arXiv subjects

J. Mares

Publications and source records attributed to J. Mares.

16 recordsLinked to original sources

arXiv2017

On the widths and binding energies of $K^-$ nuclear states and the role of $K^-$ multi-nucleon interactions

We report on our recent self-consistent calculations of $K^-$ nuclear quasi-bound states using $K^-$ optical potentials derived from chirally motivated meson-baryon coupled channels models [1,2]. The $K^-$ single-nucleon potentials were supplemented by a phenomenological $K^-$ multi-nucleon interaction term introduced to achieve good fits to $K^-$ atom data. We demonstrate a substantial impact of the $K^-$ multi-nucleon absorption on the widths of $K^-$ nuclear states. If such states ever exist in nuclear many-body systems, their widths are excessively large to allow observation.

nucl-th↗

arXiv2017

Eta-mesic nuclei

In this contribution we report on theoretical studies of $η$ nuclear quasi-bound states in few- and many-body systems performed recently by the Jerusalem-Prague Collaboration [1-5]. Underlying energy-dependent $ηN$ interactions are derived from coupled-channel models that incorporate the $N^*(1535)$ resonance. The role of self-consistent treatment of the strong energy dependence of subthreshold $ηN$ amplitudes is discussed. Quite large downward energy shift together with rapid decrease of the $ηN$ amplitudes below threshold result in relatively small binding energies and widths of the calculated $η$ nuclear bound states. We argue that the subthreshold behavior of $ηN$ scattering amplitudes is crucial to conclude whether $η$ nuclear states exist, in which nuclei the $η$ meson could be bound and if the corresponding widths are small enough to allow detection of these $η$ nuclear states in experiment.

nucl-th↗

arXiv2012

Calculations of $K^-$ nuclear quasi-bound states based on chiral meson-baryon amplitudes

In-medium ${\bar K}N$ scattering amplitudes developed within a new chirally motivated coupled-channel model due to Cieply and Smejkal that fits the recent SIDDHARTA kaonic hydrogen 1s level shift and width are used to construct $K^-$ nuclear potentials for calculations of $K^-$ nuclear quasi-bound states. The strong energy and density dependence of scattering amplitudes at and near threshold leads to $K^-$ potential depths $-Re V_K \approx 80 -120$ MeV. Self-consistent calculations of all $K^-$ nuclear quasi-bound states, including excited states, are reported. Model dependence, polarization effects, the role of p-wave interactions, and two-nucleon $K^-NN\rightarrow YN$ absorption modes are discussed. The $K^-$ absorption widths $Γ_K$ are comparable or even larger than the corresponding binding energies $B_K$ for all $K^-$ nuclear quasi-bound states, exceeding considerably the level spacing. This discourages search for $K^-$ nuclear quasi-bound states in any but lightest nuclear systems.

nucl-th↗

arXiv2009

Multi-$\bar{K}$ hypernuclei

Relativistic mean field calculations of multi-$\bar{K}$ hypernuclei are performed by adding $K^-$ mesons to particle-stable configurations of nucleons, $Λ$ and $Ξ$ hyperons. For a given hypernuclear core, the calculated $\bar{K}$ separation energy $B_{\bar{K}}$ saturates with the number of $\bar{K}$ mesons for more than roughly 10 mesons, with $B_{\bar{K}}$ bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the $\bar{K}$-meson densities peak, similarly to what was found for multi-$\bar{K}$ nuclei. The calculations demonstrate that particle-stable multistrange $\{N,Λ,Ξ\}$ configurations are stable against strong-interaction conversions $Λ\to N \bar{K}$ and $Ξ\to N \bar{K} \bar{K}$, confirming and strengthening the conclusion that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter.

nucl-th↗

arXiv2008

Dynamics of \bar{K} and multi-\bar{K} nuclei

We report on self-consistent calculations of single-K^- nuclear states and multi-Kbar nuclear states in 12C, 16O, 40Ca and 208Pb within the relativistic mean-field (RMF) approach. Gradient terms motivated by the p-wave resonance Sigma(1385) are found to play a secondary role for single-K^- nuclear systems where the mean-field concept is acceptable. Significant contributions from the Kbar N -> pi Lambda conversion mode, and from the nonmesonic Kbar NN -> YN conversion modes which are assumed to follow a rho^2 density dependence, are evaluated for the deep binding-energy range of over 100 MeV where the decay channel Kbar N -> pi Sigma is closed. Altogether we obtain K^- total decay widths of 50-100 MeV for binding energies exceeding 100 MeV in single-K^- nuclei. Multi-Kbar nuclear calculations indicate that the binding energy per Kbar meson saturates upon increasing the number of Kbar mesons embedded in the nuclear medium. The nuclear and Kbar densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor.

nucl-th↗

arXiv2007

Faddeev calculation of a $K^- p p$ quasi-bound state

We report on the first genuinely three-body ${\bar K}NN - πΣN$ coupled-channel Faddeev calculation in search for quasi-bound states in the $K^- p p$ system. The main absorptivity in the $K^- p$ subsystem is accounted for by fitting to $K^- p$ data near threshold. Our calculation yields one such quasi-bound state, with $I=1/2$, $J^π=0^-$, bound in the range $B \sim 55-70$ MeV, with a width of $Γ\sim 95-110$ MeV. These results differ substantially from previous estimates, and are at odds with the $K^- p p \to Λp$ signal observed by the FINUDA collaboration.

nucl-th↗

arXiv2005

Antiproton-nucleus potentials from global fits to antiprotonic X-rays and radiochemical data

We report on global fits of optical-model parameters to 90 data points for $\bar p$ X-rays and 17 data points of radiochemical data put together. With the help of separate fits to the two kinds of data it is possible to determine phenomenologically the radial region where the absorption of antiprotons takes place and to obtain neutron densities which represent the average behaviour over the periodic table. A finite-range attractive and absorptive $\bar p$-nuclear isoscalar potential fits the data well. Self-consistent dynamical calculations within the RMF model demonstrate that the polarization of the nucleus by the {\it atomic} antiproton is negligible.

nucl-th↗

arXiv2004

Widths of $\bar K$-nuclear deeply bound states in a dynamical model

The relativistic mean field (RMF) model is applied to a system of nucleons and a $\bar K$ meson, interacting via scalar and vector boson fields. The model incorporates the standard RMF phenomenology for bound nucleons and, for the $\bar K$ meson, it relates to low-energy ${\bar K}N$ and $K^-$ atom phenomenology. Deeply bound $\bar K$ nuclear states are generated dynamically across the periodic table and are exhibited for $^{12}$C and $^{16}$O over a wide range of binding energies. Substantial polarization of the core nucleus is found for these light nuclei. Absorption modes are also included dynamically, considering explicitly the reduced phase space for $\bar K$ absorption from deeply bound states. The behavior of the calculated width as function of the $\bar K$ binding energy is studied in order to explore limits on the possible existence of narrow $\bar K$ nuclear states.

nucl-th↗

arXiv2004

Description of Heavy Quark Systems by means of Energy Dependent Potentials

We apply, for the first time, an energy dependent Schrodinger equation to describe static properties of heavy quark systems, i.e. charmonium and bottonium. We show that a good description of the eigenstates and reasonable values for the widths can be obtained. Values of the radii and of the density at the origin are also given. We compare the results to those deduced with a Schrodinger equation implemented with potentials used so far. We note that the energy dependence of the confining potential provides a natural mechanism for the saturation of the spectra. Our results introduce a new class of potentials for the description of heavy quark systems.

hep-ph↗

arXiv2003

Wave equations with energy dependent potentials

We study wave equations with energy dependent potentials. Simple analytical models are found useful to illustrate difficulties encountered with the calculation and interpretation of observables. A formal analysis shows under which conditions such equations can be handled as evolution equation of quantum theory with an energy dependent potential. Once these conditions are met, such theory can be transformed into ordinary quantum theory.

quant-ph↗

arXiv2001

Study of chirally motivated low-energy $K^-$ optical potentials

The $K^-$ optical potential in the nuclear medium is evaluated self consistently from a free-space $K^-N$ $t$ matrix constructed within a coupled-channel chiral approach to the low-energy $\bar K N$ data. The chiral-model parameters are fitted to a select subset of the low-energy data {\it plus} the $K^-$ atomic data throughout the periodic table. The resulting attractive $K^-$ optical potentials are relatively `shallow', with central depth of the real part about 55 MeV, for a fairly reasonable reproduction of the atomic data with $χ^2 / N \approx 2.2$. Relatively `deep' attractive potentials of depth about 180 MeV, which result in other phenomenological approaches with $χ^2 / N \approx 1.5$, are ruled out within chirally motivated models. Different physical data input is required to distinguish between shallow and deep $K^-$ optical potentials. The ($K^{-}_{\rm stop},π$) reaction could provide such a test, with exclusive rates differing by over a factor of three for the two classes of potentials. Finally, forward ($K^-,p$) differential cross sections for the production of relatively narrow deeply bound $K^-$ {\it nuclear} states are evaluated for deep $K^-$ optical potentials, yielding values considerably lower than those estimated before.

nucl-th↗

arXiv1999

$K^-$ - nucleus relativistic mean field potentials consistent with kaonic atoms

$K^-$ atomic data are used to test several models of the $K^-$ nucleus interaction. The t($ρ$)$ρ$ optical potential, due to coupled channel models incorporating the $Λ$(1405) dynamics, fails to reproduce these data. A standard relativistic mean field (RMF) potential, disregarding the $Λ$(1405) dynamics at low densities, also fails. The only successful model is a hybrid of a theoretically motivated RMF approach in the nuclear interior and a completely phenomenological density dependent potential, which respects the low density theorem in the nuclear surface region. This best-fit $K^-$ optical potential is found to be strongly attractive, with a depth of 180 \pm 20 MeV at the nuclear interior, in agreement with previous phenomenological analyses.

nucl-th↗

arXiv1997

On the binding energy of double Λhypernuclei in the relativistic mean field theory

We calculate the binding energy of two $Λ$ hyperons bound to a nuclear core within the relativistic mean field theory. The starting point is a two-body relativistic equation of the Breit type suggested by the RMFT, and corrected for the two-particle interaction. We evaluate the 2 $Λ$ correlation energy and estimate the contribution of the $σ^*$ and $Φ$ mesons, acting solely between hyperons, to the bond energy $Δ{B_{ΛΛ}}$ of $^6_{ΛΛ}He$, $^{10}_{ΛΛ}Be$ and $^{13}_{ΛΛ}B$. Predictions of the $Δ{B_{ΛΛ}}$ A dependence are made for heavier $Λ$-hypernuclei.

nucl-th↗

arXiv1997

Medium effects in K^+ nuclear interactions

Total and reaction cross sections are derived self consistently from the attenuation cross sections measured in transmission experiments at the AGS for K^+ on Li^6, C, Si and Ca in the momentum range of 500-700 MeV/c by using a V_{opt}=t_{eff}(rho)rho optical potential. Self consistency requires, for the KN in-medium t matrix, that Im t_{eff}(rho) increases linearly with the average nuclear density in excess of a threshold value of 0.088+-0.004 fm^-3. The density dependence of Re t_{eff}(rho) is studied phenomenologically, and also applying a relativistic mean field approach, by fitting the integral cross sections. The real part of the optical potential is found to be systematically less repulsive with increasing energy than expected from the free-space repulsive KN interaction. When the elastic scattering data for Li^6 and C at 715 MeV/c are included in the analysis, a tendency of Re V_{opt} to generate an attractive pocket at the nuclear surface is observed.

nucl-th↗

arXiv1996

Medium effects in K^+ nucleus interaction from consistent analysis of integral and differential cross sections

Self consistency in the analysis of transmission measurements for K^+ on several nuclei in the momentum range of 500-700 MeV/c is achieved with a "t_{eff}(rho)rho" potential and new results are derived for total cross sections. The imaginary part of the t_{eff} amplitude is found to increase linearly with the average nuclear density in excess of a threshold value. This phenomenological density dependence of the K^+ nucleus optical potential also gives rise to good agreement with recent measurements of differential cross sections for elastic scattering of 715 MeV/c K^+ by Li^6 and C.

nucl-th↗

arXiv1995

Constraints on $Σ$ Nucleus Dynamics from Dirac Phenomenology of $Σ^-$ Atoms

Strong interaction level shifts and widths in $Σ^-$ atoms are analyzed by using a $Σ$ nucleus optical potential constructed within the relativistic mean field approach. The analysis leads to potentials with a repulsive real part in the nuclear interior. The data are sufficient to establish the size of the isovector meson--hyperon coupling. Implications to $Σ$ hypernuclei are discussed.

nucl-th↗