Coyne is the principal investigator (with co-principal Adj. Asst. Prof. David A. Williams) of an NSF-sponsored particle astrophysics group within SCIPP, the Santa Cruz Institute for Particle Physics. His research centers about a newly-funded research instrument called Milagro, which is an earth-based detector of gamma rays from 10 GeV up to about 1000 TeV, with its main sensitivity between 1 and 10 TeV. The Milagro detector is a large water reservoir on a New Mexico mountain-top, equipped with photomultiplier tubes which can measure the direction and energy of the initial gamma ray which created the air shower impinging on the water. They do this by virtue of the Cerenkov light generated in the water by secondary particles from the shower.
Milagro has been under construction for about 2 years. The Santa Cruz group assumes major hardware responsibilities for the front-end electronics which filters, shapes and digitizes the photomultiplier signals. Each year of construction (of a total of 3 to 4) brings to life an upgraded version of the detector, and each winter provides a data-taking period in which both shakedown data and physically interesting data can be accumulated. The group also has major responsibilities for both the utilization of high voltage (for the tubes) and protection from it (in the form of potentially disastrous lightning)! All the members of our group, including many undergrad students, have contributed to the construction.
Behind all this experimental activity lurks the reason for which we do it: the fascination with the mechanisms which have produced gamma rays at the low end of this range, and the expectation that more revelations lie at higher energies. The Santa Cruz group, and Coyne in particular, have been interested in the possible detection of Hawking radiation from the explosive evaporation of small black holes, presumed but never proven to have been produced in the Big Bang. Even Hawking's mechanism itself, while already a monument of physics, has not one iota of experimental evidence to confirm it. Such searches are a long shot, but the physics and search techniques are fascinating. In contrast, the parallel search for the location and cause of the mysterious gamma-ray bursters, which produce about one blast per day of enormous proportions, is a project in which the signal is definitely there (at least up to about 50 GeV) and the problem is to find where it cuts off and what/where these objects are. Many of our grad students and postdocs will be deeply involved in this project, as well as undergrads with senior theses on the subject.
Finally, as a sideline to the prime experimental work, Coyne continues to document and explore the connections between fundamental particles and black holes, from an experimentalist's viewpoint. He has shown that detection of a nearby evaporating black hole can prove the existence of the supersymmetric partners of fundamental particles, if such partners exist.
Search for Ultra-High-Energy Radiation from Gamma-Ray Bursts, D.E. Alexandreas, D.G. Coyne et al., Astrophys. J. 426, L1 (1994).
Astrophysics with Milagro, D.G. Coyne et al., Proceedings of the Twenty-third International Cosmic Ray Conference, Calgary, Canada, p. 436 (July 19-30, 1993).
Ramifications of Particle Physics Models for the Final Stages of Black Hole Evaporation, D.G. Coyne and R. Somerville, Internal SCIPP report 94/02.
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