14 research outputs found
Charmed signatures for phase transitions in heavy-ion collisions
The interplay of charmonium production and suppression in In+In and Pb+Pb
reactions at 158 AGeV and in Au+Au reactions at sqrt(s)=200 GeV is investigated
with the HSD transport approach within the `hadronic comover model' and the
`QGP melting scenario'. The results for the J/Psi suppression and the Psi' to
J/Psi ratio are compared to the recent data of the NA50, NA60, and PHENIX
Collaborations. We find that, at 158 AGeV, the comover absorption model
performs better than the scenario of abrupt threshold melting. However, neither
interaction with hadrons alone nor simple color screening satisfactory
describes the data at sqrt(s)=200 GeV. A deconfined phase is clearly reached at
RHIC, but a theory having the relevant degrees of freedom in this regime
(strongly interacting quarks/gluons) is needed to study its transport
properties.Comment: to appear in the proceedings of "Critical Point and Onset of
Deconfinement" - 4th International Workshop, July 9 - 13, 2007, Darmstadt,
German
What are the early degrees of freedom in ultra-relativistic nucleus-nucleus collisions?
The Parton-Hadron-String-Dynamics (PHSD) transport model is used to study the
impact on the choice of initial degrees of freedom on the final hadronic and
electromagnetic observables in Au+Au collisions at = 200 GeV.
We find that a non-perturbative system of massive gluons (scenario I) and a
system dominated by quarks and antiquarks (scenario II) lead to different
hadronic observables when imposing the same initial energy-momentum tensor
just after the passage of the impinging nuclei. In case of the
gluonic initial condition the formation of pairs in the QGP
proceeds rather slow such that the anti-strange quarks and accordingly the
mesons do not achieve chemical equilibrium even in central Au+Au
collisions at = 200 GeV. Accordingly, the rapidity
distribution is suppressed in the gluonic scenario and in conflict with the
data from the BRAHMS Collaboration. The proton and antiproton rapidity
distributions also disfavor the scenario I. Furthermore, a clear suppression of
direct photon and dilepton production is found for the pure gluonic initial
conditions which is not so clearly seen in the present photon and dilepton
spectra from Au+Au collisions at = 200 GeV due to a large
contribution from other channels. It is argued that dilepton spectra in the
invariant mass range 1.2 GeV 3 GeV will provide a definitive answer
once the background from correlated -meson decays is subtracted
experimentally.Comment: 9 pages, 9 figure
Charmed signatures for phase transitions in heavy-ion collisions
The interplay of charmonium production and suppression in In+In and Pb+Pb reactions at 158 AGeV and in Au+Au reactions at sqrt(s)=200 GeV is investigated with the HSD transport approach within the hadronic comover model' and the QGP melting scenario'. The results for the J/Psi suppression and the Psi' to J/Psi ratio are compared to the recent data of the NA50, NA60, and PHENIX Collaborations. We find that, at 158 AGeV, the comover absorption model performs better than the scenario of abrupt threshold melting. However, neither interaction with hadrons alone nor simple color screening satisfactory describes the data at sqrt(s)=200 GeV. A deconfined phase is clearly reached at RHIC, but a theory having the relevant degrees of freedom in this regime (strongly interacting quarks/gluons) is needed to study its transport properties
Dynamical equilibration in strongly-interacting parton-hadron matter
We study the kinetic and chemical equilibration in 'infinite' parton-hadron
matter within the Parton-Hadron-String Dynamics transport approach, which is
based on a dynamical quasiparticle model for partons matched to reproduce
lattice-QCD results - including the partonic equation of state - in
thermodynamic equilibrium. The 'infinite' matter is simulated within a cubic
box with periodic boundary conditions initialized at different baryon density
(or chemical potential) and energy density. The transition from initially pure
partonic matter to hadronic degrees of freedom (or vice versa) occurs
dynamically by interactions. Different thermodynamical distributions of the
strongly-interacting quark-gluon plasma (sQGP) are addressed and discussed.Comment: Contribution to the proceedings of the International Workshop on Hot
and Cold Baryonic Matter, 15-20 August 2010, Budapest, Hungary, to be
published in EPJ Web of Conference
Strangeness production in heavy-ion collisions
A study of the "horn" in the particle ratio for central heavy-ion
collisions as a function of the collision energy is presented. We
analyse two different interpretations: the onset of deconfinement and the
transition from a baryon- to a meson-dominated hadron gas. We use a realistic
equation of state (EOS), which includes both hadron and quark
degrees-of-freedom. The Taub-adiabate procedure is followed to determine the
system at the early stage. Our results do not support an explanation of the
horn as due to the onset of deconfinement. Using only hadronic EOS we
reproduced the energy dependence of the and ratios
employing an experimental parametrisation of the freeze-out curve. We observe a
transition between a baryon- and a meson-dominated regime; however, the
reproduction of the and ratios as a function of
is not completely satisfying. We finally propose a new idea for the
interpretation of the data, the roll-over scheme, in which the scalar meson
field has not reached the thermal equilibrium at freeze-out. The
rool-over scheme for the equilibration of the -field is based on the
inflation mechanism. The non-equilibrium evolution of the scalar field
influences the particle production, e.g. , however, the fixing of
the free parameters in this model is still an open issue.Comment: 10 pages, 7 figures, 9th International Workshop on Critical Point and
Onset of Deconfinement, 17-21 November, 201
NA61/SHINE online noise filtering using machine learning methods
The NA61/SHINE is a high-energy physics experiment operating at the SPS accelerator at CERN. The physics program of the experiment was recently extended, requiring a significant upgrade of the detector setup. The main goal of the upgrade is to increase the event flow rate from 80Hz to 1kHz by exchanging the read-out electronics of the NA61/SHINE main tracking detectors (Time-Projection-Chambers - TPCs). As the amount of collected data will increase significantly, a tool for online noise filtering is needed. The standard method is based on the reconstruction of tracks and removal of clusters which do not belong to any particle trajectory. However, this method takes a substantial amount of time and resources. A novel approach based on machine learning methods is presented in this proceedings
The Stuff We Swim in: Regulation Alone Will Not Lead to Justifiable Trust in AI
Recent activity in the field of artificial intelligence (AI) has given rise to large language models (LLMs) such as GPT-4 and Bard. These are undoubtedly impressive achievements, but they raise serious questions about appropriation, accuracy, explainability, accessibility, responsibility, and more. There have been pusillanimous and self-exculpating calls for a halt in development by senior researchers in the field and largely self-serving comments by industry leaders around the potential of AI systems, good or bad. Many of these commentaries leverage misguided conceptions, in the popular imagination, of the competence of machine intelligence, based on some sort of Frankenstein or Terminator-like fiction: however, this leaves it entirely unclear what exactly the relationship between human(ity) and AI, as represented by LLMs or what comes after, is or could be
Strangeness production in heavy-ion collisions
A study of the "horn" in the particle ratio for central heavy-ion collisions as a function of the collision energy is presented. We analyse two different interpretations: the onset of deconfinement and the transition from a baryon- to a meson-dominated hadron gas. We use a realistic equation of state (EOS), which includes both hadron and quark degrees-of-freedom. The Taub-adiabate procedure is followed to determine the system at the early stage. Our results do not support an explanation of the horn as due to the onset of deconfinement. Using only hadronic EOS we reproduced the energy dependence of the and ratios employing an experimental parametrisation of the freeze-out curve. We observe a transition between a baryon- and a meson-dominated regime; however, the reproduction of the and ratios as a function of is not completely satisfying. We finally propose a new idea for the interpretation of the data, the roll-over scheme, in which the scalar meson field has not reached the thermal equilibrium at freeze-out. The rool-over scheme for the equilibration of the -field is based on the inflation mechanism. The non-equilibrium evolution of the scalar field influences the particle production, e.g. , however, the fixing of the free parameters in this model is still an open issue
Strongly interacting parton-hadron matter in- and out-off equilibrium
We study the equilibrium properties of strongly-interacting infinite parton-hadron matter, characterized by the transport coefficients such as shear and bulk viscosity and electric conductivity, and the non-equilibrium dynamics of heavy-ion collisions within the Parton-Hadron-String Dynamics (PHSD) transport approach, which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We discuss in particular the possible origin for the strong elliptic flow v2 of direct photons observed at RHIC energies