RESEARCH IN THE FIELD OF ELEMENTARY PARTICLES AT THE INSTITUTE OF NUCLEAR PHYSICS AND ITS PROSPECTS

V. M. Kuznetsov

(Presented by the Scientific and Technical Seminar of the High-Energy Laboratory of the Institute of Nuclear Physics)

In 1965, with the start-up in Tomsk of the “Sirius” electron synchrotron, designed for an energy of 1500 MeV, research began in the most advanced area of physics—elementary-particle physics. This was the result of many years of effort by scientists of the oldest Siberian higher educational institution—the Polytechnic Institute—who had successfully mastered new directions in science and technology and, in particular, the development of cyclic electron accelerators.

The first experiments carried out on the synchrotron were studies of synchrotron radiation and its influence on the dynamics of acceleration [1, 2], and the study of the formation of fragments and nuclear stars in nuclei of photoemulsions. After the start-up of the ring accelerator in Armenia, irradiations of emulsions were also performed in Yerevan. Some of the data obtained have already been processed.

At the same time, in 1965–1966, preparations were under way for experiments on the production of $\pi$ mesons and $\eta$ mesons. Their specific feature was the use of fast (nanosecond) electronics and spark chambers. In order to create various types of spark and streamer chambers, and first of all the power supplies for them, the institute’s experience in developing high-voltage generators for tens and hundreds of kilovolts was used [3–6].

In 1967–1970 the institute had already published, in the domestic and foreign press, the results of several experiments in meson physics. Among them were an accurate measurement of the lifetime of the $\pi^0$ meson [7] and a measurement of the asymmetry of $\pi^+$-meson production in the region of the first pion–nucleon resonance [8]. These works were distinguished by an original methodology created with the use of spark chambers, time-of-flight techniques, and so on.

Great possibilities for setting up new experiments were opened by the production at the accelerator of a beam of polarized photons from a crystalline diamond target [9]. The large polarization of the beam (from 30 to 40%) makes it possible to obtain—as, for example, in the experiment to determine the asymmetry of $\pi^+$ mesons—information about the process that is fundamentally impossible to obtain with an ordinary, incoherent beam.

During this period, work on Compton scattering of laser light by moving electrons was also completed [10].

The program of meson-physics research currently being conducted is very extensive. At present, the first results have been obtained on measuring the cross section for the photoproduction of $\pi^-$ mesons on carbon nuclei (the induced-activity and coincidence method), of $\pi^0$ mesons on a number of nuclei (proton–photon coincidences), and of $\eta$ mesons on nuclei (correlated Cherenkov spectrometers). It is being measured with the aid of a magnetic spec—

...of the spectrometer and spark chambers, the polarization of the photon beam, previously calculated only theoretically, the asymmetry in the production of \(\pi^+\)-mesons at very small and large angles, etc.

The program of future work is closely connected with improving the physical capabilities of the electron synchrotron: increasing the intensity of the photon beams, extracting the electron beam, and creating a flat magnetic field for “stretching” the beam.

With an increase in intensity (owing to a more advanced high-frequency system and a new microtron injector), it becomes possible to begin a series of polarization-type experiments. The most important of these is the measurement of the polarization of recoil neutrons in the photoproduction of \(\pi^+\)-mesons. Here, in addition to an intense beam, a special magnetic channel is required, the construction of which has already been completed (in a strongly focusing version), as well as unique neutron detectors for energies of tens and hundreds of MeV, whose development is being actively pursued at the institute.

With the appearance of an extracted electron beam, in addition to work on meson photoproduction, a program of work on the electroproduction of \(\pi\)-mesons and \(\eta\)-mesons on nucleons and nuclei will come into effect.

The implementation of the research program in meson physics is closely connected with the automation of the physical experiment and of the accelerator itself. This purpose is served by the “experiment–computer” communication system, already created at the institute, and by the automatic control system (ACS) of the synchrotron that is being developed.

A separate place in the program is occupied by questions connected with the development and application of studies of synchrotron radiation (the vacuum ultraviolet region). This highly promising area finds application in solid-state physics and other applied investigations.

And, finally, a few words about theoretical work in the physics of particles and nuclei at high energies. The model of meson–baryon interactions created at the institute within the framework of current algebra with rigid pions [11] has been successfully used to describe low-energy \(\pi N\) scattering. In the field of hypernuclei, a model of nonmesonic decays and a model of suppression of \(\pi^-\)-meson decays have been proposed, and on their basis a theory of hypernuclear decays has been constructed [12, 13].

REFERENCES

1. A. A. Vorob’ev, A. N. Didenko, A. V. Kozhevnikov. Atomic Energy, 28, 260 (1970); 29, 389 (1970).

2. V. A. Vizir’, M. M. Nikitin. PTE, 1, 25 (1971); 5, 37 (1971).

3. I. K. Zhankov. PTE, 2, 56 (1968).

4. I. K. Zhankov, V. M. Kuznetsov, O. I. Stukov. PTE, 5, 50 (1968).

5. Yu. P. Usov, N. A. Rybakova, A. G. Sterligov. PTE, 1, 54 (1970).

6. P. S. Anan’in, Yu. P. Usov, A. G. Sterligov, V. G. Tolmachev. PTE, 4, 42 (1970).

7. V. I. Kryshkin, A. G. Sterligov, Yu. P. Usov. ZhETF, 57, 1917 (1969).

8. V. M. Kuznetsov, O. I. Stukov, E. V. Repchenko, B. N. Kalinin. Lett. Nuovo Cimento, 1, 223 (1971). Nuclear Physics, 13, 1049 (1971).

9. B. N. Kalinin, V. M. Kuznetsov, Yu. I. Sertakov, O. I. Stukov. Proceedings of the NII YaFÉA, 1 (1971), Atomizdat, 1971.

10. A. V. Peshkov, E. I. Aleksandrov, A. V. Karakutsiev. Proceedings of the 7th Interuniversity Conference on Electron Accelerators. Atomizdat, 1970.

11. G. M. Radutskii, A. N. Tabachenko. Nuclear Physics, 29B, 405 (1971).

12. V. A. Filimonov, A. G. Potashov. Nuclear Physics, 10, 130 (1969).

13. V. A. Filimonov. Nuclear Physics, 2, 334 (1972).