Susan Gardner

Barry Holstein

Jeffrey Nico

W. Michael Snow

Program Coordinator:
Laura Lee
(206) 685-3509

Tentative Program Schedule, with Week-by-Week Foci

Electric Dipole Moments and CP Violation Workshop

Application form

Talks online

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Fundamental Neutron Physics

March 19 - June 8, 2007

"Neutronic Decay" by Dawn Meson
© 2006

The growth of neutron physics facilities worldwide yield unprecedented opportunities to study the neutron's fundamental nature. Our program plans not only to support experiments planned at incipient facilities, such as at the Spallation Neutron Source (SNS), but also to nuture new experimental and theoretical directions.

Fundamental neutron physics is naturally of broad compass, with questions which span subfield boundaries. We wish to bring together theorists and experimentalists to consider and ultimately to solve problems in topics such as we describe.

Breaking of Discrete Symmetries

The violation of symmetries such as P, CP, and T can be studied in a variety of low-energy processes. Hadronic parity violation can be probed through the study of the parity-violating asymmetry in np→dg and through neutron spin rotation experiments. Essential questions include what fundamental parameters can be extracted, and how such can be rationalized from a rigorous non-perturbative formulation of QCD. The empirical bound of the neutron electric dipole moment (EDM) constrains extensions of the Standard Model (SM) with additional sources of CP violation and is relevant to the investigation of the cosmological problem of the baryon asymmetry of the universe. We hope to realize a synergy of theorists of greatly varying expertise, including those expert in few-nucleon and nuclear-structure physics, in effective-field-theory techniques, in non-perturbative methods and models of QCD, as well as those versed in building extensions of the SM, to realize fruitful studies of P, CP, and T violation in hadronic systems at low energies.

CKM Unitarity and New Interactions at the Weak Scale

The focus of the neutron lifetime and neutron b-decay asymmetry experiments is the elucidation of the CKM matrix element Vud, to realize, with Vus and Vub, the world's best test of the unitarity of the CKM matrix. The significance of this empirical test is a crucial constraint on grand unified theories which admit "new" physics at the TeV scale. This is, in turn, shaped by the surety of the "inner" radiative correction calculation which enters the determination of Vud from the empirical vector coupling constant gV. We hope to foster discussion of how effective field theory techniques employed in the study of Kl3 decay may be extended to baryonic systems, to modernize and possibly improve upon earlier work. Detailed measurements of the decay correlation coefficients can also be used to limit the presence of non-V-A weak interactions and thus bound the presence of new weak-scale physics. Exploring the manner in which these tests complement precision electroweak data is of great importance.

Gravity and New Long-Range Interactions

Two disparate experiments suggest that known quantum mechanical principles apply to gravitational potentials as well. The first is a measurement of the gravitational phase shift in neutron interferometry; the second is the recent inference of gravitational bound states of ultra-cold neutrons (UCN). The UCN results can be used to bound new long-range interactions, which occur naturally in models with "extra" dimensions, at the nanometer scale. Such experiments potentially offer an interesting complement to experiments of greater sensitivity at larger distance scales. Understanding the role neutron experiments can play in shaping our understanding of gravity in the quantum regime is a topic we would like to explore.

Neutron Structure and Interactions

At low energies, the neutron's structure is probed primarily through the n-e scattering length, which yields the rms charge radius of the neutron, and electric and magnetic polarizability measurements. Theoretical predictions of the neutron charge radius, be it from lattice QCD, or from the analysis of precision atomic and electron scattering data on the proton and deuteron, would be welcome. The precision of low-energy n scattering experiments to yield scattering lengths and polarization observables have improved greatly; here interest revolves around their theoretical interpretation to yield insight into the NN interaction.

Nuclear Astrophysics

The measured neutron lifetime is crucial to the predictions of big-bang nucleosynthesis (BBN) and ultimately to understanding the manner in which the universe has evolved throughout its history. Here, too, effective-field-theory techniques play a role in realizing precision predictions of key reaction rates, such as np→dg. It would be useful to develop a perspective on the experimental and theoretical work yet needed to sharpen the comparison with data as much as possible. Agreement of the predictions of BBN with observed element abundances can constrain the parameters of various SM extensions as well. Spallation neutrons can also be used to generate neutrinos and thus to study the physics of neutrino oscillations.