Last Update: October 2000 |
DAMA
Collaboration:
INFN - sez. Roma2 and sez. Roma
IHEP/Beijing
physical results on particular topics achieved also in
collaboration with physicists of Ukraine - INR/KieV and of
ENEA-Frascati.
Laboratory: LNGS
1. Goal of the experiment
The DAMA experiment is an
observatory for rare processes, mainly for Dark Matter particles.
The experimental set-ups are realized by developing and using
several kinds of radiopure scintillators.
The main running experimental set-ups are:
the ~100 kg highly radiopure NaI(Tl) set-up (mainly devoted to
the investigation of the WIMP annual modulation signature); we
note that the electronics and DAQ of this set-up have been fully
upgraded in August 2000.
the ~ 6.5 l liquid Xenon (LXe) scintillator set-up (devoted to
measurements with Kr-free Xenon enriched in particular isotopes);
the set-up named "R&D" that is used for
measurements with prototype detectors and for small scale
experiments; during 2000 the whole installation has been
reassembled in a new experimental site with several hardware
improvements.
the low background DAMA Ge set-up (devoted to routine
measurements of samples radiopurity).
Moreover, R&D's for the further development of higher
radiopure detectors and PMTs are regularly carried out.
Under construction: the NaI(Tl) set-up with ~250 kg exposed mass,
which will offer further increased performances and sensitivity.
2. Physics achievement
Results published from October 1999 to October
2000.
~100 kg NaI(Tl) set-up
- New results on the investigation of the
WIMP annual modulation signature have been published. The
data of two further annual cycles have been released
(38475 kgday statistics); moreover, the global analysis
on the data of the four annual cycles, released so far
(57986 kgday statistics), has been performed. A model
independent evidence for a modulation in the low energy
rate with proper features has been confirmed. All known
systematics have been further carefully investigated and
a dedicated publication has been released. A model
dependent analysis considering a particular model
framework for candidate with a dominant spin-independent
interaction and mass above 30 GeV has also been reported.
- New results on the investigation of
possible diurnal variation of the low energy rate (14962
kgday statistics) with respect to both the sidereal (to
exploit a signature which is sensitive only to high cross
section WIMPs) and the solar (to verify absence of
possible rate diurnal variation of unknown origin) time
have been published. A negative result has been achieved
in both cases. New regions in the plane "halo
fraction versus cross section" for various WIMP
masses have been excluded for high cross section
candidates (to which very small halo fraction would
correspond) in the given model frameworks.
- New results on the search for neutral
Strongly Interacting Massive Particles: SIMPs, (1.1 x 106
cm2 sr day exposure) have been published. SIMP
mass up to MSIMP ~ 4 x 1016 GeV
have been explored (given models). Furthemore, new model
independent upper limit on the flux of neutral
nuclearities has been achieved.
- New limits on the nuclear level excitation
of 127I and 23Na during charge
nonconserving processes have been published ( 34866 kgday
statistics). Restrictions up to one order of magnitude
more severe than previously available have been obtained.
~6.5 kg LXe set-up
- New results on the investigation of the
WIMP-129Xe inelastic scattering have been
published (~2500 kgday) improving our previous result.
- New limits on the nuclear level excitation
of 129Xe during charge nonconserving processes
have been published (823.1 kgday statistics). The
lifetime limits on the charge non-conserving (CNC)
electron capture with nuclear levels excitation of 129Xe
have been established for the first time. The highest
lifetime limit for similar processes has been obtained as
well as the more stringent restrictions on the relative
strength of the studied CNC process.
- The highest lifetime limit on the charge
non-conserving electron decay through the channel e-
-> electron neutrino + gamma (2257.7 kgday statistics)
has been achieved and published.
- New results on the search for nucleon and
di-nucleon decays into invisible channels or
disappearance have been published (2257.7 kgday
statistics) by using a new approach. In fact, we search
for the radioactive daughter nuclei created after the
nucleon or di-nucleon disappearance in the parent nuclei.
The achieved limits are similar or better than those
previously available; moreover the limit for the NN decay
into neutrino tau + antineutrino tau has been set for the
first time. In addition, the present limits are valid for
every possible disappearance channel.
Second CaF2(Eu) prototype
- New and highly improved half-life
limits on the double beta decays of 40Ca
and of 46Ca have been published.
3. INFN contribution to the experiment
in terms of manpower and financial support
- Manpower (Year 2000): 8 researchers, 2
Technicians
- Financial Support (Year 2000): 949 MLit
4. Number of publication in referred
journals: 8 (from October 1999 to
October 2000)
5. Number of talks to conferences: 13(from October 1999 to October 2000)
6. Number of undergraduate and doctoral
thesis on the experiment: 3
7. Leadership role in the experiment
R. Bernabei - principal investigator
8. Innovative instruments
Development of radiopure detectors, PMTs and
overall set-ups
9. Competing experiments
As regards the ~ 100 kg NaI(Tl) set-up, we
recall that no other set-up with similar features (well
known technique, radiopurity, exposed mass, complete
monitoring and control of the running parameters, energy
threshold etc.) is available to effectively search for
the WIMP annual modulation signature. Moreover, it offers
also the possibility to competitively exploit various
other approaches (pulse shape discrimination of the
electromagnetic background, search for exotic candidates
etc.) and to investigate several other rare processes.
The competitiveness of our experiment will be further
increased by the ~250 kg NaI(Tl) set-up now under
construction.
As regards the about 2 l (i.e. about 6.5
kg) liquid Xenon (LXe) pure scintillator set-up, we
recall that no other set-up with similar features
(Kr-free Xenon gas enriched in particular isotopes,
radiopurity, exposed mass, complete monitoring and
control of the running parameters, energy threshold,
effective far UV light collection, etc.) is available.
This set-up has been periodically upgraded to further
increase its performances and sensitivity. Since August
2000 it can be alternatively filled with Kr-free Xenon
gas enriched at 99.5 % in 129Xe or at 68.8 %
in 136Xe. The advantage to use Kr-free gases
as well as the enrichements in these two isotopes can be
easily inferred.
As regards the CaF2(Eu),
competitive results have been achieved with previous
prototypes; the last one is at hand and a decision on
this line of development will be taken at end of
measurements.
The features of the "R&D"
set-up assures the possibility of competitive small scale
experiments.
10. International committee which has
reviewed the experiment
The experiment is reviewed by the funding
authorities of INFN and has also been periodically reviewed by
the Scientific Commettee of the LNGS. Chinese activity is funded
by the National Natural Science Fund of China and Academia
Sinica.