Determination of the Neutron-Neutron Scattering Length from the Reactionπ−+d→2n+γ

The photon energy spectrum from the reaction ${\pi }^{-}+d\to 2n+\gamma$ at zero energy has been measured by a pair spectrometer using accoustic spark chambers to locate the pair-electron tracks. From the shape of the spectrum the neutron-neutron scattering length was determined to be $a_{\mathrm{nn}}={13.1}_{+2.4\mathrm{}}^{-3.4\mathrm{}}$. The probability of existence of a bound state of two neutrons was calculated to be less than 5 × ${10}^{-9\mathrm{}}$.