arXiv subjects

J. A. Garzón

Publications and source records attributed to J. A. Garzón.

At least 19 recordsLinked to original sources

arXiv2026

First measurement of massive virtual photon emission from N* baryon resonances

First information on the time-like electromagnetic structure of baryons in the second resonance region has been obtained from measurements of dielectron (e+ e-) invariant-mass and angular distributions in the quasi-free reaction $π-$ p $\rightarrow$ n e+ e- at $\sqrt{s_{πp}}$ = 1.49 GeV with the High Acceptance Di-Electron Spectrometer (HADES) at GSI using the pion beam impinging on a CH$_2$ target. We find a total cross section $σ$ = 2.97 $\pm$ 0.07data $\pm$ 0.21acc $\pm$ 0.31Zeff $μ$b. In complement to the analysis of the inclusive e+ e- channel, this data set provides a crucial test of the description of baryon time-like transitions. Approaches based on a Vector Meson Dominance amplitude containing direct photon and vector meson ($ρ$) couplings to the baryon provide a satisfactory agreement with the data. A good description is also obtained by electromagnetic time-like baryon transition form factors in a covariant spectator-quark model, pointing to the dominance of meson-cloud effects. The dielectron angular distributions exhibit the contributions of virtual photons ($γ^*$) with longitudinal polarization, in contrast to real photons. The virtual photon angular dependence supports the dominance of J=3/2, I=1/2 contributions observed in both the $γ^*$n and the $ππ$n channels.

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arXiv2024

Proton, deuteron and triton flow measurements in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV

High precision measurements of flow coefficients $v_{n}$ ($n = 1 - 4$) for protons, deuterons and tritons relative to the first-order spectator plane have been performed in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at the SIS18/GSI. Flow coefficients are studied as a function of transverse momentum $p_{t}$ and rapidity $y_{cm}$ over a large region of phase space and for several classes of collision centrality. A clear mass hierarchy is found for the slope of $v_{1}$, $d v_{1}/d y^{\prime}|_{y^{\prime} = 0}$ where $y^{\prime}$ is the scaled rapidity, and for $v_{2}$ at mid-rapidity. Scaling with the number of nucleons is observed for the $p_{t}$ dependence of $v_{2}$ and $v_{4}$ at mid-rapidity, which is indicative for nuclear coalescence as the main process responsible for light nuclei formation. $v_{2}$ is found to scale with the initial eccentricity $\langle ε_{2} \rangle$, while $v_{4}$ scales with $\langle ε_{2} \rangle^{2}$ and $\langle ε_{4} \rangle$. The multi-differential high-precision data on $v_{1}$, $v_{2}$, $v_{3}$, and $v_{4}$ provides important constraints on the equation-of-state of compressed baryonic matter.

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arXiv2023

Inclusive e$^+$e$^-$ production in collisions of pions with protons and nuclei in the second resonance region of baryons

Inclusive e$^+$e$^-$ production has been studied with HADES in $π^-$ + p, $π^-$ + C and $π^- + \mathrm{CH}_2$ reactions, using the GSI pion beam at $\sqrt{s_{πp}}$ = 1.49 GeV. Invariant mass and transverse momentum distributions have been measured and reveal contributions from Dalitz decays of $π^0$, $η$ mesons and baryon resonances. The transverse momentum distributions are very sensitive to the underlying kinematics of the various processes. The baryon contribution exhibits a deviation up to a factor seven from the QED reference expected for the dielectron decay of a hypothetical point-like baryon with the production cross section constrained from the inverse $γ$ n$\rightarrow π^-$ p reaction. The enhancement is attributed to a strong four-momentum squared dependence of the time-like electromagnetic transition form factors as suggested by Vector Meson Dominance (VMD). Two versions of the VMD, that differ in the photon-baryon coupling, have been applied in simulations and compared to data. VMD1 (or two-component VMD) assumes a coupling via the $ρ$ meson and a direct coupling of the photon, while in VMD2 (or strict VMD) the coupling is only mediated via the $ρ$ meson. The VMD2 model, frequently used in transport calculations for dilepton decays, is found to overestimate the measured dielectron yields, while a good description of the data can be obtained with the VMD1 model assuming no phase difference between the two amplitudes. Similar descriptions have also been obtained using a time-like baryon transition form factor model where the pion cloud plays the major role.

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arXiv2023

Hadron Production and Propagation in Pion-Induced Reactions on Nuclei

Hadron production ($π^\pm$, proton, $Λ$, $K_S^0$, $K^\pm$) in $π^- + \mathrm{C}$ and $π^- + \mathrm{W}$ collisions is investigated at an incident pion beam momentum of $1.7~\mathrm{GeV}/c$. This comprehensive set of data measured with HADES at SIS18/GSI significantly extends the existing world data on hadron production in pion induced reactions and provides a new reference for models that are commonly used for the interpretation of heavy-ion collisions. The measured inclusive differential production cross-sections are compared with state-of-the-art transport model (GiBUU, SMASH) calculations. The (semi-) exclusive channel $π^- + A \rightarrow Λ+ K_S^0 +X$, in which the kinematics of the strange hadrons are correlated, is also investigated and compared to a model calculation. Agreement and remaining tensions between data and the current version of the considered transport models are discussed.

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arXiv2023

Investigation of the $\mathbf{Σ^{0}}$ Production Mechanism in p(3.5 GeV)+p Collisions

The production of $Σ^0$ hyperons in proton proton collisions at a beam kinetic energy of 3.5 GeV impinging on a liquid hydrogen target was investigated using data collected with the HADES setup. The total production cross section is found to be $\mathrm{σ(pK^{+}Σ^{0}) [μb] = 17.7 \pm 1.7 (stat) \pm 1.6 (syst)}$. Differential cross section distributions of the exclusive channel $\mathrm{pp \rightarrow pK^{+}Σ^{0}}$ were analyzed in the center-of-mass, Gottfried-Jackson and helicity reference frames for the first time at the excess energy of 556 MeV. The data support the interplay between pion and kaon exchange mechanisms and clearly demonstrate the contribution of interfering nucleon resonances decaying to $\mathrm{K^{+}Σ^{0}}$. The Bonn-Gatchina partial wave analysis was employed to analyse the data. Due to the limited statistics, it was not possible to obtain an unambiguous determination of the relative contribution of intermediate nucleon resonances to the final state. However nucleon resonances with masses around 1.710 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1710)}$) and 1.900 $\mathrm{GeV/c^{2}}$ ($\mathrm{N^{*}(1900)}$ or $\mathrm{Δ^{*}(1900)}$) are preferred by the fit.

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arXiv2023

Production of hydrogen isotopes and charged pions in p (3.5 GeV) + Nb reactions

The double differential production cross sections, $d^2σ/dΩdE$, for hydrogen isotopes and charged pions in the reaction of p + Nb at 3.5 GeV proton beam energy have been measured by the High Acceptance DiElectron Spectrometer (HADES). Thanks to the high acceptance of HADES at forward emission angles and usage of its magnetic field, the measured energy range of hydrogen isotopes could be significantly extended in comparison to the relatively scarce experimental data available in the literature. The data provide information about the development of the intranuclear cascade in the proton-nucleus collisions. They can as well be utilized to study the rate of energy/momentum dissipation in the nuclear systems and the mechanism of elementary and composite particle production in excited nuclear matter at normal density. Data of this type are important also for technological and medical applications. Our results are compared to models developed to describe the processes relevant to nuclear spallation (INCL++) or oriented to probe either the elementary hadronic processes in nuclear matter or the behavior of compressed nuclear matter (GiBUU).

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arXiv2020

Directed, elliptic and higher order flow harmonics of protons, deuterons and tritons in Au+Au collisions at $\sqrt{s_{NN}} = 2.4$ GeV

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 to construct for the first time, at collision energies of a few GeV, a multi-differential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation-of-state of dense baryonic matter.

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arXiv2020

The TRISTAN detector -- 2018-2019 Latitude Survey of Cosmic Rays

In 2018-2019 a cosmic-ray latitude survey at sea level was performed by the TRISTAN detector, an autonomous system composed by three planes of RPCs (120 x 150 cm$^{2}$). The detector made a two-way journey on board of the Spanish vessel Sarmiento de Gamboa between Vigo (Spain) and Punta Arenas (Chile), measuring continuously the cosmic-ray rate throughout the Atlantic crossing. In this work, we present the results of the first journey, correlating the obtained variation of the cosmic-ray rate with the vertical cutoff rigidity, as well as presenting some details of the detector and its autonomous DAQ system used during the campaign.

physics.ins-det↗

arXiv2020

Identical pion intensity interferometry at sqrt(s_{NN})=2.4 GeV

High-statistics $π^-π^-$ and $π^+π^+$ 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, parametrized as three-dimensional Gaussian distribution, is studied in dependence on pair transverse momentum, azimuthal emission angle with respect to the reaction plane, collision centrality and beam energy. For all centralities and transverse momenta, a geometrical distribution of ellipsoidal shape is found in the plane perpendicular to the beam direction with the larger extension perpendicular to the reaction plane. For large transverse momenta, the corresponding eccentricity approaches the initial eccentricity. The eccentricity is smallest for most central collisions, where the shape is almost circular. The magnitude of the tilt angle of the emission ellipsoid in the reaction plane decreases with increasing centrality and increasing transverse momentum. All source radii increase with centrality, largely exhibiting a linear rise with the number of participants, irrespective of transverse momentum. A substantial charge-sign difference of the source radii is found, appearing most pronounced at low transverse momentum. The extracted source parameters are consistent with the extrapolation of their energy dependence down from higher energies.

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arXiv2020

Two-Pion production in the second resonance region in $π^- p$ collisions with HADES

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 in the intermediate $ρ$ production. Results on exclusive channels with one pion ($π^{-}p$) and two pions ($π^{+}π^{-}n$, $π^{0}π^{-}p$) in the final state measured in the $π^{-}-p$ reaction at four different pion beam momenta (0.650, 0.685, 0.733, and 0.786 GeV/c) are presented. The excitation function of the different partial waves and $Δπ$, $Nσ$ and $Nρ$ isobar configurations is obtained, using the Bonn-Gatchina partial wave analysis. The $N(1520) \frac{3}{2}^-$ resonance is found to dominate the $Nρ$ final state with the branching ratio $BR=12.2 \pm 1.9\%$.

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arXiv2019

Study of the lateral distribution functions of electron and muon bundles using Trasgo detectors

Some of the main features of the new generation Trasgo detectors are their capability in measuring the incoming direction and the arrival time of secondary cosmic particles. They also offer the identification capability between muon and electrons and a rough calorimetry for electrons. Using ground-based stations, these properties allow for the development of new tools for the measurement of primary cosmic ray fluxes. In order to verify and quantify the suitability of Trasgo detectors, whether a single one or arrays of them, to provide reliable information of the properties (mass, energy, incoming direction) of primary cosmic rays we have started an initiative for the systematic study of the 'lateral distributions' displayed by electrons and muons, or by bundles of those particles, using MonteCarlo simulations. In a first approach, electrons and muons were produced in vertical showers from primary H, He, C and Fe nuclei, and with incoming energies limited to a maximum of 10$^{15}$ eV per nucleon. This choice represents a significant component of all secondary particles, which can be measured on Earth's surface. The lateral distributions study has been done at the two locations of Santiago de Compostela (Spain) and Livingston Island (Antarctica), where Trasgo detectors are either in operation, or will be operative in the near future.

astro-ph.IM↗

arXiv2017

$Σ^0$ production in proton nucleus collisions near threshold

The production of $Σ^{0}$ 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. $Σ^{0}$s were identified via the decay $Σ^{0} \rightarrow Λγ$ with subsequent decays $Λ\rightarrow p π^{-}$ in coincidence with a $e^{+}e^{-}$ pair from either external ($γ\rightarrow e^{+} e^{-}$) or internal (Dalitz decay $γ^{*}\rightarrow e^{+} e^{-}$) gamma conversions. The differential $Σ^0$ cross section integrated over the detector acceptance, i.e. the rapidity interval $0.5 < y < 1.1$, has been extracted as $Δσ_{Σ^{0}} = 2.3 \pm (0.2)^{stat} \pm \left(^{+0.6}_{-0.6}\right)^{sys} \pm (0.2)^{norm}$ mb, yielding the inclusive production cross section in full phase space $σ^{total}_{Σ^{0}} = 5.8 \pm (0.5)^{stat} \pm \left(^{+1.4}_{-1.4}\right)^{sys} \pm (0.6)^{norm} \pm (1.7)^{extrapol}$ mb by averaging over different extrapolation methods. The $Λ_{all}$/$Σ^{0}$ ratio within the HADES acceptance is equal to 2.3 $\pm$ $(0.2)^{stat}$ $\pm$ $(^{+0.6}_{-0.6})^{sys}$. The obtained rapidity and momentum distributions are compared to transport model calculations. The $Σ^{0}$ yield agrees with the statistical model of particle production in nuclear reactions.

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arXiv2017

$Δ$(1232) Dalitz decay in proton-proton collisions at T=1.25 GeV measured with HADES

We report on the investigation of $Δ$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}γ$ have been studied and compared with the partial wave analysis of the hadronic $ppπ^{0}$ channel. They allow to access both $Δ^+ \to pπ^0(e^+e^-γ)$ and $Δ^+ \to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $π^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $Δ$ Dalitz decay is identified for the first time and the sensitivity to N-$Δ$ transition form factors is tested. The $Δ$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $\pm$ 0.62 syst. $\pm$ 0.34 stat.) $\times $ 10$^{-5}$, albeit with some model dependence.

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arXiv2017

Analysis of pion production data measured by HADES in proton-proton collisions at 1.25 GeV

Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25 GeV 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 model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the $Δ$(1232), yet with a sizable impact of the $N$(1440) and non-resonant partial waves.

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arXiv2017

Analysis of the exclusive final state npe$^+$e$^-$ in quasi-free np reaction

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 $π^{0}$ mass in the exclusive channel $dp \to npe^{+}e^{-}(p_{spect})$ as compared to the exclusive channel $ppe^{+}e^{-}$ measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double-$Δ$ excitation combined with intermediate $ρ$-meson production. Differential cross sections as a function of the $e^+e^-$ invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical side.

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arXiv2017

TRAGALDABAS. First results on cosmic ray studies and their relation with the solar activity, the Earth magnetic field and the atmospheric properties

Cosmic rays originating from extraterrestrial sources are permanently arriving at Earth atmosphere, where they produce up to billions of secondary particles. The analysis of the secondary particles reaching to the surface of the Earth may provide a very valuable information about the Sun activity, changes in the geomagnetic field and the atmosphere, among others. In this article, we present the first preliminary results of the analysis of the cosmic rays measured with a high resolution tracking detector, TRAGALDABAS, located at the Univ. of Santiago de Compostela, in Spain.

astro-ph.HE↗

arXiv2016

Inclusive Λ production in proton-proton collisions at 3.5 GeV

The inclusive production of Λ hyperons in proton-proton collisions at $\sqrt{s}$ = 3.18 GeV was measured with HADES at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. The experimental data are compared to a data-based model for individual exclusive Λ production channels in the same reaction. The contributions of intermediate resonances such as Σ(1385), Δ++ or N* are considered in detail. In particular, the result of a partial wave analysis is accounted for the abundant pK$^+$Λ final state. Model and data show a reasonable agreement at mid rapidities, while a difference is found for larger rapidities. A total Λ production cross section in p+p collisions at $\sqrt{s}$ = 3.18 GeV of σ(pp $\to$ Λ + X) = 207.3 $\pm$ 1.3 +6.0 -7.3 (stat.) $\pm$ 8.4 (syst.) +0.4 -0.5 (model) μb is found.

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arXiv2015

Study of the quasi-free $np \to np π^+π^-$ reaction with a deuterium beam at 1.25 GeV/nucleon

The tagged quasi-free $np \to npπ^+π^-$ 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 $π^{+}π^{-}$ production in $np$ collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the $np\rightarrow npπ^{+}π^{-}$ reaction are compared with different models. This comparison confirms the dominance of the $t$-channel with $ΔΔ$ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the $π^{+}π^{-}$ invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M$\sim$ 2.38 GeV and with width $Γ\sim$ 70 MeV.

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