Brian Quinn-Dept of Physics - Carnegie Mellon University

Brian Quinn

Professor, Physics

Office: Wean Hall 8412
Phone: 412-268-3523
Fax: 412-681-0648


Ph.D., Massachusetts Institute of Technology


Medium Energy Physics generally concentrates on the middle ground between conventional nuclear physics and high energy particle physics, although the boundaries are not sharply defined. We are generally interested in problems in which the quark structure of hadrons (strongly interacting particles) is relevant. The energy range of interest in Medium Energy Physics doesn't usually lend itself to the simplifications of a perturbative treatment of quantum-chromodynamics. Rather, it allows us to explore a wealth of important topics, such as the structure of the hadrons themselves, which are intrinsically non-perturbative. 

The Carnegie Mellon medium energy group has participated in a rich variety of experiments over the past few years, using anti-protons to study annihilation on protons with the resulting creation of strange (and anti-strange) quarks; kaons and pions to study the weak decay of hypernuclei and to search for un-discovered states such as the H-dibaryon; and photons and electrons to probe strangeness production and the structure of the neutron. We have contributed to many aspects of these experiments: detectors, data-acquisition hardware, on-line acquisition programs and analysis. Carnegie Mellon graduate students have taken a leading role in the analysis and interpretation of the data from many of these experiments. 

A high-current superconducting electron accelerator facility, Jefferson Laboratory (JLab), in Newport News, Virginia is an important center of Medium Energy research, and the venue for most of our experiments. I led our group's involvement in the G0 experiment which used the JLab beam to study the weak form-factors of the proton to probe the strangeness content of the nucleon.  In the HAPPEX-III experiment, we recently completed a similar measurement with even greater precision at one kinematic point.  The Compton polarimetry for that experiment was the thesis topic of my student, Megan Friend.  An on-going set of parity-violation experiments will allow us to directly measure the neutron radius of the lead nucleus.  A longer term experiment, MOLLER, will use parity violation to test the 'running' of the weak mixing angle, as a test of the standard model.  Another high profile set of experiments will take advantage of the increased beam energy available after the JLab upgrade to measure the form factors of the nucleon, with great precision, at higher momentum transfer than has previously been possible.  I am a spokesperson and have taken the lead on one of these, a measurement of the magnetic form factor of the neutron.  An important piece of equipment for these measurements, the hadron calorimeter, is being designed and prototyped here and may be built by CMU.

Selected Publications