A. Taketani

Measurement of R and search for new heavy quarks in e+e- annihilation at 50 and 52 GeV centre-of-mass energies

Abstract The total cross section for the process of the e+e- annihilation into hadrons has been measured at the centre-of-mass energies of 50 GeV and 52 GeV and a search has been made for new heavy quarks. The ratios R = σ(e+e- → hadrons)/σpoint(e+e- → μ+μ-) obtained are 4.4±0.5 at 50 GeV and 4.7±0.3 at 52 GeV, respectively. An additional systematic uncertainty is 10%. From the event shape analysis we found no evidence for a new quark with charge 2 3 e .

Energy resolution of gas ionization chamber for high-energy heavy ions

The energy resolution is reported for high-energy heavy ions with energies of nearly 340 MeV/nucleon and was measured using a gas ionization chamber filled with a 90%Ar/10%CH4 gas mixture. We observed that the energy resolution is proportional to the inverse of the atomic number of incident ions and to the inverse-square-root of the gas thickness. These results are consistent with the Bethe–Bloch formula for the energy loss of charged particles and the Bohr expression for heavy ion energy straggling. In addition, the influence of high-energy δ-rays generated in the detector on the energy deposition is discussed.

Radiation damage of silicon junction detectors by neutron irradiation

Abstract We report measurements of radiation damage in silicon PIN detectors resulting from irradiation by reactor neutrons. The fast component of the neutron flux was measured to be 10 13 –10 14 cm −2 by a foil activation method. The damage was observed as an increase in the leakage current. The leakage current constant was evaluated to be 6.6 × 10 −17 A/cm. This value is a factor 2 smaller than those of other experiments on neutron damage, and a factor 2 larger than the damage caused by high-energy proton irradiation.

Determination of the QCD scale parameter ΛMS with QCD cascade on the basis of the next-to-leading logarithmic approximation

Abstract The relative production ratio of 3-jet events to the total number of hadronic events was studied in e+e− annihilations at centre-of-mass energies between 54 and 61.4 GeV. The QCD scale parameter has been determined to be Λ MS =254 −47 +55 ±56 MeV on the basis of a QCD cascade with the next-to-leading logarithmic approximation.

Measurement of the differential cross sections ofe+e−→γγ ande+e−→γγγ at\(\sqrt s = 55,56,56.5\) and 57 GeV and search for unstable photino pair production

AbstractDifferential cross sections fore+e−→γγ have been measured at center-of-mass energies of 55, 56, 56.5 and 57 GeV. The results are in good agreement with those predicted by QED. Possible deviations from QED are studied in terms of contact interactions, and the limits on compositeness scales are obtained. Using events with a gramma pair in the final state, a search is made for the pair production of unstable photons,

e^+ e^- \to \gamma \gamma

e^ + e^ - \to \tilde \gamma \tilde \gamma

e^+ e^- \to \gamma \gamma \gamma

. No candidate events were found and a new limit on the photino mass is obtained.

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AbstractDifferential cross sections fore+e−→γγ have been measured at center-of-mass energies of 55, 56, 56.5 and 57 GeV. The results are in good agreement with those predicted by QED. Possible deviations from QED are studied in terms of contact interactions, and the limits on compositeness scales are obtained. Using events with a gramma pair in the final state, a search is made for the pair production of unstable photons,