Cross sections or upper limits are reported for 12 meson-baryon and two baryon-baryon reactions for an incident momentum of 9.9 GeV/c, near 90° c.m.: π±p→pπ±,pp±,π+°±,K+Σ±, (Λ0/Σ0)K0; K±p→pK±; p±p→pp. By studying the flavor dependence of the different reactions, we have been able to isolate the quark-interchange mechanism as dominant over gluon exchange and quark-antiquark annihilation.
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We present preliminary results on the measurement of a variety of exclusive hadron interactions at center of mass scattering angles of 90°. Data are also presented which show the relative transparency of nuclei to πp and pp elastic scattering in this kinematic range.
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The high antiproton-proton luminosity obtained by using a target system consisting of a hydrogen gas-jet crossing a coasting beam of cooled antiproton circulating in one of the rings of CERN's ISR provides the possibility to measure low cross section reactions with very high precision. We present measurements of the antiproton-proton elastic cross section at 90° CM at incident momenta between 3.5 GeV/ c and 5.7 GeV/ c . The precision of these measurements is much higher than previously reported results. The data show that the cross section of this reaction decreases faster than s −12 over this momentum range.
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Data on the reactions π − p → p π − , p p → π + π − , K − p → pK and p p → p p at 8 and 12 GeV/ c are presented. Our results agree with line reversal symmetry (between π − p → p π − and p p → π + π − ), Regge pole behaviour for non-exotic reactions ( π − p → p π − , p p → π + π − ), and universal behaviour for exotic reactions ( p p → p p , K − p → pK − ) with d σ /d u | u =0 ∼ s −10 excluding the existence of a “glory” mechanism in p p elastic backward scattering in our energy range.
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Absolute inclusive cross sections for\(\bar pp\) interactions at 7.3 GeV/c are given. The data cover prong cross sections,V0, γ production and inclusive charged particle (p/π) production. Separation has been made into annihilation and non-annihilation components. Inclusive π+, π− production in the processes of\(\bar pp\) annihilation and non-annihilation are compared with simple quark models.
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ANNIHILATION AND NON-ANNIHILATION TOPOLOGICAL CROSS SECTIONS.
We give cross sections for annihilation and non-annihilation reactions in p p interactions at 8.8 GeV. The non-annihilation data are compared with pp data from the same experiment. We compare data on resonance production and on the impact parameter structure of the final states in p p annihilation and non-annihilation and pp interactions. We investigate the charge structure of the 2 π + 2 π − π 0 final state, and find it consistent with a simple quark model.
NORMALIZED TO A TOTAL AP P CROSS SECTION OF 55.9 MB. ANNIHILATION CROSS SECTIONS.
NORMALIZED TO A TOTAL AP P CROSS SECTION OF 55.9 MB. NON-ANNIHILATION CROSS SECTIONS.
NORMALIZED TO A TOTAL P P CROSS SECTION OF 40.0 MB.
Simple inclusive cross sections for p p interactions at 12 GeV/ c are given. The data cover prong cross sections, V 0 production and resonances. Separation has been made into annihilation and non-annihilation modes. Some implications of the data are discussed. It is pointed out that the ratios of cross sections for ϱ 0 π − production are independent of incident antiproton momentum in p p annihilation processes, and that data at the highest available pp energies (ISR) tend to the same value.
NORMALIZED TO A TOTAL CROSS SECTION OF 51.7 +- 0.8 MB.
Elastic π±−p, K−−p, and p¯−p scattering cross sections have been measured using three different experimental arrangements covering the c.m. angular regions ∼20°-120°, ∼135°-169°, and ∼165°-180° at incident momenta from 6 to 17 GeV/c. In the region 130°-180°, only π±−p scattering was measured. In the angular region near 180°, the energy dependences and shapes of the π−p backward peaks were determined up to crossed-momentum transfers of u∼−2 (GeV/c)2. At all energies, the π+−p backward peak had a sharp dip at u=−0.13 (GeV/c)2, with no similar effect in the π−−p case. Nearly complete angular distributions of π−−p elastic scattering from 20° to 180° have been obtained at 6 and 10 GeV/c. These results at 6 and 10 GeV/c as well as at 8 GeV/c reveal a sharp dip in π−−p scattering at t=−3 (GeV/c)2. Several structures in the form of dips or shoulders were seen in the p¯−p angular distributions also, with less pronounced structure observed in K−−p scattering. At fixed momentum transfer, all cross sections when expressed as dσdt appear to be decreasing with increasing energy.
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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 missing mass spectrometer search was made for several two-body, double charge exchange reactions, including backward K −p and p̄p elastic scattering at 8 and 16 GeV/ c and small momentum transfer. No examples of any of these processes were observed.
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Angular distributions are presented for p¯−p elastic scattering at 8 and 16 GeV/c for |t|<1.3 (GeV/c)2. At both energies there is structure in the differential cross sections in the region 0.5<~|t|<~1.0 (GeV/c)2, similar to that observed at lower energies. The diffraction peak continues to expand with increasing incident momentum.
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Antiproton-proton elastic scattering has been measured at 3.55 GeV/ c in the c.m. angular range from 20° to 77° and from 109° to 160°. Forward elastic scattering shows a structure near t = −0.5 (GeV/ c ) 2 . In the backward region two events are observed.
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A bubble-chamber experiment based on 304 000 events of p¯p interactions at 2.32 GeV/c is described. The film was automatically scanned and measured by the POLLY II system. Details of the data-analysis methods are given. We report results on cross sections for constrained final states, tests of C invariance, and inclusive pion and ρ0 multiplicity parameters for annihilation final states.
Axis error includes +- 4/4 contribution.
Axis error includes +- 4/4 contribution.
Differential cross sections have been measured in the region of small forward angles (between 0 and ∼40 mrad) for the elastic scattering reactions pp → pp at 4.2, 7.0 and 10.0 GeV /c and p p → p p at 4.2, 6.0, 8.0 and 10.0 GeV /c . The maximum momentum transfer is ∼0.025 GeV 2 at the lowest and ∼0.10 GeV/c at the highest incident momentum. Values of the slope and the real part of the forward scattering amplitude of the above reactions have been derived; the values obtained are in good agreement with dispersion relations.
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In a single-arm spectrometer experiment, high-precision measurements of dσdt for π−p, K−p, and p¯p elastic scattering have been made at 8 and 16 GeV/c. The π−p data show rich structure at 8 GeV/c, indicative of strong non-Pomeron contributions, while the 16-GeV/c data are much smoother. For −t≳1 (GeV/c)2 there is a strong s dependence while there is very little for −t<1 (GeV/c)2. For p¯p scattering the forward region is smoothly diffractive for −t<0.4 (GeV/c)2 and shows antishrinkage. The exponential slope parameter b is measured to be 12.36 ± 0.04 (GeV/c)−2 at 8 GeV/c and 11.40 ± 0.04 (GeV/c)−2 at 16 GeV/c. The structure near −t=0.6 (GeV/c)2 seen at lower energies is still obvious at 16 GeV/c. The K−p data show some structure at 8 GeV/c, but can be represented adequately by a quadratic exponential form. At 16 GeV/c the K−p angular distribution shows antishrinkage and lies above the 8-GeV/c cross section for 0.11<−t<0.8 (GeV/c)2.
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A study of elastic scattering, one-pion production and annihilation reactions in p p interactions at 5.7 GeV/ c was carried out, from the two-prong events, obtained in the hydrogen bubble chamber exposed at CERN.
NUMBER OF EVENTS FOR -T<0.03 GEV**2 CALCULATED BY EXTRAPOLATION.
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The differential cross sections of the elastic p p reaction have been measured at 1.2, 1.4, 1.8 and 2.6 GeV/ c incident p momentum. The measurements have been performed at the CERN PS using a system of multiwire proportional chambers. The angular region covers scattering angles from 0 to ∼200 mrad. Interference effects between the Coulomb and the nuclear amplitudes are used to derive the ratio of the real to imaginary part of the forward nuclear amplitude. These ratios are compared with theoretical predictions.
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We have measured the antiproton-proton elastic differential cross section in the center-of-mass angular range cosθ=−0.985 to +0.40 at six momenta between 1.6 and 2.2 GeV/c in a bubble-chamber experiment. We use the data to look for evidence of direct-channel boson resonances.
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An extensive investigation of antiproton-proton interactions at 5.7 GeV/c without strange-particle production was carried out using a hydrogen bubble chamber. Cross-sections for different channels are given and discussed. The reliability of the analysis was checked using artificially generated events. The cross-sections for elastic scattering, for all processes involving annihilation, and for all other inelastic processes are respectively σel=(16.3±0.6)mb,σannlbil=(22.5±2.0)mb, σinel=(24.8±2.0)mb. TheN * 1:38 is present both in the single and multiple pion production channels. For the reaction MediaObjects/11539_2007_Article_BF02720569_f1.jpg a cross-section of (1.05±0.21) mb was obtained. Cross-sections forN * 1238 production in other channels are also given. Some indication of the presence ofI=1/2 isobars was found in the nucleon-pion and the nucleon-two-pion systems. The inelastic nonannihilation reactions were found to be strongly peripheral. The one-pion exchange model including either a form factor or corrections for absorption was applied to the reaction MediaObjects/11539_2007_Article_BF02720569_f2.jpg . Neither version of the model could correctly account for all features of the reaction. The average number of pions in the annihilation was found to be 7.3±0.6. The presence of an asymmetry in the angular distribution of the charged pions was confirmed at this energy; it is due mostly to high-energy pions. The production of ρ and ω mesons was observed in various annihilation channels. Rates of up to 80% for ρ production and up to 15% for ω production were obtained by fitting phase-space and Breit-Wigner curves to the effective-mass distributions of different channels.
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The elastic, the pion-production, and the multipion-annihilation cross sections for antiproton-proton interactions at 3.28 and 3.66 BeV/c incident antiproton momenta have been measured. A comparison of the elastic interactions at 3.28 BeV/c with a purely-absorbing disc optical model gave a best value for the radius of interaction of 1.3 F. The real part of the forward scattering amplitude has been found to be less than 20% of the imaginary part. A study of the asymmetries in double elastic scatters yielded a value for a polarizing power of the hydrogen consistent with zero when averaged over production angles.
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A preliminary study of single pion production with no annihilation and multiple pion annihilation in antiproton-proton interactions at 7 GeV/c indicates that the single pion production cross-section is 5.6±1.2mb, and the multipion annihilation cross-section is ∼24mb. Although there is strong evidence for resonance production in the one pion production channels, these states do not appear to be dominated by any single resonance. Resonance production in the annihilation channels is small compared to rates observed at lower energies.
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