Rare Isotopes and Fundamental Symmetries

The following sections are included:

• Series Preface

• Preface

• CONTENTS

Precision measurements of β-decays in nuclei, muons and neutrons allow to search for non V-A contributions in weak interactions and to set limits on parameters relevant to theoretical models beyond standard theory. Novel experiments are possible in particular at presently operating stable beam facilities and at new radioactive beam facilities such as the ISAC facility at TRIUMF, the upcoming RIKEN cyclotron facility in Japan, the new proposed FRIB (RIA) facility and the newly available facility TRIµP at KVI. EURISOL is the most powerful and versatile planned radioactive beam facility.

We have measured the β - ν correlation coefficient, a_βν, in ²¹Na using a laser-trapped sample. We measure the energy spectrum of the recoil nuclei by measuring their time-of-flight in coincidence with the atomic electrons shaken off in beta decay. High detection efficiency of these low-energy electrons allows good counting statistics, even with low trap density, which suppresses the photoassociation of molecular sodium, which can cause a large systematic error. Our measurement, with a 1% fractional uncertainty, agrees with the Standard Model prediction but disagrees with our previous measurement which was susceptible to error introduced by molecular sodium. We summarize precise measurements of a_βν and their consequences for searches for Beyond Standard Model scalar and tensor current couplings.

I discuss advances in nuclear structure theory and the implications for the study of fundamental symmetries in nuclei. Recent results for the properties of the neutron skin in heavy nuclei are summarized.

Measurements of atomic electric-dipole moments provide sensitive tests of CP violation and new physics. I briefly review the dependence of these moments on nuclear structure through the nuclear Schiff moment, and discuss attempts to evaluate the Schiff moment in several nuclei. After a short discussion of the uncertainty in these evaluations, I estimate the size of some previously neglected terms in the Schiff operator.

Measurements on superallowed 0⁺ → 0⁺ nuclear beta transitions currently provide the most demanding test of the Conserved Vector Current (CVC) hypothesis and the most precise value for the up-down element, V_ud, of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. Both are sensitive probes for physics beyond the Standard Model. Analysis of the experimental results depends on small radiative and isospin-symmetry-breaking corrections, the validity of which is being probed by current measurements. We report on the current status of world data in light of recent improvements in both measurement and theory.

We report new shell-model calculations of the isospin-symmetry-breaking correction, δ_C, to superallowed Fermi β decay. The most important improvement is the inclusion of core orbitals, which are demonstrated to have a significant impact on the mismatch in the radial wave functions of the parent and daughter states. These new calculations lead to a lower average corrected 𝓕t value and a higher value for V_ud. The sum of the squares of the top-row elements of the CKM matrix agrees with unitarity.

This article summarizes preparations at the University of Washington for a precision measurement of the mass ratio of H-3 (tritium) to He-3 with a new Penning trap mass spectrometer. This work will be continued at the Max-Planck-Institute for Nuclear Physics in Heidelberg in the Division of Stored and Cooled Ions. Only preliminary ion observations were performed in Seattle, but the target mass uncertainty for the measurement techniques under development is 1 part in 10¹¹.

We present a summary of recent experiments performed to: 1) optimize the extraction of the correlation coefficient from ³²Ar, and 2) determine isospin breaking in both ³³Cl and ³²Cl.

I discuss the current status of efforts to constrain the strangeness-conserving weak hadronic interaction, which can be isolated in nuclear systems because of the associated parity violation.

The experimental parity-nonconservation (PNC) studies are reviewed, and the current status of theoretical calculations is described for various types of systems. The review of the relativistic all-order method and its application to PNC study is given. The current status and future prospects for improvement of the accuracy of theoretical calculations of the PNC amplitudes are discussed.

Knowledge about parity-violating effects both from theory and experiment is reviewed. Further information that could be obtained from measurements of nuclear anapole moments is discussed.

This article presents a proposal of the FRPNC collaboration for a measurement of the anapole moment of the nucleus of francium using parity non-conservation as the signature in a hyperfine transition.

The Radon-EDM experiment will measure the permanent electric dipole moment of radon atoms produced at TRIUMF's ISAC facility. The choice of ²²³Rn is based on the potential enhancement of sensitivity to CP violation by 2-3 orders of magnitude compared to ¹⁹⁹Hg, due to octupole strength or deformation. We expect to measure the atomic EDM of ²²³Rn with precision of 10^-26 to 10^-27 e-cm and thus extend sensitivity to CP violation by one to two orders of magnitude.

Parity violating electron nucleus scattering is a clean and powerful tool for measuring the spatial distributions of neutrons in nuclei with unprecedented accuracy. Parity violation arises from the interference of electromagnetic and weak neutral amplitudes, and the Z⁰ of the Standard Model couples primarily to neutrons at low Q². Experiments are now feasible at existing facilities. We show that theoretical corrections are either small or well understood, which makes the interpretation clean. The Jefferson Laboratory Lead Radius Experiment (PREX) aims to measure the neutron radius of ²⁰⁸Pb to one %. This neutron density measurement has many implications for nuclear structure, atomic parity nonconservation experiments, and the structure of neutron stars.

Nuclear Schiff moment may have a non-zero expectation value if both parity and time-reversal invariance are violated. The Schiff moment induces the atomic electric dipole moment currently searched by a number of experimental groups. The magnitude of the Schiff moment turns out to be sensitive to many features of complex nuclear structure; especially favorable is the combination of quadrupole and octupole deformation. We discuss these aspects, along with the new ideas for the possibility of nuclear enhancements.

Searches of permanent electric dipole moments (EDMs) using neutral systems are subject to an important screening effect which is summarized in a famous theorem by Schiff. The interpretation of actual measured EDMs thus requires this effect being properly taken care of. In this talk, we briefly outline a recent re-formulation of the Schiff theorem by Liu et al.^? and discuss its differences from previous derivations with an emphasis on the so-called Schiff moment operator.

There has been exciting progress in recent years in the search for a permanent electric dipole moment (EDM) of an atom, a molecule, or the neutron. An EDM along the axis of spin violates time-reversal (T) symmetry. Although such a dipole has not yet been detected, mainstream theories of possible new physics, such as Supersymmetry, predict the existence of EDMs within reach of modern experiments. After a brief introduction to EDM experiments and their implications for the existence of new T-violating (and hence CP-violating) interactions, we review recent work on our own EDM experiment with mercury atoms at the University of Washington, describing the newest version of this experiment and discussing current measurements. We have instituted a fixed blind offset that permits us to test for systematic errors while insuring that any cuts in the data are made objectively. Compared with our 2001 result |d(¹⁹⁹Hg)| < 2.1 × 10^-28 e cm, an improvement by a factor of 5 to 10 should be forthcoming, thereby probing yet further for expected new physics.

Fundamental interaction studies at low energy can benefit from the unique properties of certain radioactive ion species. The proposed FRIB facility, an evolution on the RIA concept, will be the highest intensity source for most rare isotope species and fundamental interaction studies will be an important part of its physics program. The FRIB concept will be described and its expected capabilities for fundamental interaction studies highlighted with some illustrative examples.

A facility for collinear laser spectroscopy and beam polarization of exotic nuclei is being developed at NSCL. The facility will make use of thermalized rare isotope beams available at NSCL from projectile fragmentation and in-flight separation with subsequent gas stopping. This system provides access to new and unexplored territory in the nuclear chart and will be implemented at the next generation rare isotope facility. Laser spectroscopy and β NMR/NQR techniques will be utilized to determine nuclear charge radii and nuclear ground state electromagnetic moments as well as for fundamental interaction tests.

We construct a class of scalar field models coupled to matter that lead to the dependence of masses and coupling constants on the ambient matter density. Such models predict a deviation of couplings measured on the Earth from values determined in low-density astrophysical environments, but do not necessarily require the evolution of coupling constants with the redshift in the recent cosmological past. Additional laboratory and astrophysical tests of Δα and Δ(m_p/m_e) as functions of the ambient matter density are warranted.

Workshop Program