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Parity Violating Electron Scattering and Nuclean Structure Studies at Jefferson Lab

Description :  

The main thrust of the research program of the Louisiana Tech University TJNAF group involves parity violating electron scattering, a program which challenges our understanding of nucleon structure, probe the dynamics of QCD symmetry breaking, and provide precision tests of the Standard Model. In addition to this main effort, we are also involved in experiments to measure nucleon form factors. Two parity violating electron scattering programs at TJNAF: Qweak (E05-008), N→Δ (LOI-03-105); and a future PV Moller (E12-09-005) measurements after the 12 GeV TJNAF upgrade, represent parity violation measurements primarily at low momentum transfers (0.003 < Q2 <0.03) (GeV/c)2. The Qweak experiment measured the parity violating asymmetry in elastic ep scattering at low Qto high precision, which directly measures the running of the Standard Model coupling sinθw. The Louisiana Tech TJNAF group provided simulation, hardware, expertise, and manpower for this project and will be involved in data analysis and results publication in the upcoming years. The first results of this measured test were published in October, 2013. Of the particular interest for the Louisiana Tech group, the parity violating asymmetry in the N →Δ transition at very low Q2 which was measured using the Qweak apparatus, directly measures a new, unmeasured low energy constant, dΔ, which corresponds to a parity violating electric dipole transition. This same matrix element drives the asymmetry parameter measured in strangeness changing radiative hyperon decays, and its measurement may provide clues into the unexpectedly large QCD symmetry breaking effects observed in those decays. The Louisiana Tech TJNAF group led this effort. The measurement for this reaction channel was performed in 2012, and graduate students hired by Louisiana Tech will analyze these data, along with simulation, which will be on going in subsequent years and published. The planned PV Moller measurement will similarly constrain the running of sin2 θw to low Q2 but is sensitive to physics beyond the Standard Model in the lepton-lepton sector of the weak interaction, therefore providing complementary information about how possible new physics than that of Qweak. The experiment will be run after the 12 GeV TJNAF upgrade. In the upcoming years Louisiana Tech group will be involved in the preparation of the measurement, assurance of the quality of the data taken, and building sub-components of the experiment. The electric form factor of the neutron Gn E is a fundamental quantity of the neutron, and understanding its behavior out to large Q2 can shed light on the internal structure of the neutron in terms of its underlying quark characteristics. The TJNAF experiment E12-11-009 will measure this quantity out to Q2 = 7.0 (GeV/c)2 , and the Louisiana Tech group will help construct and test detector elements of the neutron polarimeter used for these measurements.

Principal Investigator:  Wells, Steven  --  Physics
Funding Agencies:  NSF
Amount Awarded:  219,865

Start Period:  00/00/0000 End Period:  00/00/0000
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March 30th, 2017

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