Antiproton-proton elastic scattering at 6.2 GeV/c

Antiproton-proton elastic scattering data at 6.2 GeV/c in the range 0.3 (GeV/c)² ? ?t ? 10.0 (GeV/c)² is presented. The experiment, using spark chambers and proportional chambers, was performed at the CERN Proton Synchroton.The dip at about ?t = 0.5 and the structure at about ?t = 2.2 (GeV/c)² are equally strong at 6.2 GeV/c as they are at 5.0 GeV/c. The differential cross sections around 90° c.m. are not very different at 5.0 GeV/c and at 6.2 GeV/c, whereas in the backward region there is a decrease of the order of one magnitude.     

Elastic scattering of antiprotons on protons at 5 GeV/c evidence for a backward peak

Antiproton-proton elastic scattering has been measured at 5 GeV/c. A total of 30 000 events were observed in the angular range 17° < θ_cm < 136°, corresponding to 0.3 < −t < 7.7 (GeV/c²). In addition to the known dip at −t = 0.5 (GeV/c)², we observe a structure at about −t = 2 (GeV/c)² and a backward peak with a slope4.1 ± 0.6 (GeV/c)². The extrapolated differential cross-section at u = 0 is 1.3 ± 0.8 μb/(GeV/c)².     

Elastic scattering and coherent single pion production in proton-helium interactions at 18.6 GeV/c

Proton-helium elastic scattering and coherent single-pion production have been studied at 18.6 GeV/c in the four-momentum transfer region (?0.06, ?0.17) GeV/c². The elastic t-distribution has a somewhat steeper slope than is predicted by the Glauber approximation. The invariant-mass distribution of the Nπ system agrees with the double Regge-pole model except at about 1.65 GeV/c² where an enhancement presumably due to N¹ resonances is seen. The model also predicts the correct magnitude of the slope for nπ⁺α events. By using our cross sections at t′ = ?0.06 (GeV/c)² where the impulse approximation should be valid, the isospin-zero exchange elementary cross section for the nπ⁺ production is evaluated. The inelastic angular distributions are consistent with several spinparity states contributing at all Nπ masses.     

Elastic pp scattering in the cern sps energy region

The pronounced dip-bump structure with a sharp minimum at |t| = 1.5 (GeV/c)², recently observed in elastic $\text{p}$p scattering at P_L = 50 GeV/c at the CERN SPS, is explained by the quark multiple scattering model with a realistic wavefunction for the proton and the antiproton. It is predicted that a second dip will appear around |t| = 7 (GeV/c)² at P_L = 50 GeV/ c and at higher energies.     

Elastic antiproton-deutron scattering below 1.0 GeV/c

We present differential cross sections for elastic $\text{p}$d scattering at beam momenta 0.735 and 0.940 GeV/c and momentum transfers in the range 0.04<|t|<0.5(GeV/c)². The $\text{p}$d elastic differential cross section is expressed in terms of a deutron form factor and the I=0 t-channel exchange $\text{N}$N amplitudes, enabling us to isolate the corresponding I=0 t-channel exchange cross sections.     

The charge exchange pp → nn at 5.0 and 7.76 GeV/c near the forward direction

The differential cross section for the charge exchange $\text{p}\text{p}\text{→}\text{n}\text{n}$ has been measured with high statistics at 7.76 GeV/c and at 5.0 GeV/c. The 7.76 GeV/c data show a very narrow [Δt ? 0.01 (GeV/c)²] forward peak superposed on a slow exponential fall-off.     

K−p and pp elastic scattering at 10.1 GeV/c

The differential cross sections for K^?p and $\text{p}$p elastic scattering have been measured over the range of four-momentum transfer squared 0.18<?t<3.3 (GeV/c)². The K^?p data decrease smoothly as a function of ?t, whereas, the $\text{p}\text{p}$ data shows a break at ?t = 0.6 (GeV/c)² followed by a fast drop to ?t ? 1.6 (GeV/c)² where the differential cross section levels off and stays constant out to ?t = 3 (GeV/c)².     

Measurement of the polarization in the forward peak of π−p→K0λ at 5 GeV/c

The π^?p→K⁰λ polarization has been measured at 5 GeV/c in the range 0<?t<1.4 (GeV/c)². The polarization is small for ?t?0.4 (GeV/c)², becoming negative at the higher values of ?t.     

Soft π−p and pp elastic scattering in the energy range 30 to 345 GeV

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 ? (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.The results on the real parts confirm the validity of the forward dispersion relations at high energies. Using the dispersion relations, it was shown that the experimental data on ?_{π?p(t = 0)} require a continuous rise of the total πp cross sections, at least up to the energy of 2000 GeV, thus revealing a close similarity in high-energy behaviour of πp and pp interactions.The results on the slope parameters from this experiment together with the analysis of the available world data demonstrate that the existing experimental data are consistent with the hypothesis of a universal shrinkage of the hadronic diffraction cone at high energies. The value of the asymptotic shrinkage parameter α_p^′ was found to be independent of the kind of the incident hadron and of the momentum transfer in the t range |t| ? 0.2 (GeV/c)² : 2α_{p^′ = ± 3 (GeV/c)^?2}.     

The structure of t-channel exchanges in KN scattering

Recent phase-shift solutions are used to evaluate KN FESR integrals in order to examine zeros and phases of the t-channel exchange amplitudes in the most model-independent way. The results suggest that the line reversal breaking in KN CEX observed for pL ? 5.5 GeV/c is due to a large EXD breaking component in the A₂ exchange flip amplitude. The ? exchange flip amplitude is well described by a Regge pole amplitude with NWSZ at ?t ≈ 0.5 (GeV/c)². The imaginary parts of ? and ω exchange non-flip amplitudes are both peripheral.     

Coulomb-nuclear interference in π±p and K±p elastic scattering below 3 GeV: Measurements,real parts and K±p dispersion relations

The differential cross sections for π⁺p elastic scattering at0.6, 1.0, 1.5, 2.0, GeV/c for π^-p at 1.0, 1.5, 2.0 GeV/c, for K^-p at 1.2, 1.8, 2.6 GeV/c and for K^-p at 0.9, 1.2, 1.4, 1.6, 1.8, 2.6 GeV/c have been measured with an overall accuracy ofthe order of 1 to 2% in an electronics experiment over the angular region corresponding to momentum transfer t between 0.0005 and 0.10 GeV². Making use of the interference effects between the Coulomb and the nuclear interaction, we have determined the magnitude and sign of the real part of the scattering amplitude near t = 0. The K^±p real parts have been used in a dispersion relation to derive the value of the KNΛ coupling constant.     

Measurement of high momentum transfer π−p → π0n at 5.9 GeV/c

The differential cross section for π^?p → π⁰n has been measured in the t range 1.8 ? |t| ? 8.2 (GeV/c)² by a counter-spark chamber experiment detecting the neutron and both π⁰ decay photons. A broad minimum was found, centered at |t| = 5.2 (GeV/c)².     

New limits for the exotic exchange reaction π−p → K+Σ− at 5 and 8 GeV

Measurement of the exotic exchange reaction π^?p → K⁺Σ^? has been performed at 5 and 8 GeV, in the ?0.015 to ?0.13 and ?0.009 to ?0.15 (GeV/c)² range of t repectively. We give the value near t = 0 of the differential cross section at 5 GeV, 21_?21⁺⁷⁶ nb/(GeV/c)², and an upper limit (< 37 nb/GeV/c)²) at 8 GeV. As a check the measured differential cross section is given at both energies for the reaction π⁺p → K⁺Σ⁺ in the same range of t.     

Diffractive one-pion production in the αp → αX process at Pα = 7.0 GeV/c

Inclusive coherent proton dissociation on helium has been measured for a missing mass near the threshold of one-pion production, in the |t| range 0.05–1.6 (GeV/c)² and at an alpha incident momentum of 7.0 GeV/c. A strong t-slope dependence of the cross section at |t| ? 0.2 (GeV/c)² is followed at larger |t| by a less structured distribution. Data were analyzed using the Glauber-Margolis formula and by assuming a peripheral elementary diffraction amplitude for the production process.     

On new predictions of the vector-meson dominance model for the reactions πN → ϱ0N and γN → πN

It is shown that the assumption of pole vector-meson dominance for the Ball invariant amplitude having a π-meson pole is sufficient for reproducing the longitudinal amplitude of ?⁰-production by the photoproduction amplitude at |t| < 0.1 (GeV/c)². The strong k²-dependence of the Ball invariant amplitude without the π-meson pole has been found by the deviations of theoretical predictions obtained in the VDM framework for the longitudinal ?⁰-production amplitude from the experimental data in the region |t| > 0.1 (GeV/c)². A natural explanation of the k²-dependence in the one-pion exchange model with absorption is given. The problem of A₂-exchange is discussed.     

Study of Δ production in the reaction πp→ππp at 13.1 GeV/c

We have measured the production and decay angular distributions of the reaction π⁺p→π^OΔ⁺⁺ at 13.1 GeV/c incident momentum. For −t > 0.1 (GeV/c)² the data is well described by M1 ?-exchange models, the best results being obtained from a weak cut model with a wrong signature nonsense zero. For −t < 0.1 (GeV/c)² there is evidence for the existence of other exchange mechanisms.     

ϱ and A2 amplitudes in K±N charge exchange using fixed t analyticity

Amplitudes corresponding to ? and A₂ quantum number exchanges in K^±N charge exchange scattering are obtained from data in the few GeV region using an analysis based on fixed t analyticity in the form of fixed t dispersion relations and finite-energy sum rules. Comparisons are made with amplitude analyses at 6 GeV/c and some specific high-energy models.     

A measurement of polarization in π−p→ K°Λ° at 5 GeV/c

We have measured the Λ° polarization in π^?p→ K°Λ° at 5 GeV/c, using a data sample of 3709 events. The polarization is positive for small t, passes through zero near t = ?0.3 (GeV/c)², and becomes large and negative at larger t, consistent with a value of ?1.0 for t between ?0.7 and ?1.6(GeV/c)².