arXiv subjects

O. Buss

Publications and source records attributed to O. Buss.

15 recordsLinked to original sources

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.

hep-ph↗

arXiv2009

Pion production in neutrino interactions with nuclei

Neutrino-induced pion production on nuclear targets is the major inelastic channel in all present-day neutrino-oscillation experiments. It has to be understood quantitatively in order to be able to reconstruct the neutrino-energy at experiments such as MiniBooNE or K2K and T2K. We report here results of cross section calculations for both this channel and for quasielastic scattering within the semiclassical GiBUU method. This methods contains scattering, both elastic and inelastic, absorption and side-feeding of channels all in a unitary, common theoretical framework and code. We find that charged current quasielastic scattering (CCQE) and $1 π$ production are closely entangled in actual experiments, due to final state interactions of the scattered nucleons on one hand and of the $Δ$ resonances and pions, on the other hand. We discuss the uncertainties in the elementary pion production cross sections from ANL and BNL. We find the surprising result that the recent $1 π$ production cross section data from MiniBooNE are well described by calculations without any FSI. For higher energies we study the validity of the Bloom-Gilman quark-hadron duality for both electron- and neutrino-induced reactions. While this duality holds quite well for nucleon targets, for nuclear targets the average resonance contributions to the structure function $F_2$ are always lower than the DIS values. This result indicates a significant impact of nuclear effects on observables, reducing the cross section and structure functions by at least 30-40% and changing the form of various distributions.

nucl-th↗

arXiv2009

Quasielastic Scattering at MiniBooNE Energies

We present our description of neutrino induced charged current quasielastic scattering (CCQE) in nuclei at energies relevant for the MiniBooNE experiment. In our framework, the nucleons, with initial momentum distributions according to the Local Fermi Gas model, move in a density- and momentum-dependent mean field potential. The broadening of the outgoing nucleons due to nucleon-nucleon interactions is taken into account by spectral functions. Long range (RPA) correlations renormalizing the electroweak strength in the medium are also incorporated. The background from resonance excitation events that do not lead to pions in the final state is also predicted by propagating the outgoing hadrons with the Giessen semiclassical BUU model in coupled channels (GiBUU). We achieve a good description of the shape of the CCQE Q2 distribution extracted from data by MiniBooNE, thanks to the inclusion of RPA correlations, but underestimate the integrated cross section when the standard value of MA = 1 GeV is used. Possible reasons for this mismatch are discussed.

nucl-th↗

arXiv2009

Neutrino induced pion production at MiniBooNE and K2K energies

We investigate charged and neutral current neutrino-induced incoherent pion production off nuclei within the GiBUU model at energies relevant for the MiniBooNE and K2K experiments. Special attention is paid to the entanglement between measured CCQE and CC1pi+ cross sections. We further give predictions and compare to recent data measured at MiniBooNE.

nucl-th↗

arXiv2009

Hadronic transport approach to neutrino nucleus scattering: the Giessen BUU model and its validation

We present the GiBUU model for neutrino nucleus scattering: assuming impulse approximation, this reaction is treated as a two step process. In the initial state step, the neutrinos interact with bound nucleons. In the final state step, the outgoing particles of the initial reaction are propagated through the nucleus and undergo final state interactions. In this contribution, we focus on the validation of the initial and final state interaction treatment in GiBUU using experimental data for pion-nucleus, photon-nucleus and electron-nucleus scattering.

nucl-th↗

arXiv2009

Neutrino induced pion production at MiniBooNE and K2K

We investigate charged and neutral current neutrino induced incoherent pion production off nuclei at MiniBooNE and K2K energies within the GiBUU model. We assume impulse approximation and treat the nucleus as a local Fermi gas of nucleons bound in a mean-field potential. In-medium spectral functions are also taken into account. The outcome of the initial neutrino nucleon reaction undergoes complex hadronic final state interactions. We present results for neutral current pi^0 and charged current pi^+ production and compare to MiniBooNE and K2K data.

nucl-th↗

arXiv2009

Electron- and neutrino-nucleus scattering from the quasielastic to the resonance region

We present a model for electron- and neutrino-scattering off nucleons and nuclei focussing on the quasielastic and resonance region. The lepton-nucleon reaction is described within a relativistic formalism that includes, besides quasielastic scattering, the excitation of 13 N* and Delta resonances and a non-resonant single-pion background. Recent electron-scattering data is used for the state-of-the-art parametrizations of the vector form factors; the axial couplings are determined via PCAC and, in the case of the Delta resonance, the axial form factor is refitted using neutrino-scattering data. Scattering off nuclei is treated within the GiBUU framework that takes into account various nuclear effects: the local density approximation for the nuclear ground state, mean-field potentials and in-medium spectral functions. Results for inclusive scattering off Oxygen are presented and, in the case of electron-induced reactions, compared to experimental data and other models.

nucl-th↗

arXiv2008

Neutrino scattering with nuclei - Theory of low energy nuclear effects and its applications

Current long baseline experiments aim at measuring neutrino oscillation parameters with a high precision. A critical quantity is the neutrino energy which can not be measured directly but has to be reconstructed from the observed hadrons. A good knowledge of neutrino-nucleus interactions is thus necessary to minimize the systematic uncertainties in neutrino fluxes, backgrounds and detector responses. In particular final-state interactions inside the target nucleus modify considerably the particle yields through rescattering, charge-exchange and absorption. Nuclear effects can be described with our coupled channel GiBUU transport model where the neutrino first interacts with a bound nucleon producing secondary particles which are then transported out of the nucleus. In this contribution, we give some examples for the application of our model focusing in particular on the MiniBooNE and K2K experiments.

nucl-th↗

arXiv2008

Inclusive results for electron and photon scattering in the resonance region

We present a model for electron scattering off nuclei and photon absorption in the resonance energy region (W <= 2 GeV). The elementary gamma/gamma* N-vertex is described using in-medium kinematics and up-to-date form factors for QE-scattering, pion-production form-factors and resonance helicity amplitudes of the MAID analysis. We find good agreement with inclusive data on electron scattering off Oxygen. For photon absorption in Carbon we find a large impact of the momentum dependent mean-field acting on initial- and final-state baryons.

nucl-th↗

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.

nucl-th↗

arXiv2007

Neutrino Interactions with Nuclei

We investigate neutrino-nucleus collisions at intermediate energies incorporating quasi-elastic scattering and the excitation of 13 resonances as elementary processes, taking into account medium effects such as Fermi motion, Pauli blocking, mean-field potentials and in-medium spectral functions. A coupled-channel treatment of final state interactions is achieved with the GiBUU transport model. Results for inclusive reactions, neutrino- and electron-induced, as well as for pion production and nucleon knockout are presented.

nucl-ex↗

arXiv2007

The influence of the nuclear medium on inclusive electron and neutrino scattering off nuclei

We present a model for inclusive electron and neutrino scattering off nuclei paying special attention to the influence of in-medium effects on the quasi-elastic scattering and pion-production mechanisms. Our results for electron scattering off Oxygen are compared to experimental data at beam energies ranging from 0.7-1.5 GeV. The good description of electron scattering serves as a benchmark for neutrino scattering.

nucl-th↗

arXiv2007

Exciting pions in nuclei: DCX and Electroproduction in the resonance region

We describe the double charge exchange (DCX) reaction of pions with different nuclear targets at incident kinetic energies of 120-180 MeV within the GiBUU transport framework. The DCX process is highly sensitive to details of the interactions of pions with the nuclear medium and, therefore, represents a major benchmark for any model of pion scattering off nuclei at low and intermediate energies. We achieve a good quantitative agreement with the extensive data set obtained at LAMPF. Furthermore, we present first results on electron scattering off nuclei for beam energies of 700-1500 MeV and virtualities of Q^2<700 MeV^2. Including quasi-elastic and pion- production processes and employing in-medium kinematics and realistic form factors, we evaluate inclusive cross sections and compare to data obtained at the ADONE storage ring (Frascati).

nucl-th↗

arXiv2006

Pion induced double charge exchange reactions in the Delta resonance region

We have applied the Giessen BUU (GiBUU) transport model to the description of the double charge exchange (DCX) reaction of pions with different nuclear targets at incident kinetic energies of 120-180 MeV . The DCX process is highly sensitive to details of the interactions of pions with the nuclear medium and, therefore, represents a major benchmark for any model of pion scattering off nuclei at low and intermediate energies. The impact of surface effects, such as the neutron skins of heavy nuclei, is investigated. The dependence of the total cross section on the nuclear mass number is also discussed. We achieve a good quantitative agreement with the extensive data set obtained at LAMPF. Furthermore, we compare the solutions of the transport equations obtained in the test-particle ansatz using two different schemes - the full and the parallel ensemble method.

nucl-th↗

arXiv2004

Low-energy pi pi photoproduction off nuclei

In the present paper we investigate pi0 pi0 and pi(+/-)pi0 photoproduction off complex nuclei at incident beam energies of 400-460 MeV. Simulations of two pion photoproduction on protons and nuclei are performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. Elastic scattering of the final state pions with the nucleons in the surrounding nuclear medium is found to yield a downward shift of the pi pi invariant mass distribution. We show that the target mass dependence of the pi0 pi0 invariant mass spectrum as measured by the TAPS collaboration can be explained without introducing medium effects beyond absorption and quasi-elastic scattering of the final state particles. On the other hand, we find considerable discrepancies with the data in the pi(+/-)pi0 channel, which are not understood.

nucl-th↗