Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin 53706, USA and INFN, Laboratori Nazionali di Frascati, I-00044 Frascati, Italy.
Department of Physics and Astronomy, University of Sussex, BN1 9QH Brighton, United Kingdom and Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0319, USA and PRISMA Cluster of Excellence Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany.
Phys Rev Lett. 2014 Jan 31;112(4):042501. doi: 10.1103/PhysRevLett.112.042501. Epub 2014 Jan 28.
We discuss the consequences of the approximate conservation of the vector and axial currents for the hadronic matrix elements appearing in β decay if nonstandard interactions are present. In particular, the isovector (pseudo)scalar charge gS(P) of the nucleon can be related to the difference (sum) of the nucleon masses in the absence of electromagnetic effects. Using recent determinations of these quantities from phenomenological and lattice QCD studies we obtain the accurate values gS=1.02(11) and gP=349(9) in the modified minimal subtraction scheme at μ=2 GeV. The consequences for searches of nonstandard scalar interactions in nuclear β decays are studied, finding for the corresponding Wilson coefficient εS=0.0012(24) at 90% C.L., which is significantly more stringent than current LHC bounds and previous low-energy bounds using less precise gS values. We argue that our results could be rapidly improved with updated computations and the direct calculation of certain ratios in lattice QCD. Finally, we discuss the pion-pole enhancement of gP, which makes β decays much more sensitive to nonstandard pseudoscalar interactions than previously thought.
我们讨论了在存在非标准相互作用的情况下，矢量和轴电流的近似守恒对β衰变中出现的强子矩阵元的影响。特别是，核子的同位旋（赝）标量荷 gS(P)可以与不存在电磁效应时核子质量的差（和）相关联。利用最近从唯象学和格点 QCD 研究中对这些量的确定，我们在修正的最小减除方案中得到了μ=2 GeV 时精确的数值 gS=1.02(11)和 gP=349(9)。研究了在核β衰变中寻找非标准标量相互作用的结果，发现相应的威尔逊系数 εS=0.0012(24)在 90%置信区间内，这比当前 LHC 界限和以前使用不太精确的 gS 值的低能界限严格得多。我们认为，通过更新计算和在格点 QCD 中直接计算某些比值，我们的结果可以迅速得到改善。最后，我们讨论了 gP 的π极点增强，这使得β衰变对非标准赝标量相互作用比以前认为的更为敏感。
