Measurement of the neutrino asymmetry in the β decay of laser-cooled, polarized 37K

A measurement of the. neutrino asymmetry is presented which represents the first search for new physics using polarized radioactive atoms initially cooled and confined in a magneto-optical trap. Optical pumping and photoionization techniques are used to generate and measure, in situ, a highly spin-polarized (96.5(0.8)%) sample of the short-lived beta(+)-emitter K-37. The angular distribution of neutrinos from this polarized decay, inferred from the daughter recoil asymmetry, is used to search for a hypothetical V + A current in the weak interaction. We find the v asymmetry parameter to be B-nu = -0.755 +/- 0.020(stat) +/- 0.013(syst), in agreement with the standard model's purely V-A interaction. (c) 2007 Elsevier B.V. All rights reserved.