Prof Roman Walczak

Abstract:

Production of the ηc meson in e+e- quasireal two photon collisions has been looked for in three channels. The data were obtained from an integrated luminosity of 189 pb-1. An ηc signal is observed in two decay modes (Ks0K±π∓,π+π-π+π-) with a combined statistical significance of 3.5 standard deviations. Using the known ηc branching ratios to these channels and to K+K-π+π- the combined partial ηc width to γγ is Γγγ(ηc). The first error is statistical, and the second one includes the systematic and branching ratio errors. Calculated as an upper limit we obtain Γγγ(ηc) (95% C.L., including the systematic error). © 1989 Springer-Verlag.

Abstract:

Data accumulated by the TASSO detector across the whole range of energies spanned at PETRA, 12≤ s≤46.8 GeV, have been analysed in terms of cluster algorithms. Using parameters optimised at 35 GeV CM energy, three perturbative QCD+fragmentation models were compared with the data. The O(αs2) model gives too few 4,5- cluster events, implying that higher order QCD contributions are required to describe the data. The parton cascade model, incorporating many orders in perturbation theory, gives a better description of the rates of ≥ 4 clusters, but shows a lack of hard gluon emission by giving too few 3-, and too many 2-cluster events. When hard gluon emission is taken into account, by the cascade model incorporating the O(αs) matrix element, all cluster rates are reproduced well. All the models describe the trend of the evolution of the cluster rates between 〈 s〉 = 14 and 43.8 GeV. We find that the rate of 3-jet events seen in the data decreases as s increases in a manner consistent with the Q2 dependence of αs as predicted by QCD. © 1988.

Abstract:

Hadronic events from e+e--annihilations with a high energy isolated photon have been investigated at C.M. energies between 14 GeV and 44 GeV. A forward-backward asymmetry Aγ of the positively charged jet with respect to the incident positron direction has been found:Aγγ=-0.32±0.07, providing evidence for photon bremsstrahlung from quarks. The forward-backward asymmetry of all hadronic events at C.M. energies between 30 GeV and 36 GeV has been measured. The value, corrected for the limited polar angle acceptance of the detector, is:A=+0.021±0.005. © 1988 Springer-Verlag.