Differential cross sections are presented for pion-proton elastic scattering in the angular range −0.6≳cosθc.m.≳−0.98 at 15 incident π+ momenta from 2.18−5.25 GeVc. The angular distributions rise steeply near 180° at all momenta. For laboratory momenta ≳2.75 GeVc they show a minimum at u≈−0.17 (GeVc)2 and a broad maximum near u≈−0.6 (GeVc)2. When the data are plotted versus s, for fixed u, a strong signal from the Δ(2420) resonance is observed. The data are compared with a direct-channel resonance model and with a Regge model which considers the exchange of the Nα, Nγ, and Δδ Regge trajectories. The qualitative success of both the direct-channel resonance model and the Regge model lends support to the concept of duality.
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This paper presents differential cross sections for backward π−p elastic scattering in the angular region −0.55≥cosθc.m.≥−0.98 for five incident momenta: 2.38, 2.50, 2.65, 2.80, and 3.00 GeV/c. The structure of the angular distribution undergoes a marked change over this momentum interval. A pronounced dip near 180°, which is seen for momenta ≲2.50 GeV/c, becomes a sharp peak at 2.80 and 3.00 GeV/c. A minimum in the cross section at cosθc.m.≃−0.7 is indicated at all momenta. In addition, a dip in the differential cross section appears at cosθc.m.≃−0.92 at 3.00 GeV/c. A good fit to the data from 2.1 to 3.0 GeV/c is obtained with a direct-channel resonance model.
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