New results on P -odd asymmetry of $ \gamma$ -quanta emission in 10B(n, $ \alpha$ )7Li* $ \rightarrow$ $ \gamma$ + 7Li(g.s.) nuclear reaction

Abstract

A series of ultra-sensitive experiments has been carried out in 2001-2009 at the ILL measuring P -odd asymmetry in \( \gamma\) -quanta emission in the nuclear reaction 10B (n,\( \alpha\)) 7Li*\( \rightarrow\)\( \gamma\) + $7Li$(g.s.) with polarized cold neutrons. The resulting value of the asymmetry coefficient is \(\ensuremath \alpha_{P\mbox{-}{\rm odd}}= +(0.0 \pm 2.6_{{\rm stat}} \pm 1.1_{{\rm syst}}) \times 10^{-8}\) . These experiments profited from high-intensity PF1B neutron facility and a new version of the integral measuring method: for decreasing experimental uncertainties, the frequency of neutron spin-flip was higher than a typical reactor power noise frequency. Using the new value, we constrain the weak neutral current constant in the cluster model framework to \(\ensuremath f_{\pi}^{^{10}\rm B} \leq 0.6 \times 10^{-7}\) (at 90% c.l.). This constraint agrees with that following from the nuclear reaction 6Li (n,\( \alpha\)) 3H : \(\ensuremath f_{\pi}^{^{6}\rm Li} \leq 1.1 \times 10^{-7}\) (at 90% c.l.). However, they both contradict the “best” value in the quark model by Desplanques, Donoughe, and Holstein \(\ensuremath f_{\pi}^{{\rm DDH}}=4.6\cdot 10^{-7}\) . We invite experts in the field to contribute to the theoretical analysis of the problem.