Measurement of Trilinear Gauge Couplings in e+e−e^+ e^- Collisions at 161 GeV and 172 GeV

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161~GeV and 172~GeV. Values for $WWV$ couplings ($V=Z, \gamma$) are determined from a study of the reactions \eeWW\ and \eeWev, using differential distributions from the $WW$ final state in which one $W$ decays hadronically and the other leptonically, and total cross-section data from other channels. Limits are also derived on neutral $ZV\gamma$ couplings from an analysis of the reaction \eegi

Search for neutral heavy leptons produced in ZZ decays

Weak isosinglet Neutral Heavy Leptons (νm) have been searched for using data collected by the DELPHI detector corresponding to 3.3 × 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived νm production giving monojet or acollinear jet topologies, and for long-lived νm giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 → νmν̄) of about 1.3 × 10-6 at 95% confidence level for νm masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the νm mass. The results are also interpreted in terms of limits for the single production of excited neutrinos. © Springer-Verlag 1997

Determination of vertical bar V-cb vertical bar from the semileptonic decay B-0->D*(-)l(+)nu

Semileptonic decays B --> D*(-)l(+)nu X were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*(-)pi(+) states was performed and the ratio of the branching fractions: Br(B --> D*(-)l(+)nu X)/Br(B --> D*(-)l(+)nu X) + Br(B-0 --> D*(-)l(+)nu) = 0.19 +/- 0.10(stat) +/- 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B-0 --> D*(-)l(+)nu was measured as a function of the momentum transfer from the B to the D*(-) in two separate analyses, using exclusive and inclusive methods of D*(-) reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of /V-cb/ times the normalization of the decay form factor F(q(max)(2)): F(q(max)(2))/V-cb/ = (35.4 +/- 1.9(stat) +/- 2.4(syst)) . 10(-3). The value of /V-cb/ was computed using theoretical calculations of F(q(max?2), giving: /V-cb/ = (38.9 +/- 2.0(stat) +/- 2.6(syst) +/- 1.7(theory)) . 10(-3). The total branching fraction Br(B-0 --> D*(-)l(-)nu) was determined to be: Br(B-0 --> D*(-)l(+)nu) = (5.52 +/- 0.17(stat) +/- 0.68(syst))%

MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING

Two measurements of Gamma(b ($) over bar b)/Gamma(had) are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, Gamma(b ($) over bar b)/Gamma(had) is found to be 0.2209 +/- 0.0041 (stat.) +/- 0.0042(syst.) +/- 0.0018 (Gamma(c ($) over bar c))

Observation of charge-ordering in particle production in hadronic Z(0) decay

Analysis of the rapidity structure of charge correlations in hadronic events from Z(0) decays gives evidence for chain-like charge-ordering of particle production along the thrust axis, as predicted by ‘QCD-motivated’ string-like fragmentation models. (C) 1997 Published by Elsevier Science B.V

Search for the Higgs boson in events with isolated photons at LEP 2

A search for the Higgs boson in final states with one, two or three isolated photons has been performed based on data taken at LEP 2 by the DELPHI detector. The data analysed correspond to a total integrated luminosity of 67.5 pb(-1) at centre-of-mass energies of 161 GeV (9.7 pb(-1)), 172 GeV (10.1 pb(-1)) and 183 GeV (47.7 pb(-1)). No evidence for the processes e(+)e(-) –> H gamma with H –> b (b) over bar or gamma gamma and e(+)e(-) –> Hq (q) over bar with H –> gamma gamma was observed. Model-independent limits on sigma(e(+)e(-) –> H gamma) x BR(H –> b (b) over bar), sigma(e(+)e(-) –> Hq (q) over bar) x BR(H –> gamma gamma) and sigma(e(+)e(-) –> H gamma) x BR(H –> gamma gamma) are set, as well as model-dependent limits on Higgs boson anomalous couplings to vector bosons. (C) 1999 Published by Elsevier Science B.V. All rights reserved

Measurement of the quark and gluon fragmentation functions in Z0 hadronic decays

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in e(+)e(-) collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse sigma(T) and longitudinal sigma(L) components of the total hadronic cross section sigma(tot) are evaluated from the measured fragmentation functions. They are found to be a sigma(T)/sigma(tot) = 0.949 +/- 0.001(stat.) +/- 0.007(syst.) and sigma(L)/sigma(tot) = 0.051 +/- 0.001(stat.) +/- 0.007(syst.) respectively. The strong coupling constant is calculated from sigma(L)/sigma(tot) in next-to-leading order of perturbative QCD, giving alpha(s)(M-Z) = 0.120 +/- 0.002(stat.) +/- 0.013(syst.) +/- 0.007(scale). Including non-perturbative power corrections :leads to alpha(s)(M-Z) = 0.101 +/- 0.002(stat.) +/- 0.013(syst.) +/- 0.007(scale). The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, [n(ch)] = 21.21 +/- 0.01(stat.)+/- 0.20(syst.) The fragmentation functions and multiplicities in bb and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated