Measurements have been made of the asymmetry in the scattering of π− mesons by a polarized proton target. Scattered π mesons and recoil protons were detected in arrays of scintillation counters; data were obtained at 16 scattering angles at each of 8 beam momenta between 875 and 1578 MeV/c. Analysis of these data together with earlier differential-cross-section measurements shows that there must exist at least three resonances in this energy region: (i) mass 1920 MeV/c2, Γ=170 MeV/c2, I=32, F72; (ii) mass 1682 MeV/c2, Γ=100 MeV/c2, I=12, F52; and (iii) mass 1674 MeV/c2, Γ=100 MeV/c2, I=12, D52.
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Elastic π−+p differential cross-section data are presented at the incident-pion momenta 1.72, 1.89, 2.07, 2.27 and 2.46 GeV/c. Resonant behaviour in the coefficients of a Legendre polynomial expansion indicates G- or H-wave resonance. Further analysis using an energy-dependent parametrization of G- and H-waves shows the results to be compatible with the 7−/2 assignment for the , but equally acceptable solutions are obtained with the inclusion of an additional 9+/2 resonance contribution.
No description provided.
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A precision measurement of absolute pi+p and pi-p elastic differential cross sections at incident pion laboratory kinetic energies from T_pi= 141.15 to 267.3 MeV is described. Data were obtained detecting the scattered pion and recoil proton in coincidence at 12 laboratory pion angles from 55 to 155 degrees for pi+p, and six angles from 60 to 155 degrees for pi-p. Single arm measurements were also obtained for pi+p energies up to 218.1 MeV, with the scattered pi+ detected at six angles from 20 to 70 degrees. A flat-walled, super-cooled liquid hydrogen target as well as solid CH2 targets were used. The data are characterized by small uncertainties, ~1-2% statistical and ~1-1.5% normalization. The reliability of the cross section results was ensured by carrying out the measurements under a variety of experimental conditions to identify and quantify the sources of instrumental uncertainty. Our lowest and highest energy data are consistent with overlapping results from TRIUMF and LAMPF. In general, the Virginia Polytechnic Institute SM95 partial wave analysis solution describes our data well, but the older Karlsruhe-Helsinki PWA solution KH80 does not.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and single arm pion detection. There is an additional systematic error of 1.1 PCT for PI+ beams which is not included in the errors shown in the table.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and two arm pion detection. There is an additional systematic error of 1.3 PCT for PI+ beams which is not included in the errors shown in the table.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and two arm pion detection. There is an additional systematic error of 1.3 PCT (1.6 PCT) for PI+ (PI-) beams which is not included in the errors shown in the table.
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).
A simple, large-solid-angle apparatus, specially suited for the measurement of backward elastic scattering of medium-energy pions on protons and deuterons, is described. The method of analysis which reduces background and determines elastic events from a data sample of 185 MeV negative pions incident on a D 2 O target is discussed. Results for 141 MeV π + p and 185 MeV π − p backward cross-sections are also presented and compared with cross-sections calculated from known phase shifts.
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Measurements are reported of the differential cross section for the reaction π − +p→ ω +n from threshold to a final-state c.m. momentum P ∗ of 200 MeV /c . The previously reported fall in total cross section σ/P ∗ below about 100 MeV/ c is again seen. The differential cross section remains close to isotropic over the entire range. A paralle experiment on the variation in the elastic differential cross section across the threshold shows evidence of this threshold. The elastic data cover a range of incident moments from 1010 to 1180 MeV/ c in steps of 5 MeV/ c .
CROSS SECTION DEPENDENCE ON FINAL STATE CENTRE OF MASS MOMENTUM.
ANGULAR DISTRIBUTIONS ARE ALMOST ISOTROPIC.
LEGENDRE POLYNOMIAL COEFFICIENTS NORMALIZED SUCH THAT SIG = 4*PI*LEG(L=0).
A streamer-chamber spectrometer is triggered by fast forward protons from 4-GeV/c π−p interactions at the Bevatron. Meson-resonance production in the backward, Iu=32 exchange reactions π−p→pM− are studied, where M− refers to π−, ρ−, A1−, A2−, and B−. Elastic scattering and ρ− production are observed and discussed in detail. No backward A1−, A2−, or B− production is observed at the level of approximately 5 βb.
Axis error includes +- 15/15 contribution.
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Axis error includes +- 15/15 contribution.
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IM(AMP) VIA OPTICAL THEOREM FROM TOTAL CROSS SECTIONS OF L. M. VASILYEV ET AL., PL 36B, 528 (1971).
Measurements are reported of the differential cross section for the reaction π−p→π−p,π0n,andηn at three angles close to 180° and for incident momenta in the range 0.6 to 1.0 GeV/c. The three measurements were made simultaneously at 1% intervals of beam momentum. The data on elastic scattering resolve a discrepancy between two earlier experiments. They also show clearly the effect of the opening of the ηn channel. The charge-exchange data show that I-spin bounds are not violated in the kinematic region covered. The ηn data can be adequately described with known s-channel resonances. No evidence for narrow N*'s is seen in any channel.
No description provided.
No description provided.
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