Open Collections

Feasibility test of exotic particle searches in the decay of trapped rubidium isomers

University of British Columbia

We tested the feasibility of searching for exotic particle emissions in the decay of trapped Rb isomers by measuring the recoiling momentum of the decay daughters. Massive particle emissions would cause the daughters to recoil at a momentum less than the case of a photon emission, and show up as a lower peak in the recoiling momentum spectrum. ⁸⁶mRb isomer decay (6- → 2-) was chosen as the experimental subject, which allows a search for 0⁺ and 1- massive particles with a mass range between 0 and 556 keV/c². To measure the recoiling momentum of the neutral Rb-⁸⁶g decay daughters, they must first be photoionized to be collected by the spectrometer and detected by the MCP detectors. The photoionization scheme is a two-stepwise procedure, including Doppler-free two-photon transitions from the 5S₁/₂ to 5D₅/₂ states by a 778 nm laser, and from the 5D₅/₂ state into continuum by a 1064 nm laser. The recoiling momenta of the Rb-⁸⁶g decay daughters were reconstructed by measuring the Rb ions' time-of-flight and transverse displacements on the ion detector. The achieved momentum resolution for the 556 keV/c photoions is 15(3) keV/c, which is twice the expectation due to the sagging of the spectrometer mesh. Because of the photoionization rate limitation, the achieved sensitivity is at 10% decay branch compared to gamma emissions. A feasibility study to improve the sensitivity to 10-⁵ level is outlined and compared to the conventional experiments in this field. The exotic particle search experiment requires the isotope shift knowledge for efficiently driving Doppler-free two-photon transitions in radioactive Rb isotopes. In total, we measured isotope shifts of the 5S₁/₂ to 5D₅/₂ transition for three Rb isotopes, δν{⁸⁶m,⁸⁷} = -69.46(3) MHz, δν{⁸⁶g,⁸⁷} = -83.62(2) MHz and δν{⁸¹g,⁸⁷} = -552.34(27) MHz. The precision we achieved in the isotope shift measurements allows us to deduce the specific mass shifts between the 5S₁/₂ and 5D₅/₂ states with 4 - 28 MHz precision by making a King plot. This provides a benchmark for the isotope shift calculations needed for the cosmological tests of time and space variations of the fine structure constant Alpha by astrophysical spectroscopy of alkali-like species.

Text

2012-12-21

Attribution-NonCommercial-NoDerivs 3.0 Unported

http://hdl.handle.net/2429/43743

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/3.0/