INTERNATIONAL STATEMENT ON NEUTRINOLESS DOUBLE-BETA DECAY An Open Letter to Nuclear, Particle, and Astro Physics Communities. We, the undersigned, have met on a number of occasions to discuss the status of neutrinoless double-beta decay (DBD) and to endorse a coordinated approach to executing next-generation DBD probes for fundamental properties of neutrinos. Recent works of neutrino oscillation experiments indicate that next generation neutrinoless DBD experiments have excellent physics potential. Next-generation efforts can shed much-needed light on fundamental properties of neutrinos beyond the standard electro-weak theory. We agree with the following points in order to carry out successful next-generation DBD experiments for the neutrino properties. 1). Fundamental neutrino properties to be studied by DBD include the Majorana nature of neutrinos and the lepton number non-conservation, the type of mass spectrum, the absolute neutrino mass scale, possibly the CP violation, and others. Actually, performing neutrinoless DBD experiments is the only practical method for studying all these important properties of neutrinos in the foreseeable future. Imformation on the absolute scale of neutrino masses can be obtained by tritium beta-decay experiments. 2). The data from Super-K, SNO and others, together with their theoretical analyses, clearly imply that next-generation DBD experiments with the mass sensitivities of the order of 10 meV should discover non-zero effective Majorana electron neutrino mass if the massive neutrinos are Majorana particles and the neutrino mass spectrum is of the quasi-degenerate type or with inverted hierarchy. In fact, many theories of the fundamental particle interactions predict that the massive neutrinos are Majorana in nature. DBD experiments with even higher sensitivities of the order of meV are of potential interest for further studies of the absolute neutrino mass scale and possibly of the CP violation. 3). The present running experiments and the improvements are important by themselves and are considered to be very significant steps for future detectors with higher sensitivities. 4). Neutrinoless DBD events are extremely rare low-energy processes. Accordingly the DBD experiments require necessarily large amounts of DBD isotopes, large-scale low-background detectors and very stringent selection of the signal from background events. The signal rate depends on the nuclear matrix element as well. International collaboration of the experimental groups, presently working on DBD, for performing successful new generation DBD experiments are indispensable. 5). The observation of a statistically significant signal in a single experiment cannot be considered as a discovery without clear confirmation from at least one or two independent experiments utilizing different isotopes and methods. 6). Nuclear matrix elements for neutrinoless DBD are crucial for extracting the effective Majorana mass parameter and others from the observed DBD rates. Improvements of the precision in theoretical evaluations of the matrix elements are important, and can be pursued by coherent works of nuclear theory groups. Experimental studies of nuclear structures, relevant to DBD, help perform adequate calculations of the matrix elements. 7). There are a number of natural and enriched isotopes that could be used for experiments in the range of hundreds of kilograms. These isotopes have been used in previous experiments and have the properties that allow the construction of large practical detectors. It is important to cooperate internationally to ensure that at least one experiment could be done involving each promising isotope and to accelerate its development for a full-scale next-generation experiment. 8) The sensitivities required of next generation DBD experiments can only be achieved in deep underground clean laboratory space. Radon-free clean room environments will be required for detector assembly, repair, operation, and other related works for low background studies. Such a laboratory should be open to the international science community. 9). DBD is considered to be an important physics subject at the intersection of nuclear and particle physics with a great impact on the fields of astrophysics and cosmology. Thus the future DBD experiments should be discussed among the communities of these fields as well. In recent years a growing sense of community has emerged in the DBD and neutrino physics fields. It is in this spirit that we, the undersigned, agree to form an international DBD network in order to endorse a coordinated approach to executing successful next-generation DBD probes of the fundamental neutrino properties. Sincerely yours Nov. 22, 2002 Avignone Frank USC titus3@mac.com Barabash Alexander ITEP barabash@vitep1.itep.ru Ejiri Hiro Osaka ejiri@rcnp.osaka-u.ac.jp Faessler Amand Tubingen Faessler@uni-tubingen.de Elliott Steve LANL elliotts@lanl.gov Fiorini Ettore Milano ettore.fiorini@mib.infn.it Haxton Wick UW HAXTON@emmy2.phys.washington.edu Gratta Giorgio Stanford gratta@stanford.edu Jullian Serge Orsay jullian@axs.lal.in2p3.fr Kochetov Oleg JINR kochet@nusun.jinr.ru Lalanne Dominique Orsay lalanne@lal.in2p3.fr Minakata Hisakazu TMU minakata@phys.metro-u.ac.jp Morales Angel Zaragoza amorales@posta.unizar.es Morales Julio Zaragoza Julio.Morales@posta.unizar.es Petcov Serguey Trieste petcov@he.sissa.it Simkovic Fedor Comenius simkovic@raptor.dnp.fmph.uniba. Suhonen Jouni Jyuvaskyla jouni.suhonen@phys.jyu.fi Hiro Ejiri ejiri@pop07.odn.ne.jp 81-468-56-8726 ejiri@spring8.or.jp 81-791-58-0954 ejiri@rcnp.osaka-u.ac.jp 81-6-6879-8908