ILIASN4 Cascina, November 3rd, 2005Dominique Lalanne

N4 Working group 1 : Working group 1 : coordination of double beta decay searches Working group 2 : Working group 2 : bank of pure isotopes Working group 3 : Working group 3 : theoretical developments

N4 – Table 2: Deliverables WG1- preliminary report on techniques et background issues WG2- report on the recommended program, first conclusions on isotope selection and contact with Russian WG3- first conclusions on theoretical issuesWP3JYU66

WG1 : coordination of double beta decay searches Co-ordinator : Fabrice Piquemal, CENBG, IN2P3, France The status of the double beta decay experiment is the following. The Cuoricino experiment is running and some improvement have been made on the understanding of backgrounds. The R&D for the CUORE is on the way with in particular improvement of surface cleaning, rejection methods et development of new bolometers. The GERDA experiment with enriched Ge diodes is in construction in Gran Sasso. The NEMO 3 detector continues to take data with the system to remove the radon from air surrounding the detector so decreasing the background due to radon at the requirement. The SuperNEMO project enters in a new phase. This project has been accepted by IN2P3 and PPARC and a financial support is given for a 3 year R&D programme. The SuperNEMO detector will use the same techniques as NEMO 3. This program concerns mainly the improvement of the calorimeter, the production and purification of enriched selenium (supported by ILIAS), the development of new detector to measure radiopurity at the required levels for the source foil (BiPo detector) and the radon level in the gas, the making of the thin ultra-pure source foil and the improvement of the tracking device. On the other hand, the two R&D program COBRA with ZnCdTe crystal and EDELWEISS or Ge bolometers are in progress.

WG2 : Bank of pure isotopes. Co-ordinator : Ezio Previtali, INFN, Milano, Italy During the first 18 months of activity the “Bank of pure Isotope” working group had collected a large part of information regarding the actually existing isotopes produced in the past for double beta decay experiment. This collection of information is reported in the table at the end of this document. In the table is clearly reported that some data are well established but some others not. During the last six months we had tried to solve these problems contacting directly some experimental groups working with these isotopes but without success. Our opinion is that some information on production and characterization are probably lost. The table contains some new materials respect to the previous presented in the last report thank to some new contact established at the Paris meeting with Russian researchers that supply us some new information. In particular the new 38 kg of 76Ge for Gerda is under production and it will be ready for the 2006/07. Contacts with Russian people give us also new information regarding future isotope productions in Russia and also it is now possible to define with them a real way to control not only the quality of the enriched materials but also their purity. Other important information regards the actual prices in Russia for some interesting isotopes that can be used for future strategies.

At the same time with the JRA2-WG1 of ILIAS we are preparing a different strategy for a possible isotope production in Europe. We plan to involve in this activity not only the EU institution but also some national institution like CEA (Commissariat de l’Energie Atomique -France) and INFN (Istituto Nazionale di Fisica Nucleare - Italy). We are working to complete the table with some other new information and we plan to prepare a complete data base as soon as possible.

WG3 : theoretical developments Co-ordinators : A. Faessler, F. Simkovic, J. Suhonen The theoretical groups of Tuebingen and Jyväskyla have continued their effort to reduce the uncertainties in the nuclear matrix element calculations. An overall analysis of the possible sources of differences between the various calculations has been performed. A great number of different reasons for the scatter in the values of the matrix elements could be identified. Also some possible universal features of the matrix elements related to the neutrinoless mode of double beta decay have been pointed out. These appear in the decomposition of these matrix elements to different multipoles. Further studies confirm these findings the matrix elements could be parametrized in a simple form with the parameters determined from various independent experimental probes discussed below.

A vivid discussion about the best independent probes of the matrix elements related to the neutrinoless double beta decay has been going on among the participating theorists. Processes like two-neutrino double beta decay, single beta decay, charge-exchange reactions and muon capture have been proposed and analyzed. These probes have been addressed in a meeting in Durham, England in May. A summary report of this meeting is being finalized and should appear soon as an archive article. The independent probes were discussed also in the NEDEX'05 meeting in Corfu at the end of September. This meeting served as part of the ILIAS activities focussed on training of young scientists in the fields of double beta decay and dark-matter search. Both the drawbacks and advantages of the various theoretical schemes related to these independent probes were discussed intensively in the MEDEX'05 meeting. Similar discussions were also carried out in the Erice meeting in the middle of September, just before the MEDEX'05 meeting. All these meetings served as excellent venues of discussing current problems in determining the values of the nuclear matrix elements relevant for double beta decay.