Results are presented from experiment WA7 at the CERN SPS, which has measured the elastic differential cross sections of π ± p, K ± p, p p and pp at incident momen ta of 20, 30 and 50 GeV/ c . The measurements cover the momentum transfer range 0.5 < | t | < 8 (GeV/ c ) 2 , corresponding to c.m. scattering angles between 10° and 50°. The experimental set-up, trigger logic and data analysis are described. The experimental results are compared with existing meson-proton and nucleon-proton data at lower and higher energies covering the medium- and large-| t | region. Some prominent models and their predictions for elastic scattering at WA7 energies and beyond are reviewed, with emphasis on geometrical scaling, factorizing eikonal models, lowest-order QCD and other dynamical exchange-type models. Results for p p two-body annihilation into π − π + and K − K + at 30 and 50 GeV/ c , obtained in parallel with the elastic p p data, are also presented.
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Differential cross sections for π − p and pp elastic scattering have been measured at incident momenta ranging from 30 to 345 GeV and in the t range 0.002 (GeV/ c ) 2 ⩽ | t | ⩽ 0.04 (GeV/ c ) 2 . From the analysis of the data, the ratio ϱ ( t = 0) of the real to the imaginary parts of the forward scattering amplitude was determined together with the logarithmic slope b of the diffraction cone.
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Energy, charge and strangeness flow inK+p interactions at 32 and 70 GeV/c, and π+p interactions at 32 GeV/c are studied in terms of the angular variable λ=|x|/pT. The data ondQ/dλ anddE/dλ show only a weak indication of scale breaking between 32 and 70 GeV/c. For inclusive “non-diffractive”, inclusive “diffractive” and exclusive “non-diffractive” jets, the fraction of charge in any angular region ΔΩ away from the central region is found to be proportional to the energy fraction in the same interval. The data ondQ/dE versus λ are compatible with some versions of dual-sheet models and agree also with the LUND Monte-Carlo model. The data are also compared with\(v(\bar v)p\) interactions in BEBC. In exclusive channels the average ratiodQ/dS=0.78±0.04 is consistent, in the framework of fragmentation models, with a larger probability for the fragmentation of the\(\bar s\)-valence quark than theu-valence quark in theK+-meson.
CHARGE FLOW IN NONDIFFRACTIVE PROTON-LIKE AND KAON-LIKE JETS.
CHARGE FLOW IN NONDIFFRACTIVE PROTON-LIKE AND KAON-LIKE JETS.
CHARGE FLOW IN NONDIFFRACTIVE PROTON-LIKE AND KAON-LIKE JETS.
The mass and momentum transfer spectra of the charged K K system produced in the reaction π ± p→K s 0 K ± p are analyzed. The data have been collected at the CERN SPS with the Geneva-Lausanne two-arm, non-magnetic spectrometer at 30 and 50 GeV/ c incident momenta. The general features of the reactions at these energies and the results of partial-wave analyses of the two kaon system are presented. The channel is dominated by the diffractive production of even spin resonances. The spin 4 recurrence of the A 2 (1320) is clearly observed at 2040 MeV ( Γ =380 MeV. A new resonance is observed with a mass M =2450MeV and a width Γ =400 MeV; the quantum numbers of this state are found to be I G ( J PC )=1 −(6 ++ ) . The analysis also shows the decay of the decay of the meson ϱ′(1600) through the K K channel at both energies. The production amplitudes are determined both as a function of the K K effective mass and of the momentum transfer. Isoscalar natural parity exchange is dominant. The energy dependence between 10 and 50 GeV/ c is shown to be well described by a Regge pole model based on the f-dominated pomeron hypothesis. We compare the production mechanisms of the 2 + resonances A 2 (1320) and K ∗ (1430). Finally, we estimate the K K branching ratios of the spin 4 A 2 (2040) and spin 6 A 2 (2450) resonances.
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D(SIG)/DT FOR 50 GEV IN RESONANCE REGIONS.
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A high-statistics measurement of the reaction π − p→ η n; η →2 γ has been performed at the 70 GeV Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/ c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small | t |, as exponentials with the same slopes to within a few percent. For | t | ≳ 1 (GeV/ c ) 2 there is a break in the differential cross section. In addition, the A 2 effective trajectory deviates markedly for | t | ≳ 1 GeV/ c ) 2 from the linear behaviour valid for smaller | t |.
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The differential cross section has been measured at 30, 50, 80, 100, 120 and 140 GeV/ c for 0.002 < | t | < 0.04 ( GeV / c ) 2 . The results show that the π − p real part goes from negative to positive values below 80 GeV/ c . The slope parameter in the t -region measured is significantly higher than what has been found − t = 0.2 (GeV/ c ) 2 .
FROM FIT TO D(SIG)/DT AND SIGMA TOTAL FOR -T = 0.002 TO 0.04 (0.02 AT 30 GEV/C AND 0.03 AT 140 GEV/C) GEV**2.
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The reaction π−p→ωn in the beam-momentum range from 20 to 200 GeV/c has been studied using data acquired at Fermilab. In this Letter, the integral and differential cross sections for this reaction are presented. The integral cross sections are considerably larger than those previously reported. The differential cross sections can be reproduced quite easily by Regge models. As predicted by such models, natural-parity exchange dominates production throughout this energy region.
D(SIG)/DT IS AVERAGE OVER T INTERVAL WITH NO FINITE-BIN-WIDTH CORRECTIONS.
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REPRESENTATIVE SPIN DENSITY MATRIX ELEMENTS.
We report on a study of pion charge-exchange scattering carried out at Fermilab in the energy range 20 to 200 GeV. The results can be described remarkably well by a simple Regge-pole model. The charge-exchange cross sections in the forward direction lead to a prediction for the difference in total cross sections of π−p and π+p which is in satisfactory agreement with direct measurements of this difference in another experiment at Fermilab.
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