Search for charged Higgs bosons in e+e− collisions at s=189 GeV

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.4 pb⁻¹. Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed events are consistent with the expectations from Standard Model background processes. A lower limit of 65.5 GeV on the charged Higgs mass is derived at 95% confidence level, independent of the decay branching ratio Br(H^±→τν).     

Search for charginos,neutralinos and gravitinos in e+e− interactions at s=183 GeV

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb⁻¹ recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c² higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M₂) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c² for tanβ≥ 1.     

Search for heavy isosinglet neutrinos in e+e− annihilation at 130

《Physics letters. [Part B]》1999,461(4):397-404

Production of η mesons in e+e− annihilations at √s=29 GeV

Data from e⁺e⁻ annihilations at 29 GeV have been used to measure the production cross section and fragmentation function of η mesons. The signal is observed in the η→γγ decay channel. The fragmentation for p_η>1.5 GeV/c agrees well with the prediction of the Lund model, whereas the prediction of the Webber model lies above the data. The mean multiplicity is measured to be 〈n_η〉=0.58±0.10 η mesons per hadronic event, of which 0.51 represents the direct production of η and η′ mesons in the fragmentation chain.     

Study of Z boson pair production in e+e− interactions at s=192–202 GeV

The cross section for the production of Z boson pairs is measured using the data collected by the L3 detector at LEP in 1999 in e⁺e⁻ collisions at centre-of-mass energies ranging from 192 GeV up to 202 GeV. Events in all the visible final states are selected, measuring the cross section of this process. The special case of final states containing b quarks is also investigated. All results are in agreement with the Standard Model predictions.     

Baryon pairs production ine + e − annihilation at\sqrt s = 2.4 GeV

Search for baryon pairs production ine ⁺ e ^? annihilation at \(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb^?1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe ⁺ e ^? annihilation into \(\Lambda \bar \Lambda \) and ofe ⁺ e ^?→ \(p\bar p\) at this energy are presented. First observation of a goode ⁺ e ^?→ \(n\bar n\) candidate is reported and upper limits are given fore ⁺ e ^?→ \(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and \(\Sigma ^0 \bar \Sigma ^0 \) .     

Production and fragmentation of the D10 meson in e+e− annihilations at √s=29 GeV

Neutral D¹ meson production in e⁺e⁻ annihilation at √s=29 GeV has been studied using the high resolution spectrometer. The decay of D¹⁰ into D⁰γ, where the D⁰ decays into K^−π+, has been observed. The production cross section in units of the point cross section is 0.63±0.22 for fractional energy Z⩾0.5. The fragmentation function is compared with that of the D¹⁺ meson measured in the same experiment.     

Study of scalar top quarks in the neutralino and chargino decay channel at a future e + e − linear collider

The scalar top discovery potential has been studied with a full-statistics background simulation for s = 500GeV and = 500fb^–1. The simulation is based on a fast and realistic simulation of a TESLA detector. The large simulated data sample allowed the application of an Iterative Discriminant Analysis (IDA) which led to a significantly higher sensitivity than in previous studies. The effects of beam polarization on signal efficiency and individual background channels are studied using separate optimization with the IDA for both polarization states. The beam polarization is very important to measure the scalar top mixing angle and to determine its mass. Simulating a 180 GeV scalar top at minimum production cross section, we obtain m = 1GeV and cos = 0.009 in the neutralino decay channel, and m = 0.5 GeV and cos = 0.004 in the chargino decay channel.     

Zinos and scalar muon production at e+e− colliders

Single scalar muon production is examined in detail which results in a final state particularly favourable for detection: two strongly acollinear muons plus large missing energy. Cross sections, missing energy and angular distributions are given. A strong dependence on the zino total width, common to all single production channel, is found.     

Searches for electroweak γ-Z-Z’ interference at the LEP2 e + e − collider

Indirect effects of the Z’ boson in the process e ⁺ e ^? → μ⁺μ^? as implemented at the LEP2 electron-positron collider are investigated in terms of new integrated observables σ^±. It is demonstrated that these observables furnish more definitive information about Z’-boson effects than the canonical observables σ_± and A _FB. It is established that the deviations Δσ^± induced by Z’ bosons show a specific energy dependence, which is determined primarily by the parameters of the Standard Model. This permits making unambiguous model-independent predictions. In particular, two points, $\sqrt {s_ + } \approx 78GeV$ and $\sqrt {s_ - } \approx 113GeV$ , are determined at which, respectively, σ₊ and σ_? vanish both in the Standard Model and in presence of the extra Z’ boson. These energy values can be of use in searches for phenomenological manifestations of alternative sources of new physics that are different from Z’.     

Direct photon production in proton-antiproton interactions at √s = 24.3 GeV

Direct photons have been studied in pp̄ interactions at √s = 24.3 GeV and in the transverse momentum (p_T) range 3–7 GeV/c(0.25 < x_T < 0.58). The experiment was performed using an internal H₂ cluster the target in the CERN pp̄ Collider. The measured invariant cross section is compared with recent theoretical predictions.     

Evidence for directp p interactions in the fragmentation channelp +α →p + pX at √s=88 GeV

We have investigated kinematical correlations between the outgoing beam proton and the proton emerging from the fragmentingα-particle inpα collisions at \(\sqrt {s_{p\alpha } } = 88GeV\) . Strong correlations are seen, indicating the dominance of quasi-elasticpp scattering in the fragmentation channelp+α→p+pX, for the ¦t¦ range 0.05–1.00 (GeV/c)². A Monte Carlo simulation of this process can explain the observed correlation spectra assuming an admixture of about 16% spectator protons.