THEME03-1-0994-92/2005

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03-1-0994-92/2005

Priority:

Status:

In-progress

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

Leader:

B.A. Morozov

Scientific Programme:
WASA (Wide Angle Shower Apparatus) has been built at the cooler storage ring CELSIUS (Uppsala, Sweden). About 80 researchers from Sweden, Russia, Poland, Germany and Japan are developing the sophisticated equipment. 10 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 the 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 the 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, emphasis is put on studies of production near the kinematics threshold of

- and

-- mesons in pp and pd interactions, bremsstrahlung, meson-nuclear quasi-bound systems, dibaryon states and other exotic processes. Using forward - going recoils in the pd and dd reactions, very-near-threshold measurements of meson production 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 focussed on the rare decays of light mesons

⁰,

and, if the energy is raised,

'. Among other things, these decays give knowledge of fundamental symmetries, charge conjugation and parity, formfactors, possible exotic propagators and chiral perturbation theory.

Expected main results in 2004:
In the first experiment at the newly constructed 4

-set-up, it is planned to investigate the nature of isospin violation in the

⁺

⁰ decay which is in Chiral Perturbation Theory connected with the mass difference between up and down quarks. Therefore, we propose:
- to measure the parameters of the

⁺

⁰ Dalitz plot distribution with an accuracy of about 3%,
- to measure the experimental value of the

⁺

⁰ /

branching ratio and to improve significantly the accuracy of the parameters that enter into theoretical calculations.
In accordance with this aim, our plans in 2004 are:
- to continue the study of the

⁺

⁰ decay in the CELSIUS ring (180-hour run), by using deuterium target at two proton energies, 894 MeV and 1360 MeV
- to publish two papers.

List of Activities

Activity or project

Spokespersons

Status

WASA

B.A. Morozov

Preparation

Collaboration
Country or international organization	City	Institute or Laboratory
Germany	Hamburg	Univ.
	Julich	FZJ
	Tubingen	Univ.
Japan	Osaka	RCNP
	Tsukuba	KEK
JINR	Dubna	DLNP
		LPP
Poland	Lodz	SINS
	Warsaw	IEP WU
		SINS
Russia	Moscow	SSC-ITEP
		MEPhI
	Novosibirsk	BINP SB RAS
	Petrozavodsk	PetrSU
Sweden	Uppsala	UU
The USA	Los Angeles, CA	UCLA
	Tempe, AZ	ASU

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

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