R. Bernabei

GALLEX solar neutrino observations: Results for GALLEX IV

Abstract We report the GALLEX solar neutrino results for the measuring period GALLEX III, the period from 12 October 1994-4 October 1995. Counting for these runs was completed on 29 March 1996. The GALLEX III result (14 runs) is [53.9 ± 10.6(stat.) ± 3.1 (syst.)] SNU (1σ). This is 15.8 SNU below but statistically compatible with the new combined result for GALLEX (I+II+III) (53 runs), which is [69.7 ± 6.7(stat.) −4.5 +3.9 (syst.)] SNU (1σ) or (69.7 −8.1 +7.8 ) SNU with errors quadratically added. We also give the preliminary result from our second 51 Cr-source experiment: the measured detector response is 83±10% of expectation. The combined result from both GALLEX 51 Cr-source experiments is 92±8% of expectation.

Search for WIMP annual modulation signature: Results from DAMA/NaI-3 and DAMA/NaI-4 and the global combined analysis

Data, collected by the similar or equal to 100 kg NaI(TI) DAMA set-up at the Gran Sasso National Laboratory of I.N.F.N. during two further yearly cycles (DAMA/NaI-3 and DAMA/NaI-4; statistics of 38475 kg (.) day), have been analysed in terms of WIMP annual modulation signature. The results agree with those previously achieved. The cumulative analysis of all the available data (DAMA/NaI-1 to 4; statistics of 57986 kg(.)day) favours the possible presence of a WIMP with M-W = (52(-8)(+10)) GeV and xi sigma(p) = (7.2(-0.9)(+0.4)) (.) 10(-6) pb at 4 sigma C.L., when standard astrophysical assumptions are considered. The allowed mass extends up to 105 GeV (1 sigma) when the uncertainty on the mean value of the local velocity v(0) is taken into account and up to 132 GeV(1 a) in case a possible bulk halo rotation is taken into account. Moreover, the allowed regions extend to lower xi sigma(p) values when the upper limits on the recoil differential counting rate obtained from DAMA/NaI-0 is included in the cumulative analysis (favouring, in case of standard assumptions, M-w = (44(-9)(+12)) GeV and xi sigma(p) = (5.4 +/- 1.0) (.)10(-6) pb at similar or equal to 4 sigma C.L.). The 3 sigma C.L. allowed regions in the xi sigma(p), M-w plane summarize the obtained main physical results

GNO solar neutrino observations: Results for GNO I

Abstract We report the first GNO solar neutrino results for the measuring period GNO I, solar exposure time May 20, 1998 till January 12, 2000. In the present analysis, counting results for solar runs SR1–SR19 were used till April 4, 2000. With counting completed for all but the last 3 runs (SR17–SR19), the GNO I result is [65.8 ± 10.2 9.6 (stat.) ± 3.4 3.6 (syst.)] SNU (1 σ ) or [65.8 ± 10.7 10.2 (incl. syst.)] SNU (1 σ ) with errors combined. This may be compared to the result for Gallex (I–IV), which is [77.5 ± 7.6 7.8 (incl. syst.)] SNU (1 σ ). A combined result from both GNO I and Gallex (I–IV) together is [74.1 ± 6.7 6.8 (incl. syst.)] SNU (1 σ ).

Solar neutrinos observed by GALLEX at Gran Sasso.

We have measured the rate of production of 71Ge from 71Ga by solar neutrinos. The target consists of 30.3 t of gallium in the form of 8.13 M aqueous gallium chloride solution (101 t), shielded by ≈ 3300 m water equivalent of standard rock in the Gran Sasso Underground Laboratory (Italy). In nearly one year of operation, 14 measurements of the production rate of 71Ge were carried out to give, after corrections for side reactions and other backgrounds, an average value of 83 + 19 (stat.) ± 8 (syst.) SNU (1σ) due to solar neutrinos. This conclusion constitutes the first observation of solar pp neutrinos. Our result is consistent with the presence of the full pp neutrino flux expected according to the “standard solar model” together with a reduced flux of 8B + 7Be neutrinos as observed in the Homestake and Kamiokande experiments. Astrophysical reasons remain as a possible explanation of the solar neutrino problem. On the other hand, if the result is to be interpreted in terms of the MSW effect, it would fix neutrino masses and mixing angles within a very restricted range.

New limits on WIMP search with large-mass low-radioactivity NaI(Tl) set-up at Gran Sasso

Improved limits on WIMP search have been obtained by the pulse shape analysis of the data collected with a large-mass low-radioactivity NaI(Tl) set-up at Gran Sasso National Laboratory.

The DAMA/LIBRA apparatus

The similar or equal to 250 kg highly radiopure NaI(Tl) DAMA/LIBRA apparatus, running at the Gran Sasso National Laboratory (LNGS) of the INFN, is described

Searching for WIMPs by the annual modulation signature

Abstract A set of preliminary test data, collected with large mass highly radiopure NaI(Tl) detectors, has been analysed by a maximum likelihood method to search for the WIMP annual modulation signature.

On a further search for a yearly modulation of the rate in particle Dark Matter direct search

The results achieved with a statistics of 14962 kg . day, collected with the large mass highly radiopure DAMA NaI(TI) set-up, are described and investigated in terms of WIMP annual modulation signature. A maximum likelihood analysis of these data, combined with the statistics of 4549 kg day previously published (total statistics of 19511 kg . day), favours the hypothesis of presence of an annual modulation at 99.6% C.L

First results from the 51Cr neutrino source experiment with the GALLEX detector

Abstract The radiochemical GALLEX experiment, which has been measuring the solar neutrino flux since May 1991, has performed an investigation with an intense man-made 51 Cr neutrino source (61.9 ± 1.2 PBq). The source, produced via neutron irradiation of ≈ 36 kg of chromium enriched in 50 Cr, primarily emits 746 keV neutrinos. It was placed for a period of 3.5 months in the reentrant tube in the GALLEX tank, to expose the gallium chloride target to a known neutrino flux. This experiment provides the ratio, R , of the production rate of Cr-produced 71 Ge measured in these source exposures to the rate expected from the known source activity: R = 1.04 ± 0.12. This result not only constitutes the first observation of low-energy neutrinos from a terrestrial source, but also (a) provides an overall check of GALLEX, indicating that there are no significant experimental artifacts or unknown errors at the 10% level that are comparable to the 40% deficit in observed solar neutrino signal, and (b) directly demonstrates for the first time, using a man-made neutrino source, the validity of the basic principles of radiochemical methods used to detect rare events (at the level of 10 atoms or less). Because of the close similarity in neutrino energy spectra from 51 Cr and from the solar 7 Be branch, this source experiment also shows that the gallium detector is sensitive to 7 Be neutrinos with full efficiency.

Dark matter particles in the Galactic halo: Results and implications from DAMA/NaI

The DAMA/NaI experiment (≃100 kg highly radiopure NaI(Tl)) was proposed, designed and realized to effectively investigate in a model-independent way the presence of a Dark Matter particle component in the galactic halo by exploiting the annual modulation signature. With a total exposure of 107731 kg · day, collected over seven annual cycles deep underground at the Gran Sasso National Laboratory of the I.N.F.N., it has pointed out — at 6.3σC.L. — an effect which satisfies all the peculiarities of the signature and neither systematic effects nor side reactions able to mimic the signature were found. Moreover, several (but still few with respect to the possibilities) corollary model dependent quests for the candidate particle have been carried out. In this paper the obtained results are summarized and some perspectives are discussed at some extent.