The real part of the forward amplitude for Compton scattering on protons was measured through the interference between the Compton and Bethe-Heithler amplitudes by detecting the zero-degree electron pairs asymmetrically. The measurement was made at an average photon energy of 〈k〉=2.2 GeV, and an average momentum transfer to the recoil proton 〈t〉=−0.027 (GeV/c)2. The result confirms the prediction of the Kramers-Kronig relation.
No description provided.
We have measured large-angle electron-positron pairs from the reaction γ +Be → Be+e + +e − in the e + e − invariant-mass region of 610 < m < 850 MeV/ c 2 . The phase of the photoproduction amplitude of the ϱ-meson at 4.1 – 6.1 GeV was found to deviate from pure imaginary by 11.8° ± 4.4° which corresponds to a ratio of the real to imaginary ϱ-nucleon amplitude of β = −0.2 ± 0.1.
No description provided.
The differential cross section for π − p → n π o has been measured in detail from 150 to 600 MeV. The backward cross section has a previously unobserved dramatic dip at 425 MeV. We interpret this dip in terms of interference between the P 33 (1236) and the P 11 (1470) resonances. These data provide strong evidence for the adequacy of the phase shift solutions in this energy range.
SCALED TO AGREE WITH SOLUTION AT 225 MEV AND THEN INTERPOLATED.
SCALED TO AGREE WITH SOLUTION AT 225 MEV AND THEN INTERPOLATED.
SCALED TO AGREE WITH SOLUTION AT 225 MEV AND THEN INTERPOLATED.
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.
No description provided.
No description provided.
No description provided.
Differential cross sections for the reactions e−+p→e−+p+π0 and e−+p→e−+n+π+ have been measured near the Δ(1236) resonance at four-momentum transfers of 0.05, 0.13, 0.25, and 0.4 (GeV/c)2. A few measurements of the π+ angular distribution have been obtained at a four-momentum transfer of 0.6 (GeV/c)2. Cross sections for the π0 reaction are compared with dispersion-theory predictions at several pion-nucleon c.m. energies for each four-momentum transfer. A phenomenological analysis of the π0 results leads to the determination of the magnetic dipole and electric quadrupole partial-wave amplitudes and the γNΔ transition form factor. Evidence is found for the existence of a significant scaler-transverse interference term in the cross section, which is tentatively associated with the resonant scaler quadrupole interaction. Cross sections for π+ electroproduction are compared with dispersion theories using the pion form factor as a free parameter. The results suggest a form factor similar to that of the proton. A fit to the form-factor results, using the ρ-dominance model, requires mρ=560±80 MeV. The rms pion charge radius is estimated to be 〈r2〉12=0.86±0.14 F.
No description provided.
No description provided.
No description provided.
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.
No description provided.
No description provided.
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We have measured elastic electron-proton scattering cross sections in the range of four-momentum transfers from 7 F−2[0.27 (GeV/c)2] to 150 F−2 [5.84 (GeV/c)2] and at scattered electron angles of between 20° and 34° in the laboratory. The estimated errors in the cross sections range from ±2.1% at the lowest momentum transfer to ±9.6% at the highest. Both the scattered electron and the recoil proton were detected, resulting in an overdetermination of the kinematics. When the constraint of a coincident proton is removed, there is no significant change in the estimated cross sections.
No description provided.
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We present results of measurements on photoproduction of ρ mesons. Analysis of 106 measured ρ events in a four-dimensional data matrix dσ(A, m, p, t⊥)dΩdm with dimensions 14×20×10×20 yields precise information on nuclear density distributions for ρ production. We obtain for the Woods-Saxon radii R(A)=(1.12±0.02)A13 and, using the vector dominance model, σρN=26.7±2.0 mb and γρ24π=0.57±0.10.
No description provided.
Total cross sections of K+ and K− mesons on protons and deuterons have been measured in a transmission experiment over the range of laboratory momentum 0.6-2.65 GeV/c. Measurements have been made on K− at 58 momenta at intervals of 25-50 MeV/c; the experimental accuracy is better than 1% above 700 MeV/c, and the momentum resolution of the beam is ±0.6%. Structure is observed in the total cross sections suggesting or confirming Y1∗ resonances at masses of 1665, 1768, 1905, 2020, 2250, and 2455 MeV/c2 and Y0∗ resonances at masses of 1695, 1819, 1870, 2100, and 2340 MeV/c2. The K+ measurements are less extensive, and are concentrated in the momentum range below 1.5 GeV/c; the experimental errors are typically ±0.2 mb. Structure previously reported in the K+p and K+d total cross sections near a laboratory momentum of 1.2 GeV/c is confirmed. Total cross sections of K+ and K− on carbon have been measured at a number of momenta with an accuracy of about ±2%.
No description provided.
No description provided.
Total cross sections of π+ and π− mesons on protons and deuterons have been measured in a transmission experiment to relative accuracies of ±0.2% over the laboratory momentum range 0.46-2.67 GeV/c. The systematic error is estimated to be about ±0.5% over most of the range, increasing to about ±2% near both ends. Data have been obtained at momentum intervals of 25-50 MeV/c with a momentum resolution of ±0.6%. No new structure is observed in the π±p total cross sections, but results differ in several details from previous experiments. From 1-2 GeV/c, where systematic erros are the smallest, the total cross section of π− mesons on deuterons is found to be consistently higher than that of π+ mesons by (1.3±0.3)%; about half of this difference may be understood in terms of Coulomb-barrier effects. The πd and πN total cross sections are used to check the validity of the Glauber theory. Substantial disagreements (up to 2 mb) are observed, and the conclusion is drawn that the Glauber theory is inadequate in this momentum range.
No description provided.
No description provided.
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