Hot hypernucleus formation in high-energy photonuclear reactions

Abstract

The probability of a compound residual hot hypernucleus formation at the end of pre-equilibrium phase of high energy photonuclear reactions is calculated with a time dependent Monte Carlo Multicollisional Cascade (MCMC) approach. The emission of hadrons during the rapid phase of the reaction is discussed and characteristics of the residual nucleus are obtained. Results for mass and charge distributions of the formed hot hypernucleus are shown and its excitation energy is discussed.A renewed interest in the subject of strangeness production in proton-nucleus, pion-nucleus, and kaon-nucleus reactions appeared since the observation of hypernucleus bound states for some nuclei such as -7]. The energy level density, branching ratio of non-mesonic to mesonic decays, and hypernucleus lifetime have been investigated. Another important subject is the effect of the Pauli exclusion principle on the suppression of mesonic decay in favor of the non-mesonic decay of hyperons, mainly for heavy target nuclei. Moreover, the many-body re-scattering Λ-N also contributes to the thermalization of the hyperon, and increases its probability of being confined in the nuclear environment [6,7]. Indeed, static calculations based on studies of the hyperon-nucleon potential [8,9], chiral perturbation theory [10], and statistical models [11] have provided some insight on the properties of hypernuclei such as their mass shifts, wave functions, fissioning path, and attachment probabilities of hyperons in nuclei.Theoretical and experimental interest in photonuclear kaon-production reactions has grown from the observation of new nuclear Λ-bound states, which have been experimentally detected through the excitation of the target nucleus by incident photons with energy in the range 0.8-1.4 GeV [4,12]. Also, new phenomena related to the inclusion of a Λ in the nuclear structure, such as the halo effects Λ C, which can be thought of as a Λ-particle attached to the 12 C nucleus, and the Λ-bound p-states are 11 MeV above the s-state. By measuring the spin-orbit splitting, and the gamma emission during the transition p → s, one can obtain information on the signature of the hypernucleus existence [14].In the photomesonic energy region, the gamma-nucleus reaction has been explored in the framework of a two-step interaction model. First, a rapid intranuclear cascade is developed through a sequence of hadronic binary collisions. Subsequently, the hot residual nucleus slowly reaches its final configuration through a sequence of particle-evaporation processes in competition with the residual-nucleus fission process.We have shown that quasi-free kaon production in photonuclear reactions can be an important issue to determine the strangeness content of the residual nuclei at the end of the rapid cascade phase [15]. These reactions permit to study the in-medium effects on the photonuclear absorption and the strangeness-production mechanism. The many-body cascade calculation proposed in Refs. [15,16] for the rapid phase of the photonuclear reaction takes int...

Nuclear photoproduction of vector mesons within a Monte Carlo approach

“…The photoabsorption process allows the study of the formation and propagation of several particles inside nuclear matter, such as baryonic resonances and hyperons [1][2][3][4][5][6]. It is also useful to observe the shadowing effect in the photoabsorption cross section, which is the result of the hadronization process of photons in the nuclear medium.…”

Photofission and total photoabsorption cross sections in the energy range of shadowing effects

“…Deppman Photon-nucleus reactions are excellent tools for investigating nuclear and nucleonic structures. The photonuclear absorption process, for instance, has been used to study the formation and propagation of baryonic resonances inside nuclear matter [1][2][3][4][5][6], the photon hadronization process that gives rise to the shadowing effect in the photoabsorption cross section [1,7], or the formation and propagation of hyperons in the nucleus [6]. The simplicity of photonuclear reactions as compared to reactions induced by other probes, from both the theoretical and experimental points of view, is attractive to those willing to study nuclear and subnuclear structures.…”