Spin alignment and violation of the OZI rule in exclusive ω and ϕ production in pp collisions

Exclusive production of the isoscalar vector mesons ωand φis measured with a 190GeV/cproton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable xFof the fast proton. A significant violation of the OZI rule is found, confirming earlier findings. Its kinematic dependence on xFand on the invariant mass MpVof the system formedby fast proton pfastand vector meson Vis discussed in terms of diffractive production of pfastVresonances in competition with central production. The measurement of the spin density matrix element ρ00of the vector mesons in different selected reference frames provides another handle to distinguish the contributions of these two major reaction types. Again, dependences of the alignment on xFand on MpVare found. Most of the observations can be traced back to the existence of several excited baryon states contributing to ωproduction which are absent in the case of the φmeson. Removing the low-mass MpVresonant region, the OZI rule is found to be violated by a factor of eight, independently of xF.