The yield of gamma-quanta from nuclear fusion reactions proceeding from various spin states of muonic molecules ptμ and pdμ has been measured. The work was performed on the “Triton” facility at DLNP JINR using a specially designed liquid-tritium target. For the first time, channels of the fusion reaction with the yield of double γ-quanta were observed: ptμ → 4Heμ + γ + γ, pdμ → 3Heμ + γ + γ. The data obtained for the yield of single γ-quanta in the channel of the fusion reaction ptμ → 4Heμ + γ is consistent with earlier research. The partial coefficient of sticking of a muon to a helium nucleus was determined experimentally in a channel of pt- and pd-fusion reactions with the yield of single γ-quantum.

The mechanism for the muon catalyzed fusion reaction t + t → 4He + 2n + 11.33 MeV is investigated. The model of the cascade reaction with 5He as an intermediate state is considered, both the ground and the first exited states being taken into account. The neutron energy spectrum measured in the recent experiment is compared with the Monte-Carlo-simulated one. Varying reaction parameters, we obtain optimum values for the relative weights of the 5He ground and excited states and for the excitation energy and width of the excited state.

We present R&D results of the preparation project for the experimental measurement of the (anti)neutrino magnetic moment at the level of 10(-12) mu(B) using an intense tritium source of antineutrinos and liquid helium target.

Since the pioneering discovery of the muon catalysis by Alvarez [L. W. Alvarez, K. Brander, F. S. Crawford, et al., Phys. Rev. 105, 1127 (1957)], considerable efforts were aimed at observation of various fusion processes. Results of these studies facilitated understanding the properties of lightest nuclei and dynamics of low-energy fusion reactions. There still remain unsolved theoretical and experimental problems, especially in case of pt fusion.

A search for the muon-catalyzed fusion reaction d + d -> He-4 + gamma in the dd mu muonic molecule was performed using the experimental installation TRITON with BGO detectors for gamma-quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR Phasotron to detect gamma-quanta with the energy 23.8 MeV. An experimental estimation for the yield of radiative deuteron capture from the dd mu state J = 1 was obtained at the level of eta(gamma) <= 8 x 10(-7) per fusion.

A search for the muon-catalyzed fusion reaction d + d → 4He + γ in the ddμ muonic molecule was performed using the experimental installation TRITON with BGO detectors for γ-quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR Phasotron to detect γ-quanta with the energy 23.8 MeV. An experimental estimation for the yield of radiative deuteron capture from the ddμ state J = 1 was obtained at the level of η γ ≤ 8 × 10−7 per fusion.

It is known that in a dense mixture ( p -4X cmP3) of deuterium and tritium pmesons with energy 10 keV are captured after a time 10l2 sec by highly excited states of the mesic atoms dp and tp,' go over after a time T , 2 2 x lo-" sec to the ground state,' and finally, after a time r d , =: 3 x lop9 sec, all mesons reach the ground state of the atom tp via the isotopic exchange process dp + t+tp + d.3.4 The fraction of muons that decay during the formation of the mesic atoms tp is r d , / r 0 z 1.5 X where r0 = l / A , = 2.2 X lop6 sec is the lifetime of the free muon. In collisions of the mesic atoms tp with the molecules D, and DT, the mesic molecules dtp are formed4s5 during a time T,, < lo-' sec in the resonance reactions

One of the aspects of muon catalysis research is the analysis of the dynamics of nuclear fusion reactions in muonic molecules. The information obtained is of interest for physics of few-nucleon systems and clarifies the structure of the lightest nuclei. The results obtained are generalized and urgent problems are discussed.

Study of the fusion reactions between hydrogen isotopes in muonic molecules is the first example of the accurate accounting of the nucleus charge screening by a muon in the fusion process. At LUNA installation the measurements of astrophysical reaction cross sections were extended down to collision energies of a few keV. The screening by atomic electrons of the target became substantial. The possibility to look over screening from unbound electrons is given by metal-hydrides used as targets in dd reaction measurements. The classical Debye screening in plasma, applied to quasi-free electrons in metal, provides an explanation of unexpectedly large screening potentials found for some metals in the research through the Periodic table of elements.

The cosmic muon background has been calculated for facilities placed at shallow depths. A relatively simple formula has been proposed for the muon spectrum at sea level that ensures the calculation of the depth dependences of the vertical muon intensity and integral muon flux. Calculations show that the zenith-angle distribution of the muon flux density is almost unchanged for depths from 10 to 100 m of solid rock. The muon angular distributions are presented for all three possible cases of the arrangement of the instruments in measurements carried out on the ground and at shallow depths. It has been shown that, to eliminate the cosmic muon background, it is necessary to install an active cosmic ray shielding “umbrella” covering a zenith angle ϑ of no less than 80°.

The MAMONT experiment on the direct detection of antineutrino-electron scattering using an artificial tritium source of 40 MCi activity aims at establishing a stringent laboratory limit mu(nu) <= (1 divided by 3) center dot 10(-12) mu(B) for the electron antineutrino magnetic moment during 1-2 years of data acquisition. The current status of R&D is presented.

For the experiment on the measurement of the electron antineutrino magnetic moment we suggest a new approach to the tritium source design, namely, a configuration of annular cells filled with TiT2 that are stacked into a hollow cylinder. Detectors are mounted in the hole inside.We present results of the optimization of geometrical and physical parameters of the source with respect to its experimental effectiveness and safety guaranty at all stages of its lifecycle. We discuss the choice of the construction materials and specify technological issues relevant to radiation purity of the source, being of the special concern in the experiment on the electron antineutrino magnetic moment measurement.

A search for the muon-catalyzed fusion (MCF) reaction d+d → 4He+γ in the ddμ muonic molecule was performed using the experimental MCF installation TRITON and NaI(Tl) detectors for γ quanta. A high-pressure target filled with deuterium was exposed to the negative muon beam of the JINR phasotron to detect γ quanta with an energy of 23.8 MeV. The first experimental estimation for the yield of radiative deuteron capture from the ddμ state J=1 was obtained at a level of ηγ≤2×10−5 per one fusion.

An experiment aimed at directly detecting antineutrino-electron scattering by using a 40-MCi tritium β-active source will make it possible to lower the present-day laboratory limit on the neutrino magnetic moment by two orders of magnitude. The experiment brings together novel unique technologies in studying rare processes of neutrino-electron scattering: (i) an artificial source of antineutrinos from tritium decay of 40-MCi activity with the antineutrino flux density of about 6×1014 cm−2 s−1 and (ii) new types of detectors capable of detecting electrons of energy down to about 10 eV, namely, a silicon cryogenic detector based on the ionization-into-heat conversion effect and a high-pure germanium detector with an internal signal amplification in the electric field. A compact installation located at a specially equipped underground laboratory (≤100 mwe) will provide favorable background conditions for running the experiment. With a background level of about 0.1 event/(kg keV d) and detector assembly masses of 3 and 5 kg for the silicon and germanium ones, respectively, a limit of μ ν ≤3±10−μB on the electron-antineutrino magnetic moment will be obtained within 1 to 2 years of data acquisition. The status of the experiment and the state of the art are presented.