Office: Wean Hall 8412
EducationPh.D., Massachusetts Institute of Technology
ResearchMedium 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.
- Z. Ahmed et al., New Precision Limit on the Strange Vector Form Factors of the Proton, Physical Review Letters 108, 102001 (2012)
- S. Abrahamyan et al., Measurement of the Neutron Radius of 208Pb through Parity Violation in Electron Scattering, Physical Review Letters 108, 112502 (2012)
- M. Friend, G.B. Franklin, B. Quinn, An LED pulser for measuring photomultiplier linearity, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 676, 66 (2012)
- M. Friend et al., Upgraded photon calorimeter with integrating readout for the Hall A Compton polarimeter at Jefferson Lab, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 676, 96 (2012)
- S. Riordan et al., Measurements of the Electric Form Factor of the Neutron up to Q2=3.4 GeV2 Using the Reaction 3He(ee′n)pp, Physical Review Letters 105, 262302 (2010)
- D. Androić et al., Strange Quark Contributions to Parity-Violating Asymmetries in the Backward Angle G0 Electron Scattering Experiment, Physical Review Letters 104, 012001 (2010)
- J. Lachniet et al., Precise Measurement of the Neutron Magnetic Form Factor GMn in the Few-GeV2 Region, Physical Review Letters 102, 192001 (2009)
- D. Marchand et al., electronics and data acquisition (forward-angle measurements), Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 586, 251 (2008)
- K. Paschke et al., Experimental determination of the complete spin structure for p̅p→Λ̅Λ at pp̅=1.637GeV/c, Physical Review C 74, 015206 (2006)
- J. Parker et al., Weak decays of Λ4He, Physical Review C 76, 035501 (2007)
- D. Armstrong et al., Strange-Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment, Physical Review Letters 95, 092001 (2005)
- J. Musson, T. Allison, A. Freyberger, J. Kuhn, B. Quinn, YO!—a time-of-arrival receiver for removal of helicity-correlated beam effects, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 540, 448 (2005)
- S. Ajimura et al., Observation of Spin-Orbit Splitting in Λ Single-Particle States, Physical Review Letters 86, 4255 (2001)
- F. Merrill et al., H-dibaryon search via Ξ- capture on the deuteron, Physical Review C 63, 035206 (2001)
- Kent D. Paschke, Brian Quinn, Spin observables in with a transverse initial state polarization, Physics Letters B 495, 49 (2000)