Improved Flux Limits for Neutrinos with Energies above ${10}^{22}\mathrm{eV}$ from Observations with the Westerbork Synthesis Radio Telescope

Particle cascades initiated by ultrahigh energy neutrinos in the lunar regolith will emit an electromagnetic pulse with a time duration of the order of nanoseconds through a process known as the Askaryan effect. It has been shown that in an observing window around 150 MHz there is a maximum chance for detecting this radiation with radio telescopes commonly used in astronomy. In 50 h of observation time with the Westerbork Synthesis Radio Telescope array we have set a new limit on the flux of neutrinos, summed over all flavors, with energies in excess of $4\times {10}^{22}\mathrm{eV}$.

Figure 1

Distribution of $S$ for increasingly stronger cuts. The top curve represents the distribution of raw triggers where subsequently the $T$, $TW$, and the $TWA$ cuts are applied.

Figure 2

The detection efficiency is shown as a function of pulse strength for various settings of the trigger conditions as discussed in the text. The dotted curve indicates the efficiency when no width cut is applied.

Figure 3

The currently established neutrino flux limit is compared to the limits set by ANITA [8] and FORTE [9] as well as the Waxman-Bahcall flux [5] and a TD model prediction [27]. The band shows the systematic error.