SPIN INFORMATION FROM VECTOR-MESON DECAY IN PHOTOPRODUCTION

For the photoproduction of vector mesons, all single and double spin o bservables involving vector-meson two-body decays are defined consiste ntly in the gamma N center-of-mass frame. These definitions yield a pr ocedure for extracting physically meaningful single and double spin ob servables that are subject to known rules concerning their angle and e nergy evolution. As part of this analysis, we show that measuring the two-meson decay of a photoproduced rho or phi does not determine the v ector meson's vector polarization, but only its tensor polarization. T he vector meson decay into lepton pairs is also insensitive to the vec tor meson's vector polarization, unless one measures the spin of one o f the leptons. Similar results are found for all double spin observabl es which involve observation of vector-meson decay. To access the vect or meson's vector polarization, one therefore needs to either measure the spin of the decay leptons, make an analysis of the background inte rference effects, or relate the vector meson's vector polarization to other accessible spin observables.