arXiv subjects

R. G. E. Timmermans

Publications and source records attributed to R. G. E. Timmermans.

57 records · Page 4Linked to original sources

arXiv1998

Pion and photon couplings of N* resonances from scattering on the proton

Results of a relativistic model for pion- and photon-induced reactions on the proton are presented. The model is crossing symmetric and gauge invariant. The nucleon resonances P_11 (1440), P_11 (1710), D_13 (1520), S_11 (1535), S_11 (1650), P_33 (1232), P_33 (1600), S_31 (1620), and D_33 (1700) have been included explicitly in the calculation. Unitarity within the channel space πN + γN below the two-pion production threshold has been achieved by using the K-matrix approach. Strong and electromagnetic coupling parameters of the N* resonances have been determined from a fit to the pion-nucleon phase shifts, pion-photoproduction multipoles and Compton-scattering cross sections. The model is shown to describe simultaneously most of the available data. Results for the electric and magnetic polarizabilities of the nucleon are presented.

nucl-th↗

arXiv1998

The Status of the Pion-Nucleon Coupling Constant

A review is given of the various determinations of the different piNN coupling constants in analyses of the low-energy pp, np, pbarp, and pi-p scattering data. The most accurate determinations are in the energy-dependent partial-wave analyses of the NN data. The recommended value is f^2 = 0.075 . A recent determination of f^2 by the Uppsala group from backward np cross sections is shown to be model dependent and inaccurate, and therefore completely uninteresting. We also argue that an accurate determination of f^2 using pp forward dispersion relations is not a realistic option.

nucl-th↗

arXiv1997

The $π^+$--emission puzzle in $^4_Λ$He decay

We re-examine the puzzling $π^+$ emission from the weak decay of $^4_Λ$He and propose an explanation in terms of a three-body decay of the virtual $Σ^+$. Such a resolution of the $π^+$ decay puzzle is consistent with the calculated $Σ^+$ probability in light $Λ$ hypernuclei as well as the experimentally observed $π^+$ energy spectrum and $s$--wave angular distribution.

nucl-th↗