학술논문
First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He
Document Type
Working Paper
Author
n3He Collaboration; Gericke, M. T.; Baeßler, S.; Barrón-Palos, L.; Birge, N.; Bowman, J. D.; Britton Jr., C.; Calarco, J.; Cianciolo, V.; Coppola, C. E.; Crawford, C. B.; Ezell, D.; Fomin, N.; Garishvili, I.; Greene, G. L.; Hale, G. M.; Hamblen, J.; Hayes, C.; Iverson, E.; Kabir, M. L.; McCrea, M.; Mueller, P. E.; Novikov, I.; Penttila, S.; Plemons, E.; Ramírez-Morales, A.; Scott, E. M.; Watts, J.; Wickersham, C.
Source
Phys. Rev. Lett. 125, 131803 (2020)
Subject
Language
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.