Chargino production at LEP 200

We study chargino production and decay in the energy region of LEP 200, exploring the relevant supersymmetry parameter space. We give numerical predictions for the cross sections and for the signaturesl ⁺+l ^?+p′, l+jet+p′, jet+jet+p′. New formulae are presented relating chargino masses and couplings to the supersymmetry parameters.     

Degenerate Higgs andZ Boson at LEP200

We investigate the problem of detecting the Higgs boson ifM _H ≈M _z at LEP200, the main problem being the large background fromZZ production. Since this background should be accurately calculable, we estimate that the existence of the Higgs can be established with about 3 fb^?1 of integrated luminosity. We also discuss how the signal can be improved if efficient tagging ofb quarks is available.     

QCD corrections to W pair production at LEP200

One-loop QCD corrections to hadronic W decay are calculated for arbitrary W polarizations. The results are applied to W pair production and decay at LEP200. We focus on the corrections to angular distributions with particular emphasis on azimuthal distributions and correlations. The relevance of our results to the experimental determination of possible non-standard triple gauge boson interactions is discussed.     

Signatures of virtual LSPs at TEVATRON

Relatively light sneutrinos which are experimentally allowed and are not theoretically disfavoured may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP))—the virtual LSPs (VLSPs). The lighter charginos which would be produced in pairs with reasonably large cross-sections at TEVATRON energies, decay dominantly into the hadronically quiet lepton+sneutrino (E _T ) modes with large branching ratios leading to interesting unlike sign dilepton events which are not swamped by the standard model background. The kinematical cuts required to eliminate the backgrounds from WW, Drell-Yan and τ pair production are discussed in detail. With 100pb ^?1 luminosity 10–35 background free events can be found in a large region of the SUSY parameter space.     

Production and decay of the Standard Model Higgs boson at LEP200

We collect and update theoretical predictions for the production rate and decay branching fractions of the Standard Model Higgs boson that will be relevant for the Higgs search at LEP200. We make full use of the present knowledge of radiative corrections. We estimate the systematics arising from theoretical and experimental uncertainties.     

Virtual LSPs at e+ e− colliders

Currently popular search strategies for supersymmetric particles may be significantly affected due to relatively light sneutrinos which decay dominantly into invisible channels. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP) ) — the virtual LSPs (VLSPs). A tree lavel calculation shows that if the sneutrino mass happens to be in the small but experimentally allowed range (m _≈ν ≈ 45–55 GeV), these particles together with neutralino pairs may contribute significantly to the missing energy in the process e⁺e^? → γ+ E at LEP-2 energies as an enhancement over the Standard Model or the conventional MSSM predictions. It is further shown that a much larger region of the parameter space can be scanned at a high luminosity e⁺e^? collider at 500 GeV like the proposed NLC machine. Moreover, at both LEP-2 and NLC this process may play a complementary role to direct chargino searches, which may fail due to a near mass degeneracy of the chargino and the sneutrino. Formulae for the cross sections taking into account full mixings of the charginos and the neutralinos are derived. The signal remains observable even in the context of more restricted models based onN=1 SUGRA with common scalar and gaugino masses. A preliminary study of the QED radiative corrections due to soft multiple photon emission as well as hard collinear bremsstrahlung indicates that these corrections play a crucial role in estimating the background.     

Two-photon interactions at LEP

Experimental results of investigation of two-photon interactions at LEP (CERN) are presented. Experimental conditions provided a possibility of investigation of the whole set of two-photon interactions from the production of lepton pairs in collisions of quasi-real photons to interactions of high-virtual photons.     

Limits on 3 boson vertex parameters from LEP200

LEP will be operating at cm energies above W pair threshold from 1996. The process e⁺e⁻ → W⁺W⁻ will provide a unique opportunity to test some important aspects of the Standard Model. The methodology of studying this process has been reviewed in this report. The study of the process will probe at the triple vector boson coupling. The sensitivity to anomalous coupling of W boson has been discussed in detail.     

Bottonium production at LEP

We investigate the production of Υ(³ S ₁) and η _b (¹ S ₀) with two gluons from Z decay. We find that at LEP luminosities experimental detection will hardly be feasible.     

Particle searches at LEP

This paper is based on two invited talks, one by G. Giacomelli and one by P. Giacomelli, at the 2nd Trieste Conference on Recent Developments in the Phenomenology of Particle Physics, Trieste, 19–23 October, 1992.     

B physics at LEP

The Z factory at LEP is like a mini B factory. About 20% of the time a Z decays to a pair of b flavoured hadrons. As a result, this has provided a major boost to B physics studies. The four sophisticated LEP detectors, with millions of Z events, have provided a variety of interesting results. Only a snapshot of the major developments can be covered in one review. We have considered the results related to coupling, in particular, the measurements of R_b=Γ_b/Γ_had the forward backward charge asymmetry. The b hadron properties, like inclusive and exclusive lifetime measurements are summarised briefly. Measurements of oscillation parameter as well as the evidence for time dependent evolution have been discussed. Studies of interesting decay modes have been mentioned.     

Techniques for the Calculation of Electroweak Radiative Corrections at the One-Loop Level and Results for W-physics at LEP 200

We review the techniques necessary for the calculation of virtual electroweak and soft photonic corrections at the one-loop level. In particular we describe renormalization, calculation of one-loop integrals and evaluation of one-loop Feynman amplitudes. We summarize many explicit results of general relevance. We give the Feynman rules and the explicit form of the counterterms of the electroweak standard model, we list analytical expressions for scalar one-loop integrals and reduction of tensor integrals, we present the decomposition of the invariant matrix element for processes with two external fermions and we give the analytic form of soft photonic corrections. These techniques are applied to physical processes with external W-bosons. We present the full set of analytical formulae and the corresponding numerical results for the decay width of the W-boson and the top quark. We discuss the cross section for the production of W-bosons in e⁺ e⁻ annihilation including all O(x) radiative corrections and finite width effects. Improved Born approximations for these processes are given.     

Tests of QCD at LEP

The four experiments, ALEPH, DELPHI, L3 and OPAL at LEP, have performed a large number of precise measurements to test Quantum Chromodynamics. The strong coupling constant has been measured with high precision:α _s (M_z) = 0.123±0.004. The coupling constant has been found to be independent of quark flavour. The running ofα _s has been demonstrated by the data. Second order QCD matrix element calculations have been tested from several measured distributions in 3-jet and 4-jet events. These distributions give evidence of the vector nature of the gluon and provide measurements of the QCD colour factors. The hadronic distributions are well reproduced by QCD Monte Carlo programs as well as by analytical calculations with soft gluon coherence effects.     

Heavy Higgs bosons at LEP

Production of a heavy Weinberg-Salam-type neutral Higgs boson at LEP energies is considered. We conclude that the Higgs is unlikely to be detected at LEP if its mass is greater than 150 GeV.     

Looking for the LEP at LEP. The excited neutrino scenario

It is suggested to use LEP for a systematic search of excited neutrinos. These are expected to be the lightest excited particles (LEPs) in models of substructure and therefore could be the first direct signal of compositeness in the fermionic sector. Their signatures and production are presented. It is shown how one can extract their masses and couplings or else set limits on these parameters in case of a negative search. A comparison with heavy sequential neutrinos and heavy neutrals emanating from theories of grand unification and supersymmetry is briefly made.     

b-tagging in DELPHI at LEP

The numbers of events suitable for the determination of the gluon distribution function f ^p _g (x,Q ²) in a proton at the LHC for various intervals of x and Q ² are estimated. The contributions of background events of different sources are studied and estimated in the considered intervals of x and Q ². The PYTHIA event generator was used to produce physical events for this analysis.Received: 17 June 2003, Revised: 8 July 2004, Published online: 24 August 2004N.B. Skachkov: Present address: Joliot-Curie 6, JINR, 141980, Dubna, Moscow region, Russia