Differential cross sections and spin density matrix elements for gamma p -> phi p from CLAS

Abstract

Preliminary differential cross-sections and the ${\rho }_{M{M}^{\prime }}^0$ spin density matrix elements (SDME) for the reaction $\gamma p\to \varphi p$ for both charged- ($\varphi \to K^{+}{K}^{-}$) and neutral-mode ($\varphi \to K_L^0{K}_S^0$) topologies obtained from CLAS are presented. Our kinematic coverage is from near production threshold ($\sqrt{s}\sim 1.97$ GeV) to $\sqrt{s}=2.84$ GeV, with a wide coverage in the production angle. As seen in previous LEPS results, the differential cross-sections show a localized "bump" between $\sqrt{s}\sim 2$ 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 $K^{+}\Lambda (1520)$ 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.

Contribution to the proceedings of International conference on the structure of baryons (BARYONS'10), Osaka, Japan, Dec. 7-11, 2010

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