Spin alignment and violation of the OZI rule in exclusive $\omega$ and $\varphi$ production in pp collisions

Abstract

Exclusive production of the isoscalar vector mesons $\omega$ and $\varphi$ 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 $x_F$ and on the invariant mass $M_{p\mathrm{V}}$ of the system formed by fast proton $p_{\mathrm{fast}}$ and vector meson $V$ is discussed in terms of diffractive production of $p_{\mathrm{fast}}V$ 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 $M_{p\mathrm{V}}$ 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 $\varphi$ meson. Removing the low-mass $M_{p\mathrm{V}}$ resonant region, the OZI rule is found to be violated by a factor of eight, independently of $x_{\mathrm{F}}$.

arXiv comment23 pages, 13 figures and 5 tables

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Cited by in corpus (2)

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