H. Randoll

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.

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.

Determination of the radiative widths of the η′ and A2 from two-photon exchange production

Abstract From the two-photon exchange processes e + e − → e + e − η (958) → e + e − ϱ 0 γ and e + e − → e + e − A 2 (1310) → e + e − π + π − π 0 observed using the CELLO detector at PETRA the radiative widths of the η and A 2 have been determined with the results: Γ γγ ( η ) = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γ γγ (A 2 ) = 0.59 ± 0.14[stat.] −0.08 +0.31 [syst.] keV.

Measurement of e+e− → e+e− and e+e− → λλ at energies up to 36.7 GeV

Abstract The differential cross sections of the reactions e + e − → e + e − and e + e − → λλ are measured at energies between 33.0 and 36.7 GeV. The results agree with the predictions of quantum electrodynamics. A comparison with the standard model of electroweak interaction yields sin 2 θ W = 0.25 ± 0.13.

Inclusive γ and π0 production ine+e− annihilation at 14, 22 and 34 GeV c.m. energy

We have measured the scale invariant inclusive photon and π0 cross sections atW=14, 22 and 34 GeV. A comparison with π± data shows no significant difference between neutral and charged pion production. Comparing the integrated cross sections in thex range 0.15<x<1.0 we observe a considerable decrease from 14 GeV to 34 GeV with a statistical significance of 1.5 standard deviations. This is compatible with the expectations for scaling violations from QCD.

Analysis of the energy weighted angular correlations in hadronice+e− annihilations at 22 and 34 GeV

Measurements of energy weighted angular correlations in electron positron annihilations at c.m. energies of 22 GeV and 34 GeV are presented.

Measurement of the reactione+e−→μ+μ− for\(14 \leqq \sqrt S \leqq 36.4\) GeV

AbstractThe reaction (e+e−→μ+μ−) has been measured betweenn