Contribution of the σ meson exchange to pionic double charge exchange reaction

The contribution of the σ meson exchange to the pionic double charge exchange (DCX) reaction is investigated. A concrete calculation on the forward excitation function of the low energy DCX reaction ¹⁴C(π⁺, π⁻)¹⁴O has been performed. It shows that the contribution of the σ meson exchange can reproduce well the resonance like excitation function of low energy DCX reaction. Received: 5 August 1998     

Resonant behaviour in double charge exchange reaction of πmesons on the nuclear photoemulsion

The invariant-mass spectra of the ppπ^- and pp systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the ppπ^- invariant-mass spectrum, while the M_pp spectrum exhibits a strong Migdal-Watson effect of the proton-proton final-state interaction. These findings are in favor of the NN-decoupled NNπ pseudoscalar resonance with T = 0 called d'.     

Fission probabilities across the π-nucleon delta resonance

Cross-sections for the π⁺-induced fission of ²⁰⁹Bi and ²³⁵U have been measured in small steps across the 3-3 resonance to search for any mechanisms that might signal a change in the reaction mechanism across a region where strong coupling of available energy into nuclear excitation can be expected. The bismuth data are found to be in good agreement with a statistical calculation not including new mechanisms. Received: 15 August 2000 / Accepted: 23 January 2001     

Partial-wave analysis and baryon spectroscopy<Superscript>⋆</Superscript>

We continue to update our PWA of fundamental reactions as new data become available. Of primary interest to the N^* program are πN elastic scattering and the photo- and electroproduction of pions. Other photo-reactions are more model dependent, but may reveal resonances coupling weakly to πN final states. We also mention recent results from nucleon-nucleon elastic scattering, which have a less well-known connection to experimental programs proposing to extract N ^* properties from complete experiments.     

Search for a bound trineutron with the 3He(π−pgr;+)nnn reaction

A search for the production of a bound trineutron state has been performed using the reaction ³He(π⁻,π⁺)nnn at incident pion energies of 65, 75, and 120 MeV. No evidence for the existence of the ³n was found, and an upper limit for the production cross section of approximately 30 nb/sr (2σ confidence level) was obtained. Received: 22 October 1998     

New parameterization of the trinucleon wave function and its application to the π <Superscript>3</Superscript>He scattering length

We present a new parameterization of the trinucleon wave function. As a novel feature a separable parameterization for the complete wave function is given. In this way any calculation that considers two-body currents only is largely simplified. To demonstrate this we calculate the π³He scattering length in chiral-perturbation theory. We find reasonable agreement with experimental values inferred from data on level shifts in pionic ³He bound states. The relevance of the π-triton system for an alternative determination of the πN scattering lengths is discussed. Received: 12 August 2002 / Accepted: 25 November 2002 / Published online: 25 February 2003 RID="a" ID="a"e-mail: c.hanhart@fz.juelich.de Communicated by V. Vento     

Pion absorption reactions on N, Ar and Xe

The absorption of π⁺ on Ar was studied at pion energies of 70, 118, 162, 239 and 330MeV, and on N and Xe at 239MeV. Twenty-six absorption reaction channels with at least two energetic charged particles in the final state have been evaluated. Partial cross-sections have been determined according to the number of protons, neutrons and deuterons in the final state. Received: 16 October 2000 / Accepted: 1 December 2000     

The role of the pion pair term in the theory of the weak axial meson exchange currents

The structure of the weak axial pion exchange current is discussed in various models. It is shown how the interplay of the chiral invariance and the double-counting problem restricts uniquely the form of the pion potential term, to the case when the nuclear dynamics is described by the Schrödinger equation with static nucleon-nucleon potential.     

Initial State Interaction in the (π+,3p) Reaction on N, Ar and Xe

The pion absorption reaction (π^{+,3 p} ) on Ar was studied at pion energies of 70, 118, 162 and 239 MeV, and on N and Xe at 239 MeV. The 3p cross section with a 50 MeV cut on the missing energy is presented. The existence of an initial state interaction (ISI) component to the reaction was investigated. The portion of the 3p cross section assigned to the ISI process is less than one half and at lower energies significantly so. Received: 11 December 1997     

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The ω resonance production and its π⁰γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π⁰γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively. The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the π⁰ and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated π⁰'s and γ's are produced. Received: 2 April 2001 / Accepted: 5 June 2001     

Structure functions of the deuteron and meson exchange currents

The deuteron structure functionsA(q ²)B(q ²) and polarization tensorT(q ²) are studied within the Bonn model with meson exchange currents taken into account. It is shown that it is necessary to take all these currents into consideration including the retardation effects. ForA(q ²) the contribution of retardation effects does not depend on the choice of vertex form factors; whereas forB(q ²) it essentially depends on the choice of strong vertices. The best agreement with experiment is achieved for the Bonn relativistic potential.Dedicated to the memory of M. Gmitro.     

Hard pions and axial meson exchange currents in nuclear physics

Starting from the hard meson method we develop a consistent approach to the problem of the axial meson exchange currents (MEC). This method incorporates the current algebra and PCAC together with the vector dominance and allows one to study the pion as well as heavy-meson exchanges on an equal footing. Using a minimal, chiral and approximately gauge-invariant phenomenological Lagrangian (PL) model for the A_1ρπ system we construct the two-nucleon axial MEC operator in the tree approximation. This operator automatically possesses the correct chiral SU(2) × SU(2) transformation properties and has the smoothest momentum dependence which is allowed within the combined current algebra and vector dominance approaches. In the given model, we consider the non-Born part of the amplitude N + J^A → n + π and demonstrate that in the soft pion limit, it exactly coincides with the PCAC prediction.     

Measurement of Gamma-Rays from 11ΛB and 12ΛC

From the ^12 C（π^＋,K^＋）^12 AC reaction the γ -rays of 261.6±0.24 ke V（7/2^＋ →5/2^＋）and 1481.7±0.7 ke V（1/2^＋ →5/2^＋） of ^11 A B,and 2667.3±2.8 keV（1^- 2 → 2^- 1）of ^12 A C hypernuclei have been identified using a large germanium detector array Hyperball2 at K6 beam line of KEK. The observed energies of the transitions 1481.7keV and 261.6 keV are significantly different from the values predicted by the shell model using the △ and SN parameters determined from the ^7 △ Li data.     

Sensitivity of p-3He scattering to meson exchange currents and NN phase shifts

Elastic p-³He scattering is calculated with a microscopic momentum space potential including full spin dependences. High sensitivity is found to the removal of meson exchange currents from the nuclear densities and to the choice of input NN phase shifts.     

Charmed meson decays and right-handed currents

In the presence of right-handed currents including $\text{(}\text{c}\text{s}\text{)}{}_{\mathrm{<mtext>R</mtext>}}$, it is emphasized that the dominant parity-violating (-conserving) Hamiltonian for nonleptonic decays of charmed hadrons transforms like $\text{45}\text{+}\text{45}{}^1\text{(}\text{20″ +}\text{84}\text{)}$ of SU(4), and leads to distinctive results especially in D⁺ → K_Sπ⁺, F⁺ → μ⁺ν_μ and D⁰ → K^?e⁺ν_e, etc.     

Resonance properties from a coupled channel meson exchange model

In this talk, I present the results on the pole structure of pion-nucleon scattering in an analytic model based on meson exchange. The analytic properties of scattering amplitudes provide important information. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions.     

Resonance properties from a coupled channel meson exchange model

In this talk, I present the results on the pole structure of pion-nucleon scattering in an analytic model based on meson exchange. The analytic properties of scattering amplitudes provide important informa-tion. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions.