Every day hundreds of cosmic rays arrive at Earth traveling at nearly the speed of light, with energies many orders of magnitude beyond the energies produced by our own particle accelerators. Such energetic particles carry information about the most powerful accelerators in the universe, and their precise origin remains an outstanding question. Ultra-high-energy cosmic rays can also interact with the cosmic microwave background to produce a stream of neutrinos, which would indicate the sources of cosmic rays and provide a test bed for particle physics at the highest energy scales. The recent breadth of discoveries of TeV gamma-ray sources give us a glimpse into the location and nature of the most violent cosmic accelerators. I am principally interested in developing techniques for detecting and characterizing these messsenger particles: gamma rays, cosmic rays, and neutrinos.
Particles with extreme energies
The nature and origin of the most powerful accelerators remains a mystery. Neutrinos and cosmic rays produced by these sources serve as probes of not only of the sources themselves, but also fundamental physics at the highest energies and over cosmological distance. Ultra-high energy cosmic ray neutrinos may be detected by training radio antennas on large swaths of dieletric material. Neutrinos and cosmic rays produce cascades of particles that emit coherent Cherenkov emission at radio frequencies. I am involved with a number of experiments aimed at detecting and understanding these exceptional particles including:
- ANITA (ANtarctic Impulsive Transient Antenna)
- GNO (Greenland Neutrino Observatory)
- T-510 (SLAC testbeam)
Galactic cosmic rays
The non-thermal energy distribution at the sources and propagation history is encoded in the chemical composition of cosmic rays. Satellite- and balloon-borne experiments measure the composition up to energies of a few TeV/amu, but ground-based techniques, though limited by their model dependence, are required for higher energies. I used a technique—originally pioneered in a ballon experiment—has been revived for ground-based telescopes to measure the iron spectrum with VERITAS (see my thesis). The charge of the cosmic ray is reconstructed from the flash of Cherenkov light from a cosmic ray as it enters the atmosphere. Since Cherenkov radiation scales with the square of the charge of the particle, this technique combines the sensitivity of experiments flown above the atmosphere with the large exposure of ground arrays. We also explored the possibility of using a multi-anode photomultiplier camera to improve charge resolution with the TrICE experiment.
My CV details these research topics.
My publications are listed here: