Study of ρ0 meson spin alignment in anti pp and pp interactions

The ρ0 meson spin alignment is studied inclusively in all inelasic and in some nonannihilation channels of anti pp interactions at 22.4 and 12 GeV/c, in the reaction anti pp → 2π+2π- + neutrals at 5.7 GeV/c and in pp interations at 24 GeV/c. Its dependence on multilicity, the ρ0 meson transverse momentum pperpendicularto and the Feynman variable χ is investigated. The method of the inclusive analysis is checked with the help of the Monte Carlo events. An essential ρ0 meson spin alignment, manifesting istself most clearly in the transversity frame, is observed in anti pp interactions; the values of the prabalility ρ00T of the zero ρ0 spin protection on the normal to the production plane are 0.51 ± 0.06, 0.53 ± 0.04 and 0.55 ± 0.04 for the above anti pp reactions, respectively. A significant increase of ρ00T with pperpendicularto and only a weak dependence of ρ00T on χ are obtained for anti pp data at 5.7 and 12 GeV/c. The ρ0 meson spin alignment is also observed in anti pp nonannihilation channels at 12 GeV/c (ρ00T = 0.65 ± 0.12) while no substantial effect is seen in pp interactions (ρ00T ≅ 1/3 in any frame). The results are compared with other polarization data and discussed in terms of Regge phenomenology and a quark-parton model incorporating spin-orbit interaction with the confining field. (orig.)