• Professor, Physics And Astronomy

Research Summary

My research interests are in particle astrophysics and observational astronomy. I played a major role in the HiRes and Telescope Array Cosmic Ray Observatories. I now use the HAWC Observatory to study the highest-energy gamma-rays as well as cosmic rays. I work on the development of an observational program to exploit the Willard L. Eccles optical observatory. I have recently joined the Southern Wide-field gamma ray observatory as well as the Trinity Tau Neutrino observatory.




As an experimental scientist I have been very fortunate to participate in what could be considered a wide range of physics. I was trained as an experimental high-energy physicist and worked at the European Laboratory for Particle Physics (CERN) on the OPAL experiment at the Large Electron-Positron Accelerator (LEP). There I was involved in the design, construction and implementation of several of the detector components of the OPAL experiment. The topic of my Ph.D research was the measurement of the coupling of the b quark to the Z boson. As a postdoctoral scientist, I worked on precision measurements of the electroweak parameters, such as the mass and width of the Z boson and its coupling to quarks and leptons. The bulk of my effort was in the measurement of the luminosity delivered to the OPAL experiment. The luminosity measurements were of critical importance to the measurements of the parameters of the electroweak sector of the Standard Model of Particle Physics. I was also involved in the Higgs Boson search analysis at LEP as well as the development of analysis plans for Higgs Searches at Atlas.

Since my arrival at the University of Utah in 1997, my research interests have been in the field of Ultra High Energy Cosmic Ray (UHECR) Physics and now Gamma-Ray astronomy. I played a major role in commissioning and operating the HiRes detector as well as helping to provide computing and software support to the entire HiRes collaboration. I was involved in the development of reconstruction and simulation software that was used in nearly all of the published research results of the HiRes collaboration. While on HiRes, I supervised the Ph.D thesis research of two students who have continued on to successful research positions. One of the major achievements of the HiRes experiment has been the observation of the so-called “GZK cutoff” in the energy spectrum of UHECR particles. I continue to be interested in working in the field of UHECR physics and have been involved with the Telescope Array (TA) project that has been taking UHECR data since shortly after the HiRes detector was decommissioned. The resolution of the discrepancy in the measurements by AGASA and HiRes of the UHECR spectrum is one of the major goals for TA. The measurements of AGASA indicated that the UHECR spectrum continue unabated beyond the purported GZK cutoff. While the measurements of the UHECR spectrum from HiRes support the existence of the GZK cutoff. AGASA utilized an array of ground based scintillator detectors to measure the properties of UHECRs by sampling the particles from an extensive air shower on the ground. The HiRes detector utilized what is known as the air fluorescence technique to measure the properties of the UHECRs. The telescope array project combines the complementary measurement techniques used by AGASA and HiRes into a single experiment. In this manner the two measurement techniques can be directly compared and the discrepancy thereby resolved. I have wound down my efforts on the Telescope Array project since the graduation of my last Ph.D student working on the TA project and the ramping up of my involvement in the HAWC gamma ray observatory described below.

In 2010, I joined the High Altitude Water Cerenkov Experiment, also known as HAWC. The HAWC detector is a wide-field of view continuously operating gamma ray telescope that is located on the Sierra Negra Mountain in Mexico at an altitude of 4100 m. HAWC is sensitive to gamma rays with energies between 100 Gev and above 100 TEV. HAWC is capable of observing both point sources of gamma-rays, including Gamma Ray Bursts (GRBs), as well as the diffuse gamma-ray background. This diffuse background may be related to the sources of cosmic-ray acceleration. HAWC's wide field of view is useful as both a survey instrument as well as for observing transient sources. HAWC provides candidates of gamma ray sources to other gamma-ray observatories for further investigation. HAWC also is sensitive to cosmic-ray charged particles and has performed measurements of the anisotropy of arrival directions as well as energy spectrum measurements. Construction of the first array of seven Water Cerenkov Detectors began in July 2010. The HAWC observatory main array was completed in March 2015.

I have also been involved in developing an optical astronomy program at the University of Utah. I led the effort to construct an observatory located on Frisco Peak near the town of Milford in Southern Utah. Construction of the Observatory started in July 2009 and was completed in only 3 months. Commissioning and “first-light” occurred in October, 2009. During summer 2010, work on the development of remote operation capabilities and further characterization of the site was performed. The facility has been used for coursework in the observational astronomy courses taught by the department as well as public outreach activities. The effort to fully automate the observatory has concluded with the capability for autonomous operation realized in the fall of 2013. It is planned to use this facility to support research activities in fields such as AGN multi-wavelength monitoring campaigns, GRB follow-up observations, extra-solar planetary studies and supernovae searches. An observing program of polarimetry measurements of supernova remnants (SNRs) and Blazars is under development in collaboration with astronomers from  BYU, UNAM (Universidad Nacional Autonoma de Mexico) and the University of Guadalajara.