The importance of two-photon exchange in elastic electron-proton scattering was investigated by measuring the ratio of positron-proton to electron-proton scattering. Four-momentum transfers as large as 0.756 (BeV/c)2 (19.5 F−2) were used. The data indicate that two-photon effects are (4.0±1.5)% larger than those predicted by the radiative corrections at the highest momentum transfers attained in these experiments. The two-photon corrections predicted using a static charge distribution fit the data well at lower momentum transfers and forward angles, but appear to be small at higher momentum transfers and backward angles.
Data recalculated from the data of Yount and Pine.
Data recalculated from the data of Yount and Pine. RUN_1 and RUN_2 of the Yount and Pine experiment were separated by large time interval.
Data recalculated from the data of Yount and Pine.
A study of π − + p →η + n near threshold shows that the cross section rises linearly with η momentum and that Λ η < 0.9 MeV c 2 (95% confidence limit).
Errors are statistical only.
We have analyzed 2560 events in the final-state K O 1 K O 1 n produced in π − p interactions at 5, 7 and 12 GeV/ c . We observe the S ∗ (1070), f O and A 2 decaying into K O 1 K O 1 . Resonance parameters, cross sections, and branching ratios are given.
Cross section times branching ratio.
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Measurements of the ratio (R) of positron-proton and electron-proton elastic-scattering cross sections have been made, with the square of the four-momentum transfer (q2) equal to 0.20, 0.69, 0.73, 1.54, 2.44, 3.27, 3.79, and 5.00 (GeV/c)2. The measurements, after radiative corrections, are consistent with R=1, with standard errors ranging from ±0.016 to ±0.123. The results give limits for the size of the two-photon effects.
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Cross sections for π0 photoproduction from hydrogen in the backward direction have been measured for photon energies of 6, 8, 12, and 18 GeV. The range of momentum transfer covered in these measurements is −1 (GeVc)2<u<0(GeVc)2, dσdu is found to have a backward peak and decreases with energy as s−3.0±0.2. Photoproduction of η0 and ρ0 mesons has also been observed.
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The differential cross-section of the reaction γ p→ η p has been measured at the Deutsches Elektronen Synchrotron (DESY) at mean photon energies of 4 and 6 GeV in the momentum transfer range between zero and 1.4 GeV 2 . The data show a slight maximum around t =−0.15 GeV 2 and fall off smoothly till t =−1.4 GeV 2 . There is no indication of a dip around t =−0.5 GeV 2 .
Axis error includes +- 19/19 contribution.
Axis error includes +- 19/19 contribution.
41 ± 8 events of the type X 0 → γγ have been observed in a study of the reaction π − p → n(X 0 → γγ ) at 1.6 GeV/ c incident π -momentum. This provides further evidence to our previous observation of this new X 0 decay mode and allows the determination of the branching ratio Γ(X 0 →γγ) Γ(X 0 → total =(1.7 ± 0.4)%. The theoretical implications of this result are discussed.
THIS MEASUREMENT WHEN COMBINED WITH THE ETAPRIME PRODUCTION CROSS SECTION OF M. BASILE ET AL., NC 3A, 371 (1971) YIELDS A BR(ETAPRIME --> 2GAMMA) OF 1.7 +- 0.4 PCT.
The reactions π−p→ n+(X0→total) and π−p→ n+(X0→neutrals) have been studied at 1.6 GeV/c with the Bologna-CERN neutron missing-mass spectrometer. Both reactions have been detected without the use of visual techniques. The results are: σ(X0→total)=(108±14) μb and σ(X0→neutrals)=(20.0±3.5) μb, giving a branching ratio Γ(X0→neutrals)/Γ(X0→total)=(18.5±2.2)%. The branching ratio for other possible, so far undetected, neutral decay modes of the X0 turns out to be (2.4±1.9)%.
No description provided.
Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q 2 from 1.0 to 25.0 (GeVc)2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q 2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q 2 are compared with the data.
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