Analysis of the γp → K⁺π⁺π^-(π^-)_missp Photoproduction Reaction with CLAS.

The γp → K⁺π⁺π^-(π^-)_missp photoproduction reaction was measured using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. All particles in this reaction were detected apart from a second π^-, whose kinematics were determined from the missing momentum information. Invariant mass cuts were imposed on the π⁺π^- and π⁺(π^-) combinations to select for the intermediate K⁰_S, so that the γp → K⁺K⁰_S(π^-)_missp reaction could be analyzed. To obtain a clear selection, cuts were imposed on the incoming photon energy and the target fiducial volume, based on the estimation of the reaction vertex through the points of closest approach of pairs of tracks. Additionally, K⁰_S production and decay were simulated using Monte Carlo to analyse the kinematics of a pure phase space of the particles observed in the final state. The f₁(1285) meson was clearly observed using the K⁰_S selection, with a production strength dependent on the momentum transfer. Additional activity was observed at higher energies, which calls for further inquiries into similar reactions, for instance with K⁰_L or with charged kaons.