A measurement of the total cross section for the reaction p p → π + π − has been performed for seven values of the incident momentum between 158 and 275 MeV/ c . The values obtained, if compared with previous results at higher momenta, agree with a 1/ß dependence. The differential cross section sssumed over the whole incident momentum range has also been measured and the result of a fit by Legendre polynomials is given.
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4*PI*LEG(L=0,P=4) = 1.07 +- 0.13 mb.
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DEDUCED FROM MEASUREMENTS AT EPSILON OF 0.20 AND 0.65.
We have determined the pion charge exchange cross section on hydrogen for π ° mesons emitted at 180° by measuring neutron time-of-flight. Using known values of the p-wave phase shifts we have deduced the contribution of the s-wave. We obtain a value for the quantity a 1 − a 3 (in h = c = m =1 units where m is the pion mass) =0.270±0.014 in agreement within the errors with recent theoretical calculations. We also find a value of 114±55 μb / sr for the cross section in the center of mass system for radiative pion capture at 22.6 MeV (gamma ray emitted at 180°).
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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.
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Differential cross sections for elastic π±−p scattering have been measured at lab momenta of 8 and 12 GeV/c in a momentum-transfer region corresponding to 1.2≤−t≤6 (GeV/c)2. Also, differential cross sections near 180° were measured for 4 and 8 GeV/c pions. At momentum transfers greater than −t=2 (GeV/c)2, the π−p cross sections drop much faster with increasing angle than the corresponding p−p cross sections. Also, in the region −t≃1.3 (GeV/c)2, there is structure in the π−p angular distribution but not in the p−p angular distribution. At −t≃3 (GeV/c)2, the drop in cross section appears to stop and from then on the angular distribution is consistent with isotropy. But in the angular region 170° to 180°, the cross sections have become much larger, and sharp backward peaks are observed. Information is given on the energy and charge dependences and widths of these backward peaks.
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We present an analysis of electroweak leptonic couplings from high statistics experiments on Bhabha scattering and μ pair production at an energy of 34.5 GeV. The forward-backward charge asymmetry of the μ pairs was measured to be −0.098±0.023±0.005. The data were found to agree well with the standard theory of electroweak interaction giving sin2θW=0.27±0.07. The leptonic weak couplings were determined to begv=0.000±0.170 andgA=−0.481±0.055. The data were also used to investigate a class of composite models for leptons.
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Elastic scattering of p¯ on p has been studied for cosθc.m. between -0.88 and -1.0 and Plab(p¯) between 0.70 and 2.16 GeV/c. The momentum dependence of the cross section shows a sharp dip at 0.9 GeV/c and a broad peaking around 1.4 GeV/c. The possibility of the peak resulting from direct formation of boson resonances has been studied. Alternatively, a diffraction model agrees qualitatively with our data and other elastic data at different angles.
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A high-precision measurement of the differential cross section for Bhabha scattering (e+e−→e+e−) is presented. The measurement was performed with the MAC detector at the PEP storage ring of the Stanford Linear Accelerator Center, at a center-of-mass energy of 29 GeV. Effects due to electroweak interference are observed and agree well with the predictions of the Glashow-Salam-Weinberg model. The agreement between the data and the electroweak prediction rules out substructure of the electron up to mass scales of 1 TeV.
Error contains both statistics and systematics.
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We have performed an experiment to study the reaction π−+p→η+n near threshold, preliminary to a forthcoming measurement of charge asymmetry in η-meson decay. The η was identified by the velocity of the associated neutron. We detected neutrons produced in the forward hemisphere in the center-of-mass system corresponding to the most energetic neutrons in the laboratory. Data were taken at π− momenta between 670 and 805 MeVc. The four neutron detectors made it possible to detect neutrons at angles of 0° to 21° from the incident pion beam. We present backward differential cross sections for both pion charge exchange and η production calculated from the data. We looked for η′ at pion momenta of 1.5 BeVc and observed none. We obtained σ(π−p→nη′)≤60 μb.
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Measurements of π±p elastic differential cross-sections have been performed in the forward direction, using a missing-mass spark chamber spectrometer. The films have been seanned by an automatic apparatus. A phase-shift analysis of the experimental data has been done, leading to three solutions. Various experiments are proposed in order to resolve the ambiguities.
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