E. Ya. Paryev

Determination of the η′-nucleus optical potential

Abstract The excitation function and momentum distribution of η ′ mesons have been measured in photon induced reactions on 12C in the energy range of 1250–2600 MeV. The experiment was performed with tagged photon beams from the ELSA electron accelerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the η ′ -nucleus potential. Within the model, the comparison indicates an attractive potential of − ( 37 ± 10 ( stat ) ± 10 ( syst ) ) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the η ′ -nucleus potential of − ( 10 ± 2.5 ) MeV , determined by transparency ratio measurements, a search for resolved η ′ -bound states appears promising.

Measurement of the in-medium phi-meson width in proton-nucleus collisions

The production of φ mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the φ → KK decay using the COSY-ANKE magnetic spectrometer. The φ meson production cross section follows a target mass dependence of A in the momentum region of 0.6–1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium φ width is about an order of magnitude larger than its free value.

Photoproduction of η′ mesons from nuclei and their properties in the nuclear medium

We study the photoproduction of ?? mesons from nuclei near the threshold within the collision model based on the nuclear spectral function. The model properly takes into account both the primary photon?nucleon ?N ? ??N and the secondary pion?nucleon ?N ? ??N production processes as well as the effect of the nuclear ?? mean-field potential on these processes. We find that the secondary channel ?N ? ??N plays an insignificant role in the ?? photoproduction from nuclei. We calculate the transparency ratio for ?? mesons and compare it to the available experimental data. The comparison indicates an inelastic ??N cross section of the order of 6?10 mb. We show that the existing transparency ratio measurements do not allow one to distinguish between two adopted ?? in-medium modification scenarios. Our studies also demonstrate that the momentum distribution and excitation function for ?? production in ?A reactions reveal some sensitivity to these scenarios, which means that such observables may be an important tool to get valuable information on the ?? in-medium properties.

Meson–nucleus potentials and the search for meson–nucleus bound states

Recent experiments studying the meson-nucleus interaction to extract meson-nucleus potentials are reviewed. The real part of the potentials quantifies whether the interaction is attractive or repulsive while the imaginary part describes the meson absorption in nuclei. The review is focused on mesons which are sufficiently long-lived to potentially form meson-nucleus quasi-bound states. The presentation is confined to meson production off nuclei in photon-, pion-, proton-, and light-ion induced reactions and heavy-ion collisions at energies near the production threshold. Tools to extract the potential parameters are presented. In most cases, the real part of the potential is determined by comparing measured meson momentum distributions or excitation functions with collision model or transport model calculations. The imaginary part is extracted from transparency ratio measurements. Results on

Subthreshold η production on nuclei by protons

K^+, K^0, K^-, \eta, \eta^\prime, \omega

Production of K⁺K⁻ pairs in proton-proton collisions at 2.83 GeV

, and

Subthreshold K- production in pion nucleus reactions

\phi

Non-resonant kaon pair production and medium effects in proton-nucleus collisions

mesons are presented and compared with theoretical predictions. The interaction of

Production ofK−-mesons in proton-proton and proton-nucleus interactions at various energies

K^+

Production of K+ mesons in the pp and pA interactions at different energies

and