Research Summary

Professor Kent Paschke

PREX

The charge radius of heavy nuclei, corresponding to the distribution of protons, has been well measured through form-factor measurements in electron scattering, but the information on the corresponding distribution of neutrons is much less direct. A measurement of the neutral weak form-factor of a nucleus is sensitive primarily to neutrons, as the neutron weak charge is an order-of-magnitude larger than that of the protons. In 208Pb, this radius Rn of the neutron distribution can be fixed by measurement of the parity-violating asymmetry at a single Q2. Rn is closely related to the symmetry energy of neutron rich matter, and its determination is a crucial calibration point for the present understanding of nuclear structure, including its description of neutron stars. (Home, Wiki)

News: PREX-II has been approved with an "A" rating by PAC 38. See my slides from the PAC presentation for an overview, or read the proposal here.

HAPPEX-3

Measurements of the weak vector form-factors of the proton, combined with measurements of the electromagnetic form-factors of the proton and neutron under the assuption of charge symmetry, provide a tight constraint on the possible contribution of an intrinsic strange-quark component of the proton to its electric and magnetic distributions. While previous measurements have suggested the possiblity of significant effects, recent HAPPEX-3 results have recently placed a tight constraint on strange contributions, at the level of a few percent of the proton electromagnetic form-factors. (Home)

QWeak

Qweak will measure the parity-violating asymmetry APV in elastic electron-proton scattering at low Q2 to a precision of 2%, a measurement sensitive to the vector weak charge of the proton. The result will be compared to the precise prediction from the Standard Model, with any deviation deviation attributable to new physics. ( Public Page, Wiki )

PVDIS-6

Parity-violation measured in deep-inelastic scattering from deuterium opens up sensitivity to the axial weak charges of the u and d quarks. (Home)

MOLLER

Using 11 GeV electrons, the MOLLER collaboration will measure a parity-violating asymmetry in electron-electron scattering of about 36 parts per billion to a precision of about 0.7 parts per billion. The result will be a measurement of the vector weak charge of the electron, implying a determination of the weak mixing angle to a precision approaching 0.1%. This will match the best existing measurements of this fundamental electroweak parameter, which have come from high energy colliders operating near the Z-boson resonance. This low-energy measurement will have a sensitivity to physics beyond the Standard Model to multi-TeV scales, in a manner which is highly complementary to direct searches at the Large Hadron Collider. The proposal has recieved full approval and been appropriated beam time by the JLab Program Advisory Committee, and has undergone a Director's review in 2010. A detailed technical design and R&D plan is under development, with the goal of getting the experiment ready to run by 2017. (Home)

SOLID

The measurement of parity-violating scatting from deuterium in the Deep Inelastic Scattering regime (PV-DIS) provides a unique sensitivity to the weak axial-vector coupling of the quarks, but also samples the underlying nucleonic structure of the target. A rich program of study is being designed for JLab-12GeV to explore both important topics in hadronic structure (i.e. coherent quark-quark correlations and charge symmetry violation at high momentum fraction) and potential variations from Standard Model expectations for the weak axial charge of the quarks.(Home)

Don Jones Studying Laser Optics
Don Jones studying Pockels cell alignment in the UVa lab