Welcome to the homepage of the MARE Experiment website
Short description of the MARE experiment
The MARE experiment will consist of arrays of low temperature calorimeters measuring the beta decay of 187Re (Q=2.47 keV, the lowest known in nature), with the objective to constrain or mesaure directly the neutrino mass on a pure kinematical basis.
The MARE approach would have a totally different systematics with respect to KATRIN (the only experiment for direct determination of neutrino mass presently in construction phase, based on tritium beta decay and projected to take data from 2010). The MARE intrinsic modularity allows in principle a progressive expansion of the experiment down to and perhaps lower than 0.2 eV sensitivity (the planned KATRIN's sensitivity).
The specific beta activity of natural rhenium (of the order of 1 Bq/mg), is ideally taylored to low temperature microcalorimeters, detectors consisting of a Re-based energy absorber and a sensitive thermometer which converts the temperature increase induced by a single beta decay into an electrical signal.
The MARE development is organized in two phases:
- MARE-1 (now - 2010) - Present technologies (transition edge sensors and semiconductor thermistors) allow to achieve energy resolutions of the order of 10 - 20 eV FWHM for single microcalorimeter elements, with counting rates of the order of 0.2 - 0.3 Bq, corresponding to detector masses of some hundreds of micrograms. Achieved pulse risetimes of the order of 100 - 500 microseconds allow to keep under control the pernicious effect of the pulse pile-up. The statistics target to scrutinize the tritium-based MAINZ and TROITZK experiments (which presently fix the best limit on neutrino mass, corresponding to 2.2 eV) is of the order 10 billions of events, collectable in a few years with an array of about 300 elements. This figure corresponds to the first phase of the experiment, named MARE-1. The technology of MARE-1 is achieved. The realization of this phase is only matter of funding and of "brute force" assembly. MARE-1 is crucial to cross-check the tritium approach and to assess fundamental systematics effects in view of MARE-2.
- MARE-2 (R&D: now-2011; data taking: from 2011) The sensitivity goal of 0.2 eV envisaged for MARE-2 requires a further increase of statistics by 4 orders of magnitude with respect to MARE-1, with a moderate improvement of the energy resolution. In order to keep the total numbers of elements at a reasonable level (of the order of 50000-100000), a substantial increase of the single element mass is foreseen (up to 1-5 mg). This requires that the pulse risetime be reduced down to 1-10 microseconds, in order to keep the pulse pile-up fraction low enough. This very demanding performance may require new technologies with respect to MARE-1. Three approaches will be followed in parallel in an iniatial R&D phase which is starting now. Transition edge sensor technology has the potential to provide the required microcalorimeter features and remains the baseline technique for MARE-2. A second promising technology is offered by magnetic microcalorimeters. Finally, kinetic inductance detectors will be studied and adapted to Re absorbers. In case of successful completion of the 4-5 years R&D phase, data taking will start from 2011.