Fundamental Symmetries
As part of the New Standard Model Initiative, TUNL researchers are seeking to shed
light on fundamental questions such as
Why is there now more visible matter than
antimatter in the universe? and What modifications to the
electroweak interaction are needed as we develop the New
Standard Model? To answer such questions, TUNL researchers are seeking to perform an
improved measurement of the permanent electric dipole moment (EDM) of
the neutron, as well as continuing in a program of
studies of weak decays of neutrons and nuclei.
The matter-antimatter asymmetry that arose during the formation of the
early universe could be a result of charge-conjugation-parity (CP)
violating interactions that occurred during the electroweak
symmetry-breaking phase transition. If such electroweak baryogenesis
occurred, new CP-violating interactions must exist beyond what is
observed in the neutral kaon and B-meson systems. Almost all new
extensions to the Standard Model predict significantly larger EDMs,
thus making EDM searches powerful probes of new electroweak CP
violation.
To date, extremely precise searches for permanent EDMs of the
electron, neutron, and atoms have yielded null results as
expected from the Standard Model. We are now in a regime, however,
where improvements in sensitivity offer significant
discovery potential associated with the θ-term of QCD and CP
violation on the electroweak scale.
The review of neutron science in the US captures the importance of the
EDM experiment: The successful
completion of an nEDM experiment, the initiative
with the highest scientific priority in US neutron science, would
represent an impressive scientific and technical
achievement for all of nuclear physics, with ramifications well beyond
the field.
Engineering model of the neutron EDM experiment. The neutron beam enters from the left and is incident upon two measurement cells positioned between the central high voltage electrode (red, center) and two ground planes. The constant magnetic field is in the horizontal plane and perpendicular to the beam direction. The horizontal section of the apparatus also contains the 1,000~l helium electrical insulation volume and additional magnetic coils as well as cryogenic and superconducting magnetic shielding. The vertical section of the apparatus houses the dilution refrigerator, helium injection volume, as well as the safety vent system. The entire cryovessel is surrounded by four layers of magnetic shielding. For scale, the height of the beamline is approximately 2m.
TUNL nEDM Activities
TUNL scientists play key roles in next generation measurements in fundamental symmetries tests. We lead efforts in the search for a neutron electric dipole moment, as well as measurements of the neutron lifetime and beta-decay asymmetry coefficients. In addition, we are developing an ultracold neutron source for next-generation beta-decay experiments as well as these experiments themselves.