Improved determination of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>β</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mover><mml:mi>ν</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi>e</mml:mi></mml:msub></mml:mrow></mml:math> angular correlation coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi></mml:math> in free neutron decay with the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi><mml:mi>SPECT</mml:mi></mml:math> spectrometer
M. Beck, F. Ayala Guardia, M. Borg, J. Kahlenberg, Raquel Muñoz Horta, Ch. Schmidt, Alexander Georg Wunderle, W. Heil, R. Maisonobe, Martin Simson, T. Söldner, R. Virot, O. Zimmer, Michael Klopf, Gertrud Konrad, S. Baeßler, F. Glück, Ulrich Schmidt
Abstract
This work presents the until now most precise measurement of the angular correlation coefficient $a$ between the momenta of the electron and the electron-antineutrino in free neutron decay. The coefficient $a$ is inferred from a detailed analysis of the integral proton recoil spectrum measured with the $a$SPECT setup, a MAC-E-Filter type spectrometer with $4\ensuremath{\pi}$ acceptance. The result can be used to determine the axial-vector coupling constant ${g}_{A}$ in the weak interaction and shows a tantalizing disagreement with recent measurements of ${g}_{A}$ via the $\ensuremath{\beta}$-decay asymmetry in neutron decay.