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G. Rasche

Publications and source records attributed to G. Rasche.

14 recordsLinked to original sources
arXiv2007

Phase shift analysis of low energy pi+/- p scattering data and a comparison with pionic hydrogen data

Using newly calculated electromagnetic corrections, we have made a phase shift analysis of experimental data on pi+/- p elastic scattering up to 100 MeV, assuming the effective hadronic interaction to be isospin invariant. The output consists of parametrised s and p-wave hadronic phases for isospin 1/2 and 3/2. It is not possible to fit the charge exchange data satisfactorily. We give values for the s-wave scattering lengths and effective ranges and for the p-wave scattering volumes. The combinations 2a_1 + a_3 and a_1 - a_3 of s-wave scattering lengths extracted from pionic hydrogen data are compared with those obtained from our analysis.

hep-ph↗
arXiv2007

Phase-shift analysis of low-energy pi+ p data

This work presents the results of a revised analysis of the low-energy (pion laboratory kinetic energy T(sub pi) < 100 MeV) pi+ p data using recently obtained electromagnetic corrections. The measurements are analyzed assuming extended threshold expansions for the hadronic K-matrix elements. With a few exceptions, the description of the experimental data is satisfactory. Several minimization functions have been used, yielding consistent results. The phase-shift values, obtained in the s and p(3/2) partial waves, disagree with those of the most recent VPI global-fit solution (SP98); the largest part of this disagreement is removed if we compare our numbers to their single-energy solutions. The s-wave scattering length a(sub 0+), the p-wave scattering volumes a(sub 1+) and a(sub 1-), as well as the hadronic phase shifts themselves, obtained herein, are in agreement with recent work using older electromagnetic corrections; the output of the present work (including meaningful uncertainties) is tabulated in order to enable straightforward use in other applications.

hep-ph↗
arXiv2007

Electromagnetic corrections to the hadronic phase shifts in low energy pi+ p elastic scattering

We calculate for the s-, p(1/2)- and p(3/2)-waves the electromagnetic corrections which must be subtracted from the nuclear phase shifts obtained from the analysis of low energy pi+ p elastic scattering data, in order to obtain hadronic phase shifts. The calculation uses relativised Schroedinger equations containing the sum of an electromagnetic potential and an effective hadronic potential. We compare our results with those of previous calculations and qualitatively estimate the uncertainties in the corrections.

hep-ph↗
arXiv2007

Electromagnetic corrections for the analysis of low energy $π^- p$ scattering data

We calculate the electromagnetic corrections to the isospin invariant mixing angle and to the two eigenphases for the $s$-, $p_{1/2}$- and $p_{3/2}$-partial waves for $π^- p$ elastic and charge exchange scattering. These corrections have to be applied to the nuclear quantities in order to obtain the two hadronic phase shifts for each partial wave. The calculation uses relativised Schrödinger equations containing the sum of an electromagnetic potential and an effective hadronic potential. The mass differences between $π^-$ and $π^0$ as well as between $p$ and $n$ are taken into account. We compare our results with those of previous calculations and qualitatively estimate the uncertainties in the corrections.

hep-ph↗
arXiv2007

Determination of the s-wave pion-nucleon threshold scattering parameters from the results of experiments on pionic hydrogen

We give the conversion equations which lead from experimental values of the $3p \to 1s$ transition energy in pionic hydrogen and the total width of the $1s$ level to values of the s-wave threshold scattering parameters for the processes $π^-p \to π^-p$ and $π^-p \to π^0n$ respectively. Using a three-channel potential model, we then calculate the electromagnetic corrections to these quantities, which remove the effects of the Coulomb interaction, the external mass differences and the presence of the $γn$ channel. We give the s-wave scattering parameters obtained from the present experimental data and these electromagnetic corrections. Finally we discuss the implications for isospin invariance.

hep-ph↗
arXiv2006

Phase-shift analysis of low-energy $π^{\pm}p$ elastic-scattering data

Using electromagnetic corrections previously calculated by means of a potential model, we have made a phase-shift analysis of the $π^\pm p$ elastic-scattering data up to a pion laboratory kinetic energy of 100 MeV. The hadronic interaction was assumed to be isospin invariant. We found that it was possible to obtain self-consistent databases by removing very few measurements. A pion-nucleon model was fitted to the elastic-scattering database obtained after the removal of the outliers. The model-parameter values showed an impressive stability when the database was subjected to different criteria for the rejection of experiments. Our result for the pseudovector $πN N$ coupling constant (in the standard form) is $0.0733 \pm 0.0014$. The six hadronic phase shifts up to 100 MeV are given in tabulated form. We also give the values of the s-wave scattering lengths and the p-wave scattering volumes. Big differences in the s-wave part of the interaction were observed when comparing our hadronic phase shifts with those of the current GWU solution. We demonstrate that the hadronic phase shifts obtained from the analysis of the elastic-scattering data cannot reproduce the measurements of the $π^- p$ charge-exchange reaction, thus corroborating past evidence that the hadronic interaction violates isospin invariance. Assuming the validity of the result obtained within the framework of chiral perturbation theory, that the mass difference between the $u$- and the $d$-quark has only a very small effect on the isospin invariance of the purely hadronic interaction, the isospin-invariance violation revealed by the data must arise from the fact that we are dealing with a hadronic interaction which still contains residual effects of electromagnetic origin.

hep-ph↗
arXiv2001

New light on electromagnetic corrections to the scattering parameters obtained from experiments on pionium

We calculate the electromagnetic corrections needed to obtain isospin invariant hadronic pion-pion s-wave scattering lengths a^0, a^2 from the elements a_cc, a_0c of the s-wave scattering matrix for the (π^+ π^-, π^0 π^0) system at the π^+ π^- threshold. These elements can be extracted from experiments on pionium. Our calculation uses energy independent hadronic pion-pion potentials that satisfactorily reproduce the low-energy phase shifts given by two-loop chiral pertur- bation theory. We also take into account an important relativistic effect whose inclusion influences the corrections considerably.

hep-ph↗
arXiv2001

The influence of the hadronic interaction on the pionium wave functions

The influence of the hadronic ππinteraction on the wave functions of pionium (the Coulomb bound π^+π^- system) at distances less than 10 fm is calculated for s-states with principal quantum numbers n<5. Hadronic ππpotentials are used that reproduce the scattering phase shifts of two-loop chiral perturbation theory. The pionium wave functions ψ_n (r) are obtained by integrating the coupled Schrödinger equations for the (π^+π^-,π^0π^0) system. We find that, for r<10 fm, n^{3/2} ψ_n (r) is practically independent of n. From this we conclude that the production rates of the s-states of pionium are proportional to n^{-3}, a result needed for the interpretation of the DIRAC experiment currently running at CERN.

hep-ph↗
arXiv2001

The effect of vacuum polarisation on muon-proton scattering at small energies and angles

We give a compact expression for the unpolarised differential cross section for muon-proton scattering in the one photon exchange approximation. The effect of adding the vacuum polarisation amplitude to the no-spin-flip amplitude for one photon exchange is calculated at small energies and scattering angles and is found to be negligible for present experiments.

hep-ph↗
arXiv2000

Electromagnetic corrections for the analysis of low energy pi-p scattering data

We calculate the electromagnetic corrections to the isospin invariant mixing angle and to the two eigenphases for the s and p-waves for low energy pi-p elastic and charge exchange scattering. These corrections have to be applied to the nuclear quantities obtained from phase shift analyses of the experimental data in order to obtain the hadronic phases. We compare our results with earlier calculations and estimate the uncertainties in the corrections.

hep-ph↗
arXiv1997

Hadronic Effects in the Pionium Ion

The hadronic properties of the pionium ion (Coulomb bound system of three charged pions) are estimated using the results for the positronium ion $P{s}^{-}$. It turns out that the hadronic shift of the ground state energy and the lifetime of the pionium ion are approximately the same as for pionium.

nucl-th↗
arXiv1997

The extraction of hadronic parameters from experiments on pionium

Experimental values of the lifetime of the 1s level of pionium and of the difference between the energies of the 2s and 2p levels yield values of the a(0c) and a(cc) elements of the s-wave scattering matrix for the 2-channel (pi+ pi-, pi0 pi0) system at the pi+ pi- threshold. We develop a method for obtaining the isospin invariant quanties a20 - a00 and 2a00 + a20 from a(0c) and a(cc). We emphasize that the isospin invariant scattering lengths a00 and a20 universally used in the literature cannot be considered to be purely hadronic quantities.

nucl-th↗