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03-1-0994-92/2002   Priority:
Status: 		2
Extended

Studies of the Threshold Production and Rare Decays
of Light Mesons
(Project WASA)

Leader:

B. Morozov

Scientific Programme:

WASA (Wide Angle Shower Apparatus) has been built up at the cooler storage ring CELSIUS (Uppsala, Sweden). About 80 researchers from Sweden, Russia, Poland, Germany and Japan are developing the sophisticated equipment. 12 members of the WASA collaboration are from JINR. The WASA 4 detector set-up uses an internal well localized hydrogen or deuterium pellet target. An extremely thin-walled (0.18 rad.lengths) superconducting solenoid is placed inside an electromagnetic CsI(Na) calorimeter. Within the magnet there is a track detector (17-layer straw drift chamber) surrounded by a thin layer of plastic scintillators. The tracker is able to measure momentum of leptons with an accuracy of 1 2% in the range of 20 600 MeV/c. Particles emitted in the forward direction are measured by a forward spectrometer (calorimeter, tracker and trigger).
At present the emphasis is put on studies of production near the kinematics threshold of - and -- mesons in pp- and pd- interactions, bremsstrahlung, meson-nuclear quasi-bound system, dibaryon states and other exotic processes. Very-near-threshold measurements of meson production using the forward going recoils in the pd - and dd - reactions are possible owing to a small-angle tagging spectrometer for which the quadrupoles and the first bending magnets downstream the target are used as components.
The future research is focused on the rare decays of the light mesons 0, and, if the energy is raised, '. These decays give knowledge, among other things, of fundamental symmetries, charge conjugation and parity, form factors, possible exotic propagators and chiral perturbation theory.

Expected main results in 2001:
In the first experiment at the newly constructed 4 -set-up it is planned to investigate the nature of the isospin violation in the + - 0 decay which is in Chiral Perturbation Theory connected with the mass difference between the up and down quarks. Therefore we propose:
- to measure the parameters of the + - 0 Dalitz plot distribution with an accuracy of about 1%,
- to measure the experimental value of the + - 0 / 2 branching ratio and to improve significantly the accuracy of the parameters that enter theoretical calculations.
To this end, the plans in 2001 are:
- to install the trigger of the threshold production in the dp 3He reaction,
- to carry out the first measurement of the + - 0 decay in the CELSIUS ring (100 hours run).

List of Activities
  Activity or project SpokespersonsStatus
  WASA B. Morozov Preparation

Participating Institutes and Organizations

 
Germany FZJ (Julich)
Poland IEP WU (Warsaw), SINS (Warsaw, Lodz)
JINR DLNP, LPP
Russia SSC-ITEP, MEPI (Moscow), BINP (Novosibirsk)
Sweden Univ. (Uppsala)
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