H. Mueller

Observation of a multiparticle event with two isolated energetic muons in e+e- interactions

Abstract An event from e+e− annihilation at √s = 43.450 GeV containing two topologically isolated energetic muons and two hadronic jets has been observed. The masses of the μ−μ, jet-jet and μ-jet combinations are all large. The expected number of such events from known processes is about 10−3.

The influence of fragmentation models on the determination of the strong coupling constant in e+e− annihilation into hadrons

Abstract Hadronic events obtained with the CELLO detector at PETRA were compared with first-order QCD predictions using two different models for the fragmentation of quarks and gluons, the Hoyer model and the Lund model. Both models are in reasonable agreement with the data, although they do not completely reproduce the details of many distributions. Several methods have been applied to determine the strong coupling constant α S . Although within one model the value of α S varies by 20% among the different methods, the values determined using the Lund model are 30% or more larger (depending on the method used) than the values determined with the Hoyer model. Our results using the Hoyer model are in agreement with previous results based on this approach.

Limits on spin 0 bosons in

Abstract We have studied the reactions e + e − → e + e − , e + e − → γγ , e + e − → μ + μ − , and e + e − → τ + τ − in the centre-of-mass (CM) energy range from 39.8 to 45.2 GeV using the CELLO detector at PETRA. Upper limits on the partial widths for new spin 0 bosons with masses both within and above the energy range covered are determined. No evidence for contributions of such new particles has been observed up to the highest PETRA energies in a model independent way. Under the assumptions of recently suggested models relating the existence of spin 0 bosons to the radiative width Γ τ of the Z 0 we exclude such bosons at the 95% confidence level for masses below the Z 0 -mass if Γ τ > 20 MeV.

e^+e^-

Abstract We have searched for monojet production in e + e − -annihilation with the CELLO detector operating at the highest PETRA energies. No events were found, which makes it unlikely that the recently observed monojets in p p collisions originate from unusual Z 0 decays. The upper limits on monojet cross sections are compared with various models, thus yielding upper limits on the production cross sections of Higgs bosons and higgsinos.

annihilation up to 45.2 GeV cm energy

Abstract The reactions e + e − → μ + μ − γ and e + e − →e + e − γ have been studied with the CELLO detector at the PETRA storage ring. Data have been collected from s =14 GeV up to 46.8 GeV . In a Dalitz plot analysis of the data, good agreement is found with QED, except for the region Mx μγ e>0.8 where the probability that QED describes the high energy data is at the percent level.