The differential cross-section for elastic charge-exchange scattering of neutrons on protons has been measured at 8 GeV/c over forward laboratory scattering angles (0÷90) mrad (square of four-momentum transfer 0<−t<0.5 (GeV/c)2). The method utilized acoustic spark chambers and about 1900 elastic-scattering events were analysed. A value of (dσ/dΩ)lab=(20±6) mb/sr (dσ/dt=(0.93±0.28) mb/(GeV/c)2) was obtained for the forward differential cross-section and an estimated (0.06±0.03) mb for the elastic charge exchange cross-section. Both cross-sections show the decreased values expected from Pomeranchuk’s second theorem (1) when compared with results at lower energies (2). Further comparison shows that the narrow forward peak in the distribution of dσ/dt previously observed for −t<0.05, is still present at 8 GeV/c, varying in shape only slowly, if at all, with energy. For −t>0.1 however, energy dependence is apparent. The results also suggest that the interaction is spin-dependent and/or that the real parts of the scattering amplitudes in the isospin states 0 and 1 are different. Comparisons with the theoretical predictions show good agreement with the value of forward cross-section given by the Regge pole approach ofAhmadzadeh (3). The model ofRingland andPhillips (4) for single-pion exchange with absorption agrees with our results for −t<0.01 but a predicted secondary peak at −t∼0.08 is not observed.
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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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Exclusive photoproduction cross sections have been measured for the processes γp→π+n, γp→π0p, γp→π−Δ++, γp→ρ0p, γp→K+Λ, and γp→K+Σ0 at large t and u values at several energies for each process between 4 and 7.5 GeV. These measurements taken together with past data taken at small values of t and u provide complete angular distributions. The data show the usual small t and u peaks and a central region in which the cross section decreases approximately as s−7. The results are discussed within the context of parton or constituent models.
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Differential cross sections have been measured for nucleon-isobar production and elastic scattering in p−p interactions from 6.2 to 29.7 GeVc in the laboratory angle range 8<θsc<265 mrad. N*' s at 1236, 1410, 1500, 1690, and 2190 MeV were observed. Computer fits to the mass spectra under varying assumptions of resonance and background shapes show that conclusions on t and s dependence are only slightly affected despite typical variations in absolute normalization of ± 35%. Logarithmic t slopes in the small- |t| range are ∼15 (GeVc)−2 for the N*(1410), ∼5 (GeVc)−2 for the N*'s at 1500, 1690, and 2190 MeV, and ∼9 (GeVc)−2 for elastic scattering. Also for the small- |t| data, cross sections for N*'s at 1410, 1500, 1690, and 2190 MeV and for elastic scattering vary only slightly with Pinc consistent with the dominance of Pomeranchuk exchange and with diffraction dissociation. A fit of N*(1690) total cross sections to the form σ∝P−n gives n=0.34±0.06, while for elastic scattering n=0.20±0.05. For the N*(1690) the effective Regge trajectory has the slope αeff′(0)=0.38±0.17. When compared with N* production in π−, K−, and p¯ beams these data also agree with approximate factorization of the Pomeranchuk trajectory. N*(1236) cross sections are consistent with other measurements at similar momenta. For −t>1 (GeVc)−2, elastic scattering cross sections decrease approximately as Pinc−2, and they and N*(1500)− and N*(1690)− production cross sections have t slopes consistent with 1.6 (GeVc)−2.
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We have completed measurements of the differential cross section for γ+p→π0+p, and the asymmetry with polarized photons, for incident photon energies from 4 to 18 GeV and momentum transfers between t=−0.1 and −1.4 (GeV/c)2. The experiment was performed at the Stanford Linear Accelerator Center, using the SLAC 1.6-GeV/c spectrometer to analyze protons recoiling from a hydrogen target. For the cross-section measurements a normal collimated bremsstrahlung beam was used. For the asymmetry measurements the polarized photons were produced by coherent bremsstrahlung from a diamond crystal, and a coincidence was required between the recoil proton and one of the π0 decay photons in a shower counter.
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Forward differential cross sections for isospin-1 bosons produced in p+p→d+x+ were measured using a deuteron missing-mass spectrometer at a small angle between 4.0- and 12.3−GeVc incident momentum. Differential cross sections for π+ and ρ+ were extracted from the spectra using phase-space backgrounds. They range from 10.4 to 0.4 μb/sr for π+ and from 1.4 to 0.3 μb/sr for ρ+. A bump near 6 GeVc appears in both dπ and dρ channels. No clear evidence is seen for higher-mass bosons. The possible δ+ cross sections average less than 0.01 μb/sr.
TECHNIQUE USED...ELECTRONIC. TABLE 1.
TECHNIQUE USED...MISSING MASS. BREIT WIGNER USED WITH FIXED WIDTH (150 MEV) AND VARIABLE MASS (LATTER VARIED WITH MOMENTA FROM 715 TO 765 MEV). 6 PERCENT NORMALIZATION ERROR; 20 PERCENT FROM BREIT WIGNER FIT. TABLE 1.
TECHNIQUE USED...MISSING MASS. CROSS-SECTIONS CORRESPOND TO VERY NARROW DELTA (962).
Measurements have been made on Compton scattering for photon energies between 5 and 17 GeV and t values from -0.06 to -1.1 (GeVc)2. The data were obtained by performing a coincidence between the Stanford Linear Accelerator Center 1.6-GeVc spectrometer and a Lucite shower counter. The scattering appears diffractive out to high t values, but the cross sections seem not to be in good agreement with the prediction of a strict vector-meson-dominance model.
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Polarization and differential cross section data for elastic proton-proton scattering between 0.86 and 2.74 GeV/ c are presented. A comparison is made with existing phase-shift analyses.
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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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Cross sections for π0 photoproduction from hydrogen in the backward direction have been measured for photon energies of 6, 8, 12, and 18 GeV. The range of momentum transfer covered in these measurements is −1 (GeVc)2<u<0(GeVc)2, dσdu is found to have a backward peak and decreases with energy as s−3.0±0.2. Photoproduction of η0 and ρ0 mesons has also been observed.
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