A study of 3π production in γ p → nπ+π+π− and γ p → Δ++π+π−π− with CLAS at Jefferson Lab

Abstract

Apart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the qq¯ system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of a JPC = 1−+ state decaying via ρπ. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γ p → nπ+π+π− and γ p → Δ++π+π−π−, we are analyzing a large data-set of a three pion system. In the first reaction channel, events are selected with low four-momentum transfer to the neutron, in order to enhance one pion exchange production. The latter reaction is expected to be dominated by pion exchange between the baryon and the 3π meson system, given identification of Δ++ in the event. For both 3π systems the data exhibit two intermediate decays, ρπ and f2π. An analysis of the kinematics and dynamics of those two data-sets has been performed, as well as a study of the angular distributions looking for resonance contributions.