Search

This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron beams, CEBAF's potential for a higher energy upgrade presents a unique opportunity for an innovative nuclear physics program, which seamlessly integrates a rich historical background with a promising future. The proposed physics program encompass a diverse range of investigations centered around the nonperturbative dynamics inherent in hadron structure and the exploration of strongly interacting systems. It builds upon the exceptional capabilities of CEBAF in high-luminosity operations, the availability of existing or planned Hall equipment, and recent advancements in accelerator technology. The proposed program cover various scientific topics, including Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic highlights the key measurements achievable at a 22 GeV CEBAF accelerator. Furthermore, this document outlines the significant physics outcomes and unique aspects of these programs that distinguish them from other existing or planned facilities. In summary, this document provides an exciting rationale for the energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific potential that lies within reach, and the remarkable opportunities it offers for advancing our understanding of hadron physics and related fundamental phenomena.

The HADES collaboration has extracted dilepton mass spectra for $π^-$ induced reactions on the proton from a comparison of data taken on C and CH$_2$ targets. The spectra were interpreted in terms of different versions of vector meson dominance. Here we present results obtained from the theory and generator GiBUU. We first check the subtraction procedure used and then discuss the obtained mass spectra for the proton target. We point out that any conclusions on the version of VMD requires the knowledge of the $ρ$ spectral function in the interesting mass region.

In \cite{Bodek:2020wbk} Bodek and Cai have tried to extract the potentials for nucleons and $��$ resonances from electron-nucleus inclusive scattering data. They find that the $��$ potential is considerably more attractive than that of the nucleons. This result is at variance with the results of a multitude of analyses of (e,A) and ($��A$) interactions, performed about 35 years ago.

We use the microscopic GiBUU transport model to calculate dilepton ($e^+e^-$) production in heavy-ion collisions at SIS18 energies focusing on the effect of collisional broadening of the $��$-meson. The collisional width of the $��$-meson at finite temperature and baryon density in nuclear matter is calculated on the basis of the collision integral of the GiBUU model. A systematic comparison with HADES data on dilepton production in heavy-ion collisions is performed. The collisional broadening of the $��$ improves the agreement between theory and experiment for the dilepton invariant-mass distributions near the $��$ pole mass and for the excess radiation in Au+Au at $1.23 A$ GeV. We furthermore show that some remaining underprediction of the experimental dilepton spectra in C+C at $1 A$ GeV and Au+Au at $1.23 A$ GeV at intermediate invariant masses $0.2-0.4$ GeV can be accounted for by adjusting the $pn$ bremsstrahlung cross section in a way to agree with the inclusive dilepton spectrum from $dp$ collisions at $1.25 A$ GeV., Relevant result figures replaced, correcting small bug in pion propagation, Conclusions unchanged

With the discovery of non-zero value of $\theta_{13}$ mixing angle, the next generation of long-baseline neutrino (LBN) experiments offers the possibility of obtaining statistically significant samples of muon and electron neutrinos and anti-neutrinos with large oscillation effects. In this document we intend to highlight the importance of Near Detector facilities in LBN experiments to both constrain the systematic uncertainties affecting oscillation analyses but also to perform, thanks to their close location, measurements of broad benefit for LBN physics goals. A strong European contribution to these efforts is possible., Comment: Document submitted to the European Strategy For European Particle Physics

Recent JLAB measurements of inclusive (e,A) cross sections as a function of outgoing lepton momentum may provide information on the nucleon spectral function in targets that will be relevant for the planned DUNE neutrino long-baseline experiment. They also provide an important testing ground for neutrino generators. We have therefore used the transport theoretical framework and code GiBUU to calculate the cross sections for the targets C, Ar and Ti. We compare the calculations with the experimental data. The overall agreement is good. Relatively small discrepancies appear mainly on the low-electronenergy side of the QE-peak where QE and 2p2h excitation processes overlap., 2 new refs added, note added in proof, otherwise unchanged

This short paper is an addendum to a recent publication on charged current neutrino-induced pion production (Phys.\ Rev.\ C96 (2017) no.1, 015503). It presents comparisons of pion production cross sections measured at the T2K near detector for a CH target., Comment: Addendum to, "Muon-neutrino-induced charged current pion production on nuclei". U. Mosel, K. Gallmeister. Version 1 of this present addendum was uploaded to the arXiv in August 2017. Now data points, that have become available in the meantime, have been added into the figures. Title changed for version accepted for publication in Phys. Rev. C

The $\eta$ production in the nucleon resonance energy region is studied within the unitary coupled-channels effective Lagrangian approach of the Giessen model. We demonstrate that the second peak recently observed in the cross section of $\eta$ photoproduction on the neutron at $\sqrt{s}$=1.66 GeV can be explained in terms of coupled-channel effects due to $S_{11}(1650)$ and $P_{11}(1710)$ resonance excitations.

The $��(1232) \to ��^\ast N$ magnetic dipole form factor ($G_M^\ast$) is described here within a new covariant model that combines the valence quark core together with the pion cloud contributions. The pion cloud term is parameterized by two terms: one connected to the pion electromagnetic form factor, the other to the photon interaction with intermediate baryon states. The model can be used in studies of pp and heavy ion collisions. In the timelike region this new model improves the results obtained with a constant form factor model fixed at its value at zero momentum transfer. At the same time, and in contrast to the Iachello model, this new model predicts a peak for the transition form factor at the expected position, i.e. at the $��$ mass pole. We calculate the decay of the $��\to ��N$ transition, the Dalitz decay ($��\to e^+ e^- N$), and the $��$ mass distribution function. The impact of the model on dilepton spectra in pp collisions is also discussed., 11 pages, 10 figures

The MINER$��$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$��$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$��$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., Discussion of results on QE enhanced. Added data in Fig. 5. Version close to one being published in Phys. Rev. D

We present a coupled-channel Lagrangian approach (GiM) to describe the $��N \to ��N$, $2��N$ scattering in the resonance energy region. The $2��N$ production has been significantly improved by using the isobar approximation with $��N$ and $����(1232)$ in the intermediate state. The three-body unitarity is maintained up to interference pattern between the isobar subchannels. The scattering amplitudes are obtained as a solution of the Bethe-Salpeter equation in the $K$ matrix approximation. As a first application we perform a partial wave analysis of the $��N \to ��N$, $��^0��^0 N$ reactions in the Roper resonance region. We obtain $R_{��N}(1440)=27^{+4}_{-9}$\,\% and $R_{��N}(1440)=12^{+5}_{-3}$\,\% for the $��N$ and $����$ decay branching ratios of $N^*(1440)$ respectively. The extracted $��N$ inelasticities and reaction amplitudes are consistent with the results from other groups., replaced with the published version

Excited states of the nucleon are described as RPA configurations on a mean--field ground state taken from the MIT bag model. A residual interaction of a structure as in the Nambu--Jona--Lasinio model is used. The particle-hole states are coupled to good total angular momentum and isospin. Valence excitations of particle-hole type and quark--antiquark ($q\overline{q}$) states from the Dirac--sea are included. The dependence of the baryon spectrum and multipole response functions on the coupling constant $G$ is studied. At critical values of $G$ the 3q--ground state becomes degenerate with strongly collective $q\overline{q}$ modes. The model is used to calculate the electric polarizability of the neutron $\alpha_N$. Without residual interaction $\alpha_N=7\cdot 10^{-4}fm^3$ is found. With residual interaction the value increases to $\alpha_N=(7-11)\cdot 10^{-4}fm^3$. The measured value of $\alpha_N$ is reproduced within experimental error bars., Comment: LaTeX, 19 pages, 2 figures

This document represents the response of the Intensity Frontier Neutrino Working Group to the Snowmass charge. We summarize the current status of neutrino physics and identify many exciting future opportunities for studying the properties of neutrinos and for addressing important physics and astrophysics questions with neutrinos., Report of the Community Summer Study 2013 (Snowmass) Intensity Frontier Neutrino Working Group

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., 15 pages, 15 figures; v2: misprint corrections, minor text corrections

We study the formation of single- and double-$��$ hypernuclei in antiproton-induced reactions relevant for the forthcoming PANDA experiment at FAIR. We use the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model with relativistic mean-fields for the description of non-equilibrium dynamics and the statistical multifragmentation model (SMM) for fragment formation. This combined approach describes the dynamical properties of strangeness and fragments in low energy $\bar{p}$-induced reactions fairly well. We then focus on the formation of double-$��$ hypernuclei in high energy $\bar{p}$-nucleus collisions on a primary target including the complementary $��$-induced reactions to a secondary one, as proposed by the PANDA collaboration. Our results show that a copious production of double-$��$ hyperfragments is possible at PANDA. In particular, we provide first theoretical estimations on the double-$��$ production cross section, which strongly rises with decreasing energy of the secondary $��$-beam., 20 pages, 11 figures, Nuclear Physics A, in press

The photoproduction of $��$ mesons on LH_2, C and Nb has been studied for incident photon energies from 900 to 1300 MeV using the CB/TAPS detector at ELSA. The $��$ line shape does not show any significant difference between the LH_2 and the Nb targets. The data are compared with results of transport calculations that predict a sensitivity of the $��$ line shape to in-medium modifications near the production threshold on a free nucleon of $E_��^{lab}$ = 1109 MeV.}, 5 pages, 3 figures

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., Comment: To appear in the proceedings of 45th Winter School in Theoretical Physics 'Neutrino Interactions: from Theory to Monte Carlo Simulations', Ladek-Zdroj, Poland, Feb. 2009

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., Comment: modifications to the text, especially discussion of Fig.1 and Fig.2 extended. conclusions unchanged

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., v2: definition of QE cross section clarified, minor corrections; version to be published in Phys. Rev. C

The photo production of $��$ mesons on the nuclei C, Ca, Nb and Pb has been measured using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the $��$ meson cross section on the nuclear mass number has been compared with three different types of models, a Glauber analysis, a BUU analysis of the Giessen theory group and a calculation by the Valencia theory group. In all three cases, the inelastic $��$ width is found to be $130-150 \rm{MeV/c^2}$ at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the restframe of the $��$ meson, this inelastic $��$ width corresponds to a reduction of the $��$ lifetime by a factor $\approx 30$. For the first time, the momentum dependent $��$N cross section has been extracted from the experiment and is in the range of 70 mb., 5 pages, 4 figures

We present a model for electron scattering off nuclei and photon absorption in the resonance energy region (W, Proceedings of 46th International Winter Meeting on Nuclear Physics, Bormio, Italy, 20-26 Jan 2008 11 pages, 8 figures

Photoproduction of $��$ mesons off $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{nat}$Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S$_{11}$(1535) nucleon resonance and the study of the absorption properties of nuclear matter for $��$ mesons. Careful consideration was given to contributions from $����$ final states and secondary production mechanisms of $��$-mesons e.g. from inelastic $��N$ reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross section $��_{N��}$ for $��$ mesons is constant over a wide range of the $��$ momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU-model show no unexplained in-medium modifications of the S$_{11}$(1535)., Accepted for publication in Eur. Phys. J. A

Within a fully covariant model based on an effective Lagrangian picture, we investigate the hypernuclear production in photon-nucleus interaction on $ ^{16}$O target. The explicit kaon production vertex is described via creation, propagation and decay into relevant channel of $N^*$(1650), $N^*$(1710), and $N^*$(1720) intermediate baryonic resonance states in the initial interaction of the incident photon with one of the target protons. Bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation. Using vertex parameters determined in the previous studies, contributions of the $N^*$(1710) baryonic resonance dominate the total production cross sections which are found to peak at photon energies below 1 GeV. The results show that photoproduction is the most appropriate means for studying the unnatural parity hypernuclear states, thus accessing the spin dependence of the hyperon-nucleon interaction., 12 pages, 4 figures, Dicussions revised, version to appear in Phys. Rev.C (rapid communications)

The photoproduction of vector mesons on various nuclei has been studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The vector mesons, $��$, $��$, and $��$, are observed via their decay to $e^+e^-$, in order to reduce the effects of final state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the $��$ meson. The $��$ spectral function is extracted from the data on various nuclei, carbon, iron, and titanium, and compared to the spectrum from liquid deuterium, which is relatively free of nuclear effects. We observe no significant mass shift for the $��$ meson; however, there is some widening of the resonance in titanium and iron, which is consistent with expected collisional broadening., 8 pages, 4 figures

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, 10 Pages, 10 figures, to appear in the proceedings of 45th International Winter Meeting on Nuclear Physics (Bormio 2007), Bormio, Italy, 14th-21st Jan 2007

We study inclusive omega photoproduction in nuclei and propose a measurement of the nuclear transparency ratio as a means to learn about the in-medium properties of the omega meson. To this end we are using the semi-classical coupled-channel BUU transport approach that allows for a consistent treatment of all nuclear effects. The conditions of our calculations are chosen such as to match the setup of existing experimental facilities at ELSA or MAMI C. We show that the observables (total production cross section and transparency) indeed are sensitive to the omega N interaction in the nuclear medium., Comment: 21 pages, 11 figures, submitted to Nuclear Physics A

We have extended our model for charged current neutrino-nucleus interactions to neutral current reactions. For the elementary neutrino-nucleon interaction, we take into account quasielastic scattering, Delta excitation and the excitation of the resonances in the second resonance region. Our model for the neutrino-nucleus collisions includes in-medium effects such as Fermi motion, Pauli blocking, nuclear binding, and final-state interactions. They are implemented by means of the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) coupled-channel transport model. This allows us to study exclusive channels, namely pion production and nucleon knockout. We find that final-state interactions modify considerably the distributions through rescattering, charge-exchange and absorption. Side-feeding induced by charge-exchange scattering is important in both cases. In the case of pions, there is a strong absorption associated with the in-medium pionless decay modes of the Delta, while nucleon knockout exhibits a considerable enhancement of low energy nucleons due to rescattering. At neutrino energies above 1 GeV, we also obtain that the contribution to nucleon knockout from Delta excitation is comparable to that from quasielastic scattering., Comment: 16 pages, 10 figures; v2: version to be published in Phys. Rev. C, comparison with results of Paschos et al. removed

We present a theoretical analysis of inclusive photoproduction of phi mesons in nuclei. In particular the dependence of the total phi meson yield on the target mass number is investigated. The calculations are done using the semi-classical BUU transport approach that combines the initial state interaction of the incoming photon with the coupled-channel dynamics of the final state particles. The conditions of the calculations are chosen such as to match the set up of a recent experiment performed at SPring8/Osaka. Whereas the observables prove to be rather sensitive to the phi self energy in the medium, the attribution of deviations from the standard scenario to a particular in-medium effect seems to be impossible., 6 pages, 4 figures

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., 10 pages, 4 figures, To appear in the Proceedings of the 43rd International Winter Meeting on Nuclear Physics, Bormio, Italy, 13 Mar - 20 Mar 2005

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., 8 pages, 4 figures, Contribution to the "Workshop on In-Medium Hadron Physics", Giessen, Germany, 11-13 November 2004

We investigate the $A(p,K^+){_��}B$ reaction within a covariant two nucleon model. We focus on amplitudes which are described by creation, propagation and decay into relevant channel of $N^*$(1650), $N^*$(1710), and $N^*$(1720) intermediate baryonic resonance states in the initial collision of the projectile nucleon with one of its target counterparts. This collision is modeled by the exchange of $��$ as well as $��$ and $��$ mesons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave functions in both distorted wave and plane wave approximations. Detailed numerical results are presented in the plane wave approximation; estimates of the effects of the initial and final state interactions are given in the eikonal approximation. Cross sections of 1 - 2 nb/sr at the peak positions, are obtained for favored transitions in case of heavier targets., 36 pages including 14 figures, revised version, more discussions added, to appear in Nucl. Phys. A

A unitary coupled-channel effective Lagrangian model is applied to the combined analysis of the $(��,��) N \to K��$ reactions in the energy region up to 2 GeV. To constrain the resonance couplings to the $K��$ final state the recent photoproduction data obtained by the SAPHIR, SPring-8, and CLAS groups are included into the calculations. The main resonance contributions to the process stem from the $S_{11}(1650)$, $P_{13}(1720)$, and $P_{13}(1900)$ states. The second bump at 1.9 GeV seen in the photoproduction cross section data is described as a coherent sum of the resonance and background contributions. The prediction for the beam polarization observable is presented.

Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead) has been studied for incident photon energies from 200 MeV to 800 MeV with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data were obtained for the inclusive photoproduction of neutral pions and the partial channels of quasifree single pi0, double pi0, and pi0pi+/- photoproduction. They have been analyzed in terms of the in-medium behavior of nucleon resonances and the pion - nucleus interaction. They are compared to earlier measurements from the deuteron and to the predictions of a Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon induced pion production from nuclei., 15 pages, 22 figures, accepted for publication in EPJ A

The spin-$\ffh$ resonance effects are studied within the coupled channel effective Lagrangian model for baryon resonance analysis. We extend our previous hadronic calculations to incorporate the $D_{15}$, $F_{15}$, $D_{35}$, $F_{35}$ states. While the effect of the spin-$\ffh$ resonances to the $\eta N$, $K \Lambda$, and $K \Sigma$ reactions are small, the contribution to the $\omega N$ is found to be important. The results for the 'conventional' and Pascalutsa-like spin-$\ffh$ descriptions are discussed. \PACS{{11.80.-m},{13.75.Gx},{14.20.Gk},{13.30.Gk}}, Comment: Eur. J Phys. A (in print)

The feasibility to study the in-medium properties of the omega meson in photon induced reactions on nuclei is investigated by means of a semiclassical transport model. The calculations are dedicated to an experiment presently being analyzed by the TAPS/Crystal Barrel collaborations. A full coupled-channel treatment of final state interactions allows a quantitative analysis of the influence of absorption and elastic scattering of the produced hadrons and likewise the application of kinematic cuts on the observables. Within the scope of our calculations, the preliminary data by the TAPS/Crystal Barrel collaborations indeed seem to indicate a modification of the isoscalar spectral density in the strongly interacting environment., to appear in the proceedings of the XXXII. workshop on gross properties of nuclei and nuclear excitations, Hirschegg, January 11-17, 2004, 6 pages, 5 figures

The pion- and photon induced reactions for the final states $��N$, $��N$, $2��N$, $��N$, and $��N$ are studied within a coupled-channel effective Lagrangian approach in the energy region from the pion threshold up to 2 GeV. To investigate the role of the nucleon resonances in the different reactions we include all known states with spin-$\foh$,-$\fth$, and -$\ffh$ and masses below 2 GeV. We find a strong contribution from the $D_{15}(1675)$ resonance to the $��N \to ��N$ reaction. While the $F_{15}(1680)$ state only slightly influences the $��$ meson production in the $��N$ scattering its role is enhanced in the $��$ photoproduction due to the large electromagnetic coupling of this resonance. We predict the beam asymmetry $��_X$ to be a negative in the $��p \to ��p$ reaction near to the threshold. Above the 1.85 GeV the asymmetry is found to change its sign and becomes positive at forward directions. The presented findings can be experimentally tested at GRAAL, CLAS, and CB-ELSA facilities., Typographical errors corrected

We investigate coherence length effects and hadron attenuation in lepton scattering off 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. The results of our calculations are in good agreement with the experimentally measured transparency ratio of incoherent rho0 electroproduction off Nitrogen and the multiplicity ratio R_M^h for charged hadrons, pions, kaons, protons and anti-protons in deep inelastic scattering off Nitrogen and Krypton targets., 17 pages, 4 figures. Proceedings of 2nd Int. Conf. on Nuclear and Particle Physics with CEBAF at Jefferson Lab, Dubrovnik, 26-31 May 2003, to be published in Fizika B

We investigate the influence of possible in-medium modifications of the S11(1535) in eta photoproduction in nuclei. Besides Fermi motion, Pauli blocking and binding effects also collisional broadening is accounted for. The in-medium width is obtained from a realistic resonance-hole model. Results on eta photoproduction are obtained from a semi-classical BUU transport model and compared with data. We find that calculations including a momentum dependent nucleon and resonance potential are in agreement with the recent KEK data. In contrast, collisional broadening has only little influence., 6 pages, 7 figures, minor changes in Fig. 4 and Sect. 3

Spin-$\ffh$ resonance contributions in pion-nucleon scattering are investigated within the coupled channel $K$-matrix approach for c.m. energies up to $\sqrt s=$ 2 GeV. All previously studied $\pi N$, $2\pi N$, $\eta N$, $K \Lambda$, $K \Sigma$, and $\omega N$ final states are included. We find a significant improvement of $\chi^2$ in almost all channels by inclusion of the spin-$\ffh$ states. The obtained coupling parameters are discussed., Comment: submitted to Phys. Rev. C

We present calculations of the N N -> N Delta cross section in nuclear matter within the one-pion exchange model taking into account pion collectivity, vertex renormalization by the contact nuclear interactions and Dirac effective masses of the baryons due to coupling with the scalar sigma field. Introducing the Dirac effective masses leads to an in-medium reduction of the cross section. The experimental data on pion multiplicities from the collisions of Ca+Ca, Ru+Ru and Au+Au at 0.4-1.5 A GeV are well described by BUU calculations with the in-medium cross section., 45 pages, 18 figures, minor style corrections, version to appear in Nucl. Phys. A

We present a nucleon resonance analysis by simultaneously considering all pion- and photon-induced experimental data on the final states gamma N, pi N, 2 pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The omega N production mechanism is dominated by large P_{11}(1710) and P_{13}(1900) contributions. In this second part we present the results on the photoproduction reactions and the electromagnetic properties of the resonances. The inclusion of all important final states up to sqrt(s) = 2 GeV allows for estimates on the importance of the individual states for the GDH sum rule., 41 pages, 26 figures, discussion extended, typos corrected, references updated, to appear in Phys. Rev. C

We present a way to account for coherence length effects in a semi-classical transport model. This allows us to describe photo- and electroproduction at large nuclei (A>12) and high energies using a realistic coupled channel description of the final state interactions that goes far beyond simple Glauber theory. We show that the purely absorptive treatment of the final state interactions as usually done in simple Glauber theory might lead to wrong estimates of color transparency and formation time effects in particle production. As an example we discuss exclusive rho^0 photoproduction on Pb at a photon energy of 7 GeV as well as K^+ and K^- production on C and Pb in the photon energy range 1-7 GeV., 10 pages, 6 figures, Proceedings of XL International Winter Meeting on Nuclear Physics, Bormio, Italy, Jan. 2002; corrected typos

We present a nucleon resonance analysis by simultaneously considering all pion- and photon-induced experimental data on the final states gamma N, pi N, 2 pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The omega N production mechanism is dominated by large P_{11}(1710) and P_{13}(1900) contributions. In this first part, we present the results of the pion-induced reactions and the extracted resonance and background properties with emphasis on the difference between global and purely hadronic fits., 54 pages, 26 figures, discussion extended, typos corrected, references updated, to appear in Phys. Rev. C

The pi^- p -> omega n threshold cross section measured in the seventies resisted up to now a consistent theoretical description in line with experiment, mainly caused by too large Born contributions. This led to a discussion in the literature about the correctness of the extraction of these data points. We show that the extraction method used in these references is indeed correct and that there is no reason to doubt the correctness of these data., 5 pages, discussion extended, conclusions unchanged

We describe the pi N -> omega N cross section from threshold to a center of mass energy of 2 GeV in a unitary coupled-channel model and analyze it in terms of rescattering and resonance excitations. The amplitude is mainly composed of D13, P13, and P11 contributions, where the D13 dominates over the complete considered energy range. We also outline the generalization of the standard partial-wave formalism necessary for the decomposition of the omega N final state., 8 pages, fig. 1 replaced, typos corrected, conclusions unchanged; to appear in Phys. Rev. C

In this paper we present the extension of our unitary gauge invariant effective Lagrangian model to vector meson nucleon final states. This model already included the final states $\gamma N$, $\pi N$, $2\pi N$, $\eta N$, $K \Lambda$, and $K \Sigma$ and was developed for a simultaneous analysis of all avaible experimental data for photon- and pion-induced reactions on the nucleon. We discuss how the extension to vector meson nucleon final states is realized, outline a generalization of the standard partial wave formalism, that is applicable to any meson-/photon-baryon reaction, and show first results for $\omega N$ production., Comment: 4 pages, talk given at NSTAR 2001, Workshop on the Physics of Excited Nucleons, University of Mainz, Germany, March 7-10, 2001. To be published in World Scientific

We investigate the coupling of vector mesons with nucleons to nucleon resonances in an isospin-selective VMD approach and explore the in-medium properties of vector mesons., Comment: 8 pages, 2tables, 4 figures, invited talk at NSTAR 2001, Workshop on the Physics of Excited Nucleons, University of Mainz, Germany, March 7-10, 2001. To be published in World Scientific

We study dilepton production from pp, pd and p Be collisions from 1 - 5 GeV including the $\pi^0$, $\eta$, $\omega$ and $\Delta$ Dalitz decays, direct decays of vector mesons ($\rho$, $\omega$) as well as subthreshold $\rho$ production via baryonic resonances (e.g. $D_{13}(1520), P_{11}(1710)$). Our calculations compare rather well with the pp and pd data from the DLS Collaboration, however, overestimate slightly the 'old' p Be data from that group. Futhermore, detailed predictions for differential dilepton spectra at SIS energies are made with a high mass resolution that can be controlled experimentally by the HADES Collaboration in near future., Comment: 27 pages, LaTeX, including 13 postscript figures, to be published in Nucl. Phys. A

An effective Lagrangian model in a coupled channels framework is applied to extract nucleon resonance parameters. In the K-matrix approximation, we simultaneously analyze all the available data for the transitions from pi N to five possible meson-baryon final states, pi N, pipi N, eta N, K Lambda, and KSigma, in the energy range from pi N threshold up to W = 2 GeV. In this work, we focus our efforts on the K Sigma channel. In particular, we include a set of Delta resonances around 1900 MeV: the S31(1900), P31(1910), and P33(1920) states. In most cases the parameters of nucleon resonances determined by the fits are consistent with the commonly accepted values in the literature. We find that in the low-energy region, the S11(1650), P11(1710), and P13(1720) states are important for the p(pi-,K0)Sigma0 and p(pi-,K+)Sigma- processes while the P33(1600) and D33(1700) states are significant for the pure I=3/2 reaction p(pi+,K+)Sigma+. In the high energy region, we find a D13 state at 1945 MeV which is important for the p(pi-,K0)Sigma0 reaction while the Delta resonances around 1900 MeV show up significantly in the p(pi-,K+)Sigma- and p(pi+,K+)Sigma+ processes., 9 Pages, Latex, 3 figures, to be published in the Proceeding of the 18th Indonesian National Physics Symposium

Resonances with strong couplings to strangeness channels are investigated in a coupled-channels framework of kaon production with pions and photons. We find evidence for an additional D13 resonance around 1900 MeV that has a significant decay width into the K Lambda final state. Such a state has been predicted in a relativistic quark model at 1960 MeV with significant gamma N and K Lambda branching ratios., 8 pages, Latex, 5 figures