Electromagnetic Probes of Hadronic Matter

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This NSF award supports our continuing research program at Jefferson Lab using electromagnetic probes to study hadronic matter at the fundamental level. Our group focuses on four experimental efforts that test the basic nature of particle interactions at the quark gluon level. Five particle tracking drift chambers are currently being constructed at ISU to support Jefferson Lab's Hall B 12 GeV program. One of our experiments extracts polarization observables from meson photoproduction with linearly-polarized photons on the proton and deuteron and will result in two ISU PhD theses during this funding period. Another experiment will investigate quark distributions at extreme kinematics where the quarks carry most of the nucleon's momentum. A high-precision measurement of the pion lifetime is being undertaken in Jefferson Lab's Hall B. This experimental effort seeks to probe the mechanism through which a neutral charged pion can decay into two photons to stringently test confinement-scale quantum chromodynamics. Another high-precision experiment in Hall A, MOLLER, uses the parity-violating property of the weak interaction to measure a fundamental parameter of the Standard Model known as the Weinberg (or mixing) angle to within a relative uncertainty of 0.1%. When combined with other experiments, this measurement will place strong constraints on proposed extensions to our present version of the Standard Model. These research programs at JLab, the accelerator facilities at ISU, and continuous detector construction projects in the group's Laboratory for Detector Science, combine in an active program to provide a breadth of experiences for four graduate students and to train the next generation of scientists.