We study the production of X(3872) mesons in photon-induced nuclear reactions near the threshold within the collision model based on the nuclear spectral function. The model accounts for direct ...photon-nucleon X(3872) production processes as well as five different scenarios for their internal structure. We calculate the absolute and relative excitation functions for X(3872) production off 12C and 184W target nuclei at near-threshold incident photon energies of 8–16 GeV, the absolute differential cross sections for their production off these target nuclei at laboratory angles of 0∘–10∘ and for incident photon energy of 13 GeV as well as the A dependences of the relative (transparency ratios) cross sections for X(3872) production from γA collisions at photon energies around 13 GeV within the adopted scenarios for the X(3872) meson internal structure. We show that the absolute and relative observables considered reveal distinct sensitivity to these scenarios. Therefore, the measurement of such observables in a dedicated experiment at the CEBAF facility in the near-threshold energy range will allow us to get valuable information on the X(3872) inner structure.
Accounting for the LHCb observation that the reported hidden-charm strange pentaquark Pcs(4459)0 can split into two substructures, Pcs(4455)0 and Pcs(4468)0, with a mass difference of 13 MeV as well ...as the newly observed hidden-charm pentaquark resonance Pcs(4338)0 with strangeness, we study within the double-peak scenario for the Pcs(4459)0 state the near-threshold J/ψ meson production from protons and nuclei by considering incoherent direct non-resonant (K−p→J/ψΛ) and two-step resonant (K−p→Pcsi0→J/ψΛ, i=1, 2, 3; Pcs10=Pcs(4338)0, Pcs20=Pcs(4455)0, Pcs30=Pcs(4468)0) charmonium production processes with the main goal of clarifying the possibility to observe within this scenario both above two substructures contributing to the Pcs(4459)0 state and the Pcs(4338)0 resonance in this production. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of J/ψ mesons on protons as well as on carbon and tungsten target nuclei at near-threshold incident antikaon beam momenta by assuming the spin-parity assignments of the hidden-charm resonances Pcs(4338)0, Pcs(4455)0 and Pcs(4468)0 as JP=(1/2)−, JP=(1/2)− and JP=(3/2)− within four different realistic choices for the branching ratios of their decays to the J/ψΛ mode (0.125, 0.25, 0.5 and 1%) as well as for two options for the branching fraction of their decays to the K−p channel (0.01 and 0.001%). We show that these combined observables reveal clear sensitivity to these scenarios. Hence, they may be an important tool to provide further evidence for the existence of the above strange hidden-charm pentaquark resonances.
The near-threshold pion-induced ϕ production off nuclei has been studied in the kinematical conditions of the HADES experiment using a collision model based on the nuclear spectral function. Starting ...from the elementary reaction π−p→ϕn, absolute differential and integral cross sections for the production of ϕ mesons off a light carbon and a heavy tungsten target have been calculated and compared to the recently reported experimental cross sections. The absolute cross section values are shown to be sensitive to the effective nuclear scalar ϕ and neutron potentials while the transparency ratio is governed by the ϕN absorption cross section. The experimental data are found to be consistent with an attractive ϕ-nucleus potential of ≈ -(50–100) MeV at normal nuclear matter density ρ0 and an effective ϕN absorption cross section of ≈ 12–25 mb. The extracted ϕ-nucleus potential is deeper than previous theoretical and experimental findings as well as those obtained in the present work within the (tρ) approximation with accounting for Pauli correlations from the spin-averaged ϕ-p scattering length reported in a recent ALICE experiment.
We study the antikaon-induced inclusive cascade Ξ− hyperon production from 12C and 184W target nuclei near threshold within a nuclear spectral function approach. The approach describes incoherent ...direct Ξ− hyperon production in elementary K−p→K+Ξ− and K−n→K0Ξ− processes as well as takes into account the influence of the scalar nuclear K−, K+, K0, Ξ− and their Coulomb potentials on these processes. We calculate the absolute differential and total cross sections for the production of Ξ− hyperons off these nuclei at laboratory angles ≤ 45∘ by K− mesons with momenta of 1.0 and 1.3 GeV/c, which are close to the threshold momentum (1.05 GeV/c) for Ξ− hyperon production on the free target nucleon at rest. We also calculate the momentum dependence of the transparency ratio for the 184W/12C combination for Ξ− hyperons at these K− beam momenta. We show that the Ξ− differential and total (absolute and relative) production cross sections at the considered initial momenta reveal a distinct sensitivity to the variations in the scalar Ξ− nuclear potential at saturation density ρ0, studied in the paper, in the low-momentum region of 0.1–0.6 GeV/c. We also demonstrate that for the subthreshold K− meson momentum of 1.0 GeV/c there is, contrary to the case of its above threshold momentum of 1.3 GeV/c, a strong sensitivity of the transparency ratio for Ξ− hyperons to the considered changes in the Ξ− nuclear potential at all outgoing Ξ− momenta as well, which cannot be masked, as in the case of differential and total observables mentioned above, by that associated with the possible changes in the poorly known experimentally Ξ−N inelastic cross section. Therefore, the measurement of these absolute and relative observables in a dedicated experiment at the J-PARC Hadron Experimental Facility will provide valuable information on the Ξ− in-medium properties, which will be complementary to that deduced from the study of the inclusive (K−,K+) reactions at incident momenta of 1.6–1.8 GeV/c in the Ξ− bound and quasi-free regions.
We study the near-threshold inclusive photoproduction of Ξ− hyperons off 12C and 184W target nuclei within a first-collision model relying on the nuclear spectral function and including incoherent Ξ− ...production in direct elementary γp→K+K+Ξ− and γn→K+K0Ξ− processes. The model takes into account the impact of the nuclear effective scalar K+, K0, Ξ− and their Coulomb potentials on these processes as well as the absorption of final Ξ− hyperons in nuclear matter, the binding of intranuclear nucleons and their Fermi motion. We calculate the absolute differential cross sections and their ratios for the production of Ξ− hyperons off these nuclei at laboratory polar angles ≤ 45∘ by photons with energies of 2.5 and 3.0 GeV, with and without imposing the phase space constraints on the Ξ− emission angle in the respective γp center-of-mass system. We also calculate the momentum dependence of the transparency ratio for Ξ− hyperons for the 184W/12C combination at these photon energies. We show that the Ξ− momentum distributions (absolute and relative) at the adopted initial photon energies possess a definite sensitivity to the considered changes in the scalar Ξ− nuclear mean-field potential at saturation density ρ0 in the low-momentum range of 0.1–0.8 GeV/c. This would permit evaluating the Ξ− potential in this momentum range experimentally. We also demonstrate that the momentum dependence of the transparency ratio for Ξ− hyperons for both photon energies can hardly be used to determine this potential reliably. Therefore, the precise measurements of the differential cross sections (absolute and relative) for inclusive Ξ− hyperon photoproduction on nuclei near threshold in a dedicated experiment at the CEBAF facility will provide valuable information on the Ξ− in-medium properties, which will be supplementary to that inferred from studying of the (K−,K+) reactions at initial momenta of 1.6–1.8 GeV/c.
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 K+,K0,K−,η,η′,ω, and ϕ mesons are presented and compared with theoretical predictions. The interaction of K+ and K0 mesons with nuclei is found to be weakly repulsive, while the K−,η,η′,ω and ϕ meson–nucleus potentials are attractive, however, with widely different strengths. Because of meson absorption in the nuclear medium the imaginary parts of the meson–nucleus potentials are all negative, again with a large spread. An outlook on planned experiments in the charm sector is given. In view of the determined potential parameters, the criteria and chances for experimentally observing meson–nucleus quasi-bound states are discussed. The most promising candidates appear to be the η and η′ mesons.
We study the J/ψ photoproduction from nuclei in the near-threshold beam energy region of Eγ=5–11 GeV within the nuclear spectral function approach by considering incoherent direct (γN→J/ψN) and ...two-step (γp→Pc+(4312), Pc+(4312)→J/ψp; γp→Pc+(4440), Pc+(4440)→J/ψp; γp→Pc+(4457), Pc+(4457)→J/ψp) J/ψ production processes. We calculate the absolute excitation functions for the non-resonant and resonant production of J/ψ mesons off 12C and 208Pb target nuclei within the different scenarios for in-medium modification of the directly photoproduced J/ψ mesons and for branching ratios of the decays Pc+(4312)→J/ψp, Pc+(4440)→J/ψp and Pc+(4457)→J/ψp. We show that the non-resonant subthreshold J/ψ production in γA reactions reveals some sensitivity to employed in-medium modification scenarios for J/ψ mesons, which is not masked by the resonantly produced J/ψ mesons, only if above branching ratios are less than 5%. We also demonstrate that if these branching ratios more than 5% then the presence of the Pc+(4312), Pc+(4440) and Pc+(4457) resonances in J/ψ photoproduction on nuclei produces above threshold additional enhancements in the behavior of the total J/ψ creation cross section on nuclei, which could be also studied in the future JLab experiments at the CEBAF facility to provide both further evidence for their existence and valuable information on their nature.
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