Proposal to the PAC

Study of resonances decaying into and search for the exotic meson in the reaction using the Crystal Barrel detector at ELSA

The CB-ELSA Collaboration

Spokesperson: E. Klempt
Contact Person: J. Smyrski
e-mail: thoma@iskp.uni-bonn.de

J. Smyrski
Institute of Physics, University of Crakow
H. Flemming, H. Koch, H. Matthäy
Physikalisches Institut, Universität Bochum
O. Barholomy, V. Credé, A. Ehmanns, J. Ernst, I. Fabry, M. Fuchs, C. Funke,
J. Junkersfeld, H. Kalinowsky, E. Klempt, C. Schmidt, T. Szczepanek, U. Thoma
Institut für Strahlen- und Kernphysik, Universität Bonn
Y.A. Beloglazov, A.B. Gridnev, I.V. Lopatin, D.V. Novinski, V.V. Sumachev
Leningrad Nuclear Physics Institute, Gatchina, St.Petersburg
and Institut für Strahlen- und Kernphysik, Universität Bonn
R. Bantes, H. Dutz, R. Gothe, E. Gutz, S. Höffgen, M.Konrad, B. Schoch, D. Walther
and F. Klein, D. Menze, M. Ostrick
Physikalisches Institut, Universität Bonn
A. Kozela
Institute of Nuclear Physics, Crakow
G. Anton, A. Fösel, J. Hößl, G. Suft
Physikalisches Institut, Universität Erlangen
H. Freiesleben, B. Kopf, E. Kuhlmann
Physikalisches Institut, Universität Dresden
B. Krusche, V. Metag, R. Novotny, S. Sack, S. Schadmand
Physikalisches Institut, Universität Giessen
M. Schumacher, F. Smend, W. Weihofen
Physikalisches Institut, Universität Göttingen
J. Langheinrich, R. Santo
Physikalisches Institut, Universität Münster

Bonn, October 1999

Beam specifiations

Equipment

The measurements will take place in the former SAPHIR area at ELSA using the Crystal-Barrel detector and a scintillating fibre detector for tracking of charged particles. The (upgraded) photon tagger of the SAPHIR experiment and a photon veto counter behind the target define interactions of photons. The trigger requires an interacting photon and energy deposit in the barrel detected in a fast cluster encoder. The data will be taken in parallel to the accepted proposal on photoproduction of . Polarised electrons would be welcome but are not required.

Abstract

We propose to study the reaction with the and both decaying into . Data on this reaction will allow

• a search for excitations decaying into
• a search for or excitations decaying into the S₁₁(1535).
• a search for the , a newly discovered meson with exotic quantum numbers. Thehas been observed at BNL and at CERN to decay into .
• a measurement of the cross section for a₀(980) photoproduction. The a₀(980) will be detected in its decay mode.

The Crystal Barrel detector with its excellent photon detection capability is the ideal instrument to study this reaction over the full dynamical range. We plan to perform the experiment in the SAPHIR area in which the Crystal Barrel detector is presently being set up. The SAPHIR tagger will be used covering a photon energy range from 0.31 to 0.94 times the primary electron energy.With a choice of 3.2 GeV we cover from 1.67 to 2.55 GeV and thus reach an upper limit of 1.6 GeV in the invariant mass. At this energy, the predicted production cross section has its maximum value. In the set up phase we will use a second setting in which we cover the photon energy range from 0.31 to 0.94 GeV. The lower limit is at the nominal production threshold, the energy range covers the second resonance region up to =1.62 GeV.
The 3^rd resonance region will be investigated by the choice of an e^- beam momentum of 1.5 GeV providing a bridge between the two former data sets. Interacting photons are defined by the tagger signal in anticoincidence with the photon-veto, their energy is measured through the electron deflection angle in the magnetic field of the tagger. We plan to trigger the data acquisition by the presence of an interacting photon in coincidence with a multiplicity-one signal from a scintillating fibre counter surrounding the 5 cm liquid H₂ target and in coincidence with a fast photon-cluster encoder asking for at least 3 contiguous energy deposits in the Crystal Barrel.
We plan to start with a moderate beam intensity of ~ 2 •10⁶ tagged photons/s. The data will be taken simultaneously with data on other reactions; in particular with data on production (Proposal U. Thoma, 1998), on photoproduction of and ' mesons (Proposal A. Fösel, 1999) and of and (Proposal R. Gothe, 1999).