arXiv subjects

M. Kaskulov

Publications and source records attributed to M. Kaskulov.

At least 19 recordsLinked to original sources

arXiv2015

Toward relativistic mean-field description of $\bar{\text{N}}$-nucleus reactions

In this work we study the antinucleon-nucleus optical potential in the framework of the non-linear derivative (NLD) model with momentum dependent mean-fields. We apply the NLD model to interaction of antinucleons ($\bar{\text{N}}$) in nuclear matter and, in particular, to antiproton scattering on nuclei. In nuclear matter a strong suppression of the $\bar{\text{N}}$-optical potential at rest and at high kinetic energies is found and caused by the momentum dependence of relativistic mean-fields. The NLD results are consistent with known empirical $\bar{\text{N}}$-nucleus observations and agree well with antiproton-nucleus scattering data. This makes the NLD approach compatible with both, nucleon and antinucleon Dirac phenomenologies. Furthermore, in nuclear matter an effective mass splitting between nucleons and antinucleons is predicted.

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arXiv2012

Transport-theoretical Description of Nuclear Reactions

In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30 AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100 MeV to a few 100 GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion-nucleus interactions, nuclear fragmentation, heavy ion reactions, hyper nucleus formation, hadronization, color transparency, electron-nucleus collisions and neutrino-nucleus interactions are all possible applications of GiBUU and are discussed in this article.

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arXiv2012

Energy Dependent Isospin Asymmetry in Mean-Field Dynamics

The Lagrangian density of relativistic mean-field (RMF) theory with non-linear derivative (NLD) interactions is applied to isospin asymmetric nuclear matter. We study the symmetry energy and the density and energy dependences of nucleon selfenergies. At high baryon densities a soft symmetry energy is obtained. The energy dependence of the isovector selfenergy suppresses the Lane-type optical potential with increasing energy and predicts a $ρ$-meson induced mass splitting between protons and neutrons in isospin asymmetric matter.

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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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arXiv2011

Selected topics on Hadrons in Nuclei

In this talk we report on selected topics on hadrons in nuclei. The first topic is the renormalization of the width of the $Λ(1520)$ in a nuclear medium. This is followed by a short update of the situation of the $ω$ in the medium. The investigation of the properties of $\bar{K}$ in the nuclear medium from the study of the $(K_{flight},p)$ reaction is also addressed, as well as properties of X,Y,Z charmed and hidden charm resonances in a nuclear medium. Finally we address the novel issue of multimeson states.

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arXiv2010

Color transparency in hadronic attenuation of rho0 mesons

Ongoing experiments at JLAB investigate the nuclear transparency in exclusive rho0(770) electroproduction off nuclei. In this work we present transport model predictions for the attenuation of rho0s in nuclei and for color transparency (CT) effects as observable at CLAS with a 5 GeV electron beam energy. A full event simulation presented here permits to study the impact of actual experimental acceptance conditions and kinematical cuts. The exclusive (e,e'rho0) cross section off nucleons is described by diffractive and color string breaking mechanisms extended toward the onset of the deep inelastic regime. Different hadronization and CT scenarios are compared. We show that a detailed analysis of elementary cross section, nuclear effects and experimental cuts is needed to reveal the early onset of rho0-CT at present JLAB energies.

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arXiv2010

On the background in the $γp \to ω(π^0γ) p$ reaction and mixed event simulation

In this paper we evaluate sources of background for the $γp \to ωp$, with the $ω$ detected through its $π^0 γ$ decay channel, to compare with the experiment carried out at ELSA. We find background from $γp \to π^0 π^0 p$ followed by decay of a $π^0$ into two $γ$, recombining one $π^0$ and one $γ$, and from the $γp \to π^0 ηp$ reaction with subsequent decay of the $η$ into two photons. This background accounts for the data at $π^0 γ$ invariant masses beyond 700 MeV, but strength is missing at lower invariant masses which was attributed to photon misidentification events, which we simulate to get a good reproduction of the experimental background. Once this is done, we perform an event mixing simulation to reproduce the calculated background and we find that the method provides a good description of the background at low $π^0 γ$ invariant masses but fakes the background at high invariant masses, making background events at low invariant masses, which are due to $γ$ misidentification events, responsible for the background at high invariant masses which is due to the $γp \to π^0 π^0 p$ and $γp \to π^0 ηp$ reactions.

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arXiv2009

Non-Linear derivative interactions in relativistic hadrodynamics

The Lagrangian density of Relativistic Hadrodynamics (RHD) is extended by introducing non-linear derivative (NLD) interactions of the nucleon with the meson fields. As a consequence, the nucleon selfenergy becomes both momentum and density dependent. With a single cut-off parameter, which regulates the NLD Lagrangian, our approach is compatible with results from microscopic nuclear matter calculations as well as with Dirac phenomenology. It also reproduces the correct behavior of the real part of the proton-nucleus potential both at low and at high proton energies.

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arXiv2008

Photo- and Electron-Production of Mesons on Nucleons and Nuclei

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $ηπ^0 p$ and $K^0 π^0 Σ^+$, together with related reactions will be shown, having with common denominator the excitation of the $Δ(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to ϕf_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $ω$ in nuclei, showing that present experimental results claiming a shift of the $ω$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $ω$ width in the nuclear medium.

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arXiv2007

Hadrons in Nuclei -- from High (200 GeV) to Low (1 GeV) energies

The study of the interaction of hadrons, produced by elementary probes in a nucleus, with the surrounding nuclear medium can give insight into two important questions. First, at high energies, the production process, the time-scales connected with it and the prehadronic interactions can be studied by using the nuclear radius as a length-scale. We do this here by analyzing data from the EMC and HERMES experiements on nuclear attenuation. Second, at low energies the spectral function, and thus the selfenergy of the produced hadron, can be studied. Specifically, we analyze the CBELSA/TAPS data on $ω$ production in nuclei and discuss the importance of understanding in-medium effects both on the primary production cross section and the final state branching ratio. In both of these studies an excellent control of the final state interactions is essential.

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arXiv2007

Photoproduction of $ω$ and $ω$ in the Nuclear Medium

We reanalyze data from ELSA on $ω$ production in nuclei, from where claims of a large shift of the mass were made earlier, which are tied to a certain election of the background in nuclei, very different in shape to the one on the proton. The reanalysis shows that the data demand a very large width of the $ω$ in the medium, with no need for a shift of the mass, for which the experiment is quite insensitive. We study possible $ω$ bound states in the nucleus and find that, even assuming a small width, they could not be observed with the present ELSA resolution. Finally we show that, due to the interplay of background and $ω$ signal, a two bump structure appears with the ELSA set up for the $(γ,p)$ reaction that should not be misidentified with a signal of a possible $ω$ bound state in the nucleus.

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arXiv2007

Recent developments in chiral dynamics of hadrons and hadrons in nuclei

In this talk I present recent developments in the field of hadronic physics and hadrons in the nuclear medium. I review the unitary chiral approach to meson baryon interaction and address the topics of the two dynamically generated $Λ(1405)$ resonances, with experiments testing it, the $Λ(1520)$ and $Δ(1700)$ resonances, plus the $Λ(1520)$, $Σ(1385)$ and $ω$ in the nuclear medium.

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arXiv2006

Evidence for a 'Narrow' Roper Resonance - the Breathing Mode of the Nucleon

All the time since its discovery the N$^*$(1440) baryon state, commonly known as Roper resonance, has been a state with many question marks - despite of its 4-star ranking in the particle data book. One reason is that it does not produce any explicit resonance-like structures in the observables of $π$N or $γ$N reactions. Only in partial wave analyses of $π$N scattering data a clear resonance strcuture gets obvious in the $P_{11}$ partial wave. Very recent measurements of the J/$Ψ$ decay by the BES collaboration and of the $pp \to npπ^+$ reaction at 1.3 GeV by the CELSIUS-WASA collaboration show for the first time a clear resonance structure in the invariant $nπ^+$ mass spectrum for the Roper resonance at M $\approx$ 1360 MeV with a width of about 150 MeV. These values agree very favorably with the pole position results of recent $π$N phase shift analyses. In consequence of this very low-lying pole postion, which is roughly 100 MeV below the nominal value, the decay properties have to be reinvestigated. From our two-pion production data we see that the decay mainly proceeds via N$^* \to $N$σ$, i.e. a monopole transition as expected for the breathing mode of the nucleon.

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arXiv2006

Two-Pion Production in Nucleon-Nucleon Collisions and the ABC-Effect - Approaching a Puzzleby exclusive and Kinematically complete Measurements

The ABC effect - a puzzling low-mass enhancement in the $ππ$ invariant mass spectrum - is known from inclusive measurements of two-pion production in nuclear collisions, where it always showed up, if the participating nucleons fused to a bound nuclear system in the final state. The first exclusive measurements on the ABC effect have been carried out very recently at CELSIUS-WASA for the fusion reactions leading to d, $^3$He and $^4$He nuclei in the final state. The data analyzed so far for the fusion processes to d and $^3$He reveal this effect to be a $σ$ channel phenomenon associated with the formation of a strongly attractive $ΔΔ$ system. The data for the strictly isospin-selective double-pionic fusion to $^4$He, where we expect the largest effect, are currently still analyzed. All inclusive data on this system are well described by our model, too. This case also constitutes the heaviest nuclear system, where exclusive measurements of double-pionic fusion can be carried out with present-day instruments. Surprisingly, the $pp \to ppπ^0π^0$ reaction in the $ΔΔ$ region is observed to also show a ABC-like low-$ππ$ mass enhancement, a phenomenon, which deserves special attention.

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arXiv2006

Study of possible ωbound states in nuclei with the (γ,p) reaction

We perform calculations for ωproduction in nuclei by means of the (γ,p) reaction for photon energies and proton angles suited to running and future experiments in present Laboratories. For some cases of possible ωoptical potentials we find clear peaks which could be observable provided a good resolution in the ωenergy is available. We also study the inclusive production of π^0 γin nuclei around the ωenergy and find a double hump structure for the energy spectra, with a peak around a π^0 γenergy of m_ω-100 MeV, which could easily be misidentified by a signal of a bound ωstate in nuclei, while it is due to a different scaling of the uncorrelated π^0 γproduction and ωproduction with subsequent π^0 γdecay.

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arXiv2006

Inclusive $ω$ photoproduction from nuclei and $ω$ in the nuclear medium

With the aim of extracting information on the shift of the $ω$ mass in the nuclear medium we analyze data obtained at ELSA from where claims for evidence of a mass shift of the $ω$ have been made. We develop a Monte Carlo simulation code which takes into account the possible reactions in the experimental set up of $(γ~ A \to π^0 γ~X)$ in the vicinity of the $ω$ production region with subsequent $ω\to π^0 γ$ decay. We compare our results with experiment for the distribution of $π^0 γ$ invariant masses and conclude that the distribution is compatible with an enlarged $ω$ width of about 90 MeV at nuclear matter density and no shift in the mass. This change in the width would be compatible with the preliminary results obtained from the transparency ratio in the A dependence of $ω$ production. The discrepancy of the present conclusions with former claims of an evidence for a shift of the $ω$ mass stem from a different choice of background which is discussed in the paper.

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arXiv2006

Recent developments in chiral dynamics of hadrons and hadrons in a nuclear medium

In this talk I present recent developments in chiral dynamics of hadrons and hadrons in a medium addressing the following points: interaction of the octet of pseudoscalar mesons with the octet of baryons of the nucleon, showing recent experimental evidence on the existence of two $Λ(1405)$ states, the interaction of the octet of pseudoscalar mesons with the decuplet of baryons of the $Δ$, with particular emphasis on the $Λ(1520)$ resonance, dynamically generated by this interaction. Then I review the interaction of kaons in a nuclear medium and briefly discuss the situation around the claims of deeply bound states in nuclei. The large renormalization of the $Λ(1520)$ in the nuclear medium is shown as another example of successful application of the chiral unitary techniques.

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arXiv2006

$A$ dependence of the $γ$- and $p$-induced production of the $Λ(1520)$ from nuclei

Using results of a recent calculation of the $Λ(1520)$ in the nuclear medium, which show that the medium width is about five times the free width, we study the A dependence of the $Λ(1520)$ production cross section in the reactions $γ~A \to K^+ Λ(1520) A^\prime$ and $p~ A \to p~ K^+ Λ(1520) A^\prime$. We find a sizable A dependence in the ratio of the nuclear cross sections for heavy nuclei with respect to a light one due to the large value of the $Λ(1520)$ width in the medium, showing that devoted experiments, easily within reach in present facilities, can provide good information on that magnitude by measuring the cross sections studied here.

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