arXiv subjects

Matthias F. M. Lutz

Publications and source records attributed to Matthias F. M. Lutz.

41 records · Page 3Linked to original sources

arXiv2004

The associated photoproduction of positive kaons and $π^0 Λ$ or $πΣ$ pairs in the region of the $Σ$(1385) and $Λ$(1405) resonances

The $γp \to K^+ π^0 Λ$ and $γp \to K^+ πΣ$ reactions are studied in the kinematic region where the $π^0 Λ$(1116) and $πΣ$(1192) pairs originate dominantly from the decay of the $Σ$(1385) and $Λ$(1405) resonances. We consider laboratory photon energies around 2 GeV, significantly above the threshold for producing the $K^+ Σ$(1385) and $K^+ Λ$(1405) final states. We compute for both reactions the process in which the ingoing photon dissociates into a real K$^+$ and a virtual K$^-$, the off-shell K$^-$ scattering subsequently off the proton target to produce the $π^0 Λ$ or $πΣ$ pair. The $K^- p \to π^0 Λ$ and $K^- p \to πΣ$ amplitudes are calculated in the framework of a chiral coupled-channel effective field theory of meson-baryon scattering. The structure of the amplitudes reflects the dominance of the $Λ(1405)$ in the $πΣ$ channel and of the $Σ(1385)$ in the $πΛ$ channel. The full pion-hyperon final state interaction is included in these amplitudes. We extract from the calculated cross section the gauge-invariant double kaon pole term. We found this term to be large and leading to sizeable cross sections for both the $γp \to K^+ π^0 Λ$ and $γp \to K^+ πΣ$ reactions, in qualitative agreement with the scarce data presently available. Accurate measurements of these cross sections should make it possible to extract the contribution of the double kaon pole and hence to assess the possibility of studying kaon-nucleon dynamics ust below threshold through these reactions.

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arXiv2004

e+e- pair production from nucleon targets in the resonance region

We present consistent theoretical descriptions of the $πN \to e^+e^- N$ and $γN \to e^+e^- N$ reactions on proton and neutron targets for total center of mass energies $\sqrt s$ ranging between 1.50 GeV and 1.75 GeV. These reactions are complementary to study the coupling of low-lying baryon resonances to vector meson-nucleon channels. We show in particular how the resonant structure of the amplitudes for both processes generates specific and large quantum interferences between $ρ$- and $ω$-meson decays into $e^+e^-$ pairs. Data on the $πN \to e^+e^- N$ and $γN \to e^+e^- N$ reactions are expected in the near future from the HADES program at GSI and from dilepton studies with CLAS at JLab.

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arXiv2003

Chiral symmetry, strangeness and nuclear matter

In this talk we review the important role played by chiral SU(3) symmetry in hadron physics. Exciting new results on the formation of baryon resonances as implied by chiral coupled-channel dynamics are presented and discussed. The results are the consequence of progress made in formulating a consistent effective field theory for the meson-baryon scattering processes in the resonance region. Strangeness channels are found to play a decisive role in the formation of resonances. As a further application of chiral coupled-channel dynamics the properties of antikaons and hyperon resonances in cold nuclear matter are reviewed.

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arXiv2003

Chiral symmetry and strangeness at SIS energies

In this talk we review the consequences of the chiral SU(3) symmetry for strangeness propagation in nuclear matter. Objects of crucial importance are the meson-baryon scattering amplitudes obtained within the chiral coupled-channel effective field theory. Results for antikaon and hyperon-resonance spectral functions in cold nuclear matter are presented and discussed. The importance of the Sigma(1385) resonance for the subthreshold antikaon production in heavy-ion reaction at SIS is pointed out. The in-medium properties of the latter together with an antikaon spectral function based on chiral SU(3) dynamics suggest a significant enhancement of the pi Λ-> bar K N reaction in nuclear matter.

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arXiv2002

The $πN \to e^+e^- N$ reaction close to the vector meson production threshold

The $π^-p \to e^+e^- n$ and $π^+n \to e^+e^- p$ reaction cross sections are calculated below and in the vicinity of the vector meson ($ρ^0$, $ω$) production threshold. These processes are largely responsible for the emission of $e^+e^-$ pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector meson-nucleon channels. The vector mesons materialize subsequently into $e^+e^-$ pairs. Using $πN\to ρ^0 N$ and $πN \to ωN$ amplitudes calculated in the center of mass energy interval $1.4<\sqrt s <1.8$ GeV, we compute the $π^-p \to e^+e^- n$ and $π^+n \to e^+e^- p$ reaction cross sections in these kinematics. Below the vector meson production threshold, the $ρ^0 - ω$ interference in the $e^+e^-$ channel appears largely destructive for the $π^-p \to e^+e^- n$ cross section and constructive for the $π^+n \to e^+e^- p$ cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector meson-nucleon channels to low-lying baryon resonances.

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