Forward analysis of π\piN scattering with an expansion method

The $\pi$N forward scattering data are analyzed using an expansion method, where the invariant amplitudes are represented by expansions satisfying the forward dispersion relations. The experimental errors of the data are taken into account through the covariance matrix of the coefficients of the expansions in a careful error analysis. From the results, some coefficients, $c_{n0}^\pm$, of the subthreshold expansions have been calculated with proper error bars.Comment: 5 pages, 4 figures. v2: Added some references. v3: Corrected hyphenatio

Simulation of liquid phase accumulation at centrifugal dewatering of activated sludge

Centrifugation of activated sludge is a frequently used dewatering process but there is a need for a fitting function for moderate and high sludge concentrations. In particular, liquid phase accumulation kinetics during centrifugation may be used as a source of information about sedimentation properties and governing mechanism of the cake formation. This will allow the obtention of the optimal parameters for the dewatering control and process optimisation. For this purpose, activated sludge at different concentrations was investigated on a laboratory centrifuge with centrifugation factor 2667. The following sludges were used in the experiments: 1) activated sludge from thickener (with and without floculant treatment); 2) sludge after industrial centrifuge decanter Flottweg Z62-4 collected from dumping pound; sludge (2) after anaerobic treatment; sludge (2) with a dispersed solid additive. Based on the obtained data, the following assumption was made: settling of the solid phase and cake compaction depends on the hindered settling velocity and sediment compression. Due to the applied centrifuge force, a primary cake skeleton from particular aggregates and flocs is formed. During this stage, free water is displaced from the space between aggregates/flocs with a further transition to the compaction of the sediment with the water being displaced from the pores of the flocs by a filtration mechanism until an equilibrium condition is reached. The liquid volume V vs. time t at hindered settling and sediment dewatering can be represented in the form Vα tⁿ, where n ≤1.0. Therefore, in log-log coordinates, the kinetics of liquid accumulation have a linear dependence lg(V ) α n lg(t) in both settling and compaction stages. This assumption was confirmed for different types of activated sludge. Using asymptotical analysis in the function form F(t,V) , a dimensionless fitting function was obtained that describes the centrifugation of activated sludge. For highly concentrated sludge, it was found that the dewatering occurs as cake compression. Analysis of deformation models leads to the conclusion that for the compressible cake it is necessary to introduce a parameter characterising the cake plasticity dependence on the centrifugation time. Developed model was used for fitting numerous experimental data. The main advantage of proposed model is the possibility to fit the liquid phase accumulation kinetics during centrifugation in a wide range of the activated sludge concentration, from suspension up to structured and paste-like cake consistency. The extension of this model to other slurries requires further investigation

Model-independent analysis of the neutron-proton final-state interaction region in the pp -> pn pi^+ reaction

Experimental data on the pp -> pn pi^+ reaction measured in an exclusive two-arm experiment at 800 MeV show a narrow peak arising from the strong proton-neutron final-state interaction. It was claimed, within the framework of a certain model, that this peak contained up to a 25% spin-singlet final state contribution. By comparing the data with those of pp -> d pi^+ in a largely model-independent way, it is here demonstrated that at all the angles measured the whole of the peak could be explained as being due to spin-triplet final states, with the spin-singlet being at most a few percent. Good qualitative agreement with the measured proton analysing power is also found within this approach.Comment: 10 pages including 3 eps figure

The Goldberger-Miyazawa-Oehme sum rule revisited

The Goldberger-Miyazawa-Oehme sum rule is used to extract the pion-nucleon coupling constant from experimental $\pi$N information. Chiral perturbation theory is exploited in relating the pionic hydrogen s-wave level shift and width results to the appropriate scattering lengths. The deduced value for the coupling is $f^2 = 0.075 \pm 0.002$, where the largest source of uncertainty is the determination of the s-wave $\pi^- p$ scattering length from the atomic level shift measurement.Comment: 4 pages, 1 figure. v2: Revised the second last paragraph of 5th section and clarified the electromagnetic corrections (Tromborg vs. $\chi$PT). Also removed the KH80 slope from the fig.

Delta isobar masses, large N_c relations, and the quark model

Motivated by recent remarks on the Delta+ mass and comparisons between the quark model and relations based on large-N_c with perturbative flavor breaking, two sets of Delta masses consistent with these constraints are constructed. These two sets, based either on an experimentally determined mass splitting or a quark model of isospin symmetry breaking, are shown to be inconsistent. The model dependence of this inconsistency is examined, and suggestions for improved experiments are made. An explicit quark model calculation and mass relations based on the large-N_c limit with perturbative flavor breaking are compared. The expected level of accuracy of such relations is realized in the quark model, except for mass relations spanning more than one SU(6) representation. It is shown that the Delta0 and Delta++ pole masses and Delta0 - Delta+ = (Delta- - Delta++)/3 about 1.5 MeV are more consistent with model expectations than the analogous Breit-Wigner masses and their splittings.Comment: 10 pages, including 1 eps figure, revte

Isospin splitting in heavy baryons and mesons

A recent general analysis of light-baryon isospin splittings is updated and extended to charmed baryons. The measured $\Sigma_c$ and $\Xi_c$ splittings stand out as being difficult to understand in terms of two-body forces alone. We also discuss heavy-light mesons; though the framework here is necessarily less general, we nevertheless obtain some predictions that are not strongly model-dependent.Comment: 12 pages REVTEX 3, plus 4 uuencoded ps figures, CMU-HEP93-

Inclusive K^+ meson production in proton-nucleus interactions

The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p = 1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward angles theta < 12 degrees as well as the target-mass dependence of the K^+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target-mass dependence of the cross sections at higher energies, the repulsive in-medium potential of K^+ mesons can be deduced. Using pN cross-section parameterisations from literature and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X) / sigma(pp -> K^+ X) ~ (3-4).Comment: Accepted for publication in EPJ A; 17 pages, 10 figures, 11 table

On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach

We study kaonic hydrogen, the bound K^-p state A_(Kp). Within a quantum field theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic hydrogen in terms of the amplitude of K^-p scattering for arbitrary relative momenta. The amplitude of low-energy K^-p scattering near threshold is defined by the contributions of three resonances Lambda(1405), Lambda(1800) and Sigma^0(1750) and a smooth elastic background. The amplitudes of inelastic channels of low-energy K^-p scattering fit experimental data on near threshold behaviour of the cross sections and the experimental data by the DEAR Collaboration. We use the soft-pion technique (leading order in Chiral Perturbation Theory) for the calculation of the partial width of the radiative decay of pionic hydrogen A_(pi p) -> n + gamma and the Panofsky ratio. The theoretical prediction for the Panofsky ratio agrees well with experimental data. We apply the soft-kaon technique (leading order in Chiral Perturbation Theory) to the calculation of the partial widths of radiative decays of kaonic hydrogen A_(Kp) -> Lambda^0 + gamma and A_(Kp) -> Sigma^0 + gamma. We show that the contribution of these decays to the width of the energy level of the ground state of kaonic hydrogen is less than 1%.Comment: 33 pages, 1 figure, latex, References are adde

Delta-excitations and the three-nucleon force

We study the three-nucleon force in chiral effective field theory with explicit Delta-resonance degrees of freedom. We show that up to next-to-next-to-leading order, the only contribution to the isospin symmetric three-nucleon force involving the spin-3/2 degrees of freedom is given by the two-pion-exchange diagram with an intermediate delta, frequently called the Fujita-Miyazawa force. We also analyze the leading isospin-breaking corrections due to the delta. For that, we give the first analysis of the delta quartet mass splittings in chiral effective field theory. The charge-symmetry breaking three-nucleon force due to an intermediate delta excitation is small, of the order of a few keV.Comment: 12 pages, 2 figures; minor changes, reference adde