Precision Neutron Decay Measurements

自由中子是不稳定的，通过弱相互作用衰变为质子、电子和反中微子，平均寿命约为15分钟。通过测量发射粒子和中子自旋的能量和方向，揭示了潜在相互作用的细节。 我们让一束冷中子（运动速度小于2000 m/s）通过一种装置，该装置是为了精确测量中子衰变寿命和角关联而设计的。由于中子衰变是一个相对简单的系统，没有复杂的核子波函数，这些观测值直接和明确地与基本理论参数有关。我们使用这些结果来测试标准电弱模型的预测，并寻找新物理的证据，如标量/张量力或新的CP破坏。中子寿命的精确值是计算早期宇宙中由大爆炸核合成产生的轻元素的原始丰度所必需的。中子是普通物质的关键组成部分。当从原子的束缚中释放出来时，中子是不稳定的，会衰变成其他基本粒子：质子、电子和称为反中微子的轻质中性粒子。中子衰变是一个有用的实验室，可以用来研究弱核力的细节，弱核力是自然界四种基本力之一。我们让一束自由中子通过专门的探测器，精确测量中子衰变率和发射粒子之间的角度。从这一点上，我们可以测试和完善我们的弱核力理论，更好地理解太阳、恒星、大爆炸和重要核反应的物理学。

A free neutron is unstable and decays via the weak interaction into a proton, electron, and antineutrino with a mean lifetime of about 15 minutes. By measuring the energies and directions of the emitted particles and the neutron spin, details of the underlying interaction are revealed. We pass a beam of cold neutrons (moving less than 2000 m/s) through apparatus designed to make precise measurements of the neutron decay lifetime and angular correlations. Beause neutron decay is a relatively simple system, absent the complications of nuclear wave functions, these observables are related to fundamental theoretical parameters directly and unambiguously. We use these results to test predictions of the Standard Electroweak Model and search for evidence of new physics such as scalar/tensor forces or new CP-violation. The precise value of the neutron lifetime is needed to calculate the primordial abundances of light elements produced in the early universe from Big Bang nucleosynthesis.The neutron is a key building block of ordinary matter. When freed from the confines of an atom, the neutron is unstable and will decay into other elementary particles: a proton, an electron, and a lightweight neutral particle called an antineutrino. Neutron decay is a useful laboratory for studying details of the force responsible - the weak nuclear force - one of the four fundamental forces of nature. We pass a beam of free neutrons through specialized detectors that precisely measure the neutron decay rate and the angles between the emitted particles. From this we can test and refine our theory of the weak nuclear force and better understand the physics of the sun, stars, the Big Bang, and important nuclear reactions.