arXiv subjects

H. Lenske

Publications and source records attributed to H. Lenske.

At least 55 records · Page 3Linked to original sources

arXiv2013

Coupled-channel analysis of $KΣ$ production on the nucleon up to 2.0 GeV

A coupled-channel effective Lagrangian model respecting unitary and gauge invariance is applied to the combined analysis of the $(π,γ) N \to KΣ$ reactions for the center of mass energies up to 2 GeV. The recent photoproduction data obtained by the CLAS, CBELSA, LEPS, and GRAAL groups are included into our calculations with the aim to extract the resonance couplings to the $KΣ$ state. Both resonances and background contributions are found to be important to reproduce a correct shape of the angular distributions and polarization observables. Our description to the data is of good quality. The extracted properties of isospin $I = 3/2$ resonances are discussed in detail while the $I = 1/2$ resonances are largely determined by the non-strangeness channels.

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arXiv2013

Eta-meson production in the resonance energy region

We perform an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the $S_{11}(1535)$ and $S_{11}(1560)$ states. The effect from $P_{11}(1710)$ is found to be small but still important to reproduce the correct shape of the differential cross section. For the $π^- N \to ηN$ scattering we suggest a reaction mechanism in terms of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ states. Our conclusion on the importance of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ resonances in the eta-production reactions is in line with our previous results. No strong indication for a narrow state with a width of 15 MeV and the mass of 1680 MeV is found in the analysis. $ηN$ scattering length is extracted and discussed.

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arXiv2013

In-medium effects on hypernuclear formation

We study strangeness dynamics in reactions relevant for the formation of multi-strange hypernuclei. In particular, we discuss the in-medium effects on elementary hyperon-nucleon ($YN$) channels, which are relevant for the production of hypernuclei at PANDA. The results indicate strong in-medium effects on $YN$-scattering, which might be important for hypernuclear studies at PANDA.

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arXiv2012

Strangeness production in antiproton-nucleus annihilation

The results of the microscopic transport calculations of $\bar p$-nucleus interactions within a GiBUU model are presented. The dominating mechanism of hyperon production is the strangeness exchange processes $\bar K N \to Y π$ and $\bar K N \to ΞK$. The calculated rapidity spectra of $Ξ$ hyperons are significantly shifted to forward rapidities with respect to the spectra of $S=-1$ hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of $\bar p$-nucleus annihilation. The production of the double $Λ$-hypernuclei by $Ξ^-$ interaction with a secondary target is calculated.

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arXiv2012

Non-yrast nuclear spectra in a model of coherent quadrupole-octupole motion

A model assuming coherent quadrupole-octupole vibrations and rotations is applied to describe non-yrast energy sequences with alternating parity in several even-even nuclei from different regions, namely $^{152,154}$Sm, $^{154,156,158}$Gd, $^{236}$U and $^{100}$Mo. Within the model scheme the yrast alternating-parity band is composed by the members of the ground-state band and the lowest negative-parity levels with odd angular momenta. The non-yrast alternating-parity sequences unite levels of $β$-bands with higher negative-parity levels. The model description reproduces the structure of the considered alternating-parity spectra together with the observed B(E1), B(E2) and B(E3) transition probabilities within and between the different level-sequences. B(E1) and B(E3) reduced probabilities for transitions connecting states with opposite parity in the non-yrast alternating-parity bands are predicted. The implemented study outlines the limits of the considered band-coupling scheme and provides estimations about the collective energy potential which governs the quadrupole-octupole properties of the considered nuclei.

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arXiv2012

Formation of double-$Λ$ hypernuclei at PANDA

We study the formation of single- and double-$Λ$ hypernuclei in antiproton-induced reactions relevant for the forthcoming PANDA experiment at FAIR. We use the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model with relativistic mean-fields for the description of non-equilibrium dynamics and the statistical multifragmentation model (SMM) for fragment formation. This combined approach describes the dynamical properties of strangeness and fragments in low energy $\bar{p}$-induced reactions fairly well. We then focus on the formation of double-$Λ$ hypernuclei in high energy $\bar{p}$-nucleus collisions on a primary target including the complementary $Ξ$-induced reactions to a secondary one, as proposed by the PANDA collaboration. Our results show that a copious production of double-$Λ$ hyperfragments is possible at PANDA. In particular, we provide first theoretical estimations on the double-$Λ$ production cross section, which strongly rises with decreasing energy of the secondary $Ξ$-beam.

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arXiv2011

Exploring the anomaly in the interaction cross section and matter radius of 23O

New measurements of the interaction cross sections of 22,23O at 900A MeV performed at the GSI, Darmstadt are reported that address the unsolved puzzle of the large cross section previously observed for 23O. The matter radii for these oxygen isotopes extracted through a Glauber model analysis are in good agreement with the new predictions of the ab initio coupled-cluster theory reported here. They are consistent with a 22O+neutron description of 23O as well.

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arXiv2011

How Deep is the Antinucleon Optical Potential at FAIR energies

The key question in the interaction of antinucleons in the nuclear medium concerns the deepness of the antinucleon-nucleus optical potential. In this work we study this task in the framework of the non-linear derivative (NLD) model which describes consistently bulk properties of nuclear matter and Dirac phenomenology of nucleon-nucleus interactions. We apply the NLD model to antinucleon interactions in nuclear matter and find a strong decrease of the vector and scalar self-energies in energy and density and thus a strong suppression of the optical potential at zero momentum and, in particular, at FAIR energies. This is in agreement with available empirical information and, therefore, resolves the issue concerning the incompatibility of G-parity arguments in relativistic mean-field (RMF) models. We conclude the relevance of our results for the future activities at FAIR.

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arXiv2010

Pygmy Quadrupole Resonance in Skin Nuclei

The electric quadrupole response is investigated theoretically by HFB and QPM calculations along the Sn isotopic chain with special emphasis on excitations above the first collective state and below the particle threshold. Depending on the asymmetry, additional strength clustering as a group of states similar to the known PDR mode is found. The spectral distributions and electric response functions are discussed. The transition densities of these Pygmy Quadrupole Resonances (PQR) states are closely related to the neutron excess and showing special features being compatible with an oscillation of the neutron skin against the nuclear core. These features may indicate a new nuclear quadrupole mode connected to the skin configuration.

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arXiv2010

Breathing mode in an improved transport approach

The nuclear breathing-mode giant monopole resonance is studied within an improved relativistic Boltzmann-Uehling-Uhlenbeck (BUU) transport approach. As a new feature, the numerical treatment of ground state nuclei and their phase-space evolution is realized with the same semiclassical energy density functional. With this new method a very good stability of ground state nuclei in BUU simulations is achieved. This is important in extracting clear breathing-mode signals for the excitation energy and, in particular, for the lifetime from transport theoretical studies including mean-field and collisional effects.

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arXiv2010

Spectroscopic features of low-energy excitations in skin nuclei

Systematic studies of dipole and other multipole excitations in stable and exotic nuclei are discussed theoretically. Exploring the relation of the strengths of low-energy dipole and quadrupole pygmy resonances to the thickness of the neutron (proton) skin a close connection between static and dynamic properties of the nucleus is observed. The fine structure of low-energy dipole strength in 138Ba nucleus is revealed from E1 and spin-flip M1 strengths distributions.

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arXiv2010

A relativistic description of the A(pi+,K+)_ΛA reaction

We investigate the A$(π^+,K^+){_Λ}$A reaction within a covariant model. We consider those amplitudes which are described by creation, propagation and decay into relevant channel of $N^*$(1650), $N^*$(1710), and $N^*$(1720) intermediate baryonic resonance states in the initial collision of the incoming pion with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave function in the plane wave approximation. Numerical calculations are presented for reactions on $^{12}$C, $^{40}$Ca, $^{51}$V and $^{89}$Y target nuclei. The predictions of our model are in reasonable agreement with the available experimental data.

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arXiv2010

The associated photoproduction of K+ meson off proton within a coupled-channels K-matrix approach

We investigate the p(gamma,K+)Lambda and p(gamma,K+)Sigma^0 reactions within a coupled-channels effective-Lagrangian method which is based on the K-matrix approach. The two-body final channels included are pi-N, eta-N, phi-N, rho-N, gamma-N, K-Lambda, and K-Sigma. Non-resonant meson-baryon interactions are included in the model via nucleon intermediate states in the s- and u-channels and meson exchanges in the t-channel amplitude and the u-channel resonances. The nucleon resonances S11 (1535), S11 (1650), S31 (1620), P11 (1440), P11 (1710), P13 (1720), P33 (1232), P33 (1600), D13 (1520), D13 (1700), and D33 (1700) are included explicitly in the calculations. With a single parameter set which was derived earlier from our analysis of the eta meson photoproduction, the model describes well all the available cross section and polarization data of the SAPHIR collaboration for the two investigated channels. The description of the data of the CLAS collaboration, however, is not of the same quality. In contrast to some previous studies, we do not find any compelling need for including a D13 state with mass of around 2.0 GeV in order to reproduce the data for the p(gamma,K+)Lambda reaction at photon energies corresponding to the invariant mass around 1.9 GeV.

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arXiv2009

Spin-5/2 fields in hadron physics

We show that the Lagrangian of the free spin-5/2 field in the spinor-tensor representation with the auxiliary spinor field depends on the three arbitrary parameters. The first two parameters are associated with the spin-3/2 and -1/2 sector of the theory while the latter one is related to the auxiliary degrees of freedom. We derive a corresponding propagator of the system which represents (2 x 2) matrix in the $(ψ_{μν},ξ)$ space. The diagonal terms stand for the propagation of the spin-5/2 and auxiliary fields whereas the non-diagonal ones correspond to the $ψ_{μν}-ξ$ mixing. The resulting spin-5/2 propagator contains non-pole contributions coming from the spin-3/2 and -1/2 sector of the spinor-tensor representation. A general form of the interaction vertex involving spin-5/2 field is discussed on the example of the $πN N^*_{5/2}$ coupling. It is demonstrated that lower spin degrees of freedom can be removed from the theory by using higher order derivative coupling.

hep-ph↗

arXiv2009

Formation of hypernuclei in high energy reactions within a covariant transport model

We investigate the formation of fragments with strangeness degrees of freedom in proton- and heavy-ion-induced reactions at high relativistic energies. The model used is a combination of a dynamical transport model and a statistical approach of fragment formation. We discuss in detail the applicability and limitations of such a hybrid model by comparing data on spectator fragmentation at relativistic $SIS/GSI$-energies. The theoretical results are analyzed in terms of spectator fragmentation with strangeness degrees of freedom such as the production of single-$Λ-{}^{3,4,5}He$ hypernuclei. We provide theoretical estimates on the spectra and on inclusive cross sections of light hypernuclei, which could be helpful for future experiments on hypernuclear physics at the new GSI- and J-PARC-facilities.

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arXiv2009

Theoretical investigations of isoscalar, isovector and mixed symmetry states in skin nuclei

We present recent investigations on dipole and quadrupole excitations in spherical skin nuclei, particular exploring their connection to the thickness of the neutron skin. Our theoretical method relies on density functional theory, which provides us with a proper link between nuclear many-body theory of the nuclear ground state and its phenomenological description. For the calculation of the nuclear excited states we apply QPM theory. A new quadrupole mode related to pygmy quadrupole resonance (PQR) in tin isotopes is suggested.

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arXiv2009

Excitation energy and strength of the pygmy dipole resonance in stable tin isotopes

The $^{112,120}$Sn$(γ,γ')$ reactions have been studied at the S-DALINAC. Electric dipole (E1) strength distributions have been determined including contributions from unresolved strength extracted by a fluctuation analysis. Together with available data on $^{116,124}$Sn, an experimental systematics of the pygmy dipole resonance (PDR) in stable even-mass tin isotopes is established. The PDR centroid excitation energies and summed strengths are in reasonable agreement with quasiparticle-phonon model calculations based on a nonrelativistic description of the mean field but disagree with relativistic quasiparticle random-phase approximation predictions.

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arXiv2008

On a gauge-invariant interaction of spin-$\fth$ resonances

We show that the gauge-invariant coupling suggested by Pascalutsa removes non-pole terms from a spin-$\fth$ propagator only for a specific choice of free parameter. For the general case the problem can be solved by including higher order derivatives of spin-$\fth$ fields or by modifying the original coupling. In the latter case the obtained Lagrangian depends on one free parameter pointing to the freedom in choosing an 'off-shell' content of the theory. However, the physical observables must not be affected by the 'off-shell' contributions and should not depend on the free parameter of the Lagrangian.

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