Experimental Limit on the Cosmic Diffuse Ultrahigh Energy Neutrino Flux

We report results from 120 h of live time with the Goldstone lunar ultrahigh energy neutrino experiment (GLUE). The experiment searches for $\le 10\mathrm{n}\mathrm{s}$ microwave pulses from the lunar regolith, appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of $\ge 100\mathrm{E}\mathrm{e}\mathrm{V}$ ($1\mathrm{E}\mathrm{e}\mathrm{V}={10}^{18}\mathrm{e}\mathrm{V}$ neutrinos in the lunar regolith. No candidates are yet seen, and the implied limits constrain several current models for ultrahigh energy neutrino fluxes.

Figure 1

Geometry of lunar neutrino cascade event detection.

Figure 2

GLUE trigger and data recording system.

Figure 3

An example of a GLUE triggered event.

Figure 4

Model neutrino fluxes and limits from the present work and other current experiments. The inset expands the region near the $Z$-burst predictions.