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.
Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ∼1.8 GeV couples to the ηN channel.
Cross sections for photon energies 0.775 to 0.925 GeV.
Cross sections for photon energies 0.975 to 1.125 GeV.
Cross sections for photon energies 1.175 to 1.325 GeV.
A precision measurement of absolute pi+p and pi-p elastic differential cross sections at incident pion laboratory kinetic energies from T_pi= 141.15 to 267.3 MeV is described. Data were obtained detecting the scattered pion and recoil proton in coincidence at 12 laboratory pion angles from 55 to 155 degrees for pi+p, and six angles from 60 to 155 degrees for pi-p. Single arm measurements were also obtained for pi+p energies up to 218.1 MeV, with the scattered pi+ detected at six angles from 20 to 70 degrees. A flat-walled, super-cooled liquid hydrogen target as well as solid CH2 targets were used. The data are characterized by small uncertainties, ~1-2% statistical and ~1-1.5% normalization. The reliability of the cross section results was ensured by carrying out the measurements under a variety of experimental conditions to identify and quantify the sources of instrumental uncertainty. Our lowest and highest energy data are consistent with overlapping results from TRIUMF and LAMPF. In general, the Virginia Polytechnic Institute SM95 partial wave analysis solution describes our data well, but the older Karlsruhe-Helsinki PWA solution KH80 does not.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and single arm pion detection. There is an additional systematic error of 1.1 PCT for PI+ beams which is not included in the errors shown in the table.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and two arm pion detection. There is an additional systematic error of 1.3 PCT for PI+ beams which is not included in the errors shown in the table.
Centre of mass absolute differential cross sections at pion kinetic energy 141.15 MeV using the liquid H2 target and two arm pion detection. There is an additional systematic error of 1.3 PCT (1.6 PCT) for PI+ (PI-) beams which is not included in the errors shown in the table.
A test of the QED process e+e- -> gamma gamma (gamma) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb^{-1}. The differential and total cross-sections for the process e+e- -> gamma gamma were measured, and found to be in agreement with the QED prediction. 95% Confidence Level (C.L.) lower limits on the QED cut-off parameters of Lambda+ > 330 GeV and Lambda- > 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c^2 (for lambda_gamma = 1) was obtained. s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M_S: M_S > 713 GeV/c^2 (lambda = 1) and M_S > 691 GeV/c^2 (lambda = -1).
No description provided.
No description provided.
No description provided.
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)).
The total and the differential cross-sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb −1 . The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z 0 energies) on the QED cutoff parameters are Λ + >253 GeV and Λ − >225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λ γ =1 is 231 GeV/ c 2 . All the limits are at the 95% confidence level.
The cross section of the previously published data (sqrt(s)=91.25 GeV, see PL 327B, 386) is given at the mean of the CM energies weighted by the luminosityat each point.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
Cross sections for inelastic scattering of 635 and 715 MeV/ c K + from 12 C are compared with DWIA calculations in order to check for possible density-dependent effects on K + -nucleon cross sections within nuclei. New fits to 715 MeV/ c K + scattering spectra from 6 Li give elastic and inelastic cross sections and permit an evaluation of the density dependence of these effects. The same DWIA methods are also used to estimate quadrupole non-central contributions to elastic K + scattering from the 1 + ground state of 6 Li, and these are found to be very small.
Axis error includes +- 0.0/0.0 contribution (?////NORMALIZATION UNCERTAINTIES ARE INCLUDED).
Axis error includes +- 0.0/0.0 contribution (?////NORMALIZATION UNCERTAINTIES ARE INCLUDED).
Axis error includes +- 0.0/0.0 contribution (?////NORMALIZATION UNCERTAINTIES ARE INCLUDED).
We have studied the process e+e− → 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−1 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+e− → 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.
Interest in the production of hyperon-antihyperon pairs following antiproton-proton annihilation stems largely from attempts to understand the nature of flavor production. To date the major focus of both the experimental and the theoretical effort has been on the p¯p→Λ¯Λ reaction. In this paper, we present data on the complementary channels p¯p→Σ¯0Λ and p¯p→Λ¯Σ0. Events from the kinematically similar p¯p→Λ¯Λ reaction were obtained in parallel. The procedure to distinguish these three separate reactions is described and results for all channels are presented. These include the total and differential cross sections, hyperon polarizations, and spin correlation coefficients. Data were obtained at incident antiproton lab momenta of 1.726 and 1.771 GeV/c which correspond to excess kinetic energies in the p¯p→Λ¯Σ0+c.c. reaction of 26 and 40 MeV, respectively, above threshold. Comparisons are made to earlier work at similar excess energies in the p¯p→Λ¯Λ channel. The low-energy regime has been highlighted in this experiment to reduce the complexity in the theoretical analysis. © 1996 The American Physical Society.
No description provided.
Axis error includes +- 2.3/2.3 contribution.
Axis error includes +- 2.3/2.3 contribution.
Total and differential cross sections for the process e + e − → γγ ( γ ), and the total cross section for the process e + e − → γγγ , are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron m e ∗ >146 GeV and on the QED cut-off parameters Λ + > 149 GeV and Λ _ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ , π ° and ηγ of 5.2 × 10 −5 , 5.2 × 10 −5 and 7.6 × 10 −5 respectively. The reactions e + e − → ℓ + ℓ − nγ (ℓ = e , μ , τ ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.
No description provided.
No description provided.
No description provided.
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