The exclusive reaction γp → pπ+π- was studied in the photon energy range 3.0–3.8 GeV and the momentum transfer range 0:4 < -t < 1:0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range, the integrated luminosity was about 20 pb-1. The reaction was isolated by detecting the π+ and proton in CLAS, and reconstructing the π- via the missing-mass technique. Moments of the di-pion decay angular distributions were derived from the experimental data. Differential cross sections for the S, P, and D-waves, in the Mπ + π - mass range 0.4–1.4 GeV, were derived performing a partial wave expansion of the extracted moments. Beside the dominant contribution of the ρ(770) meson in the P-wave, evidence for the ƒ0(980) and the ƒ2(1270) mesons was found in the S and D-waves, respectively. The differential production cross sections dσ / dt for individual waves in the mass range of the above-mentioned mesons were extracted. This is the first time the ƒ0(980) has been measured in a photoproduction experiment.
Copyright © 2009 American Physical Society. This article first appeared in Physical Review D 80, no. 7 (October 22, 2009): 072005:1-19. doi:10.1103/PhysRevD.80.072005.
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