S. Banerjee

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.

Topology of hadronic e+e− annihilation events at 22 and 34 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.

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.

τ Branching ratios and polarization limits in e+e− interaction at √s=34GeV

Abstract Results on the dominant decays of τ leptons produced in e + e − interactions at √ s =34 GeV are presented. We obtain the branching ratios BR( τ → ϱv )=0.228 ± 0.033, BR( τ → πv )=0.099 ± 0.021, BR( τ → e vv )=0.183 ± 0.031 , BR( τ → μvv )=0.176+- 0.033. From the laboratory momentum spectra of the observed decay products we determined the τ polarization asymmetry to (1 ± 22)% and thereby derive limits for the vector coupling constant υ τ of the τ to the weak neutral current. Tests on university and factorization are discussed.

Coupling strengths of weak neutral currents from leptonic final states at 22 and 34 GeV

AbstractDifferential cross sections fore+e−→e+e−, τ+, τ- measured with the CELLO detector at

Lepton pair production in deep inelastic e-γ scattering

\left\langle {\sqrt s } \right\rangle = 34.2GeV