We have used a commercial RF ion-source to extract a beam of metastable neon atoms. The source was easily incorporated into our existing system and was operative within a day of installation. The metastable velocity distribution, flux, flow, and effi
ciency were investigated for different RF powers and pressures, and an optimum was found at a flux density of $2times10^{12},$atoms/s/sr. To obtain an accurate measurement of the amount of metastable atoms leaving the source, we insert a Faraday cup in the beam line and quench some of them using a weak $633,$nm laser beam. In order to determine how much of the beam was quenched before reaching our detector, we devised a simple model for the quenching transition and investigated it for different laser powers. This detection method can be easily adapted to other noble gas atoms.
The Proton Radius Puzzle is the inconsistency between the proton radius determined from muonic hydrogen and the proton radius determined from atomic hydrogen level transitions and ep elastic scattering. No generally accepted resolution to the Puzzle
has been found. Possible solutions generally fall into one of three categories: the two radii are different due to novel beyond-standard-model physics, the two radii are different due to novel aspects of nucleon structure, and the two radii are the same, but there are underestimated uncertainties or other issues in the ep experiments. The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institut is a simultaneous measurement of mu^+ p and e^+ p elastic scattering, as well as mu^- p and e^- p elastic scattering, which will allow a determination of the consistency of the mu p and the ep interactions. The differences between + and - charge scattering are sensitive to two-photon exchange effects, higher-order corrections to the scattering process. The slopes of the cross sections as Q^2 -> 0 determine the proton radius. We plan to measure relative cross sections at a typical level of a few tenths of a percent, which should allow the proton radius to be determined at the level of ~0.01 fm, similar to previous ep measurements. The measurements will test several possible explanations of the proton radius puzzle, including some models of beyond-standard-model physics, some models of novel hadronic physics, and some issues in the radius extraction from scattering data.
We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the prot
on. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis.
High precision measurements of induced and transferred recoil proton polarization in d(polarized gamma, polarized p})n have been performed for photon energies of 277--357 MeV and theta_cm = 20 degrees -- 120 degrees. The measurements were motivated b
y a longstanding discrepancy between meson-baryon model calculations and data at higher energies. At the low energies of this experiment, theory continues to fail to reproduce the data, indicating that either something is missing in the calculations and/or there is a problem with the accuracy of the nucleon-nucleon potential being used.
The proton analyzing power in carbon has been measured for energies of 82 to 217 MeV and proton scattering angles of 5 to 41 degrees. The measurements were carried out using polarized protons from the elastic scattering H(pol. e, pol. p) reaction and
the Focal Plane Polarimeter (FPP) in Hall A of Jefferson Lab. A new parameterization of the FPP p-C analyzing power was fit to the data, which is in good agreement with previous parameterizations and provides an extension to lower energies and larger angles. The main conclusions are that all polarimeters to date give consistent measurements of the carbon analyzing power, independently of the details of their construction and that measuring on a larger angular range significantly improves the polarimeter figure of merit at low energies.
