Cross Section Measurement of Exclusive ϕ-Meson Electroproduction off the Proton at CLAS12

Abstract

This analysis studies the exclusive ϕ meson electroproduction process ep → e′p′ϕ at CLAS12 in the kinematic region 0.39 ≤ Q² ≤ 8.38 GeV², 1.97 ≤ W ≤ 4.03 GeV, and 0.17 ≤ −t ≤ 7.26GeV². Cross section σ(Q²,W) and differential cross section dσ/dt (Q²,W,t) measurements are reported. The scaling of the overall cross section was determined to be 1/Q⁶˙⁴⁷⁺⁻⁰˙⁹⁷, which is consistent with the Generalized Parton Distribution (GPD) prediction of 1/Q⁶. The ratios of the longitudinal and transverse cross sections, R = σL / σT , are extracted from the angular decay distributions for four values of Q² and are found to be consistent with the GPD scaling prediction. The mean-square gluonic radius of the proton ⟨b²⟩ subscript g is extracted from the t-dependence of the differential cross sections dσ / dt in the kinematic region 0.12 ≤ x subscript B ≤ 0.39, the first such measurement in the valence regime.