arXiv subjects

Horst Lenske

Publications and source records attributed to Horst Lenske.

At least 19 recordsLinked to original sources

arXiv2026

Reaction Studies of Lepton Number Violation

Nuclear isotensor spectroscopy as accessible in nuclear double charge exchange (DCE) reactions is indispensable for quantitative studies of lepton number violation as in double beta decay (DBD). For such studies heavy ion double single charge exchange (DSCE) and direct Majorana double charge exchange (MDCE) reactions are discussed. Isotensor two-body transition densities are investigated for the first time. Pion-potentials, mirroring neutrino potentials, and isotensor short range correlations are explored. Lepton DCE (LDCE) reactions on nuclei at accelerators are introduced as a promising new approach to investigate lepton number violation.

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arXiv2026

Probing short range correlations in Heavy-Ion Double Charge Exchange reactions

The Majorana Double Charge Exchange (MDCE) provides a suitable environment for studying the dynamics of the neutrinoless double beta ($0\nu\beta\beta$) decay, particularly short-range correlations among nucleons. The study of the pion potential is essential in this respect, as it represents the strong interaction counterpart of the neutrino potential, driving nucleon correlations in $0\nu\beta\beta$ decay. Numerical studies on pion potential have revealed an effective range of about 1 fm with slight dispersion around this value, confirming the short-range character of the MDCE process.

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arXiv2026

Universality of the Majorana Double Charge Exchange

The Majorana Double Charge Exchange nuclear reaction mechanism represents a powerful and novel scenario to probe the dynamics of the neutrinoless double beta decay. Recent studies presented in this manuscript have highlighted a key feature of this mechanism, namely its independence with respect to the nuclei involved in the reaction.

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arXiv2026

Nucleon Resonances in Nuclear Matter and Finite Nuclei

The theory of nuclear excitations involving nucleon resonances is revisited and significantly extended to asymmetric nuclear matter and higher P- and S-wave $N^*$ resonances. Excited states of are described as superpositions of particle-hole configurations including $NN^{'-1}$ and $N^*N^{-1}$ configurations. Configuration mixing is taken into account on the one-loop level by solving the generalized $N^*RPA$ Dyson equation. The underlying coupled channels formalism is derived and response functions is discussed. Applications of the approach are illustrated for charge-exchange modes of asymmetric nuclear matter and finite nuclei. The spectral gross structures of corresponding excitations in finite nuclei are investigated in local density approximation. Applications of the approach to resonance studies by high-energy heavy ion reactions are recapitulated.

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arXiv2025

Hadron Production Processes

The experimental search for the pion -- proposed in 1935 by Hideki Yukawa as the force carrier of the strong nucleon-nucleon interaction -- was rewarded in 1947 when in cosmic ray photographic emulsion data a charged particle was identified with the proper mass of about 300 times the electron mass, completed three years later by the discovery of the neutral pion. Since then, accelerator-driven pion and meson (photo-)production on the nucleon and the associated production of new baryons have become the key elements for ground-breaking discoveries in numerous areas of particle and nuclear physics, from fundamental symmetries and their breaking to low-energy QCD dynamics, laying also foundations for modern elementary particle physics and the Standard Model. This article is an overview of eight decades of experimental and theoretical meson production physics, from isospin to charm and beyond, forming our understanding of hadrons and their interactions.

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arXiv2025

Heavy Ion Double Charge Exchange Reactions as Probes for Two-Body Transition Densities

Collisional heavy ion double charge exchange (DCE) reactions, induced by second order nucleon-nucleon interactions, are shown to provide access to the two-body transition densities of the complementary DCE transitions in the interacting nuclei. Corresponding two-body operators are introduced, treating the second order distorted wave reaction amplitude in the s-channel interaction form. The theoretical results are applied to the reaction $^{18}O+{}^{76}Se\to {} ^{18}Ne+{}^{76}Ge$ at $T_{lab}=270$~MeV, being $^{76}Ge$ a candidate for neutrino--less double beta decay.

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arXiv2024

Probing small neutron skin variations in isotope pairs by hyperon-antihyperon production in antiproton--nucleus interactions

We propose a new method to study the evolution of the neutron periphery between different isotopes by considering antiproton--nucleus interactions close to the production threshold of $\Lambda \overline{\Lambda }$ and $\Sigma^-\overline{\Lambda }$ pairs. At low energies, $\Lambda \overline{\Lambda }$ pairs are produced in $\overline{\text{p}} +\text{p}$ collisions, while $\Sigma^-\overline{\Lambda }$ pairs can only be produced in $\overline{\text{p}} +\text{n}$ interactions. Within a simple geometrical picture we show that the double ratio for the production of $\Sigma^-\overline{\Lambda }$ and $\Lambda \overline{\Lambda }$ pairs for two different isotopes are related to the variation of the neutron skin thickness between the two nuclei. Performing high statistics calculations with the Gie\ss en Boltzmann--Uehling--Uhlenbeck (GiBUU) transport model for several isotope pairs covering a wide range of elements we verify a strong correlation between the double ratio from the full transport simulations and the schematic model. This correlation enables us to quantify the potential of the proposed method for precise studies of neutron skin variations in isotope chains.

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arXiv2024

Interactions of omega mesons in nuclear matter and with nuclei

In-medium interactions of omega-mesons in infinite nuclear matter and finite nuclei are investigated in a microscopic approach with nucleon-nucleon and nucleon-resonance particle-hole polarization modes. The nuclear polarization tensor formalism is used. Covariant mean-field self-energies are taken into account. Longitudinal and transversal self-energies are derived. The theoretical results are applied to finite nuclei in local density approximation. Applications to recent data on the in-medium width of omega mesons in 93-Nb are presented. The data are well described by self-energies containing S-wave and P-wave resonances. Low-energy parameters are determined. For the first time a spectrum of omega-nucleus bound states is obtained, albeit with reduced lifetimes.

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arXiv2024

Induced Isotensor Interactions in Heavy-Ion Double-Charge-Exchange Reactions and the Role of Initial and Final State Interactions

The role of initial state (ISI) and final state (FSI) ion-ion interactions in heavy-ion double-charge-exchange (DCE) reactions $A(Z,N)\to A(Z\pm 2,N\mp 2)$ are studied for double single-charge-exchange (DSCE) reactions given by sequential actions of the isovector nucleon-nucleon (NN) T-matrix. In momentum representation, the second-order DSCE reaction amplitude is shown to be given in factorized form by projectile and target nuclear matrix elements and a reaction kernel containing ISI and FSI. Expanding the intermediate propagator in a Taylor series with respect to auxiliary energy allows us to perform the summation in the leading-order term over intermediate nuclear states in closure approximation. %Please ensure meaning has been retained - corrected HL. The nuclear matrix element attains a form given by the products of two-body interactions directly exciting the $n^2p^{-2}$ and $p^2n^{-2}$ DCE transitions in the projectile and the target nucleus, respectively. %Please ensure meaning has been retained - corrected HL. A surprising result is that the intermediate propagation induces correlations between the transition vertices, showing that DSCE reactions are a two-nucleon process that resembles a system of interacting spin-isospin dipoles. Transformation of the DSCE NN T-matrix interactions from the reaction theoretical t-channel form to the s-channel operator structure required for spectroscopic purposes is elaborated in detail, showing that, in general, a rich spectrum of spin scalar, spin vector and higher-rank spin tensor multipole transitions will contribute to a DSCE reaction. Similarities (and differences) to two-neutrino double-beta decay (DBD) are discussed. ISI/FSI distortion and absorption effects are illustrated in black sphere approximation and in an illustrative application to data.

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arXiv2024

Theory of Majorana-Type Heavy Ion Double Charge Exchange Reactions by Pion--Nucleon Isotensor Interactions

The theory of heavy ion double charge exchange (DCE) reactions proceeding by effective rank-2 isotensor interactions is presented. Virtual pion--nucleon charge exchange interactions are investigated as the source for induced isotensor interactions, giving rise to the Majorana DCE (MDCE) reaction mechanism. MDCE is of a generic character, proceeding through pairs of complementary ($\pi^\pm,\pi^\mp$) reactions in the projectile and target nucleus. The dynamics of the elementary processes is discussed, where the excitation of pion--nucleon resonances are of central importance. Investigations of initial and final state ion--ion interactions show that these effects are acting as vertex renormalizations. In closure approximation, well justified by the finite pion mass, the second-order transition matrix elements reduce to pion potentials and effective two-body isotensor DCE interactions, giving rise also to two-body correlations in either of the participating nuclei. Connections to neutrinoless Majorana double beta decay (MDBD) are elucidated at various levels of the dynamics, from the underlying fundamental electro-weak and QCD scales to the physical scales of nuclear MDBD and MDCE physics. It is pointed out that heavy ion MDCE reactions may also proceed by competing electro-weak charge exchange processes, leading to lepton MDCE by electrons, positrons, and neutrinos.

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arXiv2024

Formal Theory of Heavy Ion Double Charge Exchange Reactions

The theory of heavy ion double charge exchange (DCE) reactions $A(Z,N)\to A(Z\pm 2,N\mp 2)$ is recapitulated emphasizing the role of Double Single Charge Exchange (DSCE) and pion-nucleon Majorana DCE (MDCE) reactions. DSCE reactions are of second--order distorted wave character, mediated by isovector nucleon-nucleon (NN) interactions. The DSCE response functions resemble the nuclear matrix elements (NME) of $2\nu 2\beta$ decay. The MDCE process proceeds by a dynamically generated effective rank-2 isotensor interaction, defined by off--shell pion--nucleon DCE scattering. In closure approximation pion potentials and two--nucleon correlations are obtained, similar to the neutrino potentials and the intranuclear exchange of Majorana neutrinos in $0\nu 2 \beta$ Majorana double beta decay (MDBD).

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arXiv2023

Interactions of $\omega$-Mesons in Nuclear Matter and with Nuclei

In--medium interactions of $\omega$--mesons are investigated microscopically by coupling to $NN^{-1}$ and $N^*N^{-1}$ particle--hole excitations of the medium, including elativistic mean--field dynamics by self--consistent scalar and vector fields. The resulting self--energies are transmitted to finite nuclei in local density approximation. Real and imaginary parts of longitudinal and transversal self--energies are discussed. The relation of the present approach to meson cloud models is addressed and an ambiguity is pointed out. Applications to recent data on the in--medium width of $\omega$ mesons scattered on a Niobium target serve to determine unknown $N^*N\omega$ in-medium coupling constants. The data are well described by $N^*N^{-1}$ self--energies containing S--wave and P--wave $N^*$ resonances. Exploratory investigations, however, show that the spectroscopic composition of self--energies depends crucially on the near--threshold properties of the width which at present is known only within large error bars. The calculations predict the prevalence of transversal self--energies, implying that vector current conservation is still maintained in the nuclear medium by slightly more than 90\%. Schr\"{o}dinger--equivalent potentials are derived and scattering lengths and effective range parameters are extracted for the longitudinal and transversal channel. Longitudinal and transversal spectral distributions are discussed and the dependencies on momentum and nuclear density are investigated. Schr\"{o}dinger--type $\omega+{}^{93}$Nb optical potentials are constructed. Low--energy parameters are determined, are used to study the pole structure of the S--matrix at threshold. The effective range expansion of the omega--nucleus K--matrix led to a $\omega +{}^{93}$Nb bound states with binding energy $Re(\varepsilon_B)=-448$~keV but of width $\Gamma_B=4445$~keV.

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arXiv2023

Data driven isospin analysis of timelike octet baryons electromagnetic form factors and charmonium decay into baryon-anti-baryon

Inspired by the recent precise data, we perform model-independently an isospin decomposition of the timelike octet baryons electromagnetic form factors. As noted in our previous work, the relative magnitude of isoscalar and isovector component is determined with the input of data on various isospin channels. Herein we further assert that {their relative phase can be constraint by the phase difference of oscillatory modulation of effective form factors} between isospin channels. The framework is extended to analyze the data of differential cross sections and applied to the form factors of nucleon and hyperons with detail and isospin non-conservation of charmonium decay into baryon-anti-baryon as well. We address that isospin analysis is meaningful when the isospin broken scale is compared to or smaller than the uncertainties of data.

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arXiv2022

Exploration of In-Medium Hyperon-Nucleon Interactions

The study focuses on exploring the changes in the hyperon-baryon interaction at various nuclear densities. This approach starts by building a vacuum hyperon-nucleon interaction model based on Boson -Exchange maintaining SU(3) flavor symmetry. Bethe-Goldstone equation is then explored to investigate the medium properties over the bare interaction. A detailed investigation of the density dependence revealed clear changes in the low energy parameters with the variation of the medium density shown for different strangeness channels.

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arXiv2022

SU(3)_f Constraints on Hypernuclear Energy Density Functionals

A covariant hyper-nuclear energy density functional (EDF) is derived from in medium nucleon meson vertex functionals, assuring the proper description of nuclear mean-field dynamics. The fundamental SU(3) coupling constants for the mean-field relevant vector (m=V) and scalar (m=S) interactions as functionals of the total baryon density are determined. Scalar and vector potentials and the resulting hyperon mean-fields in asymmetric nuclear matter are constructed and discussed, addressing also effects from three-body interactions. \Lambda- \Sigma^0 mixing in asymmetric nuclear through the coupling to the background isovector mean-field is addressed.

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arXiv2021

Timelike nucleon electromagnetic form factors: All about interference of isospin amplitudes

A striking feature of the timelike nucleon electromagnetic form factors, investigated in $e^+e^- \to N\bar N$ annihilation reactions, is the modulation by local structures of small magnitude and oscillatory form, showing up above $N\bar N$ threshold. Starting from an isospin decomposition of the proton and neutron form factors it is shown that such structures are the natural consequence of the interference of a large and a small amplitudes, resulting in a sinusoidal behavior as a function of the "invariant energy" if the relative phase shift varies with energy. Thus, periodic oscillations superimposed on a smooth background will be observed. In this scenario, an equal size of the modulation for neutron and proton discovered by recent BESIII data evidently implies the particular isoscalar or isovector nature of these local structures, or their orthogonal interference, hence specifies their origin as excited vector mesons whose widths are tied to the modulation frequency.We clarify that the phase difference of modulation between neutron and proton as BESIII data found, but not the modulation itself, is the evidence of an imaginary part of the timelike nucleon electromagnetic form factors, which is associated with the rescattering processes.

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arXiv2021

Nuclear Matrix Elements for Heavy Ion Sequential Double Charge Exchange Reactions

The theoretical approach to a sequential heavy ion double charge exchange reaction is presented. A brief introduction into the formal theory of second-order nuclear reactions and their application to Double Single Charge Exchange (DSCE) reactions by distorted wave theory is given, thereby completing the theoretical background to our recent work [1]. Formally, the DSCE reaction amplitudes are shown to be separable into superpositions of distortion factors, accounting for initial and final state ion--ion interactions, and nuclear matrix elements. A broad space is given to the construction of nuclear DSCE response functions on the basis of polarization propagator theory. The nuclear response tensors resemble the nuclear matrix elements of $2\nu\beta\beta$ decay in structure but contain in general a considerable more complex multipole and spin structure. The QRPA theory is used to derive explicit expressions for nuclear matrix elements (NMEs). The differences between the NME of the first and the second interaction vertexes in a DSCE reaction is elucidated. Reduction schemes for the transition form factors are discussed by investigating the closure approximation and the momentum structure of form factors. DSCE unit strength cross sections are derived.

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arXiv2019

Sequential Heavy Ion Double Charge Exchange Reactions and the Link to Double $β$-decay

Heavy ion double charge exchange reactions are described by sequential meson-exchange, corresponding to a double single charge exchange (DSCE) reaction mechanism. The theoretical formulation is discussed. The fully quantum mechanical distorted wave 2-step calculations are shown to be reproduced very well by approximating the intermediate propagator by its pole part. The role of ion-ion elastic interactions is discussed. As a first application, calculations are performed for the reaction $^{40}$Ca $(^{18}$O $,^{18}$Ne $)^{40}$Ar at 15 AMeV. Results are compared to the data measured at LNS by the NUMEN Collaboration. The common aspects of DSCE reactions and double $β$- decay are discussed by a detailed comparison of the respective nuclear matrix elements (NME).

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