Parity Violation in Atomic, Nuclear and Hadronic Systems: Summary of First Week

Results From Workshop
1) Neutron Radius Experiments.
   a) Present theoretical error range in the difference between the neutron and proton rms radii R_n-R_p for 208Pb is approx 0.1 to 0.3 fm with 0.0 fm very unlikely.
   b) Experimental error range in R_n-R_p from proton and pion scattering includes R_n-R_p=0.  Hard to quantify systematic error from hadronic reaction theory.  If R_n-R_p is really zero this has a great implication for nuclear structure.
   c) R_n is sensitive to the density dependence of the symmetry energy.
   d) R_n measurement constrains energy of dense neutron rich matter important in astrophysics for neutron stars, supernovae...
   e) The nuclear structure motivation for R_n measurement is very strong.
2) Atomic Parity Nonconservation: Cs atomic theory error for extracting the weak charge was    reported by two groups to be 0.7 to 1%.  There has been a slight improvement in the theory from recent measurements but it is probably not as accurate as recently claimed by the Colorado group.
3) Parity Violating Electron Scattering.
   a) Nucleon Electromagnetic form factors are a significant uncertainty in extracting strange quark contributions.
   b) Axial radiative corrections to G^e_A appear to differ in preliminary SAMPLE measurements from theoretical expectations.
   c) Strange quark contributions in the nucleon are consistent with zero.  However there are significant error bars and existing measurements are only at a very limited set of  kinematics.

 
What are the Important Experiments and Calculations to be done?
1) Neutron radius experiments.
   a) A first parity violating neutron radius measurement should be done.
   b) Study theoretical relationship between R_n in different nuclei for atomic PNC.  For example how well will a measurement of R_n in 208Pb constrain R_n in 138Ba?
   c) Further R_n measurements for additional nuclei, at other momentum transfers, or for isotope ratios should be done if they will significantly improve our knowledge of  neutron densities.
   d) Reexamine theoretical analysis of elastic proton-nucleus scattering.  What is the modern theoretical error for R_n?  Can isotope ratios be more accurately extracted?  Can the theory be calibrated with a parity violating measurement and then applied to  many nuclei?
2) Atomic PNC
   a) Improve atomic theory for Cesium:
      i) Possible given improvement in computers.
      ii) Start worldwide theory collaboration.
   b) Confirm the Boulder Cs measurement in a second experiment.
   c) Measure PNC accurately in another atom.
   d) Explore viability of combining R_n measurements, nuclear theory and atomic isotope measurements to probe standard model.
   e) Measure additional anapole moments.
3) Strange quarks in nucleon.
   a) Theoretical study of hadronic contributions to axial radiative corrections G^e_A for SAMPLE measurements and for neutron and nuclear beta-decay.
   b) Confirm SAMPLE results with additional back angle experiment(s).
   c) Separate electric and magnetic nucleon strange form factors over a range of momentum transfers.
   d) Start a Form factor working group to quantify present best values and errors of nucleon form factors.
   e) Accurate nu scattering measurement of \Delta_s
   f) Further Lattice calculations of strange form factors.
   g) Parity violating electron 4He measurement of \rho_s
4) Other Low energy Standard Model tests.
   a) Measure electron-electron parity violation.
   b) Measure proton weak charge in electron scattering.
   c) Measure A parameter in neutron beta-decay to 0.1% as well as other beta decay correlation parameters which are sensitive to new physics.
5) Support infrastructure for precision electron parity experiments such as improved measurements of beam polarization.

Conclusions.
Atomic parity nonconservation, parity violating electron-proton and electron-electron scattering, neutron and nuclear beta-decay and high energy experiments provide important complimentary probes of possible physics beyond the standard model.  Likewise forward and backward angle parity violating electron-proton, backward angle electron-deutron and forward angle electron-4He scattering as well as neutrino-nucleon scattering provide complimentary probes of strange quarks in the nucleon.  We recommend a full compliment of experiments as several quantities must be constrained and no single measurement can accomplish this.