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Observation of the radiative decay mode of the free neutron

机译：观察自由中子的辐射衰减模式

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摘要

The theory of quantum electrodynamics (QED) predicts that beta decay of the neutron into a proton, electron and antineutrino should be accompanied by a continuous spectrum of soft photons. While this inner bremsstrahlung branch has been previously measured in nuclear beta and electron capture decay, it has never been observed in free neutron decay. Recently, the photon energy spectrum and branching ratio for neutron radiative decay have been calculated using two approaches: a standard QED framework(1-3) and heavy baryon chiral perturbation theory(4) (an effective theory of hadrons based on the symmetries of quantum chromodynamics). The QED calculation treats the nucleons as point-like, whereas the latter approach includes the effect of nucleon structure in a systematic way. Here we observe the radiative decay mode of free neutrons, measuring photons in coincidence with both the emitted electron and proton. We determined a branching ratio of (3.13 +/- 0.34) x 10(-3) (68 per cent level of confidence) in the energy region between 15 and 340 keV, where the uncertainty is dominated by systematic effects. The value is consistent with the predictions of both theoretical approaches; the characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the calculated spectrum. This result may provide opportunities for more detailed investigations of the weak interaction processes involved in neutron beta decay.
机译：量子电动力学理论（QED）预测，中子的β衰减为质子，电子和反中微子应伴随着连续光谱的软光子。尽管内部inner致辐射分支先前已通过核β和电子俘获衰变进行了测量，但从未在自由中子衰变中进行过观察。近来，中子辐射衰变的光子能谱和支化比已通过两种方法计算出来：标准QED框架（1-3）和重子重子手性扰动理论（4）（基于量子对称性的强子的有效理论）色动力学）。 QED计算将核子视为点状，而后一种方法以系统的方式包括核子结构的影响。在这里，我们观察自由中子的辐射衰减模式，测量与发射电子和质子同时发生的光子。我们在15至340 keV之间的能量区域中确定了（3.13 +/- 0.34）x 10（-3）（68％的置信度）的分支比，其中不确定性受系统效应支配。该值与两种理论方法的预测均一致。辐射光子的特征能谱与不相关的背景光谱不同，也与计算出的光谱一致。这一结果可能为中子β衰变所涉及的弱相互作用过程的更详细研究提供机会。

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  • 来源
    《Nature》 |2006年第7122期|p. 1059-1062|共4页
  • 作者

    Nico JS; Dewey MS; Gentile TR; Mumm HP; Thompson AK; Fisher BM; Kremsky I; Wietfeldt FE; Chupp TE; Cooper RL;

  • 作者单位

    Natl Inst Stand & Technol, Phys Lab, Gaithersburg, MD 20899 USA;

    Tulane Univ, Dept Phys, New Orleans, LA 70118 USA;

    Univ Michigan, FOCUS, Ann Arbor, MI 48109 USA;

    Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA;

    Univ Maryland, Dept Phys, College Pk, MD 20742 USA;

    Univ Sussex, Dept Phys & Astron, Brighton BN1 9QH, E Sussex, England;

    Natl Inst Stand & Technol, Informat Technol Lab, Boulder, CO 80305 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然科学总论;
  • 关键词

    BETA-DECAY; MASS SINGULARITIES; LOW-TEMPERATURE;

    机译：Beta衰减;大量奇异;低温;

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