Measurement of beam asymmetry for π-Δ++ photoproduction on the proton at Eγ=8.5 GeV

We report a measurement of the pi(-) photoproduction beam asymmetry for the reaction (gamma) over right arrowp -> pi(-)Delta(++) using data from the GLUEX experiment in the photon beam energy range 8.2-8.8 GeV. The asymmetry Sigma is measured as a function of four-momentum transfer t to the Delta(++) and compared to phenomenological models. We find that Sigma varies as a function of t : negative at smaller values and positive at higher values of vertical bar t vertical bar. The reaction can be described theoretically by t-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.

Automated summary

This study reports a measurement of the beam asymmetry for pi(-) photoproduction in the energy range of 8.2-8.8 GeV, finding that the asymmetry varies with the four-momentum transfer t to the Delta(++) and requires t-channel particle exchange. The significance of higher-order corrections to one-pion exchange at low momentum transfer is also discussed in this first measurement of the process at this energy.