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In the past decades, considerable advances have been made both in experimentally studying and in theoretically describing properties of cold nuclear matter at short nucleon-nucleon distances. In the present study, it is shown that, in addition to the commonly known method of studying the structure of nuclei at short distances in processes of deep-inelastic lepton scattering, processes of particle production in nucleus-nucleus reactions beyond the kinematics of nucleon-nucleon collisions are an important complementary source of information. Some predictions concerning the behavior of special features that are peculiar to such processes and which one can extract from experimental data obtained for collisions of gold nuclei at an energy of 2.4 GeV in the HADES experiment at the GSI (Gemeinschaft für Schwerionenforschung) research center (Darmstadt, Germany) are presented. [ABSTRACT FROM AUTHOR]

The photoproduction of J/ψ mesons off nuclei at the energies of 8 and 11 GeV, which are close to the threshold for their production on a free nucleon, is considered on the basis of the first-collisionmodel relying on the nuclear spectral function and including incoherent processes of charmonium production in photon-nucleon collisions. The model takes into account the absorption of final J/ψ mesons, the binding of target nucleons, and their Fermi motion, as well as the effect of the scalar J/ψ-nucleus potential (or the inmedium shift of the J/ψ-meson mass) on these processes. Under various assumptions on the magnitude of this shift, the momentum dependences of various observables, such as the relative transparency of carbon and gold nuclei and the J/ψ-meson yields, are calculated for meson production on these nuclei. The observables in question include the relative transparencies of these nuclei to J/ψ mesons and the absolute and relativemeson yields from them. It is shown that, at the energy of 11 GeV, which is above the threshold, the first observable is virtually independent of the in-medium change in the J/ψ-meson mass. At the same time, it is moderately sensitive to this change at the subthreshold energy of 8 GeV. On the other hand, it is shown that, at these photon energies, the absolute and relative values of the differential cross sections, especially for the the heavy nucleus of 197 Au, in the momentum range of 4-6 GeV/с are highly sensitive to the in-medium change in the J/ψ-meson mass. Therefore, the present calculations can be used to determine the unknown shift of the J/ψ-meson mass in nuclei by means of comparing their results with data expected from experiments in Hall C at the Continuous Electron Beam Accelerator Facility (CEBAF, USA) upgraded to the energy of 12 GeV. [ABSTRACT FROM AUTHOR]

Within the spectator model, we study the reaction γ d → K −Θ+ p → K − K + np in the threshold energy region. We present the predictions for the exclusive and inclusive K −-meson angular distributions in the laboratory system for this reaction calculated for two possible parity states of the Θ+ resonance at 1.5-and 1.75-GeV beam energies with and without imposing the relevant kinematical cuts on those parts of the sampled phase space where the contribution from the main background sources, associated with the ϕ(1020), Λ(1520) production as well as with the K − p rescattering in the final state, is expected to be dominant. We show that, under the chosen kinematics, these distributions are sensitive to the Θ+ parity and, therefore, can be used as a filter for the determination of its parity. [ABSTRACT FROM AUTHOR]

Within the spectral function approach, we study the direct production and decay via the dikaon (dimuon) channel of ϕ mesons in the interactions of 2.4-and 2.7-GeV protons with light and medium target nuclei. It is shown that the K + K − (µ+ µ−) invariant-mass distribution consists of the two components, which correspond to the ϕ decay “outside” and “inside” the target nucleus. The first (narrow) component has the free ϕ width, while the second (broad) component is distorted by the nuclear matter owing to resonance-nucleon scattering and a possible in-medium modification of the kaons and ρ meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios for the ϕ width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei is larger than the free ϕ width by a factor of about 2 if the total ϕ in-medium width is used and the respective cutoff for the ϕ three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the ϕ in-medium properties owing to the strong absorption of the K − in the surrounding nuclear matter. On the other hand, because of the distortion of the K + and K − on their way out of the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for the modification of the kaon and antikaon properties in the nuclear medium. [ABSTRACT FROM AUTHOR]

Within the spectral function approach we study the direct production and decay via the dikaon (dimuon) channel of f-mesons in the interactions of 2.4 and 2.7GeVprotons with light and medium target nuclei. It is shown that theK+ K- ( µ+µ-) invariant-mass distribution consists of the two components which correspond to the f decay “outside” and “inside” the target nucleus. The first (narrow) component has the free f width, while the second (broad) component is distorted by the nuclear matter due to resonance-nucleon scattering and a possible in-medium modification of the kaons and ?-meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios for the f width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei is larger than the free f width by a factor of about two if the total f in-medium width is used and the respective cutoff for the f three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the f in-medium properties due to the strong absorption of the K- in the surrounding nuclear matter. On the other hand, because of the distortion of the K+ and K- on their way out the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for the modification of the kaon and antikaon properties in the nuclear medium. [ABSTRACT FROM AUTHOR]

The inclusive K[sup –]-meson production in proton—nucleus collisions in the subthreshold energy regime is studied in the framework of an appropriate spectral function approach for incoherent primary proton—nucleon and secondary pion—nucleon production processes, which takes properly into account the nuclear mean-field potential effects on these processes as well as the final state interaction (FSI) among the outgoing nucleons participating in the one-step antikaon creation process. A detailed comparison of the model calculations of the K[sup –] differential cross sections is given for the reactions p + [sup 9]Be, p + [sup 63]Cu, and p + [sup 197]Au at subthreshold energies with the currently available experimental data obtained recently at the ITEP proton synchrotron and at SIS/GSI. It is found that the calculations with inclusion of the influence of both the nuclear density-dependent mean-field potentials and the elementary NN-FSI effects on the K[sup –] production from direct mechanism are able to reproduce, contrary to previous estimates based on the use only of the density-dependent mean fields in calculating the K[sup –] yield from this mechanism, the energy dependences of the invariant differential cross sections for “hard” antikaon creation in p[sup 9]Be and p[sup 63]Cu collisions. It is further shown that the NN-FSI effects play a minor role in describing the data on the spectrum of relatively soft K[sup –] mesons from p[sup 197]Au interactions at incident energy of 2.5 GeV. It is also shown that the relative strength of the proton- and pion-induced reaction channels in the subthreshold energy regime is governed by the kinematics of the experiment under consideration. The influence of the nucleon, kaon, and antikaon mean-field potentials on the K[sup –] yield is explored. It is demonstrated that, in line with previous findings, the K[sup –] optical potential has a strong... [ABSTRACT FROM AUTHOR]

Inclusive K[sup -]meson production in proton-nucleus collisions in the subthreshold-energy regime is analyzed within an appropriate folding model for incoherent primary proton-nucleon and secondary pion-nucleon production processes, which takes properly into account the struck-target-nucleon momentum and removal-energy distribution (nucleon spectral function), novel elementary cross sections for proton-nucleon reaction channels close to threshold, as well as nuclear mean-field potential effects on the one-step and two-step antikaon-creation processes. A detailed comparison of the model calculations of the K- differential cross sections for the reactions p + [sup 9]Be and p + [sup 63]Cu at subthreshold energies with the first experimental data obtained at the ITEP proton synchrotron is given. It displays both the relative role of the primary and secondary production channels at incident energies considered and the contributions to K- production that come from the use of the single-particle part and high-momentum-energy part of the nucleon spectral function. It is found that the pion-nucleon production channel does not dominate in the subthreshold "hard" antikaon production in p[sup 9]Be and p[sup 63]Cu collisions and that the main contributions to the antikaon yields here come from the direct K[sup -]-production mechanism. The influence of the nucleon, kaon, and antikaon mean-field potentials on the K- yield is explored. It is shown that the effect of the nucleon mean field is of importance in explaining the considered experimental data on "hard" antikaon production, whereas the K[sup +] and K[sup -] optical potentials play a minor role. The sensitivity of subthreshold "soft" antikaon production in p[sup 9]Be reactions to the nucleon, kaon, and antikaon mean fields is studied. It is demonstrated that, contrary to the case of "hard" antikaon production, the K[sup -] potential has a very strong effect on the K[sup -] yield, which is comparable with that from the... [ABSTRACT FROM AUTHOR]

The production of η mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12C and on a liquid hydrogen (LH2) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The η mesons have been identified via the η→π0π0η→6γ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF2 array at polar angles of 2∘≤θp≤11∘. Under these kinematic constraints the η mesons are produced with relatively low kinetic energy (≈150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the η-carbon potential at low meson momenta by comparing with collision model calculations of the η kinetic energy distribution and excitation function. Fitting the latter data for η mesons going backwards in the center-of-mass system yields a potential depth of V=-(44±16(stat)±15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average η momenta of ≈1.1 GeV/c. Within the experimental uncertainties, there is no indication of a momentum dependence of the η-carbon potential. The LH2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for η photoproduction off the free proton. [ABSTRACT FROM AUTHOR]