arXiv subjects

K. Gallmeister

Publications and source records attributed to K. Gallmeister.

At least 37 records · Page 2Linked to original sources

arXiv2014

Remarkable Features of Decaying Hagedorn States

Hagedorn states (HS) are a tool to model the hadronization process which occurs in the phase transition phase between the quark gluon plasma (QGP) and the hadron resonance gas (HRG). Their abundance is believed to appear near the Hagedorn temperature $T_H$ which in our understanding equals the critical temperature $T_c$. These hadron-like resonances are characterized by being very massive and by not being limited to quantum numbers of known hadrons. To generate a whole zoo of such new states we solve the covariantly formulated bootstrap equation by regarding energy conservation and conservation of the baryon number $B$, strangeness $S$ and electric charge $Q$. To investigate their decay properties decay chain calculations of HS were conducted. One single (heavy) HS with certain quantum numbers decays by various two-body decay channels subsequently into final stable hadrons. Multiplicities of these stable hadrons, their ratios and their energy distributions are presented. Strikingly the final energy spectra of resulting hadrons show a thermal-like distribution with the characteristic Hagedorn temperature $T_H$. All hadronic properties like masses, spectral functions etc. are taken from the hadronic transport model Ultra Relativistic Quantum Molecular Dynamics (UrQMD).

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arXiv2014

Reaction Mechanisms at MINER$ν$A

The MINER$ν$A experiment investigates neutrino interactions with nucleons needed for an understanding of electroweak interactions of hadrons. Since nuclear targets are being used many-body effects may affect the extracted cross sections and the energy reconstruction. The latter is essential for the extraction of neutrino oscillation properties. We investigate the influence of nuclear effects on neutrino interaction cross sections and make predictions for charged current quasielastic (QE) scattering, nucleon-knock-out and pion- and kaon-production on a CH target. The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for the description of neutrino-nucleus reactions. Integrated and differential cross sections for inclusive neutrino scattering, QE processes and particle production for the MINER$ν$A neutrino flux are calculated. The influence of final state interactions on the identification of these processes is discussed. In particular, energy and $Q^2$ reconstruction for the MINER$ν$A flux are critically examined. The $Q^2$ dependence of the inclusive cross sections is found to be sensitive to the energy reconstruction. Cut-offs in flux distributions have a large effect. Final state interactions affect the pion kinetic energy spectra significantly and increase the kaon cross sections by cross feeding from other channels.

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arXiv2014

Thermalization of Hadrons via Hagedorn States

Hagedorn states are characterized by being very massive hadron-like resonances and by not being limited to quantum numbers of known hadrons. To generate such a zoo of different Hagedorn states, a covariantly formulated bootstrap equation is solved by ensuring energy conservation and conservation of baryon number $B$, strangeness $S$ and electric charge $Q$. The numerical solution of this equation provides Hagedorn spectra, which enable to obtain the decay width for Hagedorn states needed in cascading decay simulations. A single (heavy) Hagedorn state cascades by various two-body decay channels subsequently into final stable hadrons. All final hadronic observables like masses, spectral functions and decay branching ratios for hadronic feed down are taken from the hadronic transport model UrQMD. Strikingly, the final energy spectra of resulting hadrons are exponential showing a thermal-like distribution with the characteristic Hagedorn temperature.

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arXiv2012

Energy reconstruction in quasielastic scattering in the MiniBooNE and T2K experiments

Neutrino oscillation probabilities, which are being measured in long-baseline experiments, depend on neutrino energy. The energy in a neutrino beam, however, is broadly smeared so that the neutrino energy in a particular event is not directly known, but must be reconstructed from final state properties. In this paper we investigate the contributions from different reaction mechanisms on the energy-reconstruction method widely used in long-baseline neutrino experiments. Difference between the true-QE and QE-like cross sections in MiniBooNE experiment is investigated in details. It is shown, that fake QE-like events lead to significant distortions in neutrino energy reconstruction. Flux-folded and unfolded cross sections for QE-like scattering are calculated as functions of both true and reconstructed energies. Flux-folded momentum transfer distributions are calculated as functions of both true and reconstructed momentum transfer. Distributions versus reconstructed values are compared with the experimental data. Also presented are the conditional probability densities of finding a true energy for a given reconstructed energy. It is shown, how the energy reconstruction procedure influences the measurement of oscillation parameters in T2K experiment. For the reconstruction procedure based on quasielastic (QE) kinematics, all other reaction channels beside true-QE scattering show a shift of the reconstructed energy towards lower values as compared to the true energy. On average in the MiniBooNE and T2K experiments the shift is 100 - 200 MeV and depends on energy. The oscillation signals are similarly affected. These uncertainties may limit the extraction of a CP violating phase from an oscillation result.

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arXiv2012

Neutrino- and antineutrino-induced reactions with nuclei between 1 and 50 GeV

Background: Nuclear effects can have a significant impact on neutrino-nucleus interactions. In particular, data from neutrino experiments with broad energy distributions require complex theoretical models that are able to take all the relevant channels into account as well as incorporate nuclear effects in both initial and final-state interactions. Purpose: We investigate neutrino and antineutrino scattering on iron and carbon in the energy range from 1 to 30 GeV, which is relevant to current and coming experiments (MINOS, NOvA, and Minerva). Method: The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model, which implements all reaction channels relevant for neutrino energies under consideration, is used for an investigation of neutrino-nucleus reactions. Results: Our calculations are compared with the recent NOMAD and MINOS data for the integrated inclusive cross sections. Predictions are made for the differential cross sections for semiinclusive final states (pions, kaons, and nucleons) for the MINOS and NOvA beams. Conclusions: Nuclear effects in the initial-state interactions may slightly change the inclusive nuclear cross section as compared to the free nucleon ones. Final-state interactions noticeably change the spectra of the outgoing hadrons. In the Minerva and NOvA experiments these effects should be visible in the kinetic energy distributions of the final pions, kaons, and nucleons. Secondary interactions play an important role for strangeness production.

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arXiv2012

Transport-theoretical Description of Nuclear Reactions

In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30 AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100 MeV to a few 100 GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion-nucleus interactions, nuclear fragmentation, heavy ion reactions, hyper nucleus formation, hadronization, color transparency, electron-nucleus collisions and neutrino-nucleus interactions are all possible applications of GiBUU and are discussed in this article.

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arXiv2011

Gluons and the quark sea at high energies: distributions, polarization, tomography

This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.

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arXiv2011

Neutrino nucleus reactions within the GiBUU model

The GiBUU model, which implements all reaction channels relevant at medium neutrino energy, is used to investigate the neutrino and antineutrino scattering on iron. Results for integrated cross sections are compared with NOMAD and MINOS data. It is shown, that final state interaction can noticeably change the spectra of the outgoing hadrons. Predictions for the Miner$ν$a experiment are made for pion spectra, averaged over NuMI neutrino and antineutrino fluxes.

hep-ph↗

arXiv2011

Pion production in the MiniBooNE

We investigate one pion production processes within the Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) coupled channel transport model. Our calculations for integrated and differential cross sections for realistic experimental neutrino fluxes are compared to the data recently provided by the MiniBooNE collaboration.

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arXiv2011

Neutrino nucleus reactions at high energies within the GiBUU model

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arXiv2010

Color transparency in hadronic attenuation of rho0 mesons

Ongoing experiments at JLAB investigate the nuclear transparency in exclusive rho0(770) electroproduction off nuclei. In this work we present transport model predictions for the attenuation of rho0s in nuclei and for color transparency (CT) effects as observable at CLAS with a 5 GeV electron beam energy. A full event simulation presented here permits to study the impact of actual experimental acceptance conditions and kinematical cuts. The exclusive (e,e'rho0) cross section off nucleons is described by diffractive and color string breaking mechanisms extended toward the onset of the deep inelastic regime. Different hadronization and CT scenarios are compared. We show that a detailed analysis of elementary cross section, nuclear effects and experimental cuts is needed to reveal the early onset of rho0-CT at present JLAB energies.

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arXiv2009

Production of charged pions off nuclei with 3...30 GeV incident protons and pions

We compare calculations for the production of charged pions by pion or proton beams off nuclei calculated within our coupled channel transport model (GiBUU) with recent data of the HARP collaboration for beam energies from 3 up to 13 GeV. Predictions for the 30 GeV data for pions and kaons from the NA61/SHINE experiment are included.

hep-ex↗

arXiv2008

Time Dependent Hadronization via HERMES and EMC Data Consistency

Using QCD-inspired time dependent cross sections for pre-hadrons we provide a combined analysis of available experimental data on hadron attenuation in DIS off nuclei as measured by HERMES with 12 and 27 GeV and by EMC with 100 and 280 GeV lepton beam energies. We extract the complete four-dimensional evolution of the pre-hadrons using the JETSET-part of PYTHIA. We find a remarkable sensitivity of nuclear attenuation data to the details of the time-evolution of cross sections. Only cross sections evolving linearly in time describe the available data in a wide kinematical regime. Predictions for experimental conditions at JLAB (5 and 12 GeV beam energies) are included.

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arXiv2007

Hadrons in Nuclei -- from High (200 GeV) to Low (1 GeV) energies

The study of the interaction of hadrons, produced by elementary probes in a nucleus, with the surrounding nuclear medium can give insight into two important questions. First, at high energies, the production process, the time-scales connected with it and the prehadronic interactions can be studied by using the nuclear radius as a length-scale. We do this here by analyzing data from the EMC and HERMES experiements on nuclear attenuation. Second, at low energies the spectral function, and thus the selfenergy of the produced hadron, can be studied. Specifically, we analyze the CBELSA/TAPS data on $ω$ production in nuclei and discuss the importance of understanding in-medium effects both on the primary production cross section and the final state branching ratio. In both of these studies an excellent control of the final state interactions is essential.

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arXiv2007

Three-body collisions in Boltzmann-Uehling-Uhlenbeck theory

Aiming at a microscopic description of heavy ion collisions in the beam energy region of about 10 A GeV, we extend the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model by including a relativistic mean field, in-medium baryon-baryon cross sections and three-body collisions. The model is then compared with experimental data for central Au+Au collisions at 2-10 A GeV and central Pb+Pb collisions at 30 and 40 A GeV on the proton rapidity spectra, the midrapidity yields of $π^+$, $K^\pm$ and $(Λ+Σ^0)$, and the transverse mass spectra of $π^\pm$ and $K^\pm$. The three-body collisions increase the inverse slope parameters of the hadron $m_\perp$-spectra to a good agreement with the data.

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arXiv2006

Prediction for the transverse momentum distribution of Drell-Yan dileptons at GSI-PANDA

We predict the triple differential cross section of the Drell-Yan process (pbar p -> l^+l^-X) in the kinematical regimes relevant for the upcoming PANDA experiment, using a model that accounts for quark virtuality as well as primordial transverse momentum. We find a cross section magnitude of up to 10 nb in the low mass region. A measurement with 10% accuracy is desirable in order to constrain the partonic transverse momentum dispersion and the spectral function width within +-50 MeV and to study their evolution with M and sqrt(s).

hep-ph↗

arXiv2005

Hadronization in nuclear DIS and ultra-relativistic HIC

We present a transport theoretical analysis of hadron attenuation in deep inelastic lepton scattering (DIS) off complex nuclei in the kinematic regime of the HERMES experiment. The HERMES data indicate the presence of strong prehadronic final state interactions shortly after the elementary lepton-nucleon interaction. The contribution of such (pre-)hadronic final state interactions to the observed jet quenching in ultra-relaticistic heavy ion collisions (HIC) at RHIC is estimated under the assumption that a similar space-time picture for hadronization also holds in a hot hadronic medium. Our results show that an additional mechanism for jet quenching must be at work for most central collisions.

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arXiv2005

Hadron attenuation by (pre)hadronic FSI at HERMES

We investigate hadron production in deep inelastic lepton-nucleus scattering in the kinematic regime of the HERMES experiment. Our calculations are carried out in the framework of a BUU transport model which contains the Lund event generators PYTHIA and FRITIOF for the simulation of high-energy elementary interactions. For the first time we consistently use the complete four-dimensional information of the Lund string break up vertices as input for our transport theoretical studies of (pre)hadronic final state interactions. We compare our results with experimental HERMES data on charged hadron attenuation.

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