Towards a Measurement of the Electric Dipole Moment ofRn.

[摘要] The observed baryon asymmetry in the universe requires a greater degree of CPviolation than is contained in the CP-violating Standard Model processes discoveredthus far. Since the permanent electric dipole moment (EDM) of a particle, atom, ormolecule is a CP-odd observable, any nonzero measurement of an EDM above thesmall Standard Model background would indicate a new source of CP violation. Thenuclear structure of 223Rn is expected to enhance its sensitivity to CP-violating interactionsrelative to 199Hg, currently the most sensitive atomic EDM result, motivatingthe development of the Radon EDM experiment.In anticipation of radon production at TRIUMF, we performed a series of studiesto improve the design and predict the expected precision of the Radon EDM experiment.We designed and tested a prototype gas transfer apparatus that collectsa sample of noble gas from a beam and transfers it to a measurement cell, achievinga transfer efficiency of about 40%. We recently improved this to greater than90%. We studied the polarization and relaxation of radon using samples of 209Rnproduced at SUNY Stony Brook’s Nuclear Structure Laboratory and polarized it viaspin-exchange with optically pumped rubidium. We constructed equations for theanisotropy of the gamma rays emitted by polarized 209Rn as a function of the rubidiumpolarization, the spin-exchange cross section σSE, the wall-binding temperatureT0, the quadrupole relaxation rate Γ∞2 , and the cell temperature. Using rubidiumpolarization values measured by electron spin resonance, our radon polarization dataindicated that a silane-based wall coating improved the relaxation rate in our cells.For T0 = 350 K and σSE = 2.5×10−5˚A2, we found Γ∞2 = 0.14±0.02 Hz in uncoatedcells and Γ∞2 = 0.042 ± 0.012 Hz in coated cells. We used the coated-cell resultsto obtain a conservative estimate of the Radon EDM precision, 3 × 10−26e · cm atTRIUMF using gamma-ray anisotropies. Coupled with the enhancement effects, thisindicates sensitivity to CP violation similar to that of 199Hg in the first phase of theRadon EDM experiment.

[发布机构] University of Michigan

[效力级别] Radon

[关键词] Electric Dipole Moment;Radon;Gamma-ray Anisotropies;Adiabatic Fast Passage;Physics;Science;Physics