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.