COMPARISON BETWEEN uu AND dd PRODUCTIONS BY THE γp → π~-Δ~(++) AND π~+Δ~0 REACTIONS AT FORWARD π ANGLES AT E_γ = 1.5-3.0 GeV

摘要

Photoproduction reactions are dominated by isospin rules. In the case of πΔ pho-toproduction on the proton at forward π angles, the exchange of isospin = 1 meson (π or ρ) in the t-channel is the most dominant reaction mechanism, which is considered to give a cross section ratio σ(π~+Δ~0)/σ(π~-Δ~(++)) of 1/3. The cross section ratio has not been measured precisely experimentally. We present preliminary results for the cross section ratio at E_γ = 1.5-3.0 GeV. Larger ratios than 1/3 measured by our experiment at LEPS/SPring-8 suggest that the dd productions are enhanced compared with the uu productions in the photoproduction reactions on the proton.