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Scientific Report 2007-2009
Particle physics
1.2.1 Neutrino Physics
In the field of fundamental particle physics the neutrino has become more and more important
in the last few years, since the discovery of its mass. In particular, the ultimate nature of the
neutrino (being a Dirac or a Majorana particle) plays a crucial role not only in neutrino physics,
but in the overall framework of fundamental particle interactions and in cosmology. The only
way to disentangle its ultimate nature is to search for the so-called Neutrinoless Double Beta
Decay (0ν2β). A group of the Department has participated in Cuoricino experiment and it is
now fully engaged in the preparation of CUORE experiment at LNGS [P25]. CUORE is a 1
ton array of 988 crystals of TeO 2 that will be kept in a dilution refrigerator at a temperature
of 10mK. By using the spectacular energy resolution in the measurement of the heat released
by nuclear processes occurring inside the crystals, this experiment will cover an half-life of 130 Te
for the (0ν2β) up to 10 26 y. The Roma group has taken, amongst others, the responsibility of
procuring the crystals (done in RP China by SICCAS), by developing the entire chain of QC/QA
of the crystal production that involves ICP-MS and Ge measurements at all levels and the final
acceptance tests. A follow up of this activity has been the award of an ERC-AdG to one of
the group member for a demonstrator for the next level of background reduction in this kind
of experiments thanks to the combined read-out of heat and scintillation light in new materials
(project LUCIFER).
On the sector of neutrino oscillations, a small but significative participation of the Department
is in the OPERA experiment that exploits the CERN-LNGS neutrino beam. The search for ν τ
appearance will close the 3-neutrino picture of the oscillations and and is based on the emulsion
scanning [P26], a technique which has seen our Department on the front line, since the antiproton
search in cosmic rays by the E. Amaldi group in the ’50s of the last century.
1.2.2 Dark Matter
Dark Matter (DM) is an hot subject nowadays. This elusive component of our Universe is searched
at colliders, in space and underground. A group of this Department is active in the DAMA [P28]
experiment at LNGS. This experiment has the aim of performing a direct detection of DM particles
present in the galactic halo by using the annual modulation signature. It is based on ultra-pure,
very low background NaI scintillator and thanks to its large mass has integrated an exposure in
excess of 0.50 ton×y (the highest of this kind of experiments). The results, worldwide known,
is an intriguing, statistically significant, presence of a modulation that could be explained by
DM particles interacting with the detector. Improvements to the experiment (better quantum
efficiency photomultiplier), with a crucial involvement, of the Roma group are being made.
AMS [P29] will soon fly to space and amongst other field of investigations will be sensitive to
the product of annihilation of DM particles.
1.2.3 Gravitational Waves
Gravitational waves (GW) are space time-ripples such that the distance between free masses will
alternately decrease and increase during their transit out of phase in two perpendicular directions.
The VIRGO detector consists of a laser interferometer with two orthogonal arms each 3 km long.
The sensitivity extends from 10 to 10000 Hz with a typical value of h ∼ 10 −21 for the amplitude
of the GW (see Fig. 4).
The VIRGO group of Rome plays a crucial role in VIRGO [P30]. The group mainly contributes
to VIRGO:
• by designing , constructing and setting up the giant interferometric apparatus,
• by defining the strategy for the analysis of the collected data and developing the software
needed to attain the scientific target of the detection of the gravitational waves
Sapienza Università di Roma 106 Dipartimento di Fisica