First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He

n3He Collaboration; M. T. Gericke; S. Baeßler; L. Barrón-Palos; N. Birge; J. D. Bowman; C. Britton Jr.; J. Calarco; V. Cianciolo; C. E. Coppola; C. B. Crawford; D. Ezell; N. Fomin; I. Garishvili; G. L. Greene; G. M. Hale; J. Hamblen; C. Hayes; E. Iverson; M. L. Kabir; M. McCrea; P. E. Mueller; I. Novikov; S. Penttila; E. Plemons; A. Ramírez-Morales; E. M. Scott; J. Watts; C. Wickersham

doi:10.1103/physrevlett.125.131803

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arXiv · 2004.11535

First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He

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Abstract

We report the first precision measurement of the parity-violating asymmetry in the direction of proton emission with respect to the neutron spin, in the reaction $^{3}\mathrm{He}(\mathrm{n},\mathrm{p})^{3}\mathrm{H}$, using the capture of polarized cold neutrons in an unpolarized active $^3\rm{He}$ target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the most poorly understood aspects of electro-weak theory. The measurement provides an important benchmark for modern effective field theory (EFT) calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is $A_{PV} = \left( 1.58 \pm 0.97 ~\mathrm{(stat)} \pm 0.24~\mathrm{(sys)}\right)\times10^{-8}$, which has the smallest uncertainty of any parity-violating asymmetry measurement so far.

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n3He Collaboration, M. T. Gericke, S. Baeßler, L. Barrón-Palos, N. Birge, J. D. Bowman, C. Britton Jr., J. Calarco, V. Cianciolo, C. E. Coppola, C. B. Crawford, D. Ezell, N. Fomin, I. Garishvili, G. L. Greene, G. M. Hale, J. Hamblen, C. Hayes, E. Iverson, M. L. Kabir, M. McCrea, P. E. Mueller, I. Novikov, S. Penttila, E. Plemons, A. Ramírez-Morales, E. M. Scott, J. Watts, C. Wickersham. 2020-04-24. First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He. https://doi.org/10.1103/physrevlett.125.131803

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