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Low-energy differential cross-sections of pion proton (pi+- p) scattering. 2: Phase shifts at T(pi) = 32.7-MeV, 45.1-MeV, and 68.6-MeV

Joram, C. ; Metzler, M. ; Jaki, J. ; et al.
Phys.Rev.C 51 (1995) 2159-2165, 1995.
Inspire Record 404659 DOI 10.17182/hepdata.25955

We report on measurements of the differential π±p cross section at pion energies Tπ=32.7, 45.1, and 68.6 MeV. The measurements, covering the angular range 25°≤θlab≤123°, have been carried out at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland, employing the magnet spectrometer LEPS. The absolute normalization of the π±p cross sections have been achieved by relating them to the electromagnetic cross sections of μ±12C scattering. The results are in agreement with those of our preceding measurements at Tπ=32.2 and 45.1 MeV insofar as they overlap with the region of the Coulomb nuclear interference investigated there. A comparison with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, which has formed the basis for the determination of the ‘‘experimental’’ σ term, reveals considerable deviations. These are most pronounced for the π+p cross sections at Tπ=32.7 and 45.1 MeV. Single energy partial wave fits result in S-wave contributions, which are about 1° lower in magnitude then those specified by the KH80 solution. The data at 68.6 MeV are in good agreement with the phase shift analysis.

3 data tables
Table 1

Statistical and systematic errors are addet in quadrature.

Table 2

Statistical and systematic errors are addet in quadrature.

Table 3

Statistical and systematic errors are addet in quadrature.


Low-energy differential cross-sections of pion proton (pi+- p) scattering. 1: The Isospin even forward scattering amplitude at T(pi) = 32.2-MeV and 44.6-MeV

Joram, C. ; Metzler, M. ; Jaki, J. ; et al.
Phys.Rev.C 51 (1995) 2144-2158, 1995.
Inspire Record 404658 DOI 10.17182/hepdata.25972

The values of the pion nucleon (πN) σ term, as determined, on the one hand, from experimental pion nucleon scattering by means of dispersion relations and, on the other hand, from baryon masses by means of chiral perturbation theory, differ by 10 to 15 MeV. The origin of this discrepancy is not yet understood. If the difference between the two values is attributed to the scalar current of strange sea quark pairs within the proton, the contribution to the proton mass would be of the order of 120 MeV. The discrepancy may hint at either theoretical deficiencies or an inadequate πN database. In order to provide reliable experimental data we have measured angular distributions of elastic pion proton scattering at pion energies Tπ=32.2 and 44.6 MeV using the magnet spectrometer LEPS located at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland. From the data covering the region of the Coulomb nuclear interference, the real parts of the isospin-even forward scattering amplitude ReD+(t=0), have been determined as a function of energy. The results have been compared with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, revealing discrepancies most pronounced for the π+p data. The experimentally determined values for ReD+(t=0), however, support the KH80 prediction (which is based on πN data available in 1979).

2 data tables
Table 1

Statistical and systematic errors are addet in quadrature.

Table 2

Statistical and systematic errors are addet in quadrature.