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.

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.

We have measured charged-particle multiplicities and elastic and inelastic cross sections for π+p and pp interactions at 60 GeV/c. The data are from a 30 000-picture exposure of the 30-inch bubble chamber to a tagged but unseparated positive-particle beam at Fermilab. The low-order moments of the inelastic multiplicity distributions for all charged particles are 〈n〉 = 5.60±0.09, f2 = 0.96±0.31, and 〈n〉D = 2.19±0.06 for pp reactions and 〈n〉6.23±0.10, f2 = 1.63±0.37, and 〈n〉D = 2.22±0.06 for π+p collisions.

Absolute π±p elastic scattering differential cross sections have been measured at five incident pion energies between 87 and 139 MeV. An active target of scintillator material (CH1.1) was used to detect recoil protons in coincidence with scattered pions. Pions were detected at forward angles between 27 and 98°c.m. where the low-energy recoil protons stop in the target. The cross sections, typically 5–10% lower than phase shift predictions for π+p and 10–20% lower for the π−p cross sections, are consistent with earlier measurements by this group.

The differential cross section for elastic scattering of 3.63−GeVc π− mesons on protons was studied with a hydrogen bubble chamber, the emphasis being on large-angle scattering. From 90 to 180° in the barycentric system, the cross section is roughly flat with an average value of 2.7±1.0 μb/sr. Near and at 180°, there may be a slight peak of magnitude 10±6 μb/sr. But if such a peak exists, it is only one-third to one-fourth the size of the 180° peak found in 4.0 GeVc π++p elastic scattering. In addition to comparison with other π−+p and π++p large-angle elastic-scattering measurements, this measurement is compared with large-angle p+p elastic scattering. In the forward hemisphere a small peak or a plateau exists at cos θ*=+0.60. This appears to be a second diffraction maximum such as has been found in lower-energy π+p elastic scattering. A survey of indications of such a second diffraction maximum in other π+p measurements shows that it always occurs in the vicinity of −t=1.2 (GeVc)2, where t is the square of the four-momentum transfer. As the incident momentum increases, the relative size of this second maximum decreases.

We studied 21 187 two-prong, two-prong-with-kink, and zero-prong-V events at incident kaon momentum of 1.33 GeVc using the 72-in. hydrogen bubble chamber at the Lawrence Radiation Laboratory and two scanning and measuring projectors in Urbana. We determined the total and partial cross sections for all contributing reactions. For the two-body final states, some production and polarization angular distributions were measured. The angular distributions are discussed in terms of exchanges in the kinematical channels s, t, and u assuming the simplest Feynman graphs. Elastic scattering is analyzed as a diffraction process.

The elastic scattering of 3.55 GeV/ c π + and π − mesons by protons was measured at centre-of-mass angles between 165° and 177°. The angular distributions for 864 events show a steeply rising backward peak for π + p, while the shape is less clear for π − p.

Results on the elastic K − π − scattering have been obtained from a study of the K − π − system in 15 000 events of the type K − p→K − π − p π + at a K − beam momentum of 4.25 GeV/ c . The on-mass-shell values of the spherical harmonic moments of the K − π − scattering angular distribution and the K − π − elastic cross section have been obtained by extrapolation to the pion pole. From these values we determined the s- and p-wave phase shifts δ 0 3 and δ 1 3 as a function of the effective mass of the K − π − system between threshold and 1.25 GeV/ c 2 . The value of | δ 0 3 | is smaller than 17° for all mass values and the existence of a p-wave cannot be neglected. At m K − π − = 1.18 GeV/ c 2 there are two solutions for the phase shifts. On the average, the cross section of the K − π − elastic scattering over the region of the effective mass considered amounts to approximately 2.5 mb.

Approximately 700 events of the reaction K − d → K − π − pp s produced by 5.5 GeV/ c kaons were used to measure the cross section for Kπ elastic scattering in the T = 3 2 state by a Chew-Low extrapolation. The cross section does not exceed 2.1 mb and has no structure for Kπ masses from threshold up to 2.0 GeV.

The asymmetry parameter A in π−p elastic scattering at incident pion laboratory kinetic energies Tπ of 98, 238, and 2922 MeV and in π−p charge-exchange scattering π−p→π0n at Tπ=238, 292, and 310 MeV have been measured over a wide range of scattering angles (typically from about 60° to 130° c.m.) with a polarized proton target. The data have been used in an energy-independent phase-shift analysis to improve the precision of the pion-nucleon phase shifts, to set new limits on violation of isospin conservation in the pion-nucleon S wave, and to confirm significant charge dependence in the P32 wave.

In this paper we report measurements of the backward K−p differential cross section at 49 momenta covering the momentum range 476-1084 MeV/c. The statistical precision achieved, typically 2.5%, is an order of magnitude better than previous measurements. The systematic errors for this reaction are about 1%. The differential cross section for the reaction K−p→Σ−π+ where the π+ emerges at 0° has also been measured at 32 momenta with comparable improvement in precision over previous experiments. A partial-wave analysis of the K¯N channels including the new K−p backward elastic data is presented.

The final state K − pn has been analyzed in a K − deuterium bubble chamber experiment at K − momenta between 680 and 840 MeV/ c . Differential cross sections for elastic K − p and K − n scattering in the c.m. energy range of 1.60–1.74 GeV are presented. The results for K − p→K − p agree well with existing data obtained with hydrogen targets. The results for K − n→K − n are lower but still compatible with recent measurements from a counter experiment.

Backward elastic scattering has been measured for π + p at 2.85 and 3.30 GeV/ c and for π − p at 3.30 GeV/ c . The π + p angular distributions show steep backward peaks, whereas the π − p distribution is flatter. At 2.85 GeV/ c the π + p differential cross section close to 180° is more than twice that at 3.30 GeV/ c , supporting the assignment J P = 11 2 + for Δ δ (2420) resonance. The π + p data at 2.85 GeV/ c indicate the onset of a dip at cos θ c.m. ≈ −0.97.

The differential elastic scattering cross section for 2.24 GeV/ c K − p collisions has been measured in film from the Brookhaven 20″ bubble chamber. The total elastic cross section is found to be 6.2 ± 0.7 mb. The exponential dependence on square of the momentum t in (GeV/ c ) 2 is fitted by ( d σ d Ω elastic = (12.4 ± 1.0 mb/sr) exp (7.81 ± 0.25)t . A A fit to a black disc model requires a radius of 0.95 ± 0.05 fm.

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We present results of measurements of K ± p and p p elastic scattering and of the annihilation reactions p p →π + π − and p p → K + K − at an incident laboratory momentum of 5 GeV/ c . Nearly complete angular distributions were obtained. Results are also presented for π -meson proton elastic scattering in the momentum transfer ranges 2 < − t < 8 (GeV/ c ) 2 (for π + ) and 0.16 < − t < 7 (GeV/ c ) 2 (for π − ). All measurements were done in one experimental geometry. The measured differential cross sections range from 10 to 10 −5 mb/(GeV/ c ) 2 .

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The exclusive process π−p→ρ−p has been measured at 90° c.m. with an incident pion momentum of 9.9 GeV/c. We present data on the angular dependence of the decay ρ−→π−π0. We observe a strong azimuthal dependence in the decay in the c.m. helicity frame of the ρ. Such an azimuthal dependence is not compatible with SU(6) valence-quark perturbation calculations.

We present an analysis of ππN final states obtained from π−p interactions at 2.26 GeV/c. Strong ρ production is present in both final states. In addition, significant nucleon isobar production is observed. We observed the following cross sections: σ(π−π0p)=3.77±0.13 mb, σ(π−π+n)=5.67±0.17 mb, σ(ρ−p)=2.19±0.09 mb, σ(Δ+(1236)π−)=0.30±0.10 mb, σ(N0(1650)π0)=0.49±0.07 mb, σ(ρ0n)=2.89±0.11 mb, σ(Δ−(1236)π+)=0.11±0.06 mb, σ(N+(1470)π−)=0.24±0.06 mb, and σ(N+(1650)π−)=0.45±0.05 mb. The spin-density matrix elements are determined for the ρ0 by interpreting the ρ0 asymmetry as an interference between the resonant P wave and a T=0 S wave. A search for the ε0 in the π+π−n final state failed to yield a direct observation of this effect.

A total of 24 360 events having two charged particles in the final state from π−+p interactions at an incident π− momentum of 2.7 GeVc have been analyzed. The final states π−π+n and π−π0p are found to be dominated by rho-meson production, and in addition, significant N*(1238) production is seen. The partial cross sections for the dominant resonant channels are σ=(pρ−)=(1.3±0.2) mb, σ(nρ0)=(2.3±0.2) mb, and σ[π−N*+(→pπ0)]=(0.5±0.2) mb. The production of the ρ− and ρ0 and the decay of the ρ− agree very well with the predictions of an absorption-modified one-pion-exchange model. The production angular distributions of the ρ0 and ρ− follow an exponential of the form Ae+Bt. The results from a least-squares fit give B(ρ−)=9.32±0.08 (GeVc)−2, B(ρ0)=10.26±0.06 (GeVc)−2. A similar analysis for the elastic-scattering events gave B(el)=7.77±0.05 (GeVc)−2. The ρ0 decay distributions are asymmetric and they have been analyzed using a simple model which includes S−P-wave interference. No clear evidence is seen for a T=0, J=0 resonance at a mass near that of the ρ. The N*(1238) resonance production is found to be in agreement with the ρ-exchange model of Stodolsky and Sakurai. Indication of other resonance production with small cross section is seen, such as A1 and A2 production in the multiple missing neutral events. The masses and widths of the ρ0 and ρ− as a function of the four-momentum transfer squared to the nucleon have been determined.

In an exposure of the Brookhaven National Laboratory 20-in. hydrogen bubble chamber to a separated π+ beam at π+ momenta of 2.35 BeV/c (center-of-mass energy E*=2.30 BeV), 2.62 BeV/c (E*=2.41 BeV), and 2.90 BeV/c (E*=2.52 BeV), we have observed production of the ω0, ρ0, and η0 mesons. The production of the ω0, ρ0, and η0 is often accompanied by simultaneous production of the N*++. The momentum transfer in ω0 and ρ0 production is characteristic of peripheral collisions and suggests a single-particle exchange for the production mechanism. The decay distributions for the ω0, ρ0, and the ρ+ demonstrate the importance of modifying the single-particle-exchange model to include absorptive effects. An upper limit on the two-π decay of the ω0 is set at 2%. The width of the η0 is found to be less than 10 MeV. Elastic-scattering distributions are presented.

Interactions of 781-MeV π+ mesons with protons were investigated using the Brookhaven National Laboratory 14-in. hydrogen bubble chamber. A total of 2305 events was observed. The data were normalized to a total cross section of 22.2 mb, giving partial cross sections σ(π+p→π+p)=9.5±0.5 mb, σ(π+p→π+pπ0)=9.3±0.5 mb, σ(π+p→π+π+n)=2.15±0.17 mb, and a multiple-pion-production cross section of 1.15±0.17 mb. The elastic angular distribution was obtained and is dσdω=(0.25±0.03)+(0.90±0.11)cosθc.m.+(2.57±0.24)cos2θc.m.+(0.19±0.22)cos3θc.m.−(1.73±0.34)cos4c.m.. The kinetic-energy and angular distributions of the outgoing particles in single-pion production are given. The data are compared with other experiments in this energy region and their relevance to the shoulder in the π+p total cross section near 830 MeV is discussed.

Meson production in π−p and π+n interactions at 1.7 GeV/c has been studied in two bubble-chamber exposures. Combined results are presented with emphasis on single-pion production (4300 events) which is dominated by the formation of the ρ0 meson in peripheral interactions, and on double-pion production (1100 events) which shows strong formation of the ω meson. These data are compared with the predictions of particle-exchange models, including absorption, and the effects of competing channels are discussed. Evidence for a two-pion decay mode of the ω is examined quantitatively. Processes with higher meson multiplicities are described.

Interactions of 2.08−BeVc positive pions with protons have been studied using the 20-in. hydrogen bubble chamber and the alternating gradient synchrotron at Brookhaven National Laboratory. Using 3000 elastic and 8000 inelastic events, the partial cross sections for elastic scattering and for meson production have been measured. The ρ+, ρ0, ω0, and η0 resonances are produced strongly and emerge predominantly in the forward direction in the center-of-mass system, suggesting a peripheral mechanism for their production. The possibility of explaining these reactions by specific particle-exchange models is investigated. More than 75% of the ρ0, ω0, and η0 are produced with the N33* (1238) isobar. The N* (1688) is produced in about one-third of the π+π+N final states. Cross sections for production of ρ+p, π+pω, N33*ω, π+pη, N33*η, π+pρ0, N33*ρ0, N15*π+, and N33*π0, are given. A1, B, φ, and X mesons are not observed.

An analysis of π−p two-prong interactions at 4.16 GeV/c is presented. The total two-prong cross section is 19.11±0.40 mb, based on 33 672 events. The elastic-scattering differential cross section shows an exponential behavior, Kexp(−AΔ2). With A=7.36±0.14 GeV−2, the "absorption parameters" are derived as C+=0.846±0.017 and γ+=0.040±0.001. The final-state π−π0p exhibits a strong ρ−, and the π−π+n a strong ρ0 and f0. The partial cross sections for the dominant resonant channels pρ−, π−Δ+(1236) (→pπ0), ρ0n, and f0n are 0.59±0.03, 0.17±0.01, 1.15±0.05, and 0.53±0.06 mb, respectively. The ρ− production and decay angular distributions do not agree with the predictions of the absorption-modified one-pion-exchange model. However, an inclusion of the contribution from ω exchange adequately accounts for the discrepancy. The ρ0 asymmetry is interpreted as a result of an interference of the resonant P wave and isospin-zero S wave, and the corresponding spin-density matrix elements are obtained. In the final state π−p+neutrals, a clear peak for the η meson and some evidence for the ω meson are seen.