[en] We study the axial amplitudes for the N-Δ transition in models with quarks and chiral mesons. A set of constraints on the pion field is imposed which enforces PCAC and the off-diagonal Goldberger-Treiman relation. The quark contribution to the amplitudes in general strongly underestimates the C^A₅ amplitude as well as the πNΔ strong coupling constant. We show that the results are considerably improved in models that, in addition to the pion cloud, incorporate a fluctuating σ-field inside the baryon

[en] The Jefferson Lab Experiment E05-102 'Measurement of A_x^' and A_z^' asymmetries in the quasi-elastic ³He(e,e'd) reaction' was performed in Hall A in 2009. The main physics motivation of the experiment was to investigate the effects of small components of the ³He ground-state wave-function by a simultaneous measurement of double-polarization asymmetries in quasi-elastic kinematics for three exclusive channels, (e,e'd), (e,e'p), and (e,e'n), at almost identical momentum transfers, as well as for (e,e'). This experiment will help map the spin structure of the ³He nucleus onto the picture of the ''free'' polarized neutron. As such, it is of great relevance to the polarized-neutron programs at Jefferson Lab and beyond.

[en] The large momentum acceptance of the Kaos spectrometer at the Mainz Microtron MAMI requires the discrimination between kaons and pions for momenta ≥ 1 GeV/c. Silica aerogel with refractive index n∝1.07 has been chosen as a Cerenkov radiator for pion suppression. The area to be covered by the aerogel (H x W ∝ 40 x 200 cm²) is governed by the focal plane of the magnetic spectrometer. A prototype detector with two aerogel tiles of d=2 cm thickness and 20 x 10 cm² total area was designed, built and tested. Modifications to the basic geometry of the prototype were tried, e.g. different kinds of polished aluminum faces were used in the interior in order to improve the reflection of photons towards the PMTs. The behaviour of the prototype has been simulated by using Litrani, a C++/ROOT-based program. Different parameters of the aerogel (absorption and scattering) have been measured and used as input data to the simulation code. The characteristic lengths were of the order of 10 cm in the wavelength range of the produced Cerenkov photons. During two beam-times in Oct. and Nov. 2008 at MAMI the performance of the prototype was measured with electrons, pions, and protons. The absorption and scattering losses in the aerogel tiles lead to a very low number of detected photons. Detection efficiencies were determined at different threshold settings and particle momenta.

[en] The ³He nucleus is a calculable nuclear system, for which our theoretical understanding can be compared with data to an increasingly accurate degree. In turn, the theory faces extensive precise data sets from a series of experiments. Two laboratories are leading the way: MAMI/A1 and the Thomas Jefferson National Accelerator Facility (TJNAF). This paper reviews some of the outstanding current experimental efforts with (polarized or unpolarized) electron scattering on (polarized or unpolarized) ³He targets in these laboratories. (author)

[en] To estimate the activity concentrations of the radionuclides downstream the Sava river due to the liquid discharges from the Krsko NPP, a modified IAEA SRS-19 model was adopted in 2003. The in-site (WMT and SGBD water) measured values enter as the input data for the model. Related to the inventory of the Krsko NPP liquid discharges, only tritium activity concentration in Sava river can be detected above the detection limit. Thus, 3H measured values could serve as the key element for the comparison of modelled and the measured data. In this study we took detailed in-site measured data to calculate the activity concentration of 3H in Sava river using the model. The calculated values were compared with off-site 3H measurement results at Krsko, Brezice and Jesenice na Dolenjskem sampling sites obtained from 2009 to 2015. Various hydraulic and hydrodynamic parameters of the Sava river were considered. To validate the fit, the 3H measurement results obtained by the case study carried out in 2008, where the liquid discharge was tracked downstream at several other locations, were used. It was found out that complete vertical mixing in Sava river probably occurs immediately after the NPP dam. Continuous sampling at Brezice suggests that complete lateral mixing likely occurs before Brezice, while the study of tritium measurements along the Sava river at location 5 (old bridge in Brezice -Sernova cesta) does not support this theory and suggests that our current model might be improved. (author).

[en] We apply a coupled-channel formalism incorporating quasi-bound quark-model states to calculate pion scattering into ηN, KΛ and KΣ channels, as well ηp, ηn, K"+Λ, and K"0Σ"+ photoproduction processes. The meson-baryon and photon-baryon vertices are determined in a SU(3) version of the Cloudy Bag Model. Our model predicts sizable amplitudes in the P_1_1, P_1_3, P_3_3 and S_1_1 partial waves in agreement with the latest MAID isobar model and the recent partial-wave analyses of the Bonn-Gatchina group. We are able to give a quark-model explanation for the apparent resonance near 1685 MeV in the ηn channel. (orig.)

[en] The meson scattering and electroproduction amplitudes in the D13, D33 and D15 partial waves are calculated in a coupled-channel formalism incorporating quasi-bound quark-model states, extending our previous studies of the P11, P33 and S11 partial waves. The vertices of the baryon-meson interaction including the s - and d -wave pions and ρ -mesons, the s -wave η -meson, and the s - and p -wave σ -mesons are determined in the Cloudy Bag Model, with some changes of the parameters to reproduce the widths of the resonances. The helicity amplitudes and the electroproduction amplitudes exhibit consistent behavior in all channels but tend to be too weak compared to the experiment. We discuss possible origins of this discrepancy which arises also in the constituent quark model calculations. (orig.)

[en] We derive a method to calculate the multi-channel K -matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the πΔ and σN(σΔ) channels where the σ -meson models the correlated two-pion decay. We solve the integral equation for the K-matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the Δ(1232) and the N(1440) resonances compared to the bare quark values. (orig.)

[en] We calculate the meson scattering and electroproduction amplitudes in the S11 partial wave in a coupled-channel approach that incorporates quasi-bound quark-model states. Using the quark wave functions and the quark-meson interaction from the Cloudy Bag Model, we obtain a good overall agreement with the available experimental results for the partial widths of the N(1535) and the N(1650) resonances as well as for the pion, eta and kaon electroproduction amplitudes. Our model is consistent with the N(1535) resonance being dominantly a genuine three-quark state rather than a quasi-bound state of mesons and baryons. (orig.)

[en] The process of electroexcitation of the Δ (1232) is studied in the framework of two chiral soliton models with quarks and meson fields: the linear σ-model and the chiral chromo dielectric model. The ratios E2/M1 and C2/M1 in dependence of photon four-momentum squared, k², are similar in both models for - K² < 0.6 GeV² and compatible with the existing data. However, the helicity amplitudes are better reproduced in the linear σ-model. (author)