Differential cross sections and spin density matrix elements for γp → ϕp from CLAS

Abstract

Preliminary differential cross‐sections and the ρMM’0 spin density matrix elements (SDME) for the reaction γρ → φp for both charged‐ (φ → K+K−) and neutral‐mode (φ → KL0KS0) topologies obtained from CLAS are presented. Our kinematic coverage is from near production threshold (s∼1.97 GeV) to (s = 2.84 GeV), with a wide coverage in the production angle. As seen in previous LEPS results, the differential cross‐sections show a localized “bump” between (s∼2 and 2.2 GeV that is not expected from a simple Pomeron exchange picture. Comparisons between the charged‐ and neutral‐mode results and possible effects from the K+Λ(1520) channel are discussed. Our SDME results confirm the well‐known deviations from t‐channel helicity conservation (TCHC) for Pomeron exchange, but s‐channel helicity conservation (SCHC) is also seen to be broken.