Radial excitation of the nucleon to theP11(1440 MeV) resonance in alpha-proton scattering

Two pion decay of the Roper resonance

“…Work in this direction plus also work in the direction of obtaining microscopically a description of the NN → NN * transition obtained in [20] from the data of [19] would be a natural continuation of the present work, complementing from the chiral symmetry perspective the work already done using quark models in [37].…”

“…The influence of the Roper excitation and its decay modes in many other reactions has been discussed in [16,17,18]. Similarly, it has also been shown [19,20] in the study of the Roper excitation in the (α, α ′ ) reaction that the Roper is very efficiently excited by an isoscalar source, which should somehow be related to this scalar isoscalar decay.…”

Theoretical study of the NN → NNππ reaction

“…This diagram is only relevant at energies T p > 1 GeV in the laboratory frame, where the terms involving crossed ∆ are small ( diagrams (13)- (15) ). At lower energies all of them become negligible since they involve two p-wave couplings of the pions ( diagrams (10) and (11) involve only one p-wave coupling but they are small anyway since the s-wave coupling is comparatively small ).…”

“…The analysis of the (α, α ′ ) reaction on a proton target [10] carried out in Ref. [11] interpreted the results in base of two mechanisms: ∆ excitation in the projectile depicted in Fig.…”

“…An important step in understanding the NN → NN * reaction was given with the experiment of Ref. [10] which showed a relatively large strength for N * excitation due to the exchange of an isoscalar source, the only one allowed in the (α, α ′ ) reaction on the proton when this proton is excited to the Roper. The experiment has been analysed in Ref.…”