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The differential cross sections for the photoproduction reactions γ+p→π++n, γ+p→K++Λ0, and γ+p→K++Σ0 have ben measured for incident laboratory photon energies between 3.4 and 4.0 GeV and for meson center-of-mass angles from about 25° to 45°. The reactions were studied by observing only the charged mesons. The momenta, velocities, and angles of the mesons were measured with a magnetic spectrometer, and the equivalent of nearly monochromatic gamma rays was obtained by performing bremsstrahlung subtractions. The cross sections agree with the inequality predicted from unbroken SU(3). The measured behavior of dσdt as a function of t shows similarities to that observed in studies of mesonnucleon scattering.
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Total cross sections of π+ and π− mesons on protons and deuterons have been measured in a transmission experiment to relative accuracies of ±0.2% over the laboratory momentum range 0.46-2.67 GeV/c. The systematic error is estimated to be about ±0.5% over most of the range, increasing to about ±2% near both ends. Data have been obtained at momentum intervals of 25-50 MeV/c with a momentum resolution of ±0.6%. No new structure is observed in the π±p total cross sections, but results differ in several details from previous experiments. From 1-2 GeV/c, where systematic erros are the smallest, the total cross section of π− mesons on deuterons is found to be consistently higher than that of π+ mesons by (1.3±0.3)%; about half of this difference may be understood in terms of Coulomb-barrier effects. The πd and πN total cross sections are used to check the validity of the Glauber theory. Substantial disagreements (up to 2 mb) are observed, and the conclusion is drawn that the Glauber theory is inadequate in this momentum range.
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Measurements have been made of the total cross sections σ(p−p) and σ(p−d) over the laboratory momentum range 1.1 to 8 GeV/c, with relative errors of 0.1%. The absolute accuracies of these cross sections are limited to 0.3% by lack of information which will allow the Coulomb-nuclear interference to be calculated accurately. Values of the total cross sections σ(p−n) and σ(I=0) are deduced by assuming the Glauber correction. Structure is observed in σ(p−p) near a mass value of 2.75 GeV/c2; its interpretation is discussed. σ(I=0) rises rapidly in the range 2.3 to 2.9 GeV/c2, and this is attributed to the onset of strong inelastic scattering.
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Differential cross sections for π+p elastic scattering in the momentum region 1.2 to 2.3 GeV/c are presented for the center-of-mass angular range 0.9>cosθ>−0.9. Typically, 50 000 events were obtained at each of 16 momenta using magnetostrictive-readout wire spark chambers to detect the particles scattered from a liquid hydrogen target. The results are compared to those of the CERN-71 phase-shift analysis. The well-known dips at t≅−0.7 (GeV/c)2 and at u′=−0.2 (GeV/c)2 are observed. In addition, structure is seen at constant u′=−1.3 (GeV/c)2. The results of a pion attenuation study in iron are also presented.
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The differential cross section of the reaction γ + p → p + πo has been measured at the Deutsches Elektronen- Synchrotron, Hamburg, at mean phonon energies of 1.36, 2.0 and 3.0 GeV and pion center of mass angles between 0o and 70o. The results are compared with some theoretical calculations based on elementary and reggeized 1- meson exchange.
Axis error includes +- 12/12 contribution.
Axis error includes +- 12/12 contribution.
Axis error includes +- 12/12 contribution.
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Axis error includes +- 0.0/0.0 contribution.
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The total neutron cross-sections were measured with high precision for hydrogen and deuterium. At an average neutron momentum of 10 GeV/c we obtained σ T (np)=39.5±0.5 mb and σ T (nd)=73.3±1.1 mb. These values are in excellent agreement with p-p and p-d total cross sections. No energy dependence was found for n-p cross section between 4 and 10 GeV/c.
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Measurements of elastic proton-proton differential cross sections for angles between 65° and 90° c.m.s. have been made at 8, 9, 10, 11, 14, 15 and 21 GeV/c. The shape of the angular distribution is found to change suddenly between 8 and 11 GeV/c. An interpretation of this discontinuous behaviour in terms of the reactive effects of baryon-antibaryon pair production is proposed.
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Multihadron production by electron-positron colliding beams has been investigated for total centre-of-mass energies ranging from 1.2 to 2.4 GeV. The total cross-section, σtot ≡ σ(e+e−→π+π−+ + anything), is of the order of σμμ ≡ σ(e+e−→μ+μ−), with a threshold near 1 GeV. Partial cross-sections for the various channels are also derived. The cross-section of the specific channel e+e−→π+π−π+π− exhibits an energy dependence which is suggestive of a heavier vector meson, ρ' (mρ,≈ 1.6 GeV,Гρ, ≈ 350 Mev), having the same quantum numbers as the ρ-meson. An upper limit is given for the coupling constantfρ′ (fρ′/4π<18, wherefρ′=mρ′2e/gγρ′). Final states withG+ parity are found to be much more abundant than those withG− parity. The average multiplicity (charged plus neutral final-state pions) is found to be betweet 4 and 5 over all the energy range explored.
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VALUES OF R CALCULATED FROM TOTAL CROSS SECTION.
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Baryon resonance production in quasi-two-body reactions has been studied for the channels K + p→K°p π + , K + n π + and K + p π ° at beam momenta of 2.53, 2.76 and 3.20 GeV/ c . The production cross sections, four-momentum transfer distributions and density matrix elements are given for the Δ(1236), N ∗ (1400), N ∗ (1500) and N ∗ (1680) states. The reaction K + p→K° Δ ++ (1236) is compared to the line reversed reaction K − n → K °Δ − and the charge-exchange SU(3) sum rule for pseudo-scalar meson plus Δ(1236) is tested.
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We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.
Fractions of subprocesses from 3-parameter fit to the no-tag data.
Fractions of subprocesses from 2-parameter fit to the no-tag data in limited energy range. The Q=1R contribution is set equal to zero.
Fractions of subprocesses from 3-parameter fit to the single-tag data.
Results are presented on the charge exchange reaction\(\bar pp \to \bar nn\) and\(\bar np\) annihilations from bubble chamber exposures to antiproton beam of momenta 700 and 760 MeV/c. The differential cross section of\(\bar pp \to \bar nn\) shows a forward spike followed by a clear dip bump structure. Total annihilation cross section of\(\bar np\) for average\(\bar n\) momentum of 700 MeV/c has been evaluated to be 55.4±2.2 mb. The multiplicity, Feynmanx andpT2 distributions for inclusive charged pions in\(\bar pp\) and\(\bar np\) annihilations are found to be similar. The emission of charged pions from\(\bar np\) annihilations are found to be consistent with thermodynamic models with temperature ∼110 MeV.
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Interactions of antiprotons were studied at a momentum of 3.6 GeV/c in a hydrogen bubble chamber. Particular attention was paid to single and multiple pion production without annihilation. Cross sections for the various pion-production channels are given. The total cross section for pion production without annihilation and not including strange-particle production is 18.6−3.3+2.4 mb. Single pion production is found to agree with the predictions of the one-pion-exchange model for small values of the four-momentum transfer. Double pion production in the reaction p¯p→pp¯π+π− agrees with the one-pion-exchange model for all values of the four-momentum transfer, if all possible diagrams are taken into account. The main contribution comes from events where a 32−32 pion-nucleon isobar-anti-isobar pair is produced. For these events the Treiman-Yang angular distribution and the decay angular distributions of the isobars are also in agreement with the one-pion-exchange model.
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We have made measurements of polarization in π−p elastic scattering, with emphasis over the backward region, at 1.60 to 2.28 GeVc. The results indicate the absence of u-channel dominance in the backward region, as was observed in the case of π+p scattering. Comparisons have been made with predictions of various phase-shift analyses which show that the agreement is generally very poor in the backward region.
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