Bales M J, Alarcon R, Bass C D, Beise E J, Breuer H, Byrne J, Chupp T E, Coakley K J, Cooper R L, Dewey M S, Gardner S, Gentile T R, He D, Mumm H P, Nico J S, O'Neill B, Thompson A K, Wietfeldt F E
University of Michigan, Ann Arbor, Michigan 48104, USA.
Physikdepartment, Technische Universität München, D-85748, Germany.
Phys Rev Lett. 2016 Jun 17;116(24):242501. doi: 10.1103/PhysRevLett.116.242501. Epub 2016 Jun 14.
The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the β decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782 keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335±0.00005[stat]±0.00015[syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14 keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582±0.00023[stat]±0.00062[syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.
标准模型预测，在自由中子的β衰变中，除了一个质子、一个电子和一个反中微子外，还会发射出连续光谱的光子。我们报告了RDK II实验，该实验使用两种不同的探测器阵列测量了光子光谱。一个由铋锗氧化物闪烁体组成的环形阵列探测到了能量在14至782 keV之间的光子。光谱形状与理论一致，我们确定了分支比为0.00335±0.00005[统计]±0.00015[系统]。第二个由大面积雪崩光电二极管组成的探测器阵列直接探测到了能量在0.4至14 keV之间的光子。对于这个阵列，光谱形状与理论一致，分支比被确定为0.00582±0.00023[统计]±0.00062[系统]。我们报告了对中子辐射衰变产生的光子能谱形状的首次精确测试，以及在广泛的光子能量范围内对分支比的大幅改进测定。
