Data analysis techniques, differential cross sections, and spin density matrix elements for the reaction γ p → ϕ p

Abstract

High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γp→φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (s) from 1.97 to 2.84 GeV, with an extensive coverage in the φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (φ→K+K-) and neutral- (φ→KS0KL0) KK̄ decay modes of the φ. Further, for the charged mode, we differentiate between the cases where the final K- track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide s bins for the charged- and the neutral-modes, respectively. Possible effects from K+Λ* channels with pKK̄ final states are discussed. These present results constitute the most precise and extensive φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction. © 2014 American Physical Society.