M. Lorenz's research while affiliated with Goethe-Universität Frankfurt am Main and other places
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Publications (134)
First information on the timelike electromagnetic structure of baryons in the second resonance region has been obtained from measurements of invariant mass and angular distributions in the quasi-free reaction \pimptonee\ at $\sqrt{s_{\pi^- p}}$ = 1.49 GeV with the High Acceptance Di-Electron Spectrometer (HADES) detector at GSI using the pion beam...
In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged pion transverse-mass and rapidity spectra, as well as on pion-pion momentum correlations is investigated in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV. We show that the low-mt part of the data...
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadr...
A feasibility study has been performed in order to investigate the performance of the HADES detector to measure the electromagnetic decays of the hyperon resonances $$\Sigma (1385)^{0}$$ Σ ( 1385 ) 0 , $$\Lambda (1405)$$ Λ ( 1405 ) and $$\Lambda (1520)$$ Λ ( 1520 ) as well as the production of double strange baryon systems $$\Xi ^{-}$$ Ξ - and $$\L...
Flow coefficients vn of the orders n=1–6 are measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, and rapidity in Au+Au collisions at sNN=2.4 GeV. Combining the information from the flow coefficients of all orders allows us to construct for the...
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at \sqrt{s_{NN}} = 2.42 GeV collected with HADES. In this energy regime the population of \Delta(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic e...
A feasibility study has been performed in order to investigate the performance of the HADES detector to measure the electromagnetic decays of the hyperon resonances $\Sigma(1385)^0$, $\Lambda(1405)$ and $\Lambda{\Lambda}(1520)$ as well as the production of double strange baryon systems $\Xi^-$ and $\Lambda\Lambda$ in p+p reactions at a beam kinetic...
We present high-statistic data on charged-pion emission from Au + Au collisions at sNN=2.4GeV (corresponding to Ebeam=1.23A GeV) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nuc...
We present an analysis of proton-number fluctuations in sNN=2.4 GeV Au197+Au197 collisions measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. With the help of extensive detector simulations done with Isospin Quantum Molecular Dynamics (IQMD) transport model events including...
Pion-induced reactions provide unique opportunities for an unambiguous description of baryonic resonances and their coupling channels by means of a partial-wave analysis. Using the secondary pion beam at SIS18, the two-pion production in the second resonance region has been investigated to unravel the role of the N(1520)32
We estimate the feeddown contributions from decays of unstable A=4 and A=5 nuclei to the final yields of protons, deuterons, tritons, ³He, and ⁴He produced in relativistic heavy-ion collisions at sNN>2.4 GeV, using the statistical model. The feeddown contribution effects do not exceed 5% at LHC and top RHIC energies due to the large penalty factors...
Flow coefficients $v_{n}$ of the orders $n = 1 - 6$ are measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI for protons, deuterons and tritons as a function of centrality, transverse momentum and rapidity in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV. Combining the information from the flow coefficients of all orders allows...
We present high-statistic data on charged pion emission from Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 2.4 GeV (corresponding to $E_{beam}$ = 1.23 A GeV) in four centrality classes in the range 0 - 40$\%$ of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion mul...
High-statistics \(\pi ^-\pi ^-\) and \(\pi ^+\pi ^+\) femtoscopy data are presented for Au + Au collisions at \(\sqrt{s_\mathrm{NN}} = 2.4~\hbox {GeV}\), measured with HADES at SIS18/GSI. The experimental correlation functions allow the determination of the space-time extent of the corresponding emission sources via a comparison to models. The emis...
Pion induced reactions provide unique opportunities for an unambiguous description of baryonic resonances and their coupling channels by means of a partial wave analysis. Using the secondary pion beam at SIS18, the two pion production in the second resonance region has been investigated to unravel the role of the $N(1520) \frac{3}{2}^-$ resonance i...
We estimate the feeddown contributions from decays of unstable $A = 4$ and $A = 5$ nuclei to the final yields of protons, deuterons, tritons, $^3$He, and $^4$He produced in relativistic heavy-ion collisions at $\sqrt{s_{\rm NN}} > 2.4$ GeV, using the statistical model. The feeddown contribution effects do not exceed 5% at LHC and top RHIC energies...
We present an analysis of proton number fluctuations in $\sqrt{s_{NN}}$ = 2.4 GeV Au+Au collisions measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI. With the help of extensive detector simulations done with IQMD transport model events including nuclear clusters, various nuisance effects influencing the observed proton cumula...
We present high-statistic data on charged-pion emission from Au + Au collisions at sNN−−−√=2.4 GeV (corresponding to Ebeam=1.23 A GeV) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participati...
Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (Dalitz decays) provides important information about baryon-photon coupling at low q ² in timelike region. A prominent enhancement in the respective electromagnetic transition Form Factors (etFF) at q ² near vector mesons ρ...
High-statistics $\pi^-\pi^-$ and $\pi^+\pi^+$ femtoscopy data are presented for Au+Au collisions at $\sqrt{s_\mathrm{NN}}=2.4$ GeV, measured with HADES at SIS18/GSI. The experimental correlation functions allow the determination of the space-time extent of the corresponding emission sources via a comparison to models. The emission source, parametri...
About 10 μs after the Big Bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at temperatures close to kT = 150 MeV and densities several times higher than those found in nuclei. This quantum chromodynamics (QCD) matter can be created in the l...
We present the first observation of K− and ϕ absorption within nuclear matter by means of π−-induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K−/K+)W/(K−/K+)C is found to be 0.319±0.009(stat)−0.012+0.014(syst) indicating a larger absorption of K− in heavier targets as...
We investigate identical pion HBT intensity interferometry in central Au+Au collisions at 1.23A GeV. High-statistics π−π− and π+π+ data are measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinally comoving system and parametrized as three-dimensional Gaussian...
We present first data on sub-threshold production of K s⁰ mesons and Λ hyperons in Au+Au collisions at s NN =2.4 GeV. We observe an universal 〈A part 〉 scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their 〈A part 〉 scaling, and the shapes of the rapidity and the p t spectra...
The HADES collaboration uses the e ⁺ e ⁻ production as a probe of the resonance matter produced in collisions at incident energies of 1-3.5 GeV/nucleon at GSI. Elementary reactions provide useful references for these studies and give information on resonance Dalitz decays (R→Ne ⁺ e ⁻ ). Such processes are sensitive to the structure of time-like ele...
We present first data on sub-threshold production of K0 s mesons and {\Lambda} hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their scaling, and the shapes of the rapidity and the pt spectra...
We present the first observation of K- and \phi absorption within nuclear matter by means of \pi- -induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W / (K-/K+)C is found to be 0.319 \pm 0.009(stat)+0.014-0.012 (syst) indicating a larger absorption of K- in heavie...
For the first time, identical pion HBT intensity interferometry is investigated for a large heavy ion collision system in the energy region of 1 GeV per nucleon. High-statistics $\pi^-\pi^-$ and $\pi^+\pi^+$ data are presented for central Au+Au collisions at 1.23A GeV, measured with HADES at SIS18/GSI. The radius parameters, derived from the correl...
The centrality determination for Au + Au collisions at 1.23A GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at t...
We present data on charged kaons (K±) and ϕ mesons in Au(1.23A GeV)+Au collisions. It is the first simultaneous measurement of K− and ϕ mesons in central heavy-ion collisions below a kinetic beam energy of 10A GeV. The ϕ/K− multiplicity ratio is found to be surprisingly high with a value of 0.52±0.16 and shows no dependence on the centrality of the...
The centrality determination for Au+Au, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-...
The production of $\Sigma^{0}$ baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to $\sqrt{s_{NN}}=3.18$ GeV) is studied with the detector set-up HADES at GSI, Darmstadt. $\Sigma^{0}$s were identified via the decay $\Sigma^{0} \rightarrow \Lambda \gamma$ with subsequent decays $\Lambda \rightarrow p \pi^{-}$ in coincidence with a $e^{...
HADES is a multi-purpose charged-particle detector operated at the SIS18 synchrotron located at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. The provided ion beam energies of 1-2 A GeV are the lowest of all currently running heavy-ion experiments and result in the highest baryo-chemical potentials at freeze-out in case of...
The combination of a production target for secondary beams, an optimized ion optical beam line setting, in-beam detectors for minimum ionizing particles with high rate capability, and an efficient large acceptance spectrometer around the reaction target constitutes an experimental opportunity to study in detail hadronic interactions utilizing pion...
We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of e⁺e⁻ pairs above the π⁰ mass in the exclusive channel dp→ npe⁺e⁻(pspect) as compared to the exc...
We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25 GeV/u inpinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of $e^+e^-$ pairs above the $\pi^{0}$ mass in the exclusive channel $dp \to npe^{+}e^{-}(p_{spect...
We present first data on charged kaons and {\phi} mesons in Au+Au collisions at a kinetic beam energy of 1.23A GeV. As observed already at slightly higher beam energies, we find significantly different slopes for the K+ and K- transverse-mass spectra, and no significant increase of the the K-/K+ multiplicity ratio with increasing centrality of the...
The inclusive production of {\Lambda} hyperons in proton-proton collisions at $\sqrt{s}$ = 3.18 GeV was measured with HADES at the GSI Helmholtzzentrum f\"ur Schwerionenforschung in Darmstadt. The experimental data are compared to a data-based model for individual exclusive {\Lambda} production channels in the same reaction. The contributions of in...
We report on the first measurement of pΛ and pp correlations via the femtoscopy method in p + Nb reactions at sNN=3.18GeV, studied with the High Acceptance Di-Electron Spectrometer (HADES). By comparing the experimental correlation function to model calculations, a source size for pp pairs of r0,pp=2.02±0.01(stat)-0.12+0.11(sys)fm and a slightly sm...
The HADES data from p + Nb collisions at a center-of-mass energy of √sNN = 3.2 GeV are analyzed employing a statistical hadronization model. The model can successfully describe the production yields of the identified hadrons π0, η, Ʌ, K0s, ω with parameters Tchem = (99 ± 11) MeV and μb = (619 ± 34) MeV, which fit well into the chemical freeze-out s...
We report on the first measurement of $p\Lambda$ and $pp$ correlations via the femtoscopy method in p+Nb reactions at $\mathrm{\sqrt{s_{NN}}=3.18} ~\mathrm{GeV}$, studied with the High Acceptance Di-Electron Spectrometer (HADES). By comparing the experimental correlation function to model calculations, a source size for $pp$ pairs of $r_{0,pp}=2.02...
We present and discuss recent experimental activities of the HADES collaboration on open and hidden strangeness production close or below the elementary NN threshold. Special emphasis is put on the feed-down from mesons to antikaons, the presence of the Ξ- excess in cold nuclear matter and the comparison of statistical model rates to elementary p+p...
The HADES data from p+Nb collisions at center of mass energy of
$\sqrt{s_{NN}}$= 3.2 GeV are analyzed by employing a statistical model.
Accounting for the identified hadrons $\pi^0$, $\eta$, $\Lambda$, $K^{0}_{s}$,
$\omega$ allows a surprisingly good description of their abundances with
parameters $T_{chem}=(99\pm11)$ MeV and $\mu_{b}=(619\pm34)$ M...
Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25GeV is investigated. The multi-differential data were measured by the HADES Collaboration. Exclusive channels with one pion in the final state (npπ
+ and ppπ
0 were put to extended studies based on various observables in the framework of a one-pion exchange mode...
We present results on the K*(892)+ production in proton-proton collisions at
a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this
mesonic resonance has been observed in nucleon-nucleon reactions. The data are
interpreted within a two-channel model that includes the 3-body production of
K*(892)+ associated with the Lambda-...
The tagged quasi-free $np \to np\pi^+\pi^-$ reaction has been studied
experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI
at a deuteron incident beam energy of 1.25 GeV/nucleon ($\sqrt s \sim$ 2.42
GeV/c for the quasi-free collision). For the first time, differential
distributions for $\pi^{+}\pi^{-}$ production in $np$...
Results on the production of the double-strange cascade hyperon
$\mathrm{\Xi^-}$ are reported for collisions of p\,(3.5~GeV)\,+\,Nb, studied
with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI
Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time,
subthreshold $\mathrm{\Xi^-}$ production is observed in proton-...
This contribution aims to give a basic overview of the latest results regarding the production of resonances in different collision systems. The results were extracted from experimental data collected with HADES that is a multipurpose detector located at the GSI Helmholtzzentrum, Darmstadt. The main points discussed here are: the properties of the...
In this paper we report on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV and 3.5 GeV, based on data measured with HADES. Exclusive channels npπ+ and ppπ0 as well as ppe+e− were studied simultaneously in the framework of a one-boson exchange model. The resonance cross sections were...
This work presents the analysis of the performance of the RPC ToF wall of the HADES, located at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The behavior of the detector is studied in Au+Au collisions at 1.23 AGeV. A main characteristic of the detector is that all the active areas were designed to be electrically shielded in order to o...
We present the analysis of the inclusive $K^{0}$ production in p+p and p+Nb
collisions measured with the HADES detector at a beam kinetic energy of 3.5
GeV. Data are compared to the GiBUU transport model. The data suggest the
presence of a repulsive momentum-dependent kaon potential as predicted by the
Chiral Perturbation Theory (ChPT). For the kao...
We present the first preliminary results on the production of hadrons with strangeness content (K+K+, K−K−, Ks0, Λ and ϕ ) in Au+AuAu+Au collisions at 1.23 A GeV incident energy measured with HADES. At the corresponding center of mass energy of s=2.4 GeV all hadrons carrying strangeness are produced below their free nucleon–nucleon threshold. While...
Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have
analyzed HADES data of the reaction $p(3.5GeV)+p\to pK^{+}\Lambda$. This
reaction might contain information about the kaonic cluster "$ppK^-$" via its
decay into $p\Lambda$. Due to interference effects in our coherent description
of the data, a hypothetical $\overline{K}NN$...
The results on double-pion production in tagged quasi-free np collisions at a deutron incident beam energy of 1.25 GeV/c measured with the High-Acceptance Di-Electron Spectrometer (HADES) installed at GSI are presented. The specific acceptance of HADES allowed for the first time to obtain high-precision data on pi+pi- and pi-pi0 production in np co...
An exclusive analysis of the 4-body final states $\mathrm{\Lambda + p +
\pi^{+} + K^{0}}$ and $\mathrm{\Sigma^{0} + p + \pi^{+} + K^{0}}$ measured with
HADES for p+p collisions at a beam kinetic energy of 3.5 GeV is presented. The
analysis uses various phase space variables, such as missing mass and invariant
mass distributions, in the four particl...
We report on baryon resonance production and decay in proton-proton
collisions at a kinetic energy of $3.5$ GeV based on data measured with HADES.
The exclusive channels $pp \rightarrow np\pi^{+}$ and $pp \rightarrow
pp\pi^{0}$ as well as $pp \rightarrow ppe^{+}e^{-}$ are studied simultaneously
for the first time. The invariant masses and angular d...
Results on \( \Lambda\) hyperon production are reported for collisions of p(3.5 GeV) + Nb , studied with the High-Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope param...
