obtained by the SM $\nu N$ cross section [19]. (Right) energy spectra of the GZK $\nu$ induced muons and taus at IceCube depth with downgoing [i.e. $\cos (\mathrm{zenith})\ge 0$] geometry expected by the black hole model for $(M_D,x_{\min })=(1\mathrm{TeV},1)$. The spectra produced by the SM cross section are also shown as dashed lines for comparison. The curve labeled “Atm $\mu$” represents the atmospheric muon intensity estimated by the IceCube observation with its uncertainty expressed by the two dashed lines [21].

Figure 5

Number of events as a function of extraterrestrial neutrino flux at 1 EeV for $(M_D,x_{\min })=(1\mathrm{TeV},1)$ (solid line), (1 TeV,3) (dashed line). The 90% C.L. line determined by the Poisson statistics is also shown as a vertical line for reference.