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STATISTICAL ERRORS ONLY.
With an apparatus slightly improved with respect to a previous one we have studied multihadronic production at the Adone e + e − storage ring up to a maximum center of mass energy of 3 GeV.
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The results of an experiment performed at Adone, the 2×1.5-GeV e+e− Frascati storage ring, are presented. During ∼ 1500 hours of running time a total of 5164 electron-positron elastic scattering events (integrated luminosity L=3.5×1035 cm−2) and 605 noncoplanar events from the reaction e+e−→a±+b±+anything (effective integrated luminosity L=2.5×1035 cm−2) have been collected at c.m. energies ranging from 1.4 to 2.4 GeV. Over the energy range explored (1.4-2.4 GeV), corresponding to an average q2 ranging from 0.8 to 2.4 (GeV/c)2, the yield of wide-angle (60°<θ<120°) electron-positron elastic scattering events is found to be in good agreement with the predictions of quantum electrodynamics (QED) (R=σexpσQED=1.05±0.04). The noncoplanar events appear to be of a hadronic nature and are produced with a much higher cross section than predicted on the basis of ρ, ω, φ dominance at these energies. The total cross section for the reaction e+e−→a±b±+anything shows a rapid increase to ∼ 90 nb between 1.0 and 1.5 GeV and falls off slowly to ∼ 50 nb at 2.4 GeV. Cross sections for some of the channels contributing to this multihadron process (e+e−→π+π−π+π−, e+e−→π+π−π+π−+neutrals, e+e−→3π+3π−) have been determined and are reported.
DATA VALUES MEASURED FROM GRAPH IN JOURNAL.
VALUES OF R CALCULATED FROM TOTAL CROSS SECTION.
An optical spark-chamber counter experiment at Adone, the Italian colliding electron-positron ring, has succeeded in measuring the cross-section for the process e+e−→p\(\bar p\) near threshold (Ec.m.=2.1 GeV). The result isσ(e+e−→p\(\bar p\))=(0.91±0.22) nb.
ISOTROPIC ANGULAR DISTRIBUTION ASSUMED.
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THIS HADRON PAIR CROSS SECTION PROVIDES ONLY AN UPPER LIMIT TO THE PION FORM FACTOR ABOVE 1.5 GEV SINCE KAON PRODUCTION IS NOT DISTINGUISHED.
We have measured the total cross section for electron-positron annihilation into three or more hadrons, with at least two charged particles in the final state. The measurement was made at a center-of-mass energy of 4 GeV with a 2π−sr nonmagnetic detector. With 88 events detected, we obtain a model-independent lower limit on the hadron production cross section of 9.6 ± 1.4 nb; a calculation of detection efficiency based on invariant phase-space production of pions leads to a total cross section of 26 ± 6 nb. This cross section is 4.7 ± 1.1 times the theoretical total cross section for e+e−→μ+μ−. The average charged multiplicity is n¯=4.2±0.6.
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We have measured the cross section σ for electron - positron annihilation into three or more hadrons, with at least two charged particles in the final state, at 5 GeV center-of-mass energy. We find a model-independent lower limit of σ>9.1±1.0nb; assuming invariant phase-space production of pions, we calculate the detection efficiency of our detector to be (45 ± 11)%, yielding a cross section σ=21±5nb. The average charged hadron multiplicity is found to be n¯=4.3±0.6.
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The reactions e+e−→e+e− and e+e−→μ+μ− have been measured at center-of-mass energies 3.0, 3.8, and 4.8 GeV and production angles of 50°<θ<130° over all azimuthal angles. Agreement with quantum electrodynamics is excellent. New limits for cutoff parameters in quantum-electrodynamic-breakdown models are given.
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We have searched the mass region 3.2 to 5.9 GeV for evidence of narrow resonances in e+e−→hadrons. We find no evidence for any such resonances other than the ψ(3695) in this region with a sensitivity ranging from about 12 to 45% of the integrated cross section of the ψ(3695). The more stringent bounds apply to resonances of a few MeV width, while the looser bounds apply to resonances of up to 20 MeV width.
EXTREAMLY GOOD DATA, MUST BE ASCED FROM AUTHORS.
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