Folding model analysis of pion elastic and inelastic scattering from 6Li and 12C

π ^±-Nucleus scattering cross sections are calculated applying the Watanabe superposition model with a phenomenological Woods-Saxon potential. The phenomenological potential parameters are searched for π ^± scattering from ⁶Li and ¹²C to reproduce not only differential elastic cross sections but also inelastic and total and reaction cross sections at pion kinetic energies from 50 to 672 MeV. The optical potentials of ⁶Li and ¹²C are calculated in terms of the alpha particle and deuteron optical potentials. Inelastic scattering has been analyzed using the distorted waves from elastic-scattering data. The values of deformation lengths thus obtained compare very well with the ones reported earlier.     

Strong interaction physics from hadronic atoms

Hadronic atoms provide a unique laboratory for studying strong interactions and nuclear medium effects at zero kinetic energy. Previous results from analyses of strong-interaction data consisting of level shifts, widths and yields in π⁻, K⁻, p̄ and ∑⁻ atoms are reviewed. Recent results from fits to comprehensive sets of data in terms of density-dependent optical potentials that respect the low-density limit, where the interaction tends to the free hadron nucleon value, are discussed. The importance of using realistic nuclear density distributions is highlighted. The introduction of density dependence in most cases significantly improves the fit to the data and leads to some novel results. For K⁻ atoms, a substantial attraction of order 200 MeV in nuclear matter is suggested, with interesting repercussions for K̄ condensation and the evolution of strangeness in high-density stars. For p̄ atoms it is found that a reasonable p-wave strength can be accommodated in the fitted optical potential, in agreement with the energy dependence observed for some low-energy p̄N reactions. For ∑⁻ atoms, the fitted potential becomes repulsive inside the nucleus, implying that Σ hyperons generally do not bind in nuclei in agreement with recent measurements. This repulsion significantly affects calculated masses of neutron stars.     

Is there a narrow ε under the ϱ?

The possibility that a narrow ? resonance exists, approximately degenerate in mass and width with the ?, is considered. It is shown that data on π⁺π^? production near the ? mass, including the full set of joint moments in π⁺p → π⁺π^?Δ⁺⁺ as well as the moments obtained with a polarized target in π^?p → π^?π⁺n, are consistent with the existence of such a resonance. Our method, which involves a compromise two-parameter fit to the mass dependence of some moments and the mass-averaged values of all moments, indicates that a broad ? with a slowly varying phase shift and a rather low mass, 600 MeV, also fits the data. However, the two solutions could be distinguished by accurate measurements of the mass dependence of some moments, using existing data on π⁺p → π⁺π^?Δ⁺⁺, and the existence (or non-existence) of a narrow ? clearly demonstrated.     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Optical potential calculations for the 1s level in pionic atoms

The Ericson-Ericson optical potential for theπ-nucleuss-wave interaction was extended to be applicable also for light nuclei. In particular, terms of order A^?1 were evaluated and the (π2N) dispersion was considered. From comparison with experimental data we found that considerable improvement could be achieved by introducing terms of order A^?1. The (π2N) dispersion was found to be repulsive and of the same magnitude as the absorption. The (πN) scattering lengths were deduced to be α₃?α₁=0.258±0.008m _π ^?1 and α₁+2α₃=?0.018±0.008m _π ^?1 .     

Mass and energy dependence of pion-induced fission

Data for fission induced by pi meson beams from 80 to 500 MeV are presented for nuclei from Fe through Pu as measured by solid state track detectors. The general trends for binary fission withπ ⁺ are reproduced fairly well by a calculation in the ‘high excitation’ limit with standard level density and fission barrier parameters, butπ ^? data are underpredicted. A universal dependence of the binary fission probabilities with the fissility (Z±1)²/A is found to be valid for both pion beam charges for all beam energies below the delta resonance. Probabilities for observing three fragments withπ ⁺ are not reproduced by a ternary fission application of the model found to work for binary fission.     

Extraction of spectroscopic factors using R-matrix theory

The relation of the dimensionless reduced width of a state to its spectroscopic strength is discussed and the spectroscopic factor is calculated as the ratio of the reduced width to that of an optical potential analyzed with the same channel radius and boundary condition number. From a model square well problem, the reduced width is shown to be sensitive to these parameters. Neutron scattering to the 5.08 MeV state of ¹⁷O is analyzed with R-matrix theory and the value obtained for its spectroscopic factor is 0.80. This value is shown to be moderately independent of the parameters of the optical potential, a fact which greatly simplifies analysis by eliminating the strong dependence upon the location of the pure single particle state.     

Multipion production in photon-photon collisions

The magnitudes of the matrix elements for γγ→2π⁺2π^?, γγ→π⁺π^?2π⁰, γγ→2π⁺2π^?π⁰, γγ→2π⁺2π^?2π⁰, γγ→3π⁺3π^?3π⁺ and γγ→3π⁺3π^?π⁰are deduced from experimental data as a function of the invariant massW of the system (from 1.0 to 3.0 GeV). It is shown that the data are consistent with a universal energy dependence of the reduced channel amplitudes. A statistical model is shown to describe the peaks in the energy dependence of multipion production in γγ collisions quite well without introducing explicit intermediate resonances.     

Higher-twist effects in deep-inelastic scattering

Non-scaling, non-factorizing 1/Q² contributions to cross sections are derived for semi-inclusive deep-inelastic scattering, ?N → ?′πX. These higher twist terms are dominant at large z = p_π · p_N/Q · p_N. They provide unusual (1 ? y) terms in the cross section. as well as asymmetries in the azimuthal angle dependence. Calculations are also presented for the quark to pion fragmentation function D_π(z, Q²).     

Azimuthal correlations in 40 GeV/c π−p collisions and the independent cluster model

Data on azimuthal correlations and their rapidity dependence are presented in inclusive and semi-inclusive reactions π^?p → π⁺π⁺X,→ π^?π^?X and π⁺π^?X at 40 GeV/c. They show a long range as well as a short range effect. The short range effect, leading to different behaviour of dN/dφ near φ = 0 of like and unlike pion pairs is explained by identical and unidentical particle statistics. The predictions of the independent cluster model for the azimuthal asymmetry are in qualitative agreement with data of this experiment as well as those at 102 and 205 GeV/c.     

Improved theoretical pion-nucleus optical potentials

An approach which makes the first order pion-nucleus optical potential theoretically sound is presented. This study should permit higher order improvements to the potential to be more meaningful and the nuclear structure information extracted from pi-nucleus scattering to be more reliable. Based on multiple scattering theory, three optical potentials are constructed and studied in momentum space. These models are the popular Kisslinger potential, the local “Laplacian” potential, and an “improved off-shell potential;” the latter one is derived from absorptive separable pion-nucleon potentials which exactly reproduce on-shell πN scattering. By working in momentum space and explicitly including πN resonances and off-shell effects in the definition of the optical potential, the approach described here is capable of handling any number of pi-nucleon partial waves, is applicable over a very wide energy region, is based on a physical model for off-shell behavior, and is extended easily to include higher order effects. The optical potentials are inserted into two different relativistic wave equations to determine the total cross section and elastic differential cross section for pi-nucleus scattering. It is found that the various models for off-shell πN scattering determine significantly different πC¹² scattering, with the improved off-shell model preferred on theoretical grounds. Also discussed is the importance of properly transforming πN scattering to the pi-nucleus c.m. system, the origin of the shift in the peak position of the π^?C total cross section, and the reason for the increased diffractive nature of the differential cross section at 180 MeV.     

Regge-Mueller analysis in the pionization region

We attempt to determine the sub-asymptotic terms in the pionization region of π^±-inclusive reactions by analysing the rapidity dependence of various cross-sections.     

KNπ final states in K+p interactions at 7.3 GeV/c

Data are presented on the production of the KNπ final states in K⁺p interactions at 7.3 GeV/c. The energy dependence of the KNπ final state cross sections, the effective-mass distributions, and the spectra of c.m. longitudinal momenta are given, and features of these data are compared with predictions of the generalized Veneziano (GV) model. Furthermore, we present the momentum transfer and decay angular distributions for K¹ (890), K¹ (1420) and Δ (1236) production within the KNπ final states and discuss these quasi-two-body reactions in terms of the GV model.     

Elastic backward scattering of negative pions on protons at 25 and 38 GeV/c

The backward elastic scattering reaction π^?p → pπ^? at momenta 25 and 38 GeV/c have been measured using a magnetic spectrometer with hybrid chambers. The experimental data on the dependence of the cross section dσ/du on the momentum transfer u as well as the energy dependence dσ/du at u = 0 are given.     

Photodisintegration of 11Li and Radiation Capture of Two Neutrons by 9Li

Photodisintegration of ¹¹Li and radiation capture of two neutrons by ⁹Li are studied in the frame of algebraic version of resonating group method and in asymptotic potential approximation. The behavior of the scattering phases shows on the existence of J ^π=3/2⁺ and J ^π=5/2⁺ resonances in continuum above the three-body decay threshold ¹¹Li→⁹Li+n + n. The cross-section of photodisintegration as well as the cross-section of radiation capture have been received. Energetic dependence of the first one is in good correspondence with the experimental data.     

Impulse-approximation correction in pion-nucleus optical potential

The local density approximation is used in this paper to calculate the first-order pion-nucleus optical potential. TheπN scattering matrix in nuclear medium is computed by employing separableπN scattering matrix. This nuclear-mediumπN scattering matrix, which includes impulse-approximation correction is then used to construct the pion-nucleus optical potential.π-¹²C elastic scattering results obtained by using this potential are compared with the impulse-approximation potential results.