Mi-Beta

Collaboration:

1. Milano e gruppo collegato di Trento

Location of the experiment: LASA (Mi) for cryogenic measurements and Milano-Bicocca for Radioactivity Measurements, IRST of Trento for the preparation of Silicon implanted thermistors.

National Responsible: E. Fiorini (Mi)

1. Goal of the experiment

Development of microbolometers for high resolution measurement of X-rays and construction of an array with at least ten absorbers of Silver Perrhenate to investigate the beta decay spectrum of 187Re in view of the measurement of neutrino mass.

More on the experiment…

2.

Activities during 2001

The Rhenium spectrum has been measured with an array made by 8 crystals of Rhenium perhenate with an average mass of 300 micrograms each. About 7 million events, the largest statistics in the world, have been collected and are presently under analysis.

The gain of the 8 channels has been continuously monitored by means of fluorescence lines produced by a 55Fe source. This source is routinely open for 20 minutes every two hours, and then closed to avoid the background during the measurements. An interesting molecular problem appears: a satellite peak is present for each of the fluorescence lines, displaced by ~ 43 eV from the main peak. This phenomenon is being studied, since it could influence the measured value of the neutrino mass, not only in our, but also in other experiment.

Since the presence of the source, even when closed, produces with its bremsstrhalung a considerable contribution to the background in the high energy region of the spectrum, we have radically changed the structure of our experiment, by adding an automatically triggered mechanical displacement of the source.

The new set-up will be installed at the end of this year and will start taking data at the beginning of the next year.

The following achievements have been obtained:

Conclusion and analysis of current measurements data, new limit on electron anti-neutrino mass | 31-05-2001 | 100%
New measurements with the detector array with slightly modification or new R&D | 30-06-2001 | 80%
New measurement with micromachining thermistors and new detector using new dilution refrigerator. R&D for X ray spectroscopy | 31-10-2001 | 60%

Milestones 2002:

End of a new run with the old cryostat and re-mounting of this cryostat at Milano-Bicocca | 31-03-2002
Tests of micro-machining | 31-07-2002
New run with micro-machining with the new refrigerator | 31-12-2002
Preparation of new detectors using the old refrigerator | 31-12-2002

3. INFN contribution to the experiment in terms of manpower and financial support

Manpower: 14 researchers (6.3 FTE), 4 technicians (2 FTE)

Budget for the year 2002: 154.5 kEuro

4. Publications in refereed journals (in 2001):

5. Number of conference talks: 3

6. Number of undergraduate and doctoral thesis on the experiment:

n.1 Ph.D.;

n.1 Laura diplomas

7. Leadership role and primary responsibilities of the experiment

E. Fiorini (Mi) is the spokesman of the experiment and the leader of the contacts with the Berkeley and Trento groups;

Milano is the coordinating group of the European Network for Cryogenic detectors.

7. Innovative instruments:

The results on X-ray spectroscopy are among the best in the literature

The Genoa and Milano groups are the only ones to perform, with different cryogenic techniques, a calorimetric measurement on the neutrino mass

Application of the technique of microbolometers in Material Science and Astroparticle Physics is being pursued

8. Competing experiments

There are only four groups so far that can compete with Milano in X-ray spectroscopy, and only one uses a similar technique

For the Rhenium experiment the Milano group is proud to compete with an highly scientific and technically qualified group like the Genoa one

9. International committee which has reviewed the experiment

The INFN National Committee II annually reviews Mi-Beta.

The experiment has been reported to three meeting of the CEE TMR and successfully reviewed by the European panel. A new network on Cryogenic Detectors has been recently approved in the frame of the TMR activities