Rapidity and charge correlations of centrally produced charged particles in events with a high-momentum pi 0 near 11 degrees.

title: Design and performance of the readout electronics chain of the Delphi forward ring imaging Cherenkov detector
abstract: The front-end readout electronics chain of the forward ring imaging Cherenkov (FRICH) detector used at the Delphi experiment of the Large Electron-Positron collider (LEP) is presented. The system incorporates a wideband low-noise preamplifier, mounted in the proximity of the multiwire proportional chamber, an amplifying discriminating-multiplexing FASTBUS unit for further signal amplification, discrimination, and channel reduction, and a LEP time digitizer FASTBUS unit for time digitization. The authors give a general view of the detector and its electronics with particular emphasis on the novel characteristics and capabilities of the system.<<ETX>>

title: Kaon interference in the hadronic decays of the Z0
abstract: The first measurement of like-sign charged kaon correlations in hadronic decays of the Z0 is presented, based on data collected by the DELPHI detector. The charged kaons are identified by means of ring imaging Cherenkov detectors. A significant enhancement at small values of the four-momentum difference is observed in the ratio of like-sign to unlike-sign KK pairs and in the ratio of like-sign pairs to a simulated reference sample. An update of the measurement of Ks0Ks0 interference is also presented. An enhancement is found in the production of pairs of Ks0 of similar momenta, as compared with a simulated reference sample. The measured Bose-Einstein correlation parameters λ and r are similar for charged and neutral kaon pairs. The value of the Bose-Einstein correlation strength λ is consistent with unity.

title: Study of hadronic decays of the Z0 boson
abstract: Hadronic decays of Z 0 bosons are studied in the Delphi detector. Global event variables and singel particles inclusive distributions are compared with QCD-based predictions. The mean charged multiplicity is found to be 20.6±1.0 (stat+syst). The mean values of the sphericity, aplanarity, thrust, minor value, p in T and p out T are compared with values found at lower energy e + e − colliders.

title: Study of orientation of three-jet events in Z0 hadronic decays using the DELPHI detector
abstract: The study of the orientation of three-jet events from e + e − → Z 0 → multi-hadrons is presented, in particular the polar angle distributions of the thrust axis and of the normal to the three-jet plane, and the azimuthal correlations between the hadron plane and the one defined by the beam and thrust axes. The data are compared with results at lower energy and with QCD predictions. Good agreement with QCD predictions is observed. The scalar gluon theory is excluded by the data.

title: Measurement of the W pair cross-section and of the W mass in e+ e- interactions at 172-GeV
abstract: From a data sample of \(9.98 {\mathrm{ pb^{-1}}}\) integrated luminosity, collected by DELPHI at a centre-of-mass energy of 172 GeV, 118 events were selected as W-pair candidates. From these, the branching fraction \({\mathrm Br}({\mathrm W} \rightarrow{\mathrm q}\bar{\mathrm q})\) was measured to be \(0.660^{+0.036}_{-0.037} (\mathrm{stat.}) \pm 0.009 (\mathrm{syst.})\) and the cross-section for the doubly resonant process \(\mat hrm{e^+ e^- \rightarrow W^+ W^-}\) to be \(11.58^{+1.44}_{-1.35} (\mathrm{stat.}) \pm 0.32 (\mathrm{syst.})\) pb. The mass of the W boson, obtained from direct reconstruction of the invariant mass of the fermion pairs in the decays \(\mathrm{ WW \rightarrow \ell\nu q \bar{q}}\) and \(\mathrm{ WW \rightarrow q\bar{q}q\bar{q}}\), was determined to be \(m_{\mathrm W} = \: 80.22 \: \pm \: 0.41 (\mathrm{stat.}) \: \pm 0.04 (\mathrm{syst.}) \: \p m 0.05 (\mathrm{int.}) \: \pm 0.03 (\mathrm{LEP})\: \mathrm{GeV}/c^2\), where “int.” denotes the uncertainty from interconnection effects like colour reconnection and Bose-Einstein interference. Combined with the W mass obtained from the cross-sections measured by DELPHI at threshold, a value of \(m_{\mathrm W} = \: 80.33 \: \pm \: 0.30 (\mathrm{stat.}) \: \pm 0.05 ({\mathrm{syst.}}) \: \pm \: 0.03 (\mathrm{int.}) \: \pm \: 0.03 (\mathrm{LEP}) \: \mathrm{GeV}/c^2\) was found.

title: Ghost poles in the nucleon propagator: Vertex corrections and form factors.
abstract: Vertex corrections are taken into account in the Schwinger-Dyson equation for the nucleon propagator in a relativistic field theory of fermions and mesons. The usual Hartree-Fock approximation for the nucleon propagator is known to produce the appearance of complex (ghost) poles which violate basic theorems of quantum field theory. In a theory with vector mesons there are vertex corrections that produce a strongly damped vertex function in the ultraviolet. One set of such corrections is known as the Sudakov form factor in quantum electrodynamics. When the Sudakov form factor generated by massive neutral vector mesons is included in the Hartree-Fock approximation to the Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear and consistency with basic requirements of quantum field theory is recovered.

title: QCD sum rules for Sigma hyperons in nuclear matter.
abstract: Within the finite-density QCD sum-rule approach we investigate the self-energies of [Sigma] hyperons propagating in nuclear matter from a correlator of [Sigma] interpolating fields evaluated in the nuclear matter ground state. We find that the Lorentz vector self-energy of the [Sigma] is similar to the nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the [Sigma] is also close to the corresponding value for nucleon; however, this prediction is sensitive to the strangeness content of the nucleon and to the assumed density dependence of certain four-quark condensate. The scalar and vector self-energies tend to cancel, but not completely. The implications for the couplings of [Sigma] to the scalar and vector mesons in nuclear matter and for the [Sigma] spin-orbit force in a finite nucleus are discussed.