A. Gaidot

Cello-A New Detector at PETRA

A description of the design characteristics of CELLO, a large 4Π magnetic detector at PETRA, is given and first results of beam operation are presented.

Scalar lepton search with the CELLO detector at PETRA

Abstract We report on the search for “supersymmetric” scalar leptons conducted with the CELLO detector, at the PETRA e + e − storage ring. 11.1 pb −1 of high energy data were analysed ( 33 GeV s GeV ). At a 95% c.l., the existence of a scalar e is ruled out for masses between 2 GeV and 16.8 GeV; correspondingly, a scalar μ is excluded between 3.3 GeV and 16 GeV, and a scalar τ between 6 GeV and 15.3 GeV, as well as between the τ mass and 3.8 GeV.

Investigation of two photon final states in e+e− annihilation at <√s⪢ = 34.2 GeV

Abstract Two photon final states in e + e − annihilation have been analyzed at CM energies around 34 GeV. Good agreement with QED is observed. Lower limits for the QED cutoff parameters of Λ + > 59 GeV and Λ - > 44 GeV are determined. A search for two photons with missing energy yields an upper limit for the production of neutral particles which decay into a photon and a non-interacting particle. Constraints on the mass and the coupling strength of supersymmetric photinos are discussed.

Measurement of e+e−→τ+τ− at high energy and properties of the τ lepton

Abstract The e+e−→τ+τ− process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields Rτ=1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos2θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling aτ of the τ to the weak neutral current given by aτ=−1.12 ± 0.57.

Search for new heavy quarks in

Abstract The total e + e − annihilation onto hadron has been measured at CM energies between 33.00 and 36.72 GeV and between 38.66 and 46.78 GeV in steps of 20 and 30 MeV respectively. The average of the ratio R = σ ( e + e − → hadrons )/ σ is 〈 R 〉=3.85±0.12 and 〈 R 〉=4.04±0.10 for the two energy ranges. The systematic error on 〈 R 〉 is 0.31. Both values are consistent with the expectation for the known coloured quarks u, d, s, c and b. No evidence was found for the production of new quarks. If the largest fluctuation in R is interpreted as a narrow resonance, it corresponds to a product of the electronic width and the hadronic branching ratio Γ ee B had >2.9 keV at the 95% confidence level, well below the value expected for the toponium vector ground state with charge 2 3 e . The observed number of aplanar final states rules out the continuum production of a a new heavy flavour with pointlike cross section up to a CM energy of 45.4 GeV for a quarck charge of 1 3 e . and up to 46.6 GeV for 2 3 e at the 95% confidence level.

e^+e^-

Abstract Hadronic events obtained with the CELLO detector at PETRA are compared with second order QCD predictions using different models for the fragmentation of quarks and gluons into hadrons. We find that the model dependence in the determination of the strong coupling constant persists when going from first to second order QCD calculations.

collisions up to 46.78 GeV cm energy

Abstract The topology of hadronic e + e − annihilation events has been analysed using the sphericity tensor and a cluster method. Comparison with quark models including gluon bremsstrahlung yields good agreement with the data. The strong-coupling constant is determined in 1st order QCD to be α S =0.19±0.04 (stat) ± 0.04 (syst.) at 22 GeV and α S =0.16 ±0.02± 0.03 at 34 GeV. The differential cross section with respect to the energy fraction carried by the most energetic parton agrees with the prediction of QCD, but cannot be reproduced by a scalar gluon model. These results are stable against variations of the transverse momentum distribution of the fragmentation function within the quoted errors.

On the model dependence of the determination of the strong coupling constant in second order QCD from e+e−-annihilation into hadrons

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.

Topology of hadronic e+e− annihilation events at 22 and 34 GeV CM energy☆

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.

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

AbstractThe production of prompt leptons at PETRA has been measured for c.m. energies of 14, 22 and 34 GeV. The rate of prompt electrons and muons is presented, including a determination of the semileptonic branching ratio of thec andb quarks. We obtainn