The contradiction of the σ term of pion-nucleon scattering as deduced from the Karlsruhe-Helsinki phase shifts with the smaller value calculated by the chiral perturbation theory of QCD is well known. In an effort to clarify the discrepancy we have determined the real part of the isospin-even forward-scattering amplitude of pion-nucleon scattering at a pion energy Tπ=54.3 MeV by measurement of the elastic scattering of positive and negative pions on protons in the Coulomb-nuclear interference region. The deduced value is in agreement with the prediction of the Karlsruhe-Helsinki phase-shift analysis for that energy. The resulting large value of the σ term may be interpreted as being due to the influence of s¯s sea pairs even at large distances (small Q2) as previously suggested by the European Muon Collaboration measurement of deep-inelastic scattering of polarized muons on polarized protons.
No description provided.
The real part of the isospin-even forward-scattering amplitude of pion-nucleon scattering has been determined at a pion energy of Tπ=55 MeV by measurement of the elastic scattering of positive and negative pions on protons within the Coulomb-nuclear interference region. The value confirms the prediction of the Karlsruhe-Helsinki phase-shift analysis for that energy. These phases have been used to determine the σ term of pion-nucleon scattering by means of dispersion relations, resulting in a value for σ which is in contradiction with chiral perturbation theory of QCD.
PI- P cross sections normalised to the Coulomb cross section taken from the Karlesruhe-Helsinki phase shift analysis (R. Koch, E. Pietarinen (NP A336(80)331).
First data are presented for the polarized-target asymmetry in the reaction π+p→π+pγ at an incident pion energy of 298 MeV. The geometry was chosen to maximize the sensitivity to the radiation of the magnetic dipole moment μΔ of the Δ++(1232 MeV). A fit of the asymmetry in the cross section d5σ/dΩπ dΩγ dk as a function of the photon energy k to predictions from a recent isobar-model calculation with μΔ as the only free parameter yields μΔ=1.64(±0.19expΔ,±0.14 theor)μp. Though this value agrees with bag-model corrections to the SU(6) prediction μΔ=2μp, further clarifications on the model dependence of the result are needed, in particular since the isobar model fails to describe both the cross section and the asymmetry at the highest photon energies.
No description provided.
No description provided.
We have measured the reactions π±p→π±p and π+p→K+Σ+ at 5.0 GeV/c in the region 2.2<−t<3.5 (GeV/c)2. We find the minimum cross section of the dip at −t=2.8 (GeV/c)2 in π+p elastic scattering to be 0.16 ± 0.05 μb/GeV2. The π−p differential cross section exhibits similar structure, while the π+p→K+Σ+ channel shows a steady decline in cross section as |t| increases. The polarization of the Σ+ remains large and positive to at least −t=2.8 (GeV/c)2.
No description provided.
No description provided.
No description provided.
None
No description provided.
No description provided.
Analyzing powers for πp elastic scattering were measured using the CHAOS spectrometer at energies spanning the Δ(1232) resonance. This work presents π+ data at the pion kinetic energies 117, 130, 139, 155, 169, 180, 193, 218, 241, and 267 MeV and π− data at 87, 117, 193, and 241 MeV, covering an angular range of 50°<~θc.m.<~180° at the higher energies and 90°<~θc.m.<~180° at the lower energies. Unique features of the spectrometer acceptance were employed to reduce systematic errors. Single-energy phase shift analyses indicate the resulting S11 and S31 phases favor the results of the SM95 phase shift analysis over that of the older KH80 analysis.
Measurement of the PI+ analysing power at 117 MeV.. The data were collected in the conventional mode and may be independently floated within the systematic error.
Measurement of the PI+ analysing power at 139 MeV.. The data were collected in the conventional mode and may be independently floated within the systematic error.
Measurement of the PI- analysing power at 87 MeV.. The data were collected in the conventional mode and may be independently floated within the systematic error.
Angular distributions of the analyzing powers for π+p→ and π−p→ elastic scattering have been measured in a single-scattering experiment employing a polarized proton target. Measurements were obtained for pion energies of 98, 139, 166, 215, and 263 MeV. The addition of these data to the existing πp database significantly reduces the uncertainties in all S and P phase shifts for πp reactions over the delta resonance.
Measured values of the analyzing power for PI+ P elastic scattering at incident kinetic energy 98 MeV.
Measured values of the analyzing power for PI+ P elastic scattering at incident kinetic energy 139 MeV.
Measured values of the analyzing power for PI+ P elastic scattering at incident kinetic energy 166 MeV.
The π + p cross section for elastic scattering from hydrogen was measured at seven incident energies ranging from 20.8 to 95.9 MeV for an angular range from 60° to 145°. The experimental set-up is discussed in detail as well as the method used for data analysis. A table of results and a set of phase shifts are provided.
No description provided.
No description provided.
No description provided.
Analyzing powers of pion-proton elastic scattering have been measured at PSI with the Low Energy Pion Spectrometer LEPS as well as a novel polarized scintillator target. Angular distributions between 40 and 120 deg (c.m.) were taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic energy for pi+ p scattering, and at 67.3 and 87.2 MeV for pi- p scattering. These new measurements constitute a substantial extension of the polarization data base at low energies. Predictions from phase shift analyses are compared with the experimental results, and deviations are observed at low energies.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 87.2 MeV from the data set 1.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 68.4 MeV from the data set 1.
Analyzing power for PI+ P elastic scattering at incidient kinetic energy 57.2 MeV from the data set 1.
Elastic cross-section measurements are presented for π ± −p at 20 GeV/ c and π − −p at 30 GeV/ c incident momenta in the large angle region (50° to 90° in the c.m. system). The data are compared with published lower energy elastic cross sections. A test is made of the dimensional counting rules for π ± −p elastic scattering and some indication of a deviation from this rule is observed in the π − −p case. A comparison is also made with the predictions of the constituent interchange model. Although the broad features of the predictions are confirmed, there are some important discrepancies. Finally, the predictions of the model due to Preparata and Soffer are also compared with the new data.
No description provided.
THE UPPER LIMIT QUOTED WHEN NO EVENTS OBSERVED IS THE CROSS SECTION CORRESPONDING TO ONE DETECTED EVENT.
THE UPPER LIMIT QUOTED WHEN NO EVENTS OBSERVED IS THE CROSS SECTION CORRESPONDING TO ONE DETECTED EVENT.