Gericke M T, Baeßler S, Barrón-Palos L, Birge N, Bowman J D, Calarco J, Cianciolo V, Coppola C E, Crawford C B, Fomin N, Garishvili I, Greene G L, Hale G M, Hamblen J, Hayes C, Iverson E, Kabir M L, McCrea M, Plemons E, Ramírez-Morales A, Mueller P E, Novikov I, Penttila S, Scott E M, Watts J, Wickersham C
University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
University of Virginia, Charlottesville, Virginia 22904, USA.
Phys Rev Lett. 2020 Sep 25;125(13):131803. doi: 10.1103/PhysRevLett.125.131803.
We report the first precision measurement of the parity-violating asymmetry in the direction of proton momentum with respect to the neutron spin, in the reaction ^{3}He(n,p)^{3}H, using the capture of polarized cold neutrons in an unpolarized active ^{3}He target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the least well-understood aspects of electroweak theory. The measurement provides an important benchmark for modern effective field theory and potential model calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is A_{PV}=[1.55±0.97(stat)±0.24(sys)]×10^{-8}, which has the smallest uncertainty of any hadronic parity-violating asymmetry measurement so far.
我们报告了在反应³He(n,p)³H中，利用极化冷中子在非极化活性³He靶中的俘获，首次精确测量了质子动量方向相对于中子自旋的宇称破坏不对称性。这种不对称性是核子间弱相互作用的结果，而弱相互作用仍是电弱理论中最难以理解的方面之一。该测量为现代有效场理论和势模型计算提供了一个重要的基准。这样的测量对于确定强子弱相互作用的自旋同位旋结构是必要的。我们得到的不对称性结果为APV = [1.55±0.97(统计)±0.24(系统)]×10⁻⁸，这是迄今为止所有强子宇称破坏不对称性测量中不确定性最小的。
