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.