The Cross Section of 3He(3He,2p)4He measured at Solar Energies

We report on the results of the \hethet\ experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak ($E_{\rm 0}$=22 keV). The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the \hethet\ reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted $S_{\rm b}(E_{\rm 0})$ value for bare nuclides (=5.40 MeV b).Comment: 18 pages, 10 postscript figures, Calculations concerning hypothetical resonanz added, Submitted to Phys. Rev. C., available at this URL: HTTP://www.lngs.infn.it/lngs/htexts/luna/luna.htm

Constraining the S factor of 15N(p,g)16O at Astrophysical Energies

The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338 <Ep < 1028 keV) can dramatically effect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation the 15N(p,g)16O reaction has been remeasured covering the energy range from Ep=1800 keV down to 130 keV. The results have been analyzed in the framework of a multi-level R-matrix theory and a S(0) value of 39.6 keV b has been found.Comment: 15 pages, 9 figure

Measurement of 25Mg(p; gamma)26Al resonance strengths via gamma spectrometry

The COMPTEL instrument performed the first mapping of the 1.809 MeV photons in the Galaxy, triggering considerable interest in determing the sources of interstellar 26Al. The predicted 26Al is too low compared to the observation, for a better understanding more accurate rates for the 25Mg(p; gamma)26Al reaction are required. The 25Mg(p;gamma)26Al reaction has been investigated at the resonances at Er= 745; 418; 374; 304 keV at Ruhr-Universitat-Bochum using a Tandem accelerator and a 4piNaI detector. In addition the resonance at Er = 189 keV has been measured deep underground laboratory at Laboratori Nazionali del Gran Sasso, exploiting the strong suppression of cosmic background. This low resonance has been studied with the 400 kV LUNA accelerator and a HPGe detector. The preliminary results of the resonance strengths will be reported.Comment: Accepted for publication in Journal of Physics

Neutrino astronomy with the MACRO detector

High energy gamma ray astronomy is now a well established field and several sources have been discovered in the region from a few GeV up to several TeV. If sources involving hadronic processes exist, the production of photons would be accompanied by neutrinos too. Other possible neutrino sources could be related to the annihilation of WIMPs at the center of galaxies with black holes. We present the results of a search for point-like sources using 1100 upward-going muons produced by neutrino interactions in the rock below and inside the MACRO detector in the underground Gran Sasso Laboratory. These data show no evidence for a possible neutrino point-like source or for possible correlations between gamma ray bursts and neutrinos. They have been used to set flux upper limits for candidate point-like sources which are in the range 10^-14-10^-15 cm-2 s-1.Comment: 37 pages, 15 figures, replacement due to a typo in tab. 6, AASLaTex, submitted to Ap

Observation of the Shadowing of Cosmic Rays by the Moon using a Deep Underground Detector

Using data collected by the MACRO experiment during the years 1989-1996, we show evidence for the shadow of the moon in the underground cosmic ray flux with a significance of 3.6 sigma. This detection of the shadowing effect is the first by an underground detector. A maximum-likelihood analysis is used to determine that the angular resolution of the apparatus is 0.9+/-0.3 degrees. These results demonstrate MACRO's capabilities as a muon telescope by confirming its absolute pointing ability and quantifying its angular resolution.Comment: 14 pages, 8 figures Submitted to Phys. Rev.

First measurement of the 14N(p,gamma)15O cross section down to 70 keV

In stars with temperatures above 20*10^6 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p,gamma)15O reaction. Deep underground in Italy's Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90 - 300 *10^6 K, for the first time with negligible impact from extrapolations

Limits on dark matter WIMPs using upward-going muons in the MACRO detector

We perform an indirect search for Weakly Interacting Massive Particles (WIMPs) using the MACRO detector to look for neutrino-induced upward-going muons resulting from the annihilation of WIMPs trapped in the Sun and Earth. The search is conducted in various angular cones centered on the Sun and Earth to accommodate a range of WIMP masses. No significant excess over the background from atmospheric neutrinos is seen and limits are placed on the upward-going muon fluxes from Sun and Earth. These limits are used to constrain neutralino particle parameters from supersymmetric theory, including those suggested by recent results from DAMA/NaI.Comment: 14 pages, 7 figures, submitted to Phys. Rev.

Feasibility of low energy radiative capture experiments at the LUNA underground accelerator facility

The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross sections of the radiative capture reactions $^2$H(p,$\gamma$)3He and $^{14}$N(p,$\gamma$)$^{15}$O within their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative capture studies at energies of astrophysical interest is discussed for several experimental scenarios.Comment: Submitted to Eur. Phys. J.

Search for massive rare particles with MACRO

Massive rare particles have been searched for in the penetrating cosmic radiation using the MACRO apparatus at the Gran Sasso National Laboratories. Liquid scintillators, streamer tubes and nuclear track detectors have been used to search for magnetic monopoles (MMs). Based on no observation of such signals, stringent flux limits are established for MMs as slow as a few 10^(-5)c. The methods based on the scintillator and on the nuclear track subdetectors were also applied to search for nuclearites. Preliminary results of the searches for charged Q-balls are also presented.Comment: 20 pages, 9 EPS figures included with epsfi