Electroproduction of the Phi(1020) Vector Meson at 4 GeV

Abstract

We studied the reaction 𝑒𝑝 → 𝑒′𝑝′𝜙 with a 4.2 GeV incident electron beam in the region of the electroproduction variables Q² from 0.7 to 2.2 GeV² and W from 2.0 to 2.6 GeV. The data were taken and analyzed at the Thomas Jefferson National Accelerator Facility. For the first time, we observe the expected t-slope dependence on Q² and Δ𝜏 in 𝜙 vector meson production. We find that the width of the forward 𝜙-meson diffraction peak increases rapidly as the interaction time decreases below cΔ𝜏 ≈ 1 fm. Within a simple optical model framework, the data show that 𝜙 meson has a smaller size than the 𝜌. The measured 𝜙 cross-section dependence on Q² is in a good agreement with previous measurements and well-described by the phenomenological Pomeron-exchange model. Our cross-section data do not favor the standard Vector Meson Dominance and 𝑠𝑠̅-knockout model predictions. From the angular distribution of the decay 𝜙 → 𝐾⁺𝐾⁻, assuming the 𝑠-channel helicity conservation, we extracted the longitudinal-to-transverse cross-section ratio, 𝑅, and Vector Meson Dominance scaling parameter, 𝜉², which are consistent with the previous measurements and the model expectations.