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K. Gallmeister

Publications and source records attributed to K. Gallmeister.

At least 55 records · Page 3Linked to original sources
arXiv2005

Space-Time Picture of Fragmentation in PYTHIA/JETSET for HERMES and RHIC

We examine the space-time evolution of (pre-)hadron production within the Lund string fragmentation model. The complete four-dimensional information of the string breaking vertices and the meeting points of the prehadron constituents are extracted for each single event in Monte Carlo simulations using the Jetset-part of Pythia. We discuss the implication on the deep inelastic lepton scattering experiments at HERMES as well as on observables in ultra-relativistic heavy ion collisions at RHIC, using Pythia also for modeling the hard part of the interaction.

nucl-th↗
arXiv2005

High energy electroproduction off complex nuclei

We investigate hadron attenuation in deep-inelastic lepton scattering off complex nuclei in the kinematic regime of the HERMES experiment. Our transport theoretical simulations reveal strong prehadronic final state interactions of the reaction products with the surrounding nuclear medium early after the initial photon-nucleon interaction has taken place. In this work we compare our model results with the measured hadron multiplicity ratios for a Kr target at HERMES and provide an extended discussion of the double-hadron attenuation recently observed at HERMES.

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arXiv2005

Hadron attenuation at HERMES and JLab

We investigate the attenuation of hadrons in deep inelastic lepton-nucleus scattering in the kinematical regime of the HERMES and Jefferson Lab experiments. The calculation is carried out in the framework of a BUU transport model. Our results indicate a strong influence of (pre)hadronic final state interactions on the observed multiplicity ratios.

nucl-th↗
arXiv2005

Electromagnetic Probes of Strongly Interacting Matter: Probes of Chiral Symmetry Restoration?

The QCD sum rule approach to in-medium modifications of the omega meson in nuclear matter is reviewed with emphasis of its relation to 4-quark condensates and chiral symmetry restoration. Possible implications of the CB-TAPS experiment for the reaction gamma A -> A' omega (-> pi0 gamma) are sketched and the particularly important role of di-electron probes, accessible with HADES, is highlighted. A brief update of a parametrization of the previous dilepton and photon probes from CERES and WA98 of heavy-ion collisions at CERN-SPS energies is presented.

hep-ph↗
arXiv2004

Suppression of high transverse momentum hadrons at RHIC by (pre-) hadronic final state interactions

We investigate transverse hadron spectra from proton+proton, deuteron+Au and Au+Au collisions at sqrt{s}=200 GeV and 17.3 GeV within the Hadron-String-Dynamics (HSD) approach which is based on quark, diquark, string and hadronic degrees of freedom as well as Pythia calculations for the high pT spectra. The comparison to experimental data on transverse mass spectra from p+p, d+Au and Au+Au reactions shows that pre-hadronic effects are responsible for both the hardening of the spectra for low transverse momenta (Cronin effect) as well as the suppression of high pT hadrons. The interactions of formed hadrons are found to be negligible in central Au+Au collisions at sqrt{s}=200 GeV for pT\geq 6 GeV/c, but have some importance for the shape of the ratio R_{AA} at lower pT values (\leq 6 GeV/c). The large suppression seen experimentally is attributed to the inelastic interactions of 'leading' pre-hadrons with the dense environment, which could be partly of colored partonic nature in order to explain the large attenuation seen in most central Au+Au collisions.

hep-ph↗
arXiv2004

Jet quenching by (pre--)hadronic final state interactions at RHIC

Within a hadron-string dynamical transport approach (HSD) we investigate the attenuation of high transverse momentum ($\pT$) hadrons as well as the suppression of 'near-side' and 'far-side' jets in $Au+Au$ collisions at invariant energies $\sqrt{s}$ = 200 GeV and $\sqrt{s}$ = 62.4 GeV in comparison to the data available from the Relativistic Heavy-Ion Collider (RHIC). From our transport studies we find that a significant part of the high $\pT$ hadron attenuation seen experimentally can be attributed to inelastic interactions of 'leading' pre-hadrons with the dense hadronic environment. In addition, we also show results of 'near-side' and 'far-side' angular correlations of high $\pT$ particles from Au+Au collisions at $\sqrt{s}$ = 200 GeV and $\sqrt{s}$ = 62.4 GeV within this (pre-)hadronic attenuation scenario. It turns out that the 'near-side' correlations are unaltered -- in accordance with experiment -- whereas the 'far-side' correlations are suppressed by up to $\sim$ 60% in central collisions. Since a much larger suppression is observed experimentally for these reactions in central reactions we conclude that there should be strong additional (and earlier) partonic interactions in the dense and possibly colored medium created in Au+Au collisions at RHIC.

hep-ph↗
arXiv2004

Dileptons and Open Charm: Probes of Chiral Restoration

We summarize the status of electromagnetic probes of strongly interacting matter produced in relativistic heavy-ion collisions at CERN-SPS with respect to indications of chiral symmetry restoration. Explorative results for studying the open charm dynamics at BNL-RHIC are presented.

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arXiv2004

Hadron attenuation in deep inelastic lepton-nucleus scattering

We present a detailed theoretical investigation of hadron attenuation in deep inelastic scattering (DIS) off complex nuclei in the kinematic regime of the HERMES experiment. The analysis is carried out in the framework of a probabilistic coupled-channel transport model based on the Boltzmann-Uehling-Uhlenbeck (BUU) equation, which allows for a treatment of the final-state interactions (FSI) beyond simple absorption mechanisms. Furthermore, our event-by-event simulations account for the kinematic cuts of the experiments as well as the geometrical acceptance of the detectors. We calculate the multiplicity ratios of charged hadrons for various nuclear targets relative to deuterium as a function of the photon energy nu, the hadron energy fraction z_h=E_h/nu and the transverse momentum p_T. We also confront our model results on double-hadron attenuation with recent experimental data. Separately, we compare the attenuation of identified hadrons (pi^\pm, π^0, K^\pm, p and pbar) on Ne and Kr targets with the data from the HERMES Collaboration and make predictions for a Xe target. At the end we turn towards hadron attenuation on Cu nuclei at EMC energies. Our studies demonstrate that (pre-)hadronic final-state interactions play a dominant role in the kinematic regime of the HERMES experiment while our present approach overestimates the attenuation at EMC energies.

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arXiv2004

Hadron attenuation at HERMES by (pre)hadronic FSI

We investigate hadron formation in high energy electroproduction off complex nuclei in the framework of a BUU transport model. Our approach combines a quantum mechanical treatment of the photon's initial state interactions with a semi-classical coupled channel simulation of the (pre)hadronic final-state interactions (FSI). This allows us to study the hadron attenuation observed at HERMES and to get information on the space-time picture of hadron formation separately for $π^{\pm}$, $π^0$, $K^\pm$, $p$ and $\bar{p}$.

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arXiv2004

Hadron formation and attenuation in deep inelastic lepton scattering off nuclei

We investigate hadron formation in deep inelastic lepton scattering on N, Kr and Xe nuclei in the kinematic regime of the HERMES experiment. The elementary electron-nucleon interaction is described within the event generator PYTHIA while a full coupled-channel treatment of the final state interactions is included by means of a BUU transport model. We find a good agreement with the measured charged hadron multiplicity ratio $R_M^h$ for N and Kr targets by accounting for the deceleration and absorption of the primarily produced particles as well as for the creation of secondary hadrons in the final state interactions.

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arXiv2004

Quenching of high $p_\perp$ hadrons by (pre--)hadronic FSI at RHIC

Recently we have conjectured that (in-)elastic collisions of (pre-)hadronic high momentum states with the bulk of hadrons in the late fireball might substantially account for the attenuation of the high transverse momentum hadrons at RHIC. The potential hadronic attenuation has therefore to be addressed in further detail before definite conclusions on possible QCD effects in a deconfined QGP phase can be drawn with respect to the materializing jets. From our transport studies we find that the interactions of fully formed hadrons are practically negligible in central Au+Au collisions at \sqrt s = 200 GeV for $p_\perp\geq 6 GeV$, but have some importance for the shape of the ratio $R_{AA}$ at lower $p_\perp$ ($\leq 6 GeV$). However, a significant part of the large suppression seen experimentally is attributed to inelastic interactions of 'leading' jet-like pre-hadrons with the dense hadronic environment. In addition, we also show within this scenario first (preliminary) results of near-side and far-side correlations of high $p_\perp$ particles from central Au+Au collisions at $\sqrt{s}$ = 200 GeV. It turns out that the near-side correlations are unaltered -- in accordance with experiment -- whereas the far-side correlations are suppressed by $\sim$ 60%. Since the experimental observation is a nearly complete disappearance of the far-side jet there should be some additional and earlier partonic interactions in the dense and possibly colored medium.

hep-ph↗
arXiv2003

Dynamics of strange, charm and high momentum hadrons in relativistic nucleus-nucleus collisions

We investigate hadron production and attenuation of hadrons with strange and charm quarks (or antiquarks) as well as high transverse momentum hadrons in relativistic nucleus-nucleus collisions from 2 AGeV to 21.3 ATeV within two independent transport approaches (UrQMD and HSD). Both transport models are based on quark, diquark, string and hadronic degrees of freedom, but do not include any explicit phase transition to a quark-gluon plasma. From our dynamical calculations we find that both models do not describe the maximum in the $K^+/π^+$ ratio at 20 - 30 AGeV in central Au+Au collisions found experimentally, though the excitation functions of strange mesons are reproduced well in HSD and UrQMD. Furthermore, the transport calculations show that the charmonium recreation by $D+\bar{D} \to J/Ψ+ meson$ reactions is comparable to the dissociation by 'comoving' mesons at RHIC energies contrary to SPS energies. This leads to the final result that the total $J/Ψ$ suppression as a function of centrality at RHIC should be less than the suppression seen at SPS energies where the 'comover' dissociation is substantial and the backward channels play no role. Furthermore, our transport calculations -- in comparison to experimental data on transverse momentum spectra from $pp$, d+Au and Au+Au reactions -- show that pre-hadronic effects are responsible for both the hardening of the hadron spectra for low transverse momenta (Cronin effect) as well as the suppression of high $p_T$ hadrons. The mutual interactions of formed hadrons are found to be negligible in central Au+Au collisions at $\sqrt{s}$ = 200 GeV for $p_T \geq$ 6 GeV/c and the sizeable suppression seen experimentally is attributed to a large extent to the interactions of 'leading' pre-hadrons with the dense environment.

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arXiv2003

Hadron formation in electron induced reactions at HERMES energies

We investigate meson electroproduction off complex nuclei in the kinematic regime of the HERMES experiment using a semi-classical transport model which is based on the Boltzmann-Uehling-Uhlenbeck (BUU) equation. We discuss coherence length and color transparency effects in exclusive rho^0 production as well as hadron formation and attenuation of charged pions, kaons, protons and anti-protons in deep inelastic lepton scattering off nuclei.

nucl-th↗
arXiv2003

Quenching of High pT Hadron Spectra by Hadronic Interactions in Heavy Ion Collisions at RHIC

Typically the materialization of high energetic transverse partons to hadronic jets is assumed to occur outside the reaction zone in a relativistic heavy ion collision. In contrast, a quantum mechanical estimate yields a time on the order of only a few fm/c for building up the hadronic wavefunction for jets with typical transverse momenta of pT < 10 GeV as accessible at RHIC facilities. The role of possible elastic or inelastic collisions of these high pT particles with the bulk of hadrons inside the fireball is addressed by means of an opacity expansion in the number of collisions. This analysis shows that the hadronic final state interactions can in principle account for the modification of the (moderate) high pT spectrum observed for central collisions at RHIC.

hep-ph↗
arXiv2003

Incoherent rho^0 electroproduction off nuclei

In the present paper we investigate incoherent rho^0 electroproduction off complex nuclei. We derive a novel, simple expression for the incoherent electroproduction cross section in which one can clearly separate the final state interactions of the reaction products from the 'initial state interactions' of the photon that give rise to nuclear shadowing. In the special case of purely absorptive final state interactions we deduce from our expression the known Glauber result. A more realistic treatment of the final state interactions within a transport model is then used to compare our predictions with experimental data from the HERMES experiment.

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arXiv2002

Energy loss of quarks in deconfined matter at RHIC: photon-tagged jets, single electron and dilepton spectra from open charm

We report a first attempt (i) to derive constraints on the energy loss of charm quarks in a deconfined medium from the recent PHENIX data of single-electron transverse momentum spectra and (ii) to estimate the resulting suppression of dileptons from correlated semi-leptonic decays of open charmed mesons. The momentum imbalance of photon-tagged light-quark jets is also considered.

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arXiv2002

Thermal Parameters in Heavy Ion Collisions at SPS and RHIC: Centrality Dependence

The centrality dependence of thermal parameters describing hadron multiplicities and intermediate-mass dilepton spectra in heavy-ion collisions at SPS and RHIC is analyzed. From experimental hadron multiplicities we deduce evidence for strangeness saturation at high energy and maximum centrality. The observed dilepton spectra can be parameterized by a centrality independent temperature.

hep-ph↗