Mi-Beta

Collaboration:

1. Università di Milano Bicocca e INFN, 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 2002

An array of 10 crystals is running since June in the old cryostat (the new one , even if tested -see later- has poorer operating conditions). A paper with the first bolometric limit on electron antineutrino mass and with the best world measurement of the transition energy and half lifetime of Re-187 has been submitted to Phys.Rev.Lett.

The new cryostat has been mounted in the new laboratory of Milano-Bicocca. It has reached a record value for the base temperature (~6mK). The operating conditions of the Laboratory have however not yet beem optimized yet

Some properties of the micromachining (heat conductance of the "legs", and reproductibility of the Si:P sensors) have been studied

New detectors have been prepared at the beginning of 2002 and mounted in the presently running array

The following achievements have been obtained:

- End of a new run with the old cryostat for the measurement of neutrino mass (187Re) (90% (*))
- Re-mounting of the cryostat at Milano-Bicocca (**)
- Tests of micro-machining (100%)
- New run with micro-machining with the new refrigerator (0%(***))
- Preparation of new detectors using the old refrigerator (100%)

(*) the measurement is still in progress from June 2002

(**) this operation will be posponed after the end of the present measurement

(***)The Milano-Bicocca Cryo-laboratory is not yet ready

Milestones 2003:

Final measurement of the limit on the neutrino mass after a year of data taking with the 10 microbolometer array | 30-06-2003
Study of the internal calibration of a bolometer for the measurement of beta decay | 31-01-2003
Final decision on the participation to the KATRIN experiment or on the implementation of an array of 10 microbolometers of Rhenium compounds. | 31-10-2003

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

Manpower: 13 researchers (5.1 FTE), 5 technicians (2.3 FTE)

Budget for the year 2003: 0.7 % of the CSNII budget

4. Publications in refereed journals (in 2002): 3

5. Number of conference talks (in 2002): 1

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

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 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