Faculty Profile

Research Overview:

The proton radius puzzle, originally published by Randolf Pohl et al. in Nature in July 2010 is a recent high profile issue - the proton size appears to be different when measured with electons vs. when measured with muonic hydrogen, a result for which we have no explanations. Experts in the field think the likely explanation is either new physics or issues with electron experiments. Novel aspects of proton structure / QCD are not entirely ruled out, although almost every suggestion made to date in this area has been. The puzzle has been confirmed with a second paper by Aldo Antognini et al. with new muonic hydrogen results. The muonic hydrogen measurements were done at the Paul Scherrer Institut, a laboratory in Switzerland. A press release from PSI is here. A good podcast with Aldo Antognini describing the situation is here. You can also see informal descriptions of the Puzzle and reactions to it from may sources, including Science Daily, New Scientist, Science News, Red Orbit, arstechnica, phys.org, Huffington Post, Nature News, and Scientific American. A news conference on the Puzzle with Randolf Pohl, Jan Bernauer, and John Arrington was reported on at Huffington Post, and Yahoo news.

I co-organized a Proton Radius Puzzle Workshop at the European Center for Theory in Trento, Italy with Randolf Pohl (Munich) and Gerald Miller (Washington), and we, with Krzysztof Pachucki (Warsaw) wrote a review paper on the current status of the puzzle. I am also leading an experimental effort to study the puzzle with muon-proton elastic scattering - some materials can be found here.

I usually work with Prof. Ron Ransome and colleagues from other universities and laboratories from around the world in an area called intermediate energy nuclear physics. We mainly investigate strong QCD (mostly the structure of the proton and neutron), nuclear structure, and physics beyond the standard model. Our focus has been experiments at the Thomas Jefferson National Accelerator Facility (JLAB) 6 GeV electron accelerator, CEBAF, in Virginia and at Fermilab, in Batavia Illinois. Our JLab research is centered on studies of spin physics, studying nucleons and subnucleonic effects in light nuclei using polarized electron beams, targets, and recoil polarimeters. Our research at Fermilab uses neutrino beams and proton beams to study quark distributions and QCD through the Drell-Yan process.