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HK: Fachverband Physik der Hadronen und Kerne

HK 10: Hauptvorträge

HK 10.1: Hauptvortrag

Dienstag, 13. März 2007, 11:15–11:45, A

Improved study of possible Θ⁺ production in the pp → pK⁰Σ⁺ reaction with the COSY-TOF experiment^* — •Eduard Roderburg for the COSY-TOF collaboration — Forschungszentrum Juelich

The analysis of measurements with COSY-TOF in 2000 and 2002 of the reaction pp → pK⁰Σ⁺ revealed a structure in the pK⁰ subsystem which was interpreted as evidence for the exotic pentaquark Θ⁺ [1], predicted as a narrow state by D. Diakonov et al. [2]. In order to investigate this structure, an improved measurement was performed in October - December 2004 with an upgraded setup and higher luminosity. COSY-TOF is a non-magnetic time of flight spectrometer at an external beam line of the Proton Synchrotron COSY. Charge sensitive detectors, placed close to a tiny target, permit the identification and reconstruction of the decay of neutral into charged particles as close as 10 mm to the target. K⁰ mesons are identified by their decay into charged pions. The measurement of the 4-vector of the proton and of the decay kink of the Σ⁺ enable the reaction pp → pK⁰Σ⁺ to be exclusively identified with an acceptance of nearly 4π in the center-of-mass system. The coincident detection of a Σ⁺ hyperon proves the existence of an anti-strange quark in the pK⁰ system. The results of the recent study obtained with three independent analysis procedures will be presented and an upper limit on the cross section for the reaction pp → Σ⁺Θ⁺ will be given as a function of the assumed mass of Θ⁺. *supported by BMBF and FZ Jülich [1] The COSY-TOF Collaboration, Physics Letters B595 (2004) 127 [2] D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A359 (1997) 305