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Exclusive production of the isoscalar vector mesons omega and phi is measured with a 190 GeV/c proton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable x(F) 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-pV of the system formed by fast proton p(fast) and vector meson V is discussed in terms of diffractive production of p(fast) V resonances in competition with central production.
The measurement of the spin density matrix element rho(00) 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 x(F) and on M-pV are found.
Most of the observations can be traced back to the existence of several excited baryon states contributing to omega production which are absent in the case of the phi meson. Removing the low-mass M-pV resonant region, the OZI rule is found to be violated by a factor of eight, independently of x(F). (C) 2014 CERN for the benefit of the COMPASS Collaboration.
Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).