The total cross section of γ rays in hydrogen resulting in hadron production, σT, has been measured over the energy range 265-4215 MeV. A tagging system with narrow energy bins was employed. Structure in the resonance region followed by a steady fall with energy has been observed and the results are analyzed. The forward amplitude of γ-proton scattering is evaluated, and its behavior in the Argand diagram studied as a function of energy. The relationships of the measurements to Regge-pole theory and the vector-dominance model are detailed.
No description provided.
SPIN AVERAGED FORWARD COMPTON SCATTERING AMPLITUDE. IM(AMP) WAS CALCULATED VIA THE OPTICAL THEOREM FROM A SMOOTH FIT TO THE DATA, AND USED IN THE DISPERSION RELATION TO CALCULATE RE(AMP). AT THRESHOLD THE THOMSON AMPLITUDE IS -3.0 MUB*GEV.
The total electromagnetic cross sections of g-rays in hydrogen and deuterium have been measured over the energy range 265–4215 MeV using a photon tagging system. From these measurements, the total pair production cross sections are obtained, and the results are found to be in good agreement with the predictions of Jost, Luttinger and Slotnick.
Axis error includes +- 1/1 contribution.
The total cross section for photoproduction of hadrons on the deutron, σ T d , has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.
RESONANCE REGION. UNSMEARING CORRECTION APPLIED, GLAUBER CORRECTION NEGLIGIBLE.
We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.
No description provided.
No description provided.
No description provided.
Results are presented on the exclusive production of four-prong final states in photon-photon collisions from the TPC/Two-Gamma detector at the SLAC e+e− storage ring PEP. Measurement of dE/dx and momentum in the time-projection chamber (TPC) provides identification of the final states 2π+2π−, K+K−π+π−, and 2K+2K−. For two quasireal incident photons, both the 2π+2π− and K+K−π+π− cross sections show a steep rise from threshold to a peak value, followed by a decrease at higher mass. Cross sections for the production of the final states ρ0ρ0, ρ0π+π−, and φπ+π− are presented, together with upper limits for φρ0, φφ, and K*0K¯ *0. The ρ0ρ0 contribution dominates the four-pion cross section at low masses, but falls to nearly zero above 2 GeV. Such behavior is inconsistent with expectations from vector dominance but can be accommodated by four-quark resonance models or by t-channel factorization. Angular distributions for the part of the data dominated by ρ0ρ0 final states are consistent with the production of JP=2+ or 0+ resonances but also with isotropic (nonresonant) production. When one of the virtual photons has mass (mγ2=-Q2≠0), the four-pion cross section is still dominated by ρ0ρ0 at low final-state masses Wγγ and by 2π+2π− at higher mass. Further, the dependence of the cross section on Q2 becomes increasingly flat as Wγγ increases.
TAGGED DATA, RESULTS OBTAINED USING TRANSVERSE-TRANSVERSE LUMINOSITY ONLY. DATA FOR Q2=0 ARE FROM UNTAGGED SAMPLE, ERRORS DUE TO RELATIVE NORMALISATION OF THESE SAMPLES IS INCLUDED INTO ERRORS QUOTED.
UNTAGGED DATA.
We report measurements of the two-photon processes e+e−→e+e−π+π− and e+e−→e+e−K+K−, at an e+e− center-of-mass energy of 29 GeV. In the π+π− data a high-statistics analysis of the f(1270) results in a γγ width Γ(γγ→f)=3.2±0.4 keV. The π+π− continuum below the f mass is well described by a QED Born approximation, whereas above the f mass it is consistent with a QCD-model calculation if a large contribution from the f is assumed. For the K+K− data we find agreement of the high-mass continuum with the QCD prediction; limits on f′(1520) and θ(1720) formation are presented.
Data read from graph. Additional overall systematic error 20% not included.
Data read from graph. Additional overall systematic error 20% not included.
We have identified 262 doubly tagged two-photon events. A subset of the data shows an enhancement of 21 events in the inclusive two-photon mass squared distribution between 0.8 and 2.2 GeV 2 . If these events result from spin 2 resonance production then Γ γγ = 9.5 ± 3.9 ± 2.4 keV (statistical and systematic). From another subset of 58 events in which the final state could be classified we determine the two-photon hadron to muon cross section ratio R γγ = 1.1 ± 0.3 ± 0.3.
ELECTRON BEAM ENERGIES OF 3.0 AND 3.6 GEV.
We present new high statistics data on hadron production in photon-photon reactions. The data are analyzed in terms of an electron-photon scattering formalism. The dependence of the total cross section of Q 2 , the four-momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector-Meson Dominance and the quark model.
DEPENDENCE ON VISIBLE HADRONIC INVARIANT MASS.
We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e + e − storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.
DEPENDENCE OF CROSS SECTION FOR ELECTRON-PHOTON SCATTERING (ANALOGOUS TO HAND'S FORMULA) ON VISIBLE HADRONIC ENERGY, CALCULATED BY TAKING PION MASSES FOR ALL CHARGED PARTICLES.
Approximately 700 events of the reaction K − d → K − π − pp s produced by 5.5 GeV/ c kaons were used to measure the cross section for Kπ elastic scattering in the T = 3 2 state by a Chew-Low extrapolation. The cross section does not exceed 2.1 mb and has no structure for Kπ masses from threshold up to 2.0 GeV.
Chew-Low extrapolation is used for evaluation of the K- P elastic cross section.