MUNU

Collaboration:

- Italy: INFN and Dipartimento di Fisica dell'Università Padova
- France: Institut des Sciences Nucléaires, IN2P3-UJF, Grenoble
- Switzerland: Institut de Physique, Neuchâtel; Physik-Institut, Zürich

Location of the experiment: Nuclear reactor at Nuclear Centre Bugey (Fr)

National Responsible: Carlo Broggini (Pd)

1. Goal of the experiment

MUNU was designed to study the anti-n e e elastic scattering at low energy, in order to be sensitive to a neutrino magnetic moment in the region below 10-10 Bohr magnetons. As a matter of fact, a non-vanishing neutrino magnetic moment produces anti-ne e scattering events in addition to the ones due to the weak interaction.

Briefly, the detector consists of a 1 m3 acrylic vessel time projection chamber filled with CF4 at the pressure of 3 bar. The TPC is mounted inside a steel vessel filled with 10 m3 of liquid scintillator, which works as a muon veto and as an anti-Compton shielding. The experiment is running at 18 m from the core of a 2800 MW power reactor in Bugey, at a depth equivalent to 20 meters of water. Anti-neutrino interactions in CF4 are detected by measuring both the energy and the direction of the recoiling electron.

More on the experiment…

2.

Activities during 2002

The experiment has been running till March 2002. The data analysis based on an automatic track recognition program has been completed and the results already published.

The event rate of single reconstructed electrons fully contained inside the TPC volume, 27 counts per day/kg, is similar to the rate of very well shielded ultra-low background germanium detectors operating in underground laboratories. In addition, thanks to the tracking capability of the detector, we had, for the first time, a simultaneous measurement of signal plus background events in the forward solid angle (along the anti-neutrino direction), and background events only in the backward one. This way, background is measured on-line, while the reactor is on, and subtracted to give an event rate of 1.8±0.7 counts per day above 700 keV (electron kinetic energy). Such a rate is 1.5 sigma higher than the predicted weak rate. The analysis based on a detailed hand scanning of the events is in progress: the reduced error is expected to clarify the situation.

During the last weeks of the experiment we took data with the TPC filled with CF4 at 1 bar pressure: the analysis has shown the capability of the detector to measure the energy and to reconstruct the track of electrons with energy lower than 100 keV. This is an useful information for the future projects aiming at the spectroscopy of low energy neutrinos from the Sun.

The following achievements have been obtained:

- Completion of data taking (100%)
- Completion of the detector dismounting 3: the authorization from EDF arrived only at the end of December 2002. The detector is going to be dismounted in 2003.

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

4. Publications in refereed journals (in 2002): 2

5. Number of conference talks (in 2002): 2

6. Number of undergraduate and doctoral thesis on the experiments (2002)

7. Leadership roles and primary responsibilities in the experiment:

C.Broggini (INFN Pd): Spokesman

Padova group: they had the responsibility for the design and construction of the acrylic TPC, of the system to regulate the pressure in the TPC and in the anti-Compton and of the system to store and to transfer the liquid scintillator from the anti-Compton They also developed the slow control system and the software for the event display.

8. Innovative Instruments

The low background acrylic vessel TPC is still a quite unique detector.

9. Competing experiments

A Russian group is preparing a detector to measure the neutrino magnetic moment at Krasnoyarsk reactor.

10. International committee which has reviewed the experiment

INFN annually reviews the experiment.