Measurement of Differential Cross Sections and Spin Density matrix elements along with a Partial Wave Analysis for γp → pω Using CLAS at JLab

Abstract

This work presents measurements of differential cross sections, dσ/dcosθ$ω\atop{CW}$, and spin density matrix elements, P$0\atop{MM'}$, for the reaction γp → pω in the energy range 1.72 GeV< √s <2.84 GeV. The data were collected at Jefferson Lab, using the CLAS detector, as part of the g11a run period in 2004. Our P$0\atop{MM'}$ measurements vastly increase the precision of the world s data and extend the large angle measurements by over 400 MeV in √s. Our data confirms that for √s < 2.1 GeV, the forward angle (small |t|) production amplitude is dominated by t-channel π0 exchange. At higher energies, existing non-resonant models do a poor job of describing our data. In particular, u-channel models fail to reproduce our highest energy backwards P$0\atop{MM'}$ measurements. A mass-independent partial wave analysis has also been performed. Near threshold, the dominant resonance contributions extracted are the **** F15(1680) and *** D13(1700). Together with the t-channel π0 exchange, these three waves provide a remarkably good description of our differential cross section and spin density matrix element measurements for √s < 2 GeV. Strong, but not conclusive, evidence for the **** G17(2190) has also been extracted. Improved non-resonant models may be necessary to irrefutably show whether this state contributes to ω photoproduction. Evidence for missing resonances is suggestive, but inconclusive without theoretical input.