arXiv subjects

J. Adam Jr

Publications and source records attributed to J. Adam Jr.

4 recordsLinked to original sources

arXiv2005

Charged and neutral pion production in the S-matrix approach

The S-matrix approach is used to calculate charged as well as neutral pion production reactions from NN scattering, with the same set of underlying processes and interactions. The chiral perturbation theory piN scattering amplitude is used. For the nucleon-nucleon distortions a newly developed realistic potential within the Bonn family of potentials, valid well above the pion production threshold, is considered. In the pi+ production case, the NN potential, the piN relative p-waves and the treatment of the exchanged pion energy build up the observed cross-section strength.

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arXiv2005

Neutral and charged pion production in the S-matrix approach

The S-matrix approach is applied to charged and neutral pion production in pp collisions, in which the spin/isospin channels filter differently the rescattering mechanism. The chiral perturbation theory rescattering amplitude is employed. The contributions from the single-nucleon, Z-diagrams and Delta-isobar mechanisms are also included. For the reactions investigated, the convergence of the partial wave series is quite satisfactory and J=0 is enough to describe the data close to threshold.

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arXiv2004

Pion re-scattering operator in the S-matrix approach

The pion re-scattering operator for pion production, derived recently in time-ordered perturbation theory, is compared with the one following from the simple S-matrix construction. We show that this construction is equivalent to the on-shell approximation introduced in previous papers. For a realistic NN interaction, the S-matrix approach, and its simplified fixed threshold-kinematics version, work well near threshold.

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arXiv2002

Trinucleon Photo Reactions with $Δ$-Isobar Excitation: Radiative Nucleon-Deuteron Capture and Two-Body Photo Disintegration of the Three-Nucleon Bound State

Radiative nucleon-deuteron capture and photo disintegration of the three-nucleo n bound state with two-body final states are described. The description uses nucleon degrees of freedom extended to include the excitation of a single nucleon to a \diso. The baryonic interaction and the electromagnetic cu rrent couple nucleonic states and states with a \diso. Exact solutions of three-p article scattering equations are employed for the initial or final states of the reactions. The current has one-baryon and two-baryon contributions. The role of t he \diso in the description of the considered photo reactions is discussed and fo und to be moderate. The spin observables $A_{yy}$ and $T_{20}$ at $90^{\circ}$ la b scattering angle can be calculated model-independently from the $E1$ Siegert te rm in the long-wavelength limit.

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