arXiv subjects

C. Schütz

Publications and source records attributed to C. Schütz.

4 recordsLinked to original sources

arXiv1995

$πNN$ and $πNΔ$ formfactors determined from a microscopic model for $πN$ scattering

We determine the $πNN$ and $πNΔ$ formfactors from the $P_{11}$ resp. $P_{33}$ partial wave of $πN$ scattering by dressing corresponding bare vertices with the help of $πN$ non--pole contributions. The underlying model is based on meson exchange, and involves nucleon and delta--isobar pole and crossed--pole terms together with correlated $ππ$--exchange in the $J^P=0^+$ ($σ$) and $1^-$ ($ρ$) channel. The results are very similar for $πNN$ and $πNΔ$ and can be roughly parametrized by a monopole with cutoff mass $>$ 500 MeV, with some variation due to model dependencies. Thus the formfactors are much less soft than derived before for the $πNN$ case by Saito and Afnan using the same procedure but different $πN$ interaction models.

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arXiv1995

The reaction $pp \to ppπ^0$ near threshold

We perform a momentum-space calculation of the reaction $pp \rightarrow ppπ^0$ near threshold. Direct production and pion rescattering are taken into account. For the latter a T-matrix obtained from a microscopic model of the $πN$ interaction is employed. The effects of some approximations commonly used in studies of $ pp \rightarrow ppπ^0$ \ are discussed. We find that those approximations overestimate the cross section and also modify its energy dependence. We obtain a significant contribution from rescattering, but not nearly enough to describe the data.

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arXiv1995

Short range correlations in the pion s-wave self-energy of pionic atoms

We evaluate the contribution of second order terms to the pion-nucleus s-wave optical potential of pionic atoms generated by short range nuclear correlation. The corrections are sizeable because they involve the isoscalar s-wave $πN$ amplitude for half off-shell situations where the amplitude is considerably larger than the on-shell one. In addition, the s-wave optical potential is reanalyzed by looking at all the different conventional contributions together lowest order, Pauli corrected rescattering term, second order absorptive effects, terms from the interaction of pions with the virtual pion cloud (chiral corrections) and correlation effects. Different off-shell extrapolations for the $πN$ amplitude are used and it is found that, although some individual terms are sensitive to the extrapolation, the sum of them is rather insensitive. The results are compared with empirical values from best fits to the data and are found to be compatible, within theoretical and empirical uncertainties. The results do not rule out further contributions but they put stringent constraints on their strength.

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arXiv1994

A dynamical model for correlated two-pion-exchange in the pion-nucleon interaction

A microscopic model for the $N\bar N\toππ$ process is presented in the meson exchange framework, which in the pseudophysical region agrees with available quasiempirical information. The scalar ($σ$) and vector ($ρ$) piece of correlated two--pion exchange in the pion--nucleon interaction is then derived via dispersion integrals over the unitarity cut. Inherent ambiguities in the method and implications for the description of pion--nucleon scattering data are discussed.

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