NuBE:
A Deep ocean detector for ultra high energy neutrinos from
the most energetic sources in the universe.
Our group continues to explore new ways to measure ultra high energy (UHE)
extra-terrestrial neutrinos. Such neutrinos are expected to originate in the
most energetic events in the universe, in Active Galactic Nuclei (AGN) and in
Gamma-Ray Bursts (GRB). We organized a small neutrino workshop in December
1997 focussing on neutrino signals that may be observable in a large area detector.
Several leading theorists were present and the discussions resulted in a clear set of
experimental goals.
We have completed a review paper titled "Sources of Ultra High Energy
Neutrinos", based in part on these discussions, which has been submitted to the
journal "Astroparticle Physics". This incorporates all different
astrophysical models for predicting UHE neutrinos and the expected neutrino
flux in common units. We are now combining this information on flux with
our understanding of neutrino interactions to calculate the signals from each
type of source expected in a detector. This is the basic experimental design
tool we are using in tuning the design of our gamma-ray burst -neutrino burst
coincidence experiment.
Bahcall and Waxman have predicted UHE neutrinos in coincidence with GRB
emission, in which neutrinos have typical energies of 10-100 TeV. The
neutrinos interact with electrons resulting in short, intense electromagnetic
showers, or with quarks to form muons whose energy loss is dominated by
radiative effects. Both of these types of events produce large amounts of
light in a Cherenkov detector of sufficient volume. The detector size scale
of interest is a square kilometer.
Because of long distance coherence of the produced light signal (a 10 TeV muon
travels many km), it is possible to construct a sparsely instrumented array
covering a large volume of deep ocean water to detect these signals. A time
tag included in the data stream for each event can be used to search offline
for coincidence with GRB signals from satellite-borne detectors.
We have completed a Phase-I SBIR program with the Deep Ocean Engineering company
in Alameda to investigate the design of a robot capable of being used to place
and to service detectors in the deep ocean. We completed the control code
for the robot to work essentially autonomously in placing the detectors at the
correct location in an array, and the same code is the basis of the autonomous
operations of repair and service. The robot can use this code as its primary
mode of operation, or it can be controlled via a single fiber optic line from
the tending ship. The key concept investigated was the fabrication of a deep ocean
robotic vehicle that operates without a power and control tether, a mechanical
constaint that makes the robot work expensive and cumbersome.
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