A high statistics experiment was performed on Bhabha scattering at energies between 14 and 34 GeV. Good agreement with QED was observed. The combined data on Bhabha scattering and μ pair production were found to agree with the standard theory of electroweak interaction giving sin 2 θ = 0.27 −0.07 +0.06 . Assuming for the Z 0 mass a value of 90 GeV the leptonic weak coupling constants were determined to g V 2 = −0.04 ± 0.06 and g A 2 = 0.35 ± 0.09. A search for scalar leptons sets lower limits on the mass of scalar electrons of M s e > 16.6 GeV and of scalar muons of M s μ > 16.4 GeV.
No description provided.
No description provided.
Direct electrons are observed in baryon events produced in e+e− annihilation at center-of-mass energies above the ΛcΛ¯c threshold. These events are attributed to charmed-baryon pair production and subsequent Λc semileptonic decay. Various semileptonic branching ratios of the Λc are determined, including B(Λc→e+X)=(4.5±1.7)%.
ELECTRON-BARYON RATIO ABOVE AND BELOW LAMBDA/C THRESHOLD.
No description provided.
We have measured the electron, muon, and charged-hadron pair production rates in two-phonon interactions for invariant masses above 2.0 GeV over a large of momentum transfer. The cross sections for electron and muon pairs show good agreement with the QED predictions at both small and large momentum transfer. The observed rate of hadron production is less than 6% of the rate that QED predicts for point-like hadrons, consistent with recent leading-order QCD calculations.
LOW Q**2 CROSS SECTIONS.
DIFFERENTIAL CROSS SECTIONS IN THE INVARIANT MASS FOR MUON AND ELECTRON PAIRS IN THE UNTAGGED, LOW Q**2 REGION.
HIGH Q**2 CROSS SECTIONS.
The reaction e + e - → e + e - η' has been observed in the JADE experiment at PETRA, by detecting the final state π + π - γ, resulting from the decay η' → γϱ 0 . The cross section was measured at an average beam energy of 17.15 GeV to be σ(e + e - → e + e - η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ η'γγ = 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.
No description provided.
Inclusive e+e− production in 17-GeV/c π−p collisions has been measured. An excess of e+e− pairs over those from known sources for 0.1<~mee<~0.6 GeV and x<0.5 was found. No evidence is found for enhancements in specific final states involving electrons and photons or charged particles. The photon multiplicity associated with these pairs is measured.
No description provided.
We investigate the four-photon final state produced in γγ colissions. In the π 0 π 0 channel we observe f(1270) production with predominantly helicity 2 and measure a partial width Γ γγ 2.9 +0.6 −0.4 ± keV (independent of assumptions on the helicity). We observe A 2 (1310) production in the π 0 η channel and find a partial width Γ γγ = 0.77 ± 0.18 ± 0.27 KeV (assuming helicity 2). We give an upper limit for f ≈ ηη .
Data read from graph. Systematic error on M is of order of 2% or less.
Data read from graph.
No description provided.
Two-photon interactions have been studied with the SLAC-LBL Mark II magnetic detector at SPEAR. The cross section for η′ production by the reaction e+e−→e+e−η′ has been measured at beam energies from 2.0 to 3.7 GeV. The radiative width Γγγ(η′) has been determined to be 5.8±1.1 keV (±20% systematic uncertainty). Upper limits on the radiative widths of the f(1270), A2(1310), and f′(1515) tensor mesons have been determined. A search has been made for production of the E(1420) by γγ collisions, but no signal is observed.
No description provided.
NO SIGNAL ABOVE BACKGROUND SEEN. UPPER LIMITS AT 95 PCT CL GIVEN.
We have measured the inclusive cross section for η production in e+e− interactions near charm threshold using the Crystal Ball detector. No pronounced structure in the energy dependence is observed. By comparing cross sections above and below charm threshold we obtain the limits (90% confidence limit): R(e+e−→FF¯X)RB(F→ηx)<0.15−0.32 (for Ec.m. from 4.0 to 4.5 GeV), RB(D→ηx)<0.13. Our results are inconsistent with a previous report of a large energy dependence of the η cross section ascribed to the crossing of the FF* and F*F* production thresholds.
Axis error includes +- 0.0/0.0 contribution (?////DECAY PI0 --> 2GAMMA//RES-DEF(RES=ETA,BACK=CORRECTED,DEF=340 < M( 2GAMMA ) < 800 MEV)//DECAY-BR(BRN=ETA --> 2GAMMA,BR=38 PCT)).
THE 4.028 GEV DATA ARE NOT INCLUDED IN THE 4.005-4.082 GEV BIN. Axis error includes +- 0.0/0.0 contribution (?////DECAY PI0 --> 2GAMMA//RES-DEF(RES=ETA,BACK=CORRECTED,DEF=340 < M( 2GAMMA ) < 800 MEV)//DECAY-BR(BRN=ETA --> 2GAMMA,BR=38 PCT)).
AT FIXED ENERGIES.
We report a measurement of the cross section for the process γγ → π + π − at invariant masses 500 MeV/ c 2 < m ππ <2000 MeV/ c 2 . A value for the radiative width of the f(1270) tensor meson Γ f→ γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum.
DATA REQUESTED FROM AUTHORS.
The differential cross sections of the reactions e + e − → e + e − and e + e − → λλ are measured at energies between 33.0 and 36.7 GeV. The results agree with the predictions of quantum electrodynamics. A comparison with the standard model of electroweak interaction yields sin 2 θ W = 0.25 ± 0.13.
No description provided.
No description provided.