Differential cross sections for the reaction $\gamma p \to p \pi^0$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.675 to 2.875 GeV. The results reported here possess greater accuracy in the absolute normalization than previous measurements. They disagree with recent CB-ELSA measurements for the process at forward scattering angles. Agreement with the SAID and MAID fits is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been extended to 3 GeV. Resonance couplings have been extracted and compared to previous determinations.
Differential cross section for indicent photon energy 675 MeV.
Differential cross section for indicent photon energy 725 MeV.
Differential cross section for indicent photon energy 775 MeV.
The ep -> e'pi^+n reaction was studied in the first and second nucleon resonance regions in the 0.25 GeV^2 < Q^2 < 0.65 GeV^2 range using the CLAS detector at Thomas Jefferson National Accelerator Facility. For the first time the absolute cross sections were measured covering nearly the full angular range in the hadronic center-of-mass frame. The structure functions sigma_TL, sigma_TT and the linear combination sigma_T+epsilon*sigma_L were extracted by fitting the phi-dependence of the measured cross sections, and were compared to the MAID and Sato-Lee models.
Structure functions for Q**2 = 0.30 GeV**2 and W = 1.11 GeV.
Structure functions for Q**2 = 0.30 GeV**2 and W = 1.13 GeV.
Structure functions for Q**2 = 0.30 GeV**2 and W = 1.15 GeV.
Differential cross sections for the reaction gamma p -> eta-prime p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data indicate for the first time the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710) resonances, known to couple strongly to the eta N channel in photoproduction on the proton, and the importance of j=3/2 resonances in the process.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.527, 1.577 and 1.627 GeV. The errors shown are combined statistical and systematic.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.677, 1.728 and 1.779 GeV. The errors shown are combined statistical and systematic.
Differential cross sections for ETAPRIME photoproduction on the proton at photon energies 1.829, 1.879 and 1.930 GeV. The errors shown are combined statistical and systematic.
The differential cross section for the gamma +n --> pi- + p and the gamma + p --> pi+ n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The pi- and pi+ photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing pi+ data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV. The differential cross section ratios at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 5.614 GeV.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 4.236 GeV.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 3.400 GeV.
Nearly complete angular distributions of the two-body deuteron photodisintegration differential cross section have been measured using the CLAS detector and the tagged photon beam at JLab. The data cover photon energies between 0.5 and 3.0 GeV and center-of-mass proton scattering angles 10-160 degrees. The data show a persistent forward-backward angle asymmetry over the explored energy range, and are well-described by the non-perturbative Quark Gluon String Model.
Angular distributions of the photodisintegration cross section for angle between 10 and 50 degrees in the CM.
Angular distributions of the photodisintegration cross section for angle between 50 and 90 degrees in the CM.
Angular distributions of the photodisintegration cross section for angle between 90 and 130 degrees in the CM.
Electroproduction of the omega meson was investigated in the p(e,e'p)omega reaction. The measurement was performed at a 4-momentum transfer Q2 ~ 0.5 GeV2. Angular distributions of the virtual photon-proton center-of-momentum cross sections have been extracted over the full angular range. These distributions exhibit a strong enhancement over t-channel parity exchange processes in the backward direction. According to a newly developed electroproduction model, this enhancement provides significant evidence of resonance formation in the gamma* p -> omega p reaction channel.
Differential cross section for an average W of 1.75 GeV.
Differential cross section for an average W of 1.79 GeV.
The total and differential cross sections of the process e+e- -> n gamma with n >= 2 are measured using data collected by the L3 experiment at centre-of-mass energies of \sqrt{s}=183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.
Measured cross section.
Measured differential cross sections corrected for efficiency and additional photons as a function of cos(theta) where theta is the polar angle of the event defined as. cos(theta)=ABS((sin(theta1-theta2)/2)/(sin(theta1+theta2)/2)).
We have studied the process e<sup loc="post">+</sup>e<sup loc="post">−</sup> → nγ (n ≥ 2) at an average center-of-mass energy of 133 GeV using the L3 detector at LEP. For an integrated luminosity of 4.95 pb<sup loc="post">−1</sup> we find one γγγγ(γ) final state with only hard photons. The rates of both γγγ and γγ events are consistent with QED expectations. The cross section of the reaction e<sup loc="post">+</sup>e<sup loc="post">−</sup> → γγ(γ) in the polar range 16° < θγ < 164° is measured to be 22.6 ± 2.2 pb. Decays into photons of narrow scalar resonances with masses between 90 and 130 GeV are not observed. The observation of the event with four energetic photons is consistent with QED although the kinematic configuration of the photons is atypical.
Cross section for process E+ E- --> GAMMA GAMMA (GAMMA) with two hard photons.Error is purely statistical, systematic effects are neglected.
No description provided.
The total and the differential cross sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb −1 . The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ + > 143 GeV and Λ − > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λ γ = 1 is 132 GeV/ c 2 . Upper limits on the branching ratios for the decays Z 0 → γγ , Z 0 → π 0 γ , Z 0 → ηγ and Z 0 → γγγ have been determined to be 5.5 × 10 −5 , 5.5 × 10 −5 , 8.0 × 10 −5 , and 1.7 × 10 −5 respectively. All the limits are at the 95% confidence level.
1990 energies are 88.223, 89.222, 90.217, 91.217, 92.209, 93.208 and 94.202 GeV.. 1991 energies are 88.465, 89.460, 90.208, 91.225, 91.954, 92.953, and 93.703 GeV.. 1992 energy is 91.278 GeV.
Average of all data.
No description provided.
The differential cross section for the reaction H2(γ,p)n has been measured at several center-of-mass angles ranging from 50° to 143° for photon energies between 0.8 and 1.8 GeV. The experiment was performed at the SLAC-NPAS facility with the use of the 1.6 GeV/c spectrometer to detect the high energy protons produced by a bremsstrahlung beam directed at a liquid deuterium target. Contributions from concurrent disintegration by the residual electron beam were determined by measuring the proton yield without the Cu photon radiator. At angles not very far from 90°, the energy dependence of the cross sections is consistent with predictions of scaling using counting rules for constituent quarks. At least one theoretical calculation based on a meson-baryon picture of the reaction is able to reproduce the magnitude and energy dependence of the 90° cross section. The angular distribution exhibits a large enhancement at backward angles at the higher energies.
THE QUOTED ERRORS ARE STATISTICAL ONLY.
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