The search for radiative decays of vector mesons in the Radphi experiment

Date of Completion

January 2006


Physics, Nuclear




The Radphi experiment (E94-016) carried out at the Thomas Jefferson National Accelerator Facility (Jlab) was designed to study all-neutral decays of vector mesons. Vector mesons, such as ω and &phis;, were produced by a 5.6 GeV tagged photon beam scattered in a 9Be target. The radiative decays of the &phis;(1020) meson &phis; → a0γ and &phis; → f0γ are of special interest because the ratio of the respective branching ratios provides information regarding the a0(980) and f0(980) quark sub-structure. Both of these radiative &phis; decays can be observed in 5γ final states through the channels f0γ → π0π0γ and a0γ → π0ηγ, where the π0 and η undergo γγ decays. Other all-neutral final states of vector mesons accessible to the Radphi detector include ω and &phis; decaying to π0γ and ηγ, observed in the 3γ channel. The differential cross section as a function of t, the square of the transferred momentum from the incoming photon to the outgoing meson, extracted from these channels can be used to test current models of meson photoproduction in the energy range of a few GeV. The cross sections for ω and &phis; photoproduction were measured by analyzing their 3γ decays, assuming that the nuclear cross section is given by the nucleon cross section multiplied by the atomic weight. The differential ω photoproduction cross section was measured for the first time with high statistics in the -t region from 0.2-1.5 GeV 2. This measurement does not give evidence of hard quark-interchange which has been proposed as an important mechanism for ω photoproduction in the few GeV energy region. Based on the measured &phis; photoproduction cross section, upper bounds for the decay rates of &phis; into π 0π0γ and π0ηγ final states were determined. ^