The OZI Rule and Spin Alignment of Vector Mesons at COMPASS

Abstract

The reaction pp → pV p (V = ω, φ) has been studied with the COMPASS spectrometer in 2008 and 2009, using a 190 GeV/c proton beam impinging on a liquid hydrogen target. The measured cross section ratio ratio violates the OZI prediction by a factor of ≈4. Its kinematic dependence of the Feynman xF and the MpV mass is discussed in terms of diffractive production of baryon resonances in competition with central production. The Mpω spectrum has a rich structure, indicating the importance of baryon resonances decaying into pω, in sharp contrast to the structureless Mpφ spectrum. Outside the resonant region, the OZI violation factor is about 8, independently of xF . The spin density matrix element ρ00 of the vector mesons is studied in selected reference frames. Dependences of the vector meson spin alignment on xF and MpV are found.