Meson Physics Laboratory

Petersburg
Nuclear
Physics
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Petersburg Nuclear Physics Institute

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Meson Physics Laboratory
Introduction
Meson Physics Laboratory The Meson Physics Laboratory (MPL) was officially formed in 1964. That time it was named a division Mesons and Mesoatoms, the existing title of the Laboratory has been approved in 1986. From 1964 till 2002 the Laboratory was headed by Sergei Pavlovich Kruglov, who was an initiator of the MPL creation and a permanent leader of the Laboratory. At the end of 2002 Viktotin Vladislavovich Sumachev has been elected a Head of the Laboratory.
             The Meson Physics Laboratory was created at the time when there were hot discussions of a scientific program of experiments at the PNPI synchrocyclotron which was under construction in 60s. And the study of pion-nucleon interaction at the pion channel of the PNPI synchrpcyclotron was chosen that time as a primary scientific direction of the MPL.
             After 1969, scientists and engineers of the Laboratory took active part in designing and tuning the pion channel and in investigating characteristics of this channel. The pion channel allows to get intense (up to 105106 1/s) beams of positively- and negatively-charged pions with energies up to 650 MeV. At that time, pion beams of comparable intensity in the above energy range existed only at Brookhaven National Laboratory (USA) and at KEK (Japan). First physics measurements at the pion channel started at the end of 1970.
             At the first stage, a series of experiments were carried out in the framework of a general program "Baryon spectroscopy in the region of low-lying pion-nucleon resonances with pion beams". The experiments included measurements of the differential cross sections and polarization parameters
P, A, R for pion-proton elastic scattering and covered the energy range from 300 to 640 MeV (corresponding range of the incident pions momenta is 417-765 MeV/c). In total, more than 500 new experimental points were obtained during these experiments. These new results were used as a main part of the database when performing a new phase shift analysis PNPI-94.
             In 90s, after completion the investigation of elastic pion-proton scattering new experiments on the study pion-proton charge exchange scattering started at the PNPI pion channel. Different types of devices for registering the recoil neutrons and photons emitted as a result of the decay of produced neutral pion into two photons were developed in the Laboratory: neutron detectors on the base of big scintillators, total absorption electromagnetic calorimeters made of lead glass Cerenkov blocks and of CsI(Na) crystals and, at last, the Neutral Meson Spectrometer consisting of two electromagnetic calorimeters, each including 24 CsI(Na) crystals. Using the Neutral Meson Spectrometer, we have measured the differential cross sections of the charge exchange scattering at the angles close to 0o
(i.e. for the forward scattering). The experiment was carried out in the range of the incident pions momenta (from 417 to 710 MeV/c) where all existed to that time experimental data were scarce, contradictory and inaccurate. Our measurements were performed with a high precision at ten values of the incident pions momentum in the above mentioned range. The results of these measurements have been served as a base of the Candidate Dissertation defended in 2004 by MPL scientist D.E. Bayadilov.
             At the present time, the Neutral Meson Spectrometer is used to for perform at the PNPI pion channel a series of experiments were carried out, in which the differential cross sections of pion-proton reactions with eta meson produced in the final state were measured at several momenta of the incident pions in the near-threshold region. The goal of these measurements is to make more clear the mechanism of this process, the characteristic feature of which is that its threshold is very close to the position of the S11(1535)resonance.
             At the end of 80s, a new series of experiments on measuring the spin rotation parameters A and R in elastic pion-proton scattering at the second resonance region started at the pion channel of the ITEP synchrotron. Such measurements were performed in the above mentioned energy region for the first time in the world. The experimental program is carried out by PNPI scientists and engineers in collaboration with physicists of Institute for Theoretical and Experimental Physics (Moscow). Measurement of the spin rotation parameter A and R is a key experiment in the whole program of studying elastic pion-proton scattering since only such measurements permit to remove discrete ambiguities arising in the course of a partial-wave analysis. The results of measurements of the spin rotation parameters A and R obtained at the incident pions momenta of 1430 and 1620 MeV/c allowed to make very important conclusion that the widely used analysis KH (all the characteristics of pion-nucleon resonances presented in Listings of the Review of Particle Physics are obtained just on the base of this analysis) seems to be not entirely correct in some energy ranges.




NRC "Kurchatov Institute"    Russian Academy of Sciences    Petersburg Nuclear Physics Institute
    High Energy Physics Division     Neutron Research Department
    Molecular and Radiation Biophysics Department     Theoretical Physics Division

PNPI RAS, Gatchina, Leningrad district 188300, Russia.
Telephone: +7 (813  71)  46733.       Fax: +7 (813  71)  30010

Last update on:   by   S.F. Udalova