Ag Collisions Research Articles

Σ0 reconstruction in Ag+Ag collisions at 1.58 AGeV with the HADES experiment

In this contribution we will discuss the production of Σ0 baryons in Ag+Ag collisions at 1.58AGeV beam energy measured by HADES. The experimental upgrade with an electromagnetic calorimeter enables a clear reconstruction of the Σ0. The first sub threshold Σ0 production in A+A collisions is compared to available p+p data as well as transport calculations and statistical hadronisation models.

HADES Overview

In this contribution we present results from Au+Au collisions at √SNN = 2.42 GeV as well as Ag+Ag collisions at √SNN = 2.42 and 2.55 GeV measured by HADES. We focus on three different observables: electromagnetic probes, collective and bulk-matter phenomena and strangeness production which are discussed in the following.

Photon-photon correlations in Ag+Ag collisions at √SNN = 2.55 GeV

Abstract. Photons, as penetrative probes, can deliver information about early stages of heavy-ion collisions, in contrast to hadrons, whose kinematics are determined after the freeze-out era. Given that, they provide access to quantities inaccessible for many other particle species. However, due to technical challenges of photon detection and dominance of photons from particle decays, exploiting their properties requires significant effort. Femtoscopy, a technique used to investigate the space-time characteristics of the source area, is sensitive to the emission sequence of studied particles. Hence, it can be utilized as a tool to separate photons originating from different sources. Studying femto-scopic correlations of photons can offer a new and unique perspective on source parameters before kinematic freeze-out. Using data from Ag+Ag collisions at √SNN = 2.55 GeV, collected by the HADES spectrometer, a preliminary study of photon-photon correlations was performed.

Proton-cluster femtoscopy with the HADES experiment

The matter created in Ag+Ag collisions at √SNN = 2.55 GeV, as measured with the HADES experiment, can be characterized by similar thermodynamic quantities as Neutron Star Mergers, thus becoming an essential reference for the understanding of these compact stellar objects. One of the methods applied to investigate heavy-ion collisions are femtoscopic correlations. They are a unique tool for the determination of the interactions between hadrons and allow to search for possible exited or unbound states of nuclear matter. We performed precise experimental studies of the correlations between protons and different clusters and compared them with the existing theoretical descriptions.

Neutral meson production in Ag+Ag at √SNN = 2.55 GeV

Abstract. Relativistic nucleus-nucleus collisions offer a unique possibility for studying nuclear matter under the influence of high temperature and pressure. During the collision a system of interacting nucleons, resonances, and mesons, called hadronic fireball, is created. HADES is a unique experiment capable of simultaneously measuring all three species of pions for this energy regime. Results on neutral pion production in Ag + Ag collisions at √SNN = 2.55 GeV (beam energy 1.58 A GeV) with 14 billion collected events will be presented. A measurement of a directed and elliptic flow, and yields of neutral pions corrected for detector acceptance and efficiency will be shown with respect to transverse momentum and rapidity for certain centrality classes; and further compared with the data, and charged pion data measured in the same experiment. In addition, the obtained results will be confronted with up-to-date model calculations.

Two-particle femtoscopy at the HADES experiment

An experimental study of γ-γ, p-Λ, and p-cluster femtoscopic correlations from Ag+Ag collisions at √SNN = 2.55 GeV has been conducted using the HADES detector. The results reveal an HBT-like structure for γ-γ correlations, provide estimations of strong interaction parameters for p-Λ correlations, and indicate potential decay signatures of light nuclei for p-cluster correlation functions.

Systematics of yields of strange hadrons from heavy-ion collisions around threshold energies

The parametrizations of experimental yields of K±,0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\pm ,0}$$\\end{document}, ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi $$\\end{document} and Λ+Σ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda +\\Sigma ^0$$\\end{document} are proposed as function of available energy, sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_{\ extrm{NN}}}$$\\end{document} , and number of participants, ⟨Apart⟩b\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle A_{\ extrm{part}} \\rangle _{\ extrm{b}}$$\\end{document} , for sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_{\ extrm{NN}}}$$\\end{document} from 2.15 to 3 GeV. For all the dataset the ⟨Apart⟩b\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle A_{\ extrm{part}} \\rangle _{\ extrm{b}}$$\\end{document} was extracted using the Glauber Monte Carlo method. The α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} exponent of yield dependency on ⟨Apart⟩b\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle A_{\ extrm{part}} \\rangle _{\ extrm{b}}$$\\end{document} appears not to change with beam energy and is found to be 1.30 ± 0.02. Our parametrization and the predictions of public versions of RQMD.RMF, SMASH and UrQMD transport models are compared to the HADES experimental data for Ar+KCl at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s_{\ extrm{NN}}}$$\\end{document} of 2.61 GeV. The phenomenological parametrization currently offers the best overall description of these yields. Predictions are given for yields from Ag + Ag collisions at available energies of 2.41 and 2.55 GeV, analysed by HADES, Au + Au experiment at 2.16 and 2.24 GeV planned by this collaboration, some yields for STAR’s Au + Au collisions at 3 GeV, and for Au + Au collisions planned by CBM, up to 3.85 GeV.

Reconstruction of charged Kaons and ɸ(1020) in Ag+Ag collisions at √SNN = 2.55 GeV with HADES

In March 2019, the HADES collaboration recorded 13:7 · 09 Ag(1.58A GeV)+Ag events as part of the FAIR Phase-0 program. The analysis steps necessary to extract the phase space information for K+, K− and ϕ(1020) are presented in this proceeding.

Production of Strange Mesons, Hyperons and Hypernuclei in Ag\(+\)Ag Collisions at \(\sqrt {s_{NN}}=2.55\)~GeV measured with HADES

Production of Strange Mesons, Hyperons and Hypernuclei in Ag\(+\)Ag Collisions at \(\sqrt {s_{NN}}=2.55\)~GeV measured with HADES

Comparison of heavy ion transport simulations: Ag + Ag collisions at E lab = 1.58A GeV

Abstract We compare the microscopic transport models UrQMD, PHSD, PHQMD, and SMASH to make predictions for the upcoming Ag + Ag data at E lab = 1.58A GeV ( s NN = 2.55 GeV) by the HADES collaboration. We study multiplicities, spectra and effective source temperatures of protons, π ±,0, K ±, the η, Λ + Σ0 and the Ξ− within these models. Despite variations in the detailed implementation of the dynamics in the different models, the employed transport approaches all show consistent multiplicities of the bulk of investigated hadrons. The main differences are in the Ξ− production, which is treated differently between UrQMD/SMASH on one side employing high mass resonance states with explicit decays to Resonance → Ξ + K + K in contrast to PHSD/PHQMD which account only non-resonant Ξ production channels. A comparison of the spectra, summarized by effective source temperatures, shows that all models provide similar source temperatures around T source = 80–95 MeV, and show substantial radial flow on the order of ⟨v T ⟩ = 0.18c − 0.24c even for such a small system.

Dielectron measurements with the HADES at GSI

In this work we present the dielectron analysis of 4.5 billion Ag+Ag collisions ((0−40)% centrality) at a center-of-mass energy of √sNN = 2.55 GeV measured with HADES. The obtained dielectron signal spectrum is compared to simulated hadronic cocktail and nucleon-nucleon reference spectra revealing a strong contribution from the hot and dense phases. The average temperature of the collision system can be extracted from the slope of the in-medium contribution. In a momentum differential analysis we observe modifications of the dielectron signal shape in the ω−ρ invariant mass region. Furthermore we compare the results to previous measurements in Au+Au collisions at slightly lower energy. The suggested modifications of the ρ spectral function is further studied within the HADES pion-beam program. Here, we present recently published results on the electromagnetic and hadronic coupling of baryonic resonances to the ρ − N final state.

HADES Overview

In March 2019 the HADES experiment recorded 14 billion Ag+Ag collisions at √SNN = 2.55 GeV as a part of the FAIR phase-0 physics program. With the capabilities to measure and analyze particles forming the bulk matter, namely pions, protons and light nuclei, as well as rare probes like dilepton decays of vectormesons and strange hadrons, the HADES experiment allows to study the properties of matter at high densities in great detail. In this contribution a special focus is put on the reconstruction of weakly decaying strange hadrons.

New results on light nuclei, hyperons and hypernuclei from HADES (HADES collaboration)

In March 2019 the HADES experiment recorded 14 billion Ag+Ag collisions at √sNN = 2.55 GeV as a part of the FAIR phase-0 physics program. In this contribution, we present and investigate our capabilities to reconstruct and analyze weakly decaying strange hadrons and hypernuclei emerging from these collisions. The focus is put on measuring the mean lifetimes of these particles.

Systematics in the global polarization measurements of Λ hyperons with HADES at SIS18

The global polarization of Λ hyperons has been measured in Au+Au and Ag+Ag collisions at √SNN = 2.4 and 2.55 GeV recorded with HADES. An increase of the polarization is observed following the trend measured by the STAR Collaboration. The high statistics Ag+Ag data allowed for differential measurements of the polarization. The study of acceptance effects is very important in the fixed target setup, as the phase-space coverage is not symmetric. These studies are reported together with the evaluation procedure of the systematic uncertainties.

Reconstruction of γγ mass spectra in Ag+Ag collisions at 1.23 and 1.58 AGeV beam energies with ECal detector of the HADES experiment

HADES is a high acceptance di-electron spectrometer operating at SIS18, GSI, Germany aimed at study of hadron-proton, hadron-nucleus and nucleus-nucleus collisions at 1-4 AGeV beam energies. The new electromagnetic calorimeter (ECal) was added to the experimental setup in order to measure γ-quanta and thus extend its capabilities in study of π 0-, η-mesons, production of neutral hyperons and to improve electron-to-hadron separation for the partcles with momenta p > 300 MeV/c. The first data taking with the ECal detector was carried out in March 2019 when Ag+Ag collisions at 1.23 AGeV and 1.58 AGeV beam energies were studied. The methods of reconstruction of the γγ invariant mass spectra from these data are discussed. The analysis includes several steps: calibration of each module of the ECal detector, identification of γ-quanta, reconstruction of γγ invariant mass spectra and subtraction of combinatorial background. The obtained results show experimental capabilities of the new detector and, after efficiency corrections, will allow to normalize yields of other particles.

Odd--Even Staggering in the Yields of Intermediate Mass Fragments from $p$+Ag collisions at $Ep=480$ MeV

Odd--Even Staggering in the Yields of Intermediate Mass Fragments from $p$+Ag collisions at $Ep=480$ MeV

Ranking and validation of the spallation models for description of intermediate mass fragment emission from p + Ag collisions at 480 MeV incident proton beam energy

Double-differential cross-sections $d^{2}\sigma/d\Omega dE$ for isotopically identified intermediate mass fragments ( 6Li up to 27Mg from nuclear reactions induced by 480 MeV protons impinging on a silver target were analyzed in the frame of a two-step model. The first step of the reaction was described by the intranuclear cascade model INCL4.6 and the second one by four different models (ABLA07,GEM2, GEMINI++, and SMM). The experimental spectra reveal the presence of low-energy, isotropic as well as high-energy, forward-peaked contributions. The INCL4.6 model offers a possibility to describe the latter contribution for light intermediate mass fragments by coalescence of the emitted nucleons. The qualitative agreement of the model predictions with the data was observed but the high-energy tails of the spectra were significantly overestimated. The shape of the isotropic part of the spectra was reproduced by all four models. The GEM2 model strongly underestimated the value of the cross-sections for heavier IMF whereas the SMM and ABLA07 models generally overestimated the data. The best quantitative description of the data was offered by GEMINI++, however, a discrepancy between the data and the model cross-sections still remained for almost all reaction products, especially at forward angles. It indicates that non-equilibrium processes are present which cannot be reproduced by the applied models. The goodness of the data description was judged quantitatively using two statistical deviation factors, the H-factor and the M-factor, as a tool for ranking and validation of the theoretical models.

Production of negatively charged particles in nucleus–nucleus collisions at 200A GeV

Three isotropic emission fireballs are used to describe the rapidity (or pseudorapidity) and transverse momentum distributions of negatively charged particles produced in nucleus–nucleus collisions at high energy. The calculated results are compared and shown to be in agreement with the experimental data of 16O–Au, 32S–S, and 32S–Ag collisions at 200A GeV. PACS Nos.: 25.75-q, 24.10Pa

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton–nucleus and deuteron–gold interactions, as well as central oxygen–gold and sulphur–nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus–nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with ‘temperatures’ between $145 \pm 11$ MeV (p+S interactions) and $244 \pm 43$ MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.