Influence of the In-medium Nucleon Swelling on Pion-Nucleus Scattering at High Energy

We investigated the influence of the in-medium nucleon swelling on pion-nu-cleus scattering at energy above the Δ33 resonance.An increased theoretical π+-12Cdifferential cross section at 800 MeV/c was found as a result of the nucleon swellingeffect.

Analyses of <i>π</i>^±- 12C Elastic Scattering and Reaction Cross-Section Data Below, Atop and Above the Δ-Resonance

The pion-nucleus elastic scattering and reaction cross-section data at incident energies below, atop and above the Δ-resonance are analyzed using the full Klein-Gordon equation using an optical potential. Analytic forms of the potential are determined using the inverse scattering theory in those cases where phase shift analyses were available. The Coulomb effect is incorporated using Stricker’s prescription. Both elastic scattering data and the reaction cross sections between 120 and 400 MeV are well reproduced. Both real and imaginary parts of the potential are local. The potential points determined by the inverse scattering theory in the interior region at 230 MeV clearly establish that the real part is repulsive. This remains the case at higher incident energies. The real part turns repulsive above the resonance, whereas the imaginary part reflects the dominance of surface absorption, which is maximum near atop the Δ-resonance and then falling off at higher energies.

Analyses of Low-Energy <i>π</i>^--¹²C Elastic Scattering Data

A new updated simple local optical potential is proposed for analyzing low-energy π--12C elastic scattering data at 80 MeV and below. This potential is composed of two real terms and an imaginary term. The nature of the real part of the potential is repulsive at smaller radii and attractive at larger ones. In fact, the height of the repulsive term is found to change linearly with the incident pion kinetic energy. On the other hand, the imaginary part of the potential is attractive, shallow and non-monotonic with a dip at about 1.6 fm. Such a nature of the potential makes it feasible to predict π--12C cross sections at other energies in the energy region considered herein. Coulomb effects are incorporated by following Stricker’s prescription. This study will serve positively in studying both pionic atoms and the role of negative pions in radiotherapy.

Momentum dependence of pion-inducedφmeson production on nuclei near threshold

We study the near-threshold pion-induced production ofφmesons off nuclei in the kinematical conditions of the HADES experiment,recently performed at GSI.The calculations have been performed within a collision model based on the nuclear spectral function.The model accounts for both the primaryπ^-meson–protonπ^-p→φn and the secondary pion–nucleonπN→φNφproduction processes as well as the effects of the nuclearφand nucleon mean-field potentials.We find that the primary reaction channelπ^-p→φn dominates in theφproduction off 12C and^（184）W target nuclei in the HADES acceptance window at incident pion momentum of 1.7 Ge V/c.We calculate the momentum dependence of the absolute and relative（transparency ratio）φmeson yields from the above direct channel.The calculations have been performed for this initial pion momentum allowing for different options for theφN absorption cross sectionσ（φN ）and different scenarios for the in-medium mass shifts of theφmeson and secondary neutron,produced together withφin this channel.We demonstrate that the transparency ratio for theφmesons has,contrary to the absolute cross sections,an insignificant sensitivity to theφmeson and secondary neutron in-medium mass shifts atφmomenta studied in the HADES experiment.On the other hand,we show that there are measurable changes in the transparency ratio due to theφN absorption cross section,which means that such a relative observable can be useful to help determine this cross section from the data taken in the HADES experiment.

Near-threshold K^*(892)^+ meson production in the interaction of π−mesons with nuclei

We study the inclusive production of strange vector K^∗(892)^+ mesons in π−A reactions at near-threshold laboratory incident pion momenta of 1.4-2.0 GeV/c via a nuclear spectral function approach.The approach accounts for incoherent primary π−meson-proton π−p→K^∗(892)^+Σ^− production processes as well as the influence of the scalar K^∗(892)^+-nucleus potential(or the K^∗(892)^+ in-medium mass shift)on these processes.We calculate the absolute differential and total cross sections for the production of K∗(892)+mesons from carbon and tungsten nuclei at laboratory angles of 0∘-45∘and at the aforementioned momenta in five scenarios for the aforenoted shift.We show that the K^∗(892)^+ momentum distributions and their excitation functions(absolute and relative)possess a high sensitivity to changes in the in-medium K^∗(892)^+ mass shift in the low-momentum region of 0.1-0.6 GeV/c.Therefore,the measurement of such observables in a dedicated experiment at the GSI pion beam facility in the near-threshold momentum domain will allow us to get valuable information on the K^∗(892)^+ in-medium properties.