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.     

Electroproduction of neutral pions at energies above the resonance region

The reaction e p→e'pπ⁰ has been measured at W=2.55 GeV a fixed electron scattering angle of 10.3°. Two magnetic spectrometers and a lead glass hodoscope were used to detect all four final state particles. Electroproduction cross sections in the t range ?0.15 to ?1.4 (GeV/c)² at q² = ?0.22, ?0.55 and ?0.85 (GeV/c)² are presented. Above |t|=0.6 (GeV/c)² the cross sections are considerably smaller than those for photoproduction.     

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.     

Target asymmetry for neutral π meson photoproduction on polarized protons at 4 GeV in the forward direction

The asymmetry $\text{A =}\text{(σ}{}^{\mathrm{+}}\text{?σ}{}^{\mathrm{?}}\text{)}\text{(σ}{}^{\mathrm{+}}\text{+σ}{}^{\mathrm{?}}\text{)}$ of the reaction γp↑↓ → π⁰p was measured at the Deutsches Elektronen Synchrotron DESY, Hamburg at a mean photon energy of 4.0 GeV in the four-momentum transfer range 0.2 (GeV/c)² ? ?t ? 1.1 (GeV/c)² in steps of approximately 0.08 (GeV/c)². The π⁰-meson and the proton were detected in coincidence. The asymmetry is compatible with zero in the t-range 0.2 (GeV/c)² ? ?t ? 0.4 (GeV/c)² and negative in the t-range ? 0.5 (GeV/c)².     

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.     

The pion-nucleon scattering amplitudes at 40 GeV/c

The helicity amplitudes for isospin-0 exchange are determined at 40 GeV/c. For isospin-1 exchange only partial information is obtained. The model-independent analysis is extended to the four-momentum transfer interval from t = 0 to t = ?0.6 (GeV/c)². One of the two solutions presented has a behaviour similar to the previous results at lower energy.     

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.     

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.     

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.     

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}.     

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.     

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.     

Neutron-proton elastic scattering from 10 to 70 GeV/c

The neutron-proton elastic differential cross section has been measured for incident momenta between 10 and 70 GeV/c and for values of the momentum transfer squared between 0.1 and 2.8 (GeV/c)². The forward peak and the break at about ∣t∣ = 1 (GeV/c)² are very similar to corresponding pp data.     

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.     

Amplitude analysis of πN charge exchange at large momentum transfer

We have found evidence for the right-signature zero at t ≈ ?1.5 (GeV/c)² and the second wrong-signature zero at t ≈ ?2.5 (GeV/c)² in the helicity flip ?-Regge-pole exchange from an amplitude analysis of πN charge exchange extended to large momentum transfer. Reconstruction of the imaginary part of the nonflip amplitude suggests a remarkable degree of Regge behaviour out to large ?t. Confirmation of such behaviour would undermine the basic features of absorptive cut models.     

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.     

Measurement of np elastic scattering at high energies and very small momentum transfers

The np elastic differential cross section has been measured for incident neutron momenta 100–400 GeV/c in the |t| range 6 · 10^?6 ? 5 · 10^?1 (GeV/c)². The np data of this experiment provide a first direct measurement of the hadronic amplitude for |t| < 10^?2 (GeV/c)², which is consistent with the extrapolations from higher |t| values. Our data for |t| < 10^?4 (GeV/c)² are consistent with a rise which can be attributed to Schwinger scattering, caused by the interaction of the neutron magnetic moment with the proton.     

Measurement of the polarization parameter in π−p elastic scattering at 40 GeV/c

We report our first measurements of the polarization in the elastic scattering of negative pions from polarized protons at an incident pion momentum of 40 GeV/c. The momentum-transfer region covered was 0.08 < |t| < 1.3 (GeV/c)². The angular distribution of the polarization exhibits a first minimum of ～ ? 5% and the well-known zero around t ≈ ? 0.6 (GeV/c)². The energy variation of the first minimum (at around t = ? 0.2) may be expressed in a simple form, $\text{P}{}_{\mathrm{<mtext>avr</mtext>}}\text{= ?(0.48±0.06) s}{}^{\mathrm{?0.52\pm 0.05}}$.     

Search for narrow four-baryon states

Highly excited (4.10?mass?5.35 GeV/c²) four-baryon resonances have been searched for in the missing-mass spectrum of the reaction π^?+⁴He→π^?+X at 5 GeV/c in the region of small four-momentum transfer (0.005?6t6?0.15 (GeV/c)²), where one of the decay products of the X is either proton or deuteron or triton. No resonance signal is seen in the mass spectrum of X. Within our limited acceptance, the cross section for the production of a narrow (Γ ～ 20 MeV/c²) four-baryon state with mass 4.9 GeV/c² is estimated to be smaller than ～ 100 nb.     

A measurement of the KL0p → KS0p reaction between 4 and 14 GeV/c in the range 0.1 ⩽|t|⩽ 2 GeV2

We present experimental data on the K_L⁰p → K_S⁰p reaction between 4 and 14 GeV/c in the range 0.1 ? |t| ? 2 GeV². This experiment has been performed at the CERN PS, using spark chambers and a large aperture magnet. The results show a break of slope at t = ?0.3 GeV². The ω trajectory deduced from the data has an intercept α(0) = 0.5 and a slope α′ = 0.88. A comparison with various models shows that the non-flip amplitude is dominant.