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Presented are the characteristics of systems for monitoring the intensity of the bremsstrahlung photon beam of the PAKHRA accelerator based on Cherenkov counters., Comment: 12 pages, 8 figures, 7 references, scientific article

The results of calibration by cosmic muons of a shower lead-scintillation spectrometer of the sandwich type designed to work in high-intensity photon and electron beams with an energy of 0.1 - 1.0 GeV are presented. It was found that the relative energy resolution of the spectrometer depends on the angle of entry of cosmic muons into the spectrometer in the vertical plane and does not depend on the angle of entry in the horizontal plane. The relative energy resolution of the spectrometer was 16%. Placing an additional lead-scintillation assembly in front of the spectrometer improved the relative energy resolution of the spectrometer to 9%., Comment: 8 pages, 5 figures, 5 references

The characteristics of the secondary electrons` calibration quasi-monochromatic beam of the accelerator S-25R "Pakhra" of the Lebedev Physical Institute of the Russian Academy of Sciences (LPI) on the basis of magnet SP-57 are presented. With an electron energy in the range of 45-280 MeV, a collimator diameter in front of the trigger counters of 3 mm and copper Converter thicknesses of 1-3 mm, the energy resolution and beam intensity were 4.4-2.2% and around 16 e/sec, respectively.

A brief review of searches for eta-mesic nuclei is presented with emphasis on photoreactions and results of a new experiment done at the LPI electron synchrotron are reported. Decay products of eta-mesic nuclei presumably formed by photons in a carbon target, namely correlated back-to-back (pi+ n) and (p n) pairs, have been studied with a two-arm time-of-flight setup. The obtained data show that apart from previously observed (pi+ n) pairs from one-nucleon annihilation of stopped etas (via eta N --> pi N) correlated (p n) pairs from two-nucleon absorption of eta in the nucleus (via eta NN --> NN) are also ejected with a comparable rate. The cross section of eta-mesic nuclei photoproduction off carbon was estimated from the obtained data to be less than 10 microbarn., Comment: 17 pages, 13 figures. Extended text of a talk given by V. V. Polyanskiy at the XXI Int. Baldin Seminar on High Energy Physics Problems, Sep 10-15, 2012, Dubna and at the XIII Int. Seminar on Electromagnetic Interactions of Nuclei, Sep 20-23, 2012, Moscow. To appear in the conference proceedings, PoS(Baldin ISHEPP XXI)102

An approved experiment at the internal proton beam of the JINR nuclotron on a search for eta-mesic nuclei in the reaction pA --> np + eta(A-1) --> np + pi-p + X is briefly presented., Comment: 6 pages, 3 figures. List of authors corrected

First experimental results on photoproduction of eta-mesic nuclei are analyzed. In an experiment performed at the 1 GeV electron synchrotron of the Lebedev Physical Institute, correlated (pi+,n) pairs arising from the reaction \gamma + C12 -> N + (A-1)_eta -> N + (pi+,n) + (A-2) and flying transversely to the photon beam have been observed. When the photon energy exceeds the eta-meson production threshold, a distribution of the (pi+,n) pairs over their total energy is found to have a peak in the subthreshold region of the internal-conversion process eta p -> pi+ n which signals about formation of eta-mesic nuclei., Comment: 9 pages, 8 figures. Talk given by G.A.S. at the IX Intern. Seminar "Electromagnetic Interactions of Nuclei at Low and Medium Energies", Sep 20-22, 2000, Moscow

First experimental results on photoproduction of eta-mesic nuclei are analyzed. In an experiment performed at the 1 GeV electron synchrotron of the Lebedev Physical Institute, correlated pi+n pairs arising from the reaction gamma + 12C -> N + eta(A-1) -> N + pi+ + n + (A-2) and flying transversely to the photon beam have been observed. When the photon energy exceeds the eta-meson production threshold, a distribution of the pi+n pairs over their total energy is found to have a peak in the subthreshold region of the internal-conversion process eta p -> pi+ n which signals about formation of eta-mesic nuclei., Comment: 6 pages, 6 figures. Talk at CIPANP, May 2000, Quebec

Preliminary results of an experiment performed at the Lebedev Physical Institute with the bremsstrahlung photon beams of the end-point energies 650 and 850 MeV are presented. Correlated pi+n pairs with the opening angle theta = 180 deg and the energies E_\pi = 300 MeV, E_n = 100 MeV from the process gamma + 12C -> N + eta(A-1) -> N + pi+ n + (A-2) were observed. They provide an evidence for an existence of the eta-11B and eta-11C eta-mesic nuclei., Comment: 6 pages, 5 figures. Talk given by G.A. Sokol at the 14th International Seminar on High Energy Physics Problems (Aug 17-22, 1998, Dubna). To appear in proceedings