arXiv subjects

Miklós Zétényi

Publications and source records attributed to Miklós Zétényi.

8 recordsLinked to original sources

arXiv2021

Role of baryon resonances in the $π^-p \to ne^+e^-$ reaction within an effective-Lagrangian model

We present a study of the reaction $π^-p \to ne^+e^-$ for $\sqrt{s}=1.49\,\textrm{GeV}$, including non-resonant Born terms and contributions of the $N(1440)$, $N(1520)$, $N(1535)$ resonances ($R$), using an effective-Lagrangian model, which we extended by a phenomenological phase factor at the $RNρ$ vertex function. We give predictions for both the differential cross section $dσ/dm$ and the spin density matrix elements of the virtual photon that decays into the lepton pair. In the studied energy range, the cross section is dominated by the Born and $N(1520)$ contributions.

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arXiv2018

Influence of anisotropic $Λ/Σ$ creation on the $Ξ^-$ mutiplicity in subthreshold proton-nucleus collisions

We present an analysis of $Ξ^-$ baryon production in subthreshold proton--nucleus ($p+A$) collisions in the framework of a BUU type transport model. We propose a new mechanism for $Ξ$ production in the collision of a secondary $Λ$ or $Σ$ hyperon and a nucleon from the target nucleus. We find that the $Ξ^-$ multiplicity in $p+A$ collisions is sensitive to the angular distribution of hyperon production in the primary $N+N$ collision. Using reasonable assumptions on the unknown elementary cross sections we are able to reproduce the $Ξ^-$ multiplicity and the $Ξ^-/(Λ+Σ^0)$ ratio obtained in the HADES experiment in $p$+Nb collisions at $\sqrt{s_{NN}} = $ 3.2 GeV energy.

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arXiv2018

Polarization and dilepton angular distribution in pion-nucleon collisions

We study hadronic polarization and the related anisotropy of the dilepton angular distribution for the reaction $πN \to Ne^+e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2 to compute their contribution to the anisotropy coefficient. We show that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We present results for the anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, which are essential at the collision energy of the recent data obtained by the HADES collaboration on this reaction. We conclude that the anisotropy coefficient provides useful constraints for unraveling the resonance contributions to this process.

hep-ph↗

arXiv2017

Influence of the axial anomaly on the decay $N(1535) \rightarrow Nη$

The decay width of $N(1535)\rightarrow Nη$ is as large as that of $N(1535)\rightarrow Nπ$. This is in evident conflict with simple expectations based on flavor symmetry and phase space. Similarly, the decay width of $Λ(1670) \rightarrow Λ(1116) η$ is larger than predicted by flavor symmetry. In this work, we propose that the axial $U(1)_{A}$ anomaly is responsible for an enhanced coupling of (some) excited baryons to the $η$ meson. We test this idea by including a new, chirally symmetric but $U(1)_{A}$ anomalous, term in an effective hadronic model decribing baryons and their chiral partners in the mirror assignment. This term enhances the decay of the chiral partners into baryons and an $η$ meson, such as $N(1535)\rightarrow Nη$. Moreover, a strong coupling of $N(1535)$ to $N η^\prime $ emerges (this is important for studies of $η^\prime$ production processes). Our approach shows that $N(1535)$ is predominantly the chiral partner of $N(939)$, and $Λ(1670)$ the chiral partner of $Λ(1116)$. Finally, our formalism can be used to couple the pseudoscalar glueball $\tilde{G}$ to baryons. We expect a large cross section for the reaction $\bar{p}p \rightarrow \tilde{G} \rightarrow \bar{p}p(1535)$, which can be experimentally tested in the future PANDA experiment.

hep-ph↗

arXiv2016

Polarization and dilepton anisotropy in pion-nucleon collisions

Hadronic polarization and the related anisotropy of the dilepton angular distribution are studied for the reaction $πN \rightarrow Ne^+ e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2, where non-physical degrees of freedom are eliminated, to compute the anisotropy coefficients for isolated intermediate baryon resonances. It is shown that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We then compute the anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, which are essential at the collision energy of the recent data obtained by the HADES collaboration on this reaction. We conclude that the anisotropy coefficient provides useful constraints for unravelling the resonance contributions to this process.

hep-ph↗

arXiv2016

A Three-Flavor Chiral Effective Model with Four Baryonic Multiplets within the Mirror Assignment

In the case of three quark flavors, (pseudo)scalar diquarks transform as antiquarks under chiral transformations. We construct four spin-1/2 baryonic multiplets from left- and right-handed quarks as well as left- and right-handed diquarks. The fact that two of these multiplets transform in a "mirror" way allows for chirally invariant mass terms. We then embed these baryonic multiplets into the Lagrangian of the so-called extended Linear Sigma Model, which features (pseudo)scalar and (axial-)vector mesons, as well as glueballs. Reducing the Lagrangian to the two-flavor case, we obtain four doublets of nucleonic states. These mix to produce four experimentally observed states with definite parity: the positive-parity nucleon $N(939)$ and Roper resonance $N(1440)$, as well as the negative-parity resonances $N(1535)$ and $N(1650)$. We determine the parameters of the nucleonic part of the Lagrangian from a fit to masses and decay properties of the aforementioned states. Studying the limit of vanishing quark condensate, we conclude that $N(939)$ and $N(1535)$, as well as $N(1440)$ and $N(1650)$ form pairs of chiral partners.

hep-ph↗

arXiv2013

Dilepton production in pion-nucleon collisions in an effective field theory approach

We present a model of electron-positron pair production in pion-nucleon collisions in the exclusive reaction πN -> Ne^+e^-. The model is based on an effective field theory approach, incorporating 16 baryon resonances below 2 GeV. Parameters of the model are fitted to pion photoproduction data. We present the resulting dilepton invariant mass spectra for π^- p collisions up to sqrt(s)=1.9 GeV center-of-mass collision energy. These results are meant to give predictions for the planned experiments at the HADES spectrometer in GSI, Darmstadt.

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arXiv2010

Studying freeze-out and hadronization in the Landau hydrodynamical model

We study the rapidity spectra in ultra-relativistic heavy ion collisions in the framework of the Landau hydrodynamical model. We find that thermal smearing effects improve the agreement with experimental results on pion rapidity spectra. We describe a simple model of the hadronization and discuss its consequences regarding the pion multiplicity and the increasing entropy condition.

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