arXiv subjects
Publications and source records attributed to F. Cano.
We report on reactions producing two pions induced by real and virtual photons or nucleons. The role of different resonances in these reactions is emphasized. Novel results on coherent two pion photoproduction in nuclei are also reported.
We study the electromagnetic transitions of the Roper N(1440) resonance. Our results, when combined with the previously obtained for the mass and the pionic strong decay widths of the Roper, show that within a non-relativistic constituent quark model scheme, a comprehensible understanding of the Roper phenomenology can be achieved. They also seem to support the view of the Roper as a radial excitation of the nucleon, though more experimental data are needed to reach a definitive conclusion.
Strong pionic decays of baryons are studied in a non-relativistic quark model framework via a convergent (p/E) expansion of the transition operator. Results are compared to the ones obtained within a more conventional (p/m) expansion.
From a refined non-relativistic quark model that fits the baryonic low-energy spectrum the study of strong pion decay processes within an elementary emission model scheme points out the need of incorporating size-contributing components into the baryon wave functions. In particular the effect of a (qqq qantiq) component is investigated in the framework of a quark pair creation model.
The gamma p ---> pi+ pi- p reaction, in combination with data from the pi N ---> pi pi N reaction, allows one to obtain the s- and d-wave amplitudes for the N*(1520) decay into Delta pi with absolute sign with respect to the N*(1520) ---> N gamma helicity amplitudes. In addition one obtains the novel information on the q dependence of the amplitudes. This dependence fits exactly with the predictions of the non-relativistic constituent quark models. The absolute values provided by these models agree only qualitatively, and a discussion is done on the reasons for it and possible ways to improve.
In this talk we cover several issues concerning pion production. The first one is the p p ----> p p pi^0 reaction where an alternative explanation based on the off shell extrapolation of the pi N amplitude is offered. A recent model for the gamma N ----> pi pi N reaction is presented and a new kind of exchange current is constructed from it which allows one to address problems like double Delta photoproduction from the deuteron. Finally the (gamma, pi pi) reaction in nuclei is studied and shown to be highly sensitive to the renormalization of the pions in nuclei.