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

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 ${}^3\mathrm{He}$ 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 $A_{PV}=\left(1.58\pm 0.97(\mathrm{stat})\pm 0.24(\mathrm{sys})\right)\times 10^{-8}$, which has the smallest uncertainty of any parity-violating asymmetry measurement so far.

References in corpus (5)

• The parity-violating nucleon-nucleon force in the 1/N_c expansion
• Fundamental Neutron Physics Beamline at the Spallation Neutron Source at ORNL
• A chiral effective field theory study of hadronic parity violation in few-nucleon systems
• The parity-violating asymmetry in the 3He(n,p)3H reaction
• Experimental Upper Bound and Theoretical Expectations for Parity-Violating Neutron Spin Rotation in 4He