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P. Cabanelas

Publications and source records attributed to P. Cabanelas.

At least 19 recordsLinked to original sources
arXiv2022

Quasi-free (p,2p) reactions in inverse kinematics for studying the fission yield dependence on temperature

Despite the recent experimental and theoretical progress in the investigation of the nuclear fission process, a complete description still represents a challenge in nuclear physics because it is a very complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. To improve on the existing data on nuclear fission, we produce fission reactions of heavy nuclei in inverse kinematics by using quasi-free (p,2p) scattering, which induce fission through particle-hole excitations that can range from few to ten's of MeV. The measurement of the four-momenta of the two outgoing protons allows to reconstruct the excitation energy of the fissioning compound nucleus and therefore to study the evolution of the fission yields with temperature. The realization of this kind of experiment requires a complex experimental setup, providing full isotopic identification of both fission fragments and an accurate measurement of the momenta of the two outgoing protons. This was realized recently at the GSI/FAIR facility and here some preliminary results are presented.

nucl-ex↗
arXiv2022

Comprehensive investigation of fission yields by using spallation- and (p,2p)-induced fission reactions in inverse kinematics

In the last decades, measurements of spallation, fragmentation and Coulex induced fission reactions in inverse kinematics have provided valuable data to accurately investigate the fission dynamics and nuclear structure at large deformations of a large variety of stable and non-stable heavy nuclei. To go a step further, we propose now to induce fission by the use of quasi-free (p,2p) scattering reactions in inverse kinematics, which allows us to reconstruct the excitation energy of the compound fissioning system by using the four-momenta of the two outgoing protons. Therefore, this new approach might permit to correlate the excitation energy with the charge and mass distributions of the fission fragments and with the fission probabilities, given for the first time direct access to the simultaneous measurement of the fission yield dependence on temperature and fission barrier heights of exotic heavy nuclei, respectively. The first experiment based on this methodology was realized recently at the GSI/FAIR facility and a detailed description of the experimental setup is given here.

nucl-ex↗
arXiv2020

Performance recovery of long CsI(Tl) scintillator crystals with APD-based readout

CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy light charged particles and gamma rays in scattering experiments, and is being commissioned during the Phase-0 experiments at FAIR, between 2018 and 2020. It surrounds the reaction target in a segmented configuration with 2432 detection units made of long CsI(Tl) finger-shaped scintillator crystals. CALIFA has a 10 year intended operational lifetime as the R3B calorimeter, necessitating measures to be taken to ensure enduring performance. In this paper we present a systematic study of two groups of 6 different detection units of the CALIFA detector after more than four years of operation. The energy resolution and light output yield are evaluated under different conditions. Tests cover the aging of the first detector units assembled and investigates recovery procedures for degraded detection units. A possible reason for the observed degradation is given, pointing to the crystal-APD coupling.

physics.ins-det↗
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

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.

nucl-ex↗
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

Cross Sections for proton induced high energy $γ$-ray emission (PIGE) in reaction $^{19}$F(p,$αγ$)$^{16}$O at incident proton energies between 1.5 and 4 MeV

We have studied the high energy gamma-rays produced in the reaction $^{19}$F(p,$αγ$)$^{16}$O for incident proton energies from 1.5 to 4.0 MeV over NaF/Ag and CaF$_2$/Ag thin targets in two different sets of data. Gamma-rays were detected with a High Purity Ge detector with an angle of 130$^{o}$ with respect to the beam axis. The cross-sections for the high energy gamma-rays of 6.129, 6.915 and 7.115 MeV have been measured for the whole group between 5 and 7.2 MeV with accuracy better than 10\%. A new energy range was covered and more points are included in the cross-sections data base expanding the existing set of data. Results are in agreement with previous measurements in similar conditions.

nucl-ex↗
arXiv2015

Statistical model analysis of hadron yields in proton-nucleus and heavy-ion collisions at SIS 18 energies

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 $π^0$, $η$, $Λ$, $K^{0}_{s}$, $ω$ allows a surprisingly good description of their abundances with parameters $T_{chem}=(99\pm11)$ MeV and $μ_{b}=(619\pm34)$ MeV, which fits well in the chemical freeze-out systematics found in heavy-ion collisions. In supplement we reanalyze our previous HADES data from Ar+KCl collisions at $\sqrt{s_{NN}}$= 2.6 GeV with an updated version of the statistical model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit. Special emphasis is put on feed-down contributions from higher-lying resonance states which have been proposed to explain the experimentally observed $Ξ^-$ excess present in both data samples.

nucl-ex↗
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.

nucl-ex↗
arXiv2015

K*(892)+ production in proton-proton collisions at E_beam = 3.5 GeV

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- or Sigma-hyperon. The relative contributions of both channels are estimated. Besides the total cross section sigma(p+p -> K*(892)+ + X) = 9.5 +- 0.9 +1.1 -0.9 +- 0.7 mub, that adds a new data point to the excitation function of the K*(892)+ production in the region of low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment.

nucl-ex↗
arXiv2015

Subthreshold Xi- Production in Collisions of p(3.5 GeV)+Nb

Results on the production of the double-strange cascade hyperon $\mathrm{Ξ^-}$ 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 $\mathrm{Ξ^-}$ production is observed in proton-nucleus interactions. Assuming a $\mathrm{Ξ^-}$ phase-space distribution similar to that of $\mathrmΛ$ hyperons, the production probability amounts to $P_{\mathrm{Ξ^-}}=(2.0\,\pm0.4\,\mathrm{(stat)}\,\pm 0.3\,\mathrm{(norm)}\,\pm 0.6\,\mathrm{(syst)})\times10^{-4}$ resulting in a $\mathrm{Ξ^-/(Λ+Σ^0)}$ ratio of $P_{\mathrm{Ξ^-}}/\ P_{\mathrm{Λ+Σ^0}}=(1.2\pm 0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}$. Available model predictions are significantly lower than the estimated $\mathrm{Ξ^-}$ yield.

nucl-ex↗
arXiv2014

Partial Wave Analysis of the Reaction $p(3.5 GeV)+p \to pK^+Λ$ to Search for the "$ppK^-$" Bound State

Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction $p(3.5GeV)+p\to pK^{+}Λ$. This reaction might contain information about the kaonic cluster "$ppK^-$" via its decay into $pΛ$. Due to interference effects in our coherent description of the data, a hypothetical $\overline{K}NN$ (or, specifically "$ppK^-$") cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like $pΛ$. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a $\overline{K}NN$ cluster. At a confidence level of CL$_{s}$=95\% such a cluster can not contribute more than 2-12\% to the total cross section with a $pK^{+}Λ$ final state, which translates into a production cross-section between 0.7 $μb$ and 4.2 $μb$, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.

nucl-ex↗
arXiv2014

Medium effects in proton-induced $K^{0}$ production at 3.5 GeV

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 kaon at rest and at normal nuclear density, the ChPT potential amounts to $\approx 35$ MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p+p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of the experimental results from p+Nb collisions to the in-medium kaon potential.

nucl-ex↗
arXiv2014

Lambda hyperon production and polarization in collisions of p(3.5 GeV) + Nb

Results on $Λ$ 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 parameter of about $90\,$MeV at a rapidity of $y=1.0$, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, $y_{cm}=1.12$. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The $Λ$ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for $Λ$ production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing $Λ$ polarization in the weak decay $Λ\rightarrow p π^-$. Finite negative values of the polarization in the order of $5-20\,\%$ are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for $p_t>300\,$MeV/c and increases with decreasing rapidity for $y < 0.8$.

nucl-ex↗
arXiv2014

Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

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 $pp \rightarrow npπ^{+}$ and $pp \rightarrow ppπ^{0}$ as well as $pp \rightarrow ppe^{+}e^{-}$ are studied simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon systems were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (R) with masses $<2~$ GeV/$c^2$. A very good description of the one-pion production is achieved allowing for an estimate of individual baryon-resonance production-cross-sections which are used as input to calculate the dielectron yields from $R\rightarrow pe^+e^-$ decays. Two models of the resonance decays into dielectrons are examined assuming a point-like $RN γ^*$ coupling and the dominance of the $ρ$ meson. The results of model calculations are compared to data from the exclusive $ppe^{+}e^{-}$ channel by means of the dielectron and $pe^+e^-$ invariant mass distributions.

nucl-ex↗
arXiv2014

Associate K^0 production in p+p collisions at 3.5 GeV: The role of Delta(1232)++

An exclusive analysis of the 4-body final states $\mathrm{Λ+ p + π^{+} + K^{0}}$ and $\mathrm{Σ^{0} + p + π^{+} + K^{0}}$ 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 particle event selection (p, $π^+$, $π^+$, $π^-$) to find cross sections of the different production channels, contributions of the intermediate resonances $\mathrm{Δ^{++}}$ and $\mathrm{Σ(1385)^{+}}$ and corresponding angular distributions. A dominant resonant production is seen, where the reaction $\mathrm{Λ+ Δ^{++} + K^{0}}$ has an about ten times higher cross section ($\mathrm{29.45\pm0.08^{+1.67}_{-1.46}\pm2.06\,μb}$) than the analogous non-resonant reaction ($\mathrm{2.57\pm0.02^{+0.21}_{-1.98}\pm0.18\,μb}$). A similar result is obtained in the corresponding $Σ^{0}$ channels with $\mathrm{9.26\pm0.05^{+1.41}_{-0.31}\pm0.65\,\ mu b}$ in the resonant and $\mathrm{1.35\pm0.02^{+0.10}_{-1.35}\pm0.09\,μb}$ in the non-resonant reactions.

nucl-ex↗
arXiv2013

An upper limit on hypertriton production in collisions of Ar(1.76 AGeV)+KCl

A high-statistic data sample of Ar(1.76 AGeV)+KCl events recorded with HADES is used to search for a hypertriton signal. An upper production limit per centrality-triggered event of $1.04$ x $10^{-3}$ on the $3σ$ level is derived. Comparing this value with the number of successfully reconstructed $Λ$ hyperons allows to determine an upper limit on the ratio $N_{_Λ^3H}/N_Λ$, which is confronted with statistical and coalescence-type model calculations.

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