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The Beta-Neutrino Correlation in Sodium-21 and Other Nuclei

Description: We have measured the mbox beta - nu correlation coefficient,a_beta nu, in 21Na using a laser-trapped sample. We measure the energyspectrum of the recoil nuclei by measuring their time-of-flight incoincidence with the atomic electrons shaken off in beta decay. Highdetectionefficiency of these low-energy electrons allows good countingstatistics, even with low trap density, which suppresses thephotoassociation of molecular sodium, which can cause a large systematicerror. Our measurement, with a 1 percent fractional uncertainty, agreeswith the Standard Model prediction but disagrees with our previousmeasurement which was susceptible to error introduced by molecularsodium. We summarize precise measurements of a_ beta nu and theirconsequences for searches for Beyond Standard Model scalar and tensorcurrent couplings.
Date: January 16, 2008
Creator: Vetter, Paul A.; Abo-Shaeer, Jamil; Freedman, Stuart J. & Maruyama, Reina
Partner: UNT Libraries Government Documents Department

Measurement of the beta-neutrino correlation of sodium-21 usingshakeoff electrons

Description: The beta-neutrino correlation coefficient, a_beta nu, ismeasured in 21Na by detecting the time-of-flight of the recoil nucleusdetected in coincidence with the atomic electrons shaken off in betadecay. The sample of 21Na is confined in a magneto-optic trap. Highdetection efficiency allows low trap density, which suppresses thephotoassociation of molecular sodium, which can cause a large systematicerror. Suppressing the fraction of trapped atoms in the excited stateusing a dark trap also reduces the photoassociation process, and datataken with this technique are consistent. The main remaining systematicuncertainties come from the measurement of the position and size of theatom trap, and the subtraction of background. We find mbox a_betanu=0.5502(60), in agreement with the Standard Model prediction of mboxa_beta nu=0.553(2), and disagreeing with a previous measurement which wassusceptible to an error introduced by the presence of molecularsodium.
Date: January 16, 2007
Creator: Vetter, Paul A.; Abo-Shaeer, Jamil R.; Freedman, Stuart J. & Maruyama, Reina
Partner: UNT Libraries Government Documents Department