Spin Density Matrix Elements from diffractive φ meson production at HERMES

Abstract

Exclusive production of φ mesons on hydrogen and deuterium targets is studied in the HERMES kinematic region 1 < Q 2 < 7 GeV 2 and 3.0 < W < 6.3 GeV. Spin density matrix elements and their Q 2 and t dependences are presented. These data are consistent with s-channel helicity conservation in exclusive φ meson production. No statistically significant evidence for the contribution of unnatural-parity-exchange amplitudes is found.

Ratios of helicity amplitudes for exclusive ρ0 electroproduction

“…A large phase difference δ 11 ≈ 20 degrees was measured by the H1 Collaboration for exclusive ρ 0 and φ meson electroproduction at 2.5 GeV 2 < Q 2 < 60 GeV 2 [21]. A large value of δ 11 = (33.0 ± 7.4) degrees was measured also in φ meson production at HERMES [52]. As two-gluon exchange dominates in φ meson production at HERMES kinematics, the measured large value of δ 11 for ρ 0 cannot be attributed solely to the quark-antiquark exchange essential for ρ 0 meson production.…”