This paper cited by :
- "An apparatus to search for mirror dark matter via the invisible decay of orthopositronium in vacuum", A.Badertscher, A. Belov, P. Crivelli, M. Felcini, W. Fetscher, S.N. Gninenko, N.A. Golubev, M.M. Kirsanov, L.L. Kurchaninov, J.P. Peigneux, A. Rubbia, D. Sillou, Int.J.Mod.Phys.A19:3833-3848,2004; e-Print Archive: hep-ex/0311031