46520640
Comparison of low-PT photon production in high- and low-multiplicity collisions at the CERN ISR.
Low-transverse-momentum photon production at the CERN ISR is compared in high- and low-multiplicity events. High-transverse-energy pp collisions and low-multiplicity ..cap alpha cap alpha.. and pp collisions are studied. Relative photon-to-charged-track production is found to be the same in pp minimum bias, ..cap alpha cap alpha.. minimum bias, and pp high-transverse-energy collisions, to within 15%. No low-P/sub T/ excess is seen; the limits are dominated by systematic uncertainties.
27391246
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.
117725799
Kaon interference in the hadronic decays of the Z0
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.
119911764
Measurement of the W pair cross-section and of the W mass in e+ e- interactions at 172-GeV
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.
33520649
Design and performance of the readout electronics chain of the Delphi forward ring imaging Cherenkov detector
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>>
120128691
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.
44544605
Casimir energy for a piecewise uniform string.
The Casimir energy for the transverse oscillations of a piecewise uniform closed string is calculated. The string consists of two parts I and II, endowed in general with different tensions and mass densities, although adjusted in such a way that the velocity of sound always equals the velocity of light. The dispersion equation is worked out under general conditions and the frequency spectrum is determined in special cases. When the ratio {ital L}{sub II}/L{sub I} between the string lengths is an integer, it is in principle possible to determine the frequency spectrum through solving algebraic equations of increasingly high degree. The Casimir energy relative to the uniform string is in general found to be negative, although in the special case {ital L}{sub I}=L{sub II} the energy is equal to zero. Delicate points in the regularization procedure are discussed; in particular, it turns out that a straightforward use of the Riemann {zeta}-function regularization method leads to an incorrect expression for the Casimir energy.
12483632
Casimir energy for a three-piece relativistic string.
The Casimir energy for the transverse oscillations of a piecewise uniform closed string is calculated. The string consists of three pieces I, II, III of equal length, endowed with different tensions and mass densities, but adjusted in such a way that the velocity of sound always equals the velocity of light. In this sense the string forms a relativistic mechanical system. In the present paper the string is subjected to the following analysis: the dispersion function is derived and the zero-point energy is regularized using (i) a contour integration technique, being most convenient for the generalization of the theory to the case of finite temperatures, and (ii) the Hurwitz {zeta}-function technique, being usually the most compact method when the purpose is to calculate the Casimir energy numerically at {ital T}=0. The energy, being always nonpositive, is shown graphically in some cases as functions of the tension ratios I/II and II/III. The generalization to finite temperature theory is also given. {copyright} {ital 1996 The American Physical Society.}