Probing low-x QCD with cosmic neutrinos at the Pierre Auger Observatory

Abstract

The sources of the observed ultra-high energy cosmic rays must also generate ultra-high energy neutrinos. Deep inelastic scattering of these neutrinos with nucleons on Earth probe center-of-mass energies $\sqrt{s} \sim 100$ TeV, well beyond those attainable at terrestrial colliders. By comparing the rates for two classes of observable events, any departure from the benchmark (unscreened perturbative QCD) neutrino-nucleon cross-section can be constrained. Using the projected sensitivity of the Pierre Auger Observatory to quasi-horizontal showers and Earth-skimming tau neutrinos, we show that a `Super-Auger' detector can thus provide an unique probe of strong interaction dynamics.

Figures (2)

• Figure 1: Predicted cross-sections for neutrino-nucleon scattering at high energies. The line with its $1 \sigma$ error band is the fit (Eq.\ref{['nlo']}) to our calculated $\sigma_{\rm uns}^{\rm NLO} (E_\nu)$ (points with error bars). For comparison we show $\sigma_{\rm uns}^{\rm LO} (E_\nu)$ (dotted line) Gandhi:1998ri, $\sigma_{\rm scr}^{\rm KK} (E_\nu)$ (dashed line) Kutak:2003bd, and $\sigma_{\rm scr}^{\rm HJ} (E_\nu)$ (dot-dashed line) Henley:2005ms.
• Figure 2: The expected number of Earth-skimming and quasi-horizontal neutrino events above $10^8$ GeV for different models of the $\nu-N$ cross-section; for each model, one of the lines assumes the cosmogenic spectrum and the other line the Waxman-Bahcall spectrum. We show as squares and stars respectively, the corresponding hypothetical measurements (with $1 \sigma$ statistical errors) that could be made in 10 yr with an Auger-like detector scaled up to 10000 square miles.