Search and Measurement of P -Odd Asymmetry in the Emission of Secondary Particles Produced in Reactions of Polarized Thermal and Cold Neutrons with Light Nuclei

Investigation of spatial parity in reactions of polarized neutrons with light nuclei is an important topic in the framework of exploring the fundamental problem of understanding the manifestation of the weak interaction in nuclear reactions and for estimating the parameters of the weak nucleon–nucleon interaction. In this paper, the ongoing experimental program of highly sensitive and high-precision measurements of P‑odd asymmetries in the reactions of polarized thermal and cold neutrons with lithium and boron nuclei is reviewed. Within this program, the coefficients of P-odd asymmetry of reaction products in the reactions induced by cold- and thermal-neutrons on the isotopes of light nuclei 6Li and 10B were measured with record-high sensitivity ~10–8 as $$\alpha _{{P{\text{ - odd}}}}^{{^{{\text{6}}}{\text{Li}}{\text{,exp}}}} = - (8.8 \pm 2.1) \times {{10}^{{ - 8}}}$$ , $$\alpha _{{P{\text{ - odd}}}}^{{^{{10}}{\text{B}},\gamma ,\exp }} = (0.0 \pm {{2.6}_{{{\text{stat}}.}}} \pm {{1.1}_{{{\text{syst}}{\text{.}}}}}) \times {{10}^{{ - 8}}},$$ and $$\alpha _{{P{\text{ - odd}}}}^{{{{\alpha }_{0}} + {{\alpha }_{1}}{{,}^{{10}}}B,\exp }} = - (11.2 \pm 3.4) \times {{10}^{{ - 8}}}$$ . For the first time ever, nonzero values were obtained for two of these asymmetries. Our data for tritium emission in the $$^{6}{\text{Li(}}n,a{{)}^{3}}{\text{H}}$$ reaction and γ emission in the $$^{{10}}{\text{B}}{{(n,a)}^{{74}}}{\text{Li}}^{*} \to \gamma \to {{\,}^{7}}{\kern 1pt} {\text{Li(gr}}{\text{.st}}{\text{.)}}$$ reaction agree with those of other experiments when interpreted within the cluster model, but rule out the so-called “best DDH values” of weak-interaction coupling constants. Interpreting the data on these reactions relying on “first principles” only would be highly desirable.