Some of the ultrahigh-energy cosmic ray neutrinos striking the Moon are expected to set up shock waves of Cerenkov radiation, the light given off by particles -- in this case charged particles spawned by neutrinos -- traveling faster than light itself in that medium.(Editor's Note: See schematic drawing at this URL.)
For the cosmic rays of greatest interest, those with an energy above 10^20 eV, the Cerenkov radiation peaks in the microwave region of the electromagnetic spectrum.
To test the validity of this "Askaryan effect" (named for the Armenian-Russian scientist Gurgen Askaryan), a consortium of scientists including David Saltzberg and Peter Gorham have shot gamma rays into a bed of sand at the SLAC Final Focus Test Beam.
As expected, the coherent microwaves appeared.
The scientists are now pointing two JPL radio telescopes (part of the Deep Space Network) toward the Moon to look for such radiation from cosmic ray neutrinos. (Right now, their calibration involves pointing at distant quasars, but they say it would be nice to have some source of microwave pulses on the Moon itself, a luxury not possible at present.)
Some optimistic estimates place the number of possible 10^20 eV cosmic ray neutrino events on the Moon as high as one every 10 to 20 hours or so.
(Reference: Saltzberg et al., Physical Review Letters, 26 March.)
(Editor's Note: This story is based on PHYSICS NEWS UPDATE, the American Institute of Physics Bulletin of Physics News Number 531 March 22, 2001 by Phillip F. Schewe, Ben Stein, and James Riordon. Also see recent UniSci story, High-Energy Neutrinos From Space Detected And Tracked.)
Related website:
Beam Tests
[Contact: David Saltzberg, Peter Gorham, Ben Stein]
26-Mar-2001
