arXiv subjects

Ulrich Mosel

Publications and source records attributed to Ulrich Mosel.

At least 37 records · Page 2Linked to original sources

arXiv2014

Energy reconstruction in the Long-Baseline Neutrino Experiment

The Long-Baseline Neutrino Experiment aims at measuring fundamental physical parameters to high precision and exploring physics beyond the standard model. Nuclear targets introduce complications towards that aim. We investigate the uncertainties in the energy reconstruction, based on quasielastic scattering relations, due to nuclear effects. The reconstructed event distributions as a function of energy tend to be smeared out and shifted by several 100 MeV in their oscillatory structure if standard event selection is used. We show that a more restrictive experimental event selection offers the possibility to reach the accuracy needed for a determination of the mass ordering and the $CP$-violating phase. Quasielastic-based energy reconstruction could thus be a viable alternative to the calorimetric reconstruction also at higher energies.

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arXiv2013

Pion production in the MiniBooNE experiment

Background: Charged current pion production gives information on the axial formfactors of nucleon resonances. It also introduces a noticeable background to quasi-elastic measurements on nuclear targets. Purpose: Understand pion production in neutrino interactions with nucleons and the reaction mechanism in nuclei. Method: The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for an investigation of neutrino-nucleus reactions. Results: Theoretical results for integrated and differential cross sections for the MiniBooNE neutrino flux are compared to the data. Two sets of pion production data on elementary targets are used to obtain limits for the neutrino-nucleus reactions. Conclusions: The MiniBooNE pion production data are consistent with the BNL elementary data if a small flux renormalization is performed while the ANL input data lead to significantly too low cross sections. A final determination of in-medium effects requires new data on elementary (p,D) targets.

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arXiv2013

Comparison of GiBUU calculations with MiniBooNE pion production data

Background. Neutrino-induced pion production can give important informationon the axial coupling to nucleon resonances. Furthermore, pion production represents a major background to quasielastic-like events. Single pion production data from the MiniBooNE in charged current neutrino scattering in mineral oil appeared higher than expected within conventional theoretical approaches. Purpose. We aim to investigate which model parameters affect the calculated cross section and how they do this. Method. The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for an investigation of neutrino-nucleus reactions. Results. Presented are integrated and differential cross sections for 1π^+ and 1π^0 production before and after final state interactions in comparison with the MiniBooNE data. Conclusions. For the MiniBooNE flux all processes (QE, 1π-background, Δ, higher resonance production, DIS) contribute to the observed final state with one pion of a given charge. The uncertainty in elementary pion production cross sections leads to a corresponding uncertainty in the nuclear cross sections. Final state interactions change the shape of the muon-related observables only slightly, but they significantly change the shape of pion distributions.

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arXiv2013

Investigating in-medium properties of the $ω$ meson via the $ω\rightarrowπ^0γ$ decay

We investigate the feasibility of studying in-medium properties of the $ω$ meson in photoproduction experiments via the decay $ω\rightarrowπ^0γ$. We use the GiBUU transport model to compare different methods of obtaining in-medium information, such as the invariant mass spectrum, transparency ratio, excitation function and momentum spectrum. We show that the final-state interaction of the pion poses a major obstacle for the interpretation of the invariant mass spectrum. The other three observables turn out to be fairly independent of final-state interactions and thus can give access to the $ω$'s in-medium properties.

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arXiv2012

Dilepton production at SIS energies with the GiBUU transport model

We present dilepton spectra from nucleus-nucleus collisions at SIS energies, which were simulated with the GiBUU transport model in a resonance-model approach. These spectra are compared to the data published by the HADES collaboration. We argue that the interpretation of dilepton spectra at SIS energies critically depends on the couplings between the ρ meson and the baryonic resonances.

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arXiv2012

Dilepton production in proton-induced reactions at SIS energies with the GiBUU transport model

We present dilepton spectra from p+p, d+p and p+Nb reactions at SIS energies, which were simulated with the GiBUU transport model in a resonance model approach. These spectra are compared to the data published by the HADES and DLS collaborations. It is shown that the $ρ$ spectral function includes non-trivial effects already in elementary reactions, due to production via baryon resonances, which can yield large contributions to the dilepton spectrum. Dilepton spectra from nuclear reactions in the energy range of the HADES experiment are thus found to be sensitive also to properties of nucleon resonances in the nuclear medium.

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arXiv2012

Neutrino-Long-Baseline Experiments and Nuclear Physics

Neutrino long-baseline experiments nowadays all use nuclear targets. The extraction of neutrino oscillation parameters from such experiments requires a good understanding of the interaction of neutrinos with nuclei. In this talk we discuss results on quasielastic scattering and pion production which are the relevant processes in the neutrino energy regime around 1 GeV. We also discuss implications of the reaction mechanisms for the reconstruction of the neutrino energy which is not known a priori.

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arXiv2011

Primakoff production of $π^0$, $η$ and $η'$ in the Coulomb field of a nucleus

Photoproduction of neutral pseudoscalar mesons $π^0,η(547)$ and $η'(958)$ in the Coulomb field of an atomic nucleus is studied using a model which describes the Primakoff and nuclear parts of the production amplitude. At high energies the nuclear background is dominated by the exchange of $C$-parity odd Regge trajectories. In the coherent production the isospin filtering makes the $ω(782)$ a dominant trajectory. The calculations are in agreement with $π^0$ data from JLAB provided the photon shadowing and final state interactions of mesons are taken into account. The kinematic conditions which allow to study the Primakoff effect in $η$ and $η'$ photoproduction off nuclei are further discussed. We also give predictions for the higher energies available at the JLAB upgrade.

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arXiv2011

Experimental approaches for determining in-medium properties of hadrons from photo-nuclear reactions

Properties of hadrons and their modification within strongly interacting matter provide a link between experimental observables and Quantum Chromodynamics (QCD) in the non-perturbative sector. The sensitivity of various observables to in-medium modifications of mesons is discussed. The transparency ratio, comparing the meson yield per nucleon within a nucleus relative to that on a free nucleon, is related to the in-medium width of the meson. While the transparency ratio can be determined for any meson lifetime the meson line shape only contains information on in-medium properties if the meson is so short-lived that it decays in the medium after production in a nuclear reaction. Light vector mesons are thus particularly suited for these investigations. The momentum distribution of mesons produced in a photo-nuclear reaction as well as the excitation function also show some sensitivity to different in-medium modification scenarios. As an example, high statistics data taken at MAMI-C on the photoproduction of ω mesons are presented.

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arXiv2011

Resonance-Parton Duality in $(e,e'π)$ off Nucleons

Regge-pole based descriptions of pion-electroproduction on nucleons have given a very good description of the longitudinal components of the cross sections. However, these very same models grossly underestimate the transverse components. A related problem appears in QCD-based scaling arguments that predict the predominance of longitudinal over transverse electroproduction of pions by terms $\propto Q^2$. However, data from JLAB, Cornell and DESY, covering a wide kinematical range $1 < Q^2 < 11\, {\rm GeV}^2$ and $2\, {\rm GeV} < W < 4\, {\rm GeV}$, do not show this expected behavior. We address here this issue of the transverse response in pion-electroproduction by considering the contributions of high-lying ($W > 2$ GeV) nucleon resonances to pion production. The coupling strengths and form factors are obtained through resonance-parton duality. We show that in a wide range of electron energies and four-momentum transfers such a model describes all the available data very well.

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arXiv2011

Neutrino-Nucleus Interactions around 1 GeV

The extraction of neutrino oscillation parameters often requires the unambiguous identification of the reaction mechanism to be used for the energy determination. The use of nuclear targets and of beams with broad energy distributions complicates this task because it requires the reliable description of many different elementary processes and the use of event generators to isolate and identify them. In this talk I briefly summarize our present understanding of this task.

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arXiv2011

Description of fully differential Drell-Yan pair production

We investigate Drell-Yan pair production in a QCD inspired model, which takes into account all relevant hard processes up to $O(α_s)$. To address the known shortfalls of such a fixed order calculation we introduce phenomenological parton distributions for initial transverse momentum and quark mass, and devise a subtraction scheme to avoid double-counting when utilizing the standard longitudinal parton distribution functions. We show that we can reproduce Drell-Yan transverse momentum and invariant mass spectra from different proton-proton, proton-nucleus and antiproton-nucleus experiments and at different energies without the need for a $K$ factor. Fixing our parameters at these spectra, we make predictions for Drell-Yan transverse momentum spectra at low hadronic energies, which will be measured for example at $\bar{\text{P}}$ANDA in antiproton-proton collisions.

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arXiv2011

Resonance-Parton Duality and the Transverse Response of Nucleons

QCD-based scaling arguments predict the predominance of longitudinal over transverse electroproduction of pions by terms $\propto Q^2$. However, data from JLAB, Cornell and DESY, covering a wide kinematical range $1 < Q^2 < 11\, {\rm GeV}^2$ and $2\, {\rm GeV} < W < 4\, {\rm GeV}$, do not show this expected behavior. At the same time standard descriptions of pion-electroproduction on nucleons have given a very good description of the longitudinal components of the cross sections. However, these very same models have failed grossly in describing the transverse component. We discuss here a common solution to these two problems by considering the contributions of high-lying ($W > 2$ GeV) nucleon resonances to pion production. The coupling strengths and form factors are obtained through hadron-parton duality. We show that an excellent description of data in a wide range of electron energies and four-momentum transfers can be obtained in such a model.

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arXiv2011

Nuclear Effects in Generators: the Path Forward

The extraction of neutrino oscillation parameters requires the determination of the neutrino energy from observations of the hadronic final state. The use of nuclear targets then requires the use of event generators to isolate the interesting elementary processes and to take experimental acceptances into account. In this talk I briefly summarize the history of event generators and their use in nuclear physics, talk briefly about the generators used in the neutrino community and then discuss future necessary developments.

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arXiv2011

Entanglement of Quasielastic Scattering and Pion Production

The extraction of neutrino oscillation parameters requires the determination of the neutrino energy from observations of the hadronic final state. Here we discuss the difficulties connected with this energy reconstruction for the ongoing experiments MiniBooNE and T2K. We point out that a lower limit to the uncertainty in the reconstructed energy from Fermi motion alone amounts to about 15%. The entanglement of very different elementary processes, in this case quasielastic scattering and pion production, in the actual observables leads to considerably larger errors. We discuss the sensitivity of the energy reconstruction to detection techniques and experimental acceptances. We also calculate the misidentification cross section for electron appearance in the T2K experiment due to neutral pion production.

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arXiv2011

In-Medium Properties of Vector Mesons in a Transport Approach

We present dilepton spectra from p+p and p+Nb collisions at a kinetic beam energy of 3.5 GeV, which were simulated with the GiBUU transport model assuming different in-medium scenarios. We compare these spectra to preliminary HADES data and show that GiBUU can describe the data reasonably well. Our simulations indicate that the intermediate dilepton-mass region is sensitive to the N-Delta electromagnetic transition form factor, which up to now is unmeasured in the time-like region.

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arXiv2011

Exclusive pion electroproduction off nucleons and nuclei

We present our results for the exclusive electroproduction of pions off nucleons and nuclei at high values of $Q^2$. In electroproduction of nuclei $A(e,e'π)$ we consider the Color Transparency (CT) effect recently observed at JLAB. It is shown that the description of $π$ production off nucleons is mandatory for the proof of the CT signal at JLAB. We further develop the models for exclusive production of $π$ off nucleons at JLAB and HERMES. At first we describe a model based on exclusive-inclusive connection. In the second approach we combine a Regge pole approach with the residual effect of nucleon resonances. The nucleon resonances are described using a dual connection between the exclusive form factors and inclusive deep inelastic structure functions. We present the results for the beam spin azimuthal asymmetries measured at JLAB in exclusive electroproduction of charged and neutral pions.

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arXiv2011

Beam spin asymmetry in deeply virtual $π$ production

An interpretation of the beam spin azimuthal asymmetries measured at JLAB in deep exclusive electroproduction of charged and neutral pions is presented. The model combines a Regge pole approach with the effect of nucleon resonances. The $s$- and $u$-channel contributions are described using a dual Bloom-Gilman connection between the exclusive form factors and inclusive deep inelastic structure functions. The results are in agreement with data provided the excitations of nucleon resonances are taken into account.

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