A. Augustinus

Experimental study of the triple-gluon vertex

Abstract In four-jet events from e+e− →Z0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor Nc to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models ) ± 0.2 ( error in bias ) in agreement with the value 2.25 expected in QCD from Nc=3 and C F = 4 3 .

The forward ring imaging Cherenkov detector of DELPHI

The Forward Ring Imaging Cherenkov detector of the DELPHI experiment at LEP provides hadron identification at polar angles15° < θ < 35° and 145° < θ < 165°. Two radiator media, a layer of liquid C6F14 and a volume of gaseous C4F10, in combination provide coverage of momenta up to 40 GeV/c. A single array of photosensitive Time Projection Chambers registers the impact points of ultraviolet photons from both radiators. The design of the detector and of its readout system is described. First results obtained with a partly installed detector are reported.

Operation, optimisation, and performance of the DELPHI RICH detectors

The Ring Imaging Cherenkov detectors of DELPHI represent a large-scale particle identification system which covers almost the full angular acceptance of DELPHI. The combination of liquid and gas radiators (C4F10, C5F12, and C6F14) provides particle identification over the whole secondary particle momentum spectrum at LEP I and LEP II. Continuing optimisation on the hardware as well as on the online and offline software level have resulted in a stable operation of the complete detector system for more than five years at full physics performance.

A search for heavy stable and long-lived squarks and sleptons in

A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov D ...

e^{+}e^{-}

The forward-backward asymmetry of bottom quarks is measured with statistics of approximately 80 000 hadronic Z0 decays produced in e+e− collisions at a centre of mass energy of √s≈Mz. The tagging of b quark events has been performed using the semileptonic decay channel b→X+μ. Because the asymmetry depends on the weak coupling, this leads to a precise measurement of the electroweak mixing angle sin2θw. The experimental result is AFBb = 0.115±0.043(stat.)±0.013(syst.). After correcting the value for the B0B0 mixing this becomes AFBb=0.161±0.060(stat.)±0.021(syst.) corresponding to sin2θWMS=0.221±0.011(stat.)±0.004(syst.).

collisions at energies from 130 to 183 GeV

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector.These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 1/pb. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from

A measurement of the bb forward-backward asymmetry using the semileptonic decay into muons

134 GeV/c^2

Search for Leptoquarks and FCNC in e+e− annihilations at S(1/2) = 183-GeV

to

Search for composite and exotic fermions at LEP 2

171 GeV/c^2

Current achievements of the DELPHI ring imaging Cherenkov detector

for electromagnetic type couplings) and couplings of the leptoquark states.A search for top-charm flavour changing neutral currents(