Search for Acoustic Signals from Ultra-High Energy Neutrinos in 1500 km^3 of Sea Water

An underwater acoustic sensor array spanning ~1500 km^3 is used to search for cosmic-ray neutrinos of ultra-high energies (UHE, E > 10^18 eV). Approximately 328 million triggers accumulated over an integrated 130 days of data taking are analysed. The sensitivity of the experiment is determined from a Monte Carlo simulation of the array using recorded noise conditions and expected waveforms. Two events are found to have properties compatible with showers in the energy range 10^24 to 5x10^24 eV and 10^22 to 5x10^22 eV. Since the understanding of impulsive backgrounds is limited, a flux upper limit is set providing the most sensitive limit on UHE neutrinos using the acoustic technique.Comment: Submitted to PRD. 8 pages, 12 figure

Detecting Nanometer-Scale New Forces with Coherent Neutron Scattering

Significant effort has been devoted to searching for new fundamental forces of nature. At short length scales (below approximately 10 nm), the strongest experimental constraints come from neutron scattering from individual nuclei in gases. The leading experiments at longer length scales instead measure forces between macroscopic test masses. We propose a hybrid of these two approaches: scattering neutrons off of a target that has spatial structure at nanoscopic length scales. Such structures will give a coherent enhancement to small-angle scattering, where the new force is most significant. This can considerably improve the sensitivity of neutron scattering experiments for new forces in the 0.1 - 100 nm range. We discuss the backgrounds due to Standard Model interactions and a variety of potential target structures that could be used, estimating the resulting sensitivities. We show that, using only one day of beam time at a modern neutron scattering facility, our proposal has the potential to detect new forces as much as four orders of magnitude beyond current laboratory constraints at the appropriate length scales.Comment: 42 pages, 7 figure