Search

Axions of energy 14.4 keV that originated from the M1 transition in 57Fe nuclei in the Sun were sought by using the resonance-absorption reaction A+57Fe → 57Fe* → 57Fe+γ (14.4 keV). Asectioned Si(Li) detector arranged in a low-background facility was used to record photons from this reaction. This resulted in setting a new limit on the axion couplings to nucleons, |−1.19g 0 + g 3 | ≤ 3.0×10−6. Within the hadronic-axion model, the respective constraint on the axion mass is m A ≤ 145 eV (at a 95% C.L.).

The Pauli exclusion principle was tested for nucleons in the 12C nucleus by using data from the Borexino detector. The approach used consisted in seeking photons, neutrons, and protons, as well as electrons and positrons, emitted in the Pauli-forbidden transitions of nucleons from the 1P 3/2 shell to the filled 1S 1/2 shell. Owing to a uniquely low background level in the Borexino detector and its large mass, the currently most stringent experimental limits were obtained for the probabilities and relative intensities of Pauli-forbidden transitions for the electromagnetic, strong, and weak channels.

Data of the Borexino experiment on the detection of the reaction involving elastic solar-neutrino scattering on an electron are presented. The fraction of electron neutrinos in the fluxes of 7Be and 8B neutrinos is in agreement with the LMA MSW oscillation solution. The uniquely low level of the Borexino detector background made it possible to set new limits on the effective magnetic moment of the neutrino, on the possible violation of the Pauli exclusion principle, and on some other rare processes.

It is shown that a large volume liquid organic scintillator detector with an energy resolution of 10 keV at 200 keV 1 sigma will be sensitive to solar pp-neutrino, if operated at the target radiopurity levels for the Borexino detector, or the solar neutrino project of KamLAND., 18 pages, 2 figures, 4 tables. Contributed paper to the Nonaccelerating New Neutrino Physic. NANP-2003, Dubna. To be published in Phys.At.Nucl.(2004)

The possibility of using ultrapure liquid organic scintillator as a low-energy solar neutrino detector is discussed. The detector with an active volume of 10 t and 4π coverage will count 1.8 pp neutrinos and 5.4 7Be neutrinos per day with an energy threshold of 170 keV for the recoil electrons. The evaluation of the detector sensitivity and backgrounds is based on the results obtained by the Borexino collaboration with the Counting Test Facility (CTF). The detector can be build at the LNGS underground laboratory as an upgrade of the CTF detector using already developed technologies.

Searches for invisible axions emitted in the electromagnetic transitions of isomeric nuclei are continued. It is found experimentally that the probability of axion emission in an M1 transition in 125mTe is less than 8.5×10−6 (90% C.L.).