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

Exclusive production of the isoscalar vector mesons ω and φ is measured with a 190GeV/c proton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable _xF of the fast proton. A significant violation of the OZI rule is found, confirming earlier findings. Its kinematic dependence on _xF and on the invariant mass _{M p V} of the system formed by fast proton _pfast and vector meson V is discussed in terms of diffractive production of _pfastV resonances in competition with central production. The measurement of the spin density matrix element _ρ00 of 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 _xF and on _{M p V} are found. Most of the observations can be traced back to the existence of several excited baryon states contributing to ω production which are absent in the case of the φ meson. Removing the low-mass _{M p V} resonant region, the OZI rule is found to be violated by a factor of eight, independently of _xF.