Neutron-neutron scattering length from the reaction γd → πnn employing chiral perturbation theoryV. Lensky, V. Baru, E. Epelbaum, C. Hanhart, J. Haidenbauer, A. Kudryavtsev and U. -G. MeißnerEur. Phys. J. A, 33 4 (2007) 339-348DOI: https://doi.org/10.1140/epja/i2007-10461-y