R. Clare

We report the analysis of the spatial energy distribution of data for ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadrons}$ obtained with the MARK-J detector at PETRA. We define the quantity "oblateness" to describe the flat shape of the energy configuration and the three-jet structure which is unambiguously observed for the first time. Our data can be explained by quantum chromodynamic predictions for the production of quark-antiquark pairs accompanied by hard noncollinear gluons.

The application of hydrodynamics to the study of heavy ion collisions is presented with emphasis on the relativistic regime. Current theoretical and experimental knowledge of the nuclear equations of state along with the possible roles played by viscosity, single- and double-shock waves and solitons during the collision are examined. Constraints imposed by relativity on the equation of state and numerical results from one- and three-dimensional one-fluid relativistic calculations are reviewed. Also considered are sources of entropy production arising from irreversible processes. Some alterations and additions to the basic equations of relativistic hydrodynamics are proposed to describe phenomena associated with relativistic heavy ion collisions. The equations of relativistic chromohydrodynamics are reviewed as a possible framework in which to consider the nuclear to quark-gluon phase transition. Transparency is introduced by a two-fluid model; results for center-of-mass bombarding energies up to 20 GeV per nucleon are presented. Recent work on pion production, the entropy problem and global analysis are reviewed.

We report the results of first physics runs of the L3 detector at LEP. Based on 2538 hadron events, we determined the mass mz0 and the width Γz0 of the intermediate vector boson Z0 to be mz0=91.132±0.057 GeV (not including the 46 MeV LEP machine energy uncertainty) and Γz0=2.588±0.137 GeV. We also determined Γinvisible=0.567±0.080 GeV, corresponding to 3.42±0.48 number of neutrino flavors. We also measured the muon pair cross section and determined the branching ratio Γμμ=Γh=0.056±0.006. The partial width of Z0→e+e− is Γee=88±9±7 MeV.

The reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ has been analyzed using 97 ${\mathrm{pb}}^{\ensuremath{-}1}$ of data taken with the Crystal Ball detector at the DESY ${e}^{\ensuremath{-}}{e}^{+}$ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ for ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ mvariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for $W={m}_{{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}}<0.8$ GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction based on an unitarized Born-term model. At higher invariant masses we observe formation of the ${f}_{2}(1270)$ resonance and a hint of the ${f}_{0}(975)$. We deduce the following two-photon widths: ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({f}_{2}(1270))=3.19\ifmmode\pm\else\textpm\fi{}{0.16\ifmmode\pm\else\textpm\fi{}}_{0.28}^{0.29}$ keV and ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({f}_{0}(975))<0.53$ keV at 90% C.L. The decay-angular distributions show the ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ system to be dominantly spin 0 for $W<0.7$ GeV and spin 2, helicity 2 in the ${f}_{2}(1270)$ region, with helicity 0 contributing at most 22% (90% C.L.).

We discuss a simple magnetic spectrometer to be installed on a satellite or space station. The purpose of this spectrometer is to search for primordial antimatter to the level of antimatter/matter ≈10−9, improving the existing limits obtained with balloon flights by a factor of 104 to 105. The design of the spectrometer is based on an iron-free, NdFeB permanent magnet, scintillation counters, drift tubes, and silicon or time projection chambers. Different design options are discussed. Typically, the spectrometer has a weight of about 2 tons and an acceptance of about 1.0 m2 sr. The availability of the new NdFeB material makes it possible for the first time to put a magnet into space economically and reliably.

A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set.

Single- and multi-photon events with missing energy are selected in 619 pb−1 of data collected by the L3 detector at LEP at centre-of-mass energies between 189 and 209 GeV. The cross sections of the process e+e−→νν̄γ(γ) are found to be in agreement with the Standard Model expectations, and the number of light neutrino species is determined, including lower energy data, to be Nν=2.98±0.05±0.04. Selection results are given in the form of tables which can be used to test future models involving single- and multi-photon signatures at LEP. These final states are also predicted by models with large extra dimensions and by several supersymmetric models. No evidence for such models is found. Among others, lower limits between 1.5 and 0.65 TeV are set, at 95% confidence level, on the new scale of gravity for the number of extra dimensions between 2 and 6.

In this Report, QCD results obtained from a study of hadronic event structure in high energy e+e- interactions with the L3 detector are presented. The operation of the LEP collider at many different collision energies from 91 to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, αs, from hadronic event shapes and the study of effects of soft gluon coherence in charged particle multiplicity and momentum distributions.

The absolute muon flux between 20 GeV and 3000 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 degree to 58 degree. Due to the large exposure of about 150 m2 sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3 % at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 GeV and 500 GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003 (stat.) +- 0.019 (syst.).

Scalar partners of quarks and leptons, predicted in supersymmetric models, are searched for in e^+e^- collisions at centre-of-mass energies between 192GeV and 209GeV at LEP. No evidence for any such particle is found in a data sample of 450 pb^-1. Upper limits on their production cross sections are set and lower limits on their masses are derived in the framework of the Minimal Supersymmetric Standard Model.

We search for neutral heavy leptons that are isosinglets under the standard SU (2)L gauge group. Such neutral heavy leptons are expected in many extensions of the standard model. Three types of heavy leptons Ne, Nμ, Nτ associated with the three neutrino types ve, vμ, vτ have been directly searched for and no evidence for a signal has been found. We set the limit Br(NSu0 → vℓNℓ) < 3 x 10−5 at the 95% CL for mass range from 3 GeV up to Mz.

We present a study of jet multiplicities based on 37 000 hadronic Z0 boson decays. From this data we determine the strong coupling constant αs=0.115±0.005 (exp.)−0.010+0.012 (theor.) to second order QCD at √s=91.22GeV.

We present a study of the inclusive production of neutral pions and charged particles from 112 000 hadronic Z0 decays. The measured inclusive momentum distributions can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results to e+e− data between √s = 9 and 91 GeV, we findfind that the evolution of the spectra with center of mass energy is consistent with the QCD predictions.

Measurements of the reactions ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}+{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{+}+{\ensuremath{\mu}}^{\ensuremath{-}}$, and ${\ensuremath{\tau}}^{+}+{\ensuremath{\tau}}^{\ensuremath{-}}$ at PETRA energies (${s}^{\frac{1}{2}}=13,17,27.4,30 \mathrm{and} 31.6$ GeV) are reported. The results show that these reactions agree well with the predictions of quantum electrodynamics thus determining that all the known charged leptons are pointlike particles to a distance \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ cm.

This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).

The formation of the η′ in the reaction e+e−→e+e−η′→e+e−π+π−γ has been measured by the L3 detector at a centre-of-mass energy of 91GeV. The radiative width of the η′ has been found to be Γγγ=4.17±0.10(stat.)±0.27(sys.)keV. The Q2 dependence of the η′ formation cross section has been measured for Q2≤10GeV2 and the η′ electromagnetic transition form factor has been determined. The form factor can be parametrised by a pole form with Λ=0.900±0.046(stat.)±0.022(sys.)GeV. It is also consistent with recent non-perturbative QCD calculations.

The structure of hadronic events fromZ 0 decay is studied by measuring event shape variables, factorial moments, and the energy flow distribution. The distributions, after correction for detector effects and initial and final state radiation, are compared with the predictions of different QCD Monte Carlo programs with optimized parameter values. These Monte Carlo programs use either the second order matrix element or the parton shower evolution for the perturbative QCD calculations and use the string, the cluster, or the independent fragmentation model for hadronization. Both parton shower andO(α 2 s matrix element based models with string fragmentation describe the data well. The predictions of the model based on parton shower and cluster fragmentation are also in good agreement with the data. The model with independent fragmentation gives a poor description of the energy flow distribution. The predicted energy evolutions for the mean values of thrust, sphericity, aplanarity, and charge multiplicity are compared with the data measured at different center-of-mass energies. The parton shower based models with string or cluster fragmentation are found to describe the energy dependences well while the model based on theO(α 2 s calculation fails to reproduce the energy dependences of these mean values.

We have measured the decay properties of Z0 → bb from a study of inclusive muon and electron events. The average (e and μ) b-quark semileptonic branching ratio has been determined to be BR (b → ℓ + X) = 0.119 ± 0.003 (stat.) ± 0.006 (syst.), assuming the standard model prediction of Γbb = 378 ± 3 MeV. From the ratio of the number of dilepton events to single lepton events, we find BR (b → ℓ + X) = 0.113 ± 0.010 (stat.) ± 0.006 (syst.), without assumptions on Λbb. The partial decay width of the Z0 into bb has been measured to be Λbb = 385 ± 7 (stat.) ± 11 (syst.) MeV with an additional 19 MeV error from the uncertainty in BR (b → ℓ + X). The average fractional energy of bottom hadrons in Z0 → bb events has been determined to be 〈xE〉 = 0.686 ± 0.006 (stat.) ± 0.016 (syst.).

We have made a precise measurement of the cross section for e+e−→Z0→hadrons with the L3 detector at LEP, covering the s range from 88.28 to 95.04 GeV. From a fit to the Z0 mass, total width, and the hadronic cross section to be MZ0=91.160 ± 0.024 (experiment) ±0.030(LEP) GeV, ΓZ0=2.539±0.054 GeV, and σh(MZ0)=29.5±0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine Γinvisible=0.548±0.029 GeV, which corresponds to 3.29±0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4σ confidence level.

We have searched for scalar muons μ, scalar electrons ẽ, and winos W̃ from the reactions e+e− →ẽ+ẽ−, μ+μ−, W̃+W̃− at √s ∼ 91 GeV with an integrated luminosity of 157 nb −1. We have searched for μ+μ−, e+e−, or e−μ final states with missing transverse momentum PT > 6 GeV. These final states are signatures for the production of ẽ, μ, and W̃. We found no events. Our results are Mμ > 41 GeV, Mẽ > 41 GeV, and MW̃ > 44 GeV at the 95% confidence level.

Single top production in e+e- annihilations is searched for in data collected by the L3 detector at centre-of-mass energies from 189 to 209 GeV, corresponding to a total integrated luminosity of 634 pb-1. Investigating hadronic and semileptonic top decays, no evidence of single top production at LEP is obtained and upper limits on the single top cross section as a function of the centre-of-mass energy are derived. Limits on possible anomalous couplings, as well as on the scale of contact interactions responsible for single top production are determined.

We have studied the reactionse + e −→hadrons,e + e −, μ+ μ− and τ+ τ−, in the energy range 88.2 $$ \leqq \sqrt s \leqq 94.2$$ GeV. A total luminosity of 5.5 pb−1, corresponding to approximately 115000 hadronic and 10000 leptonicZ 0 decays, has been recorded with the L3 detector. From a simultaneous fit to all of our measured cross section data, we obtain assuming lepton universality: $$\begin{gathered} M_z = 91.181 \pm 0.010 \pm 0.02 (LEP) GeV, \hfill \\ \Gamma _z = 2501 \pm 17 MeV, \hfill \\ \Gamma _{had} = 1742 \pm 19 MeV, \Gamma _t = 83.6 \pm 0.8 MeV. \hfill \\ \end{gathered}$$ If we do not assume lepton universality, we obtain for the partial decay widths of theZ 0 intoe + e − μ+ μ− and τ+ τ−: $$\begin{gathered} \Gamma _e = 83.3 \pm 1.1 MeV, \Gamma _\mu = 84.5 \pm 2.0 MeV, \hfill \\ \Gamma _\tau = 84.0 \pm 2.7 MeV. \hfill \\ \end{gathered}$$ From the measured ratio of the invisible and the leptonic decay widths of theZ 0, we determine the number of light neutrino species to beN v =3.05±0.10. We include our measurements of the forward-backward asymmetry for the leptonic channels in a fit to determine the vector and axial-vector neutral current coupling constants of charged leptons to theZ 0. We obtain $$\bar g_V = - 0.046_{ - 0.012}^{ + 0.015}$$ and $$\bar g_A = - 0.500 \pm 0.003$$ . In the framework of the Standard Model, we estimate the top quark mass to bem t =193 −69 +52 ±16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin2θ W =1−(M W /M Z )2=0.222 ± 0.008, corresponding to an effective weak mixing angle of $$\sin ^2 \bar \theta _W = 0.2315 \pm 0.0025$$ .

We present a study of the global event shape variables thrust and heavy jet mass, of energy-energy correlations and of jet multiplicities based on 250 000 hadronic Z0 decays. The data are compared to new QCD calculations including resummation of leading and next-to-leading logarithms to all orders. We determine the strong coupling constant αs (91.2 GeV) = 0.125±0.003 (exp) ± 0.008 (theor). The first error is the experimental uncertainty. The second error is due to hadronization uncertainties and approximations in the calculations of the higher order corrections.

We report the measurement of the reaction e+ + e− → hadronic jets at a center-of-mass energy √s=30 GeV using the MARK-J detector at PETRA. By measuring the energy and angular distribution of both neutrals and charged particles we were able to isolate unambiguously the three-jet events in a kinematic region where the backgrounds from qq and phase space contributions and other processes are small. Various comparisons of the data with quantum chromodynamics were made. The relative yield of three-jet events and the shape distribution of the events enable us to determine αs = 0.23 ± 0.02 (statistical error) with a systematic error of ± 0.04.

The results of a high-statistics study of inclusive muon spectra at PETRA are reported.Improved mass limits have been obtained for heavy quarks, heavy leptons, and charged Higgs particles.It is shown that the fragmentation properties of b quarks and c quarks

This report reviews the experimental investigation of high energy e+e− interactions by the MARK J collaboration at PETRA, the electron-positron colliding beam accelerator at DESY in Hamburg, Germany. The physics objectives include studies of several purely electromagnetic processes and hadronic final states, which further our knowledge of the nature of the fundamental constituents and of their strong, electromagnetic and weak interactions. Before discussing the physics results, the main features and the principal components of the MARK J detector are discussed in terms of design, function, and performance. Several aspects of the on-line data collection and the off-line analysis are also outlined. Results are presented on tests of quantum electrodynamics using e+e− → e+e−, μ+μ− and τ+τ−, on the measurement of R, the ratio of the hadronic to the point-like muon pair cross section, on the search for new quark flavors, on the discovery of three jet events arising from the radiation of hard noncollinear gluons as predicted by quantum chromodynamics, and on the determination of the strong coupling constant αs.

In a search for the Standard Model Higgs boson, carried out on 212.5 pb-1 of data collected by the L3 detector at the highest LEP centre-of-mass energies, including 116.5 pb-1 above root(s) = 206GeV, an excess of candidates for the process e+e- -> Z* -> HZ is found for Higgs masses near 114.5GeV. We present an analysis of our data and the characteristics of our strongest candidates.

We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)_L gauge group. The data collected with the L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used.The decay channel N_e --> eW is investigated and no evidence is found for a heavy neutrino, N_e, in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived.

We analyse e+e−→ττγ events using 100pb−1 of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively: aτ=0.004±0.027±0.023;dτ=(0.0±1.5±1.3)×10−16e·cm.This is a direct measurement of these τ form factors at q2=0.

Doubly-charged Higgs bosons are searched for in e^+e^- collision data collected with the L3 detector at LEP at centre-of-mass energies up to 209 GeV. Final states with four leptons are analysed to tag the pair-production of doubly charged Higgs bosons. No significant excess is found and lower limits at 95% confidence level on the doubly-charged Higgs boson mass are derived. They vary from 95.5 GeV to 100.2 GeV, depending on the decay mode. Doubly-charged Higgs bosons which couple to electrons would modify the cross section and forward-backward asymmetry of the e^+e^- -> e^+e^- process. The measurements of these quantities do not deviate from the Standard Model expectations and doubly-charged Higgs bosons with masses up to the order of a TeV are excluded.

The ηπ+π− final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6 pb−1. The f1(1285) meson is observed and the Q2 dependence of its production is compared to different form factor models. The γγ-coupling parameter Γγγ is found to be 3.5±0.6(stat.)±0.5(sys.) keV. The branching fraction Γ(f1(1285)→a0π)/Γ(f1(1285)→ηππ) is also measured.

A method to calibrate the L3 electromagnetic calorimeter with cosmic muons has been tested on a matrix of 100 tapered BGO crystals. Calibration constants in the energy range of 20–30 MeV were measured at the 2% level collecting about 200 muons per crystal. The results are in agreement with the calibration constant determined using a 10 GeV electron beam.

We present a study of 4200 4-jet events from Z0 boson decays. The measured angular correlations between jets are reproduced well by QCD. An alternative abelian model fails to describe the data.

With use of the MARK-J detector at $\sqrt{s}=34.7$ GeV 21 000 ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadron}$ events have been collected. By measurement of the asymmetry in angular energy correlations the strong coupling constant ${\ensuremath{\alpha}}_{s}=0.13\ifmmode\pm\else\textpm\fi{}0.01 (\mathrm{statistical})\ifmmode\pm\else\textpm\fi{}0.02 (\mathrm{systematic})$ is determined, in complete second order, and independent of the fragmentation models and QCD cutoff values used.

We have measured the properties of Z0 → bb decays using a sample of 944 inclusive muon events, corresponding to 18 000 hadron events obtained with the L3 detector at LEP. We measured the partial decay width of the Z0 into bb, Γbb=353±48 MeV, and we determined the vector coupling of the Z0 to the b quark; grmv2(b)=0.095±0.047. We measured the forward-backward charge asymmetry in e+e− → bb events at √s≈Mv, and obtained Abb=13.3±9.9%.

We present the results from a search for the light neutral scalar Higgs boson h° and the pseudoscalar Higgs boson A° of the minimal super-symmetric standard model. The analysis is based on a data sample corresponding to 71 000 hadronic Z° decays recorded with the L3 detector at LEP. No evidence for the existence of the neutral Higgs bosons h° and A° has been found. The region of h° and A° masses up to 41.5 GeV is excluded at 95% confidence level.

The reaction \ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$\ensuremath{\eta} has been investigated with the Crystal Ball detector at the DESY storage ring DORIS II. Formation of \ensuremath{\delta}(980) and ${A}_{2}$(1320) has been observed with \ensuremath{\gamma}\ensuremath{\gamma} partial widths ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}$(${A}_{2}$)=1.14\ifmmode\pm\else\textpm\fi{}0.20\ifmmode\pm\else\textpm\fi{}0.2 6 keV and ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}$(\ensuremath{\delta})B(\ensuremath{\delta}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta})=0.19\ifmmode\pm\else\textpm\fi{}0.07 $_{\mathrm{\ensuremath{-}}0.07}^{+0.10}$ keV.

With a PETRA energy scan in \ensuremath{\le}30-MeV steps, the continuum production of open top quark up to 38.54 GeV is excluded. Over regions of energy scan from 29.90 to 38.63 GeV limits are set on the product of hadronic branching ratio and electronic width ${B}_{h}{\ensuremath{\Gamma}}_{\mathrm{ee}}$ for toponium to be less than 2.0 keV at the 95% confidence level. By a search for flavor-changing neutral currents in $b$ decay, models without a top quark are excluded.

The measurement of the nonelectromagnetic forward-backward charge asymmetry in the reaction e+eiz'tz at ~s-34.6 GeV and in the angular region 0& IcosOI&0.8 is re- ported.With a systematic error less than 1%, we observe an asymmetry of (-8.1+2.1)/p.This is in agreement with the standard electroweak theory prediction of (-7.6+ 0.6)%.The weak-current coupling constants are also reported.

Using a data sample of 1 475 000 Z → qq̄(γ) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, Ds− → τ−ντ and B− → τ−ντ. A signal is observed in the invariant mass distribution M(γDs−) corresponding to the decay sequence D∗− → γDs−, Ds− → τ−ντ, τ− → l−νlντ. The branching fraction for Ds− → τ−ντ decays is measured to be β(Ds− → τ−ντ) = 0.074 ± 0.028(stat) ± 0.016(syst) ± 0.018(norm). No signal of B− → τ−ντ decays is observed in the data, corresponding to an upper limit on the branching franction β(B− → τ−ντ) < 5.7 × 10−4 at 90% CL.

The measurements of hadron and lepton-pair production cross sections and leptonic forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 189 GeV are used to search for new physics phenomena such as: contact interactions, exchange of virtual leptoquarks, scalar quarks and scalar neutrinos, effects of TeV strings in models of quantum gravity with large extra dimensions and non-zero sizes of the fermions. No evidence for these phenomena is found and new limits on their parameters are set.

We report the result of a search for charginos and neutralinos, in e+e− collisions at 189 GeV centre-of-mass energy at LEP. No evidence for such particles is found in a data sample of 176 pb−1. Improved upper limits for these particles are set on the production cross sections. New exclusion contours in the parameter space of the Minimal Supersymmetric Standard Model are derived, as well as new lower limits on the masses of these supersymmetric particles. Under the assumptions of common gaugino and scalar masses at the GUT scale, we set an absolute lower limit on the mass of the lightest neutralino of 32.5 GeV, and a limit on the mass of the lightest chargino of 67.7 GeV for M2<2TeV.

We present a study of the inclusive production of π0, η, Ks0 and Λ based on 929,000 hadronic Z decays recorded with the L3 detector at LEP. The measured inclusive momentum distributions have been compared with predictions from parton shower models as well as an analytical Quantum Chromodynamics calculation. Comparing to low energy e+e- data, we find that QCD describes the energy evolution of the hadron spectrum.

We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected in the years 1990, 1991 and 1992 corresponds to 1.09·106 hadronic and 0.98·105 leptonicZ decays observed. These data allow us to determine the electroweak parameters. From the cross sections we derive the properties of theZ boson: $$\begin{gathered} M_Z = 91195 \pm 9MeV\Gamma _{\rm Z} = 2494 \pm 10MeV \hfill \\ \Gamma _{had} = 1748 \pm 10MeV\Gamma _\ell = 83.49 \pm 0.46MeV \hfill \\ \end{gathered} $$ assuming lepton universality. We obtain an invisible width of Γinv=496.5±7.9 MeV which, in the Standard Model, corresponds to a number of light neutrino species ofN v=2.981±0.050. Using also the three leptonic forward-backward asymmetries and the average tau polarization, we determine the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons to be: $$\bar g^\ell v = - 0.0378_{ - 0.0042}^{ + 0.0045} \bar g^\ell _A = - 0.4998 \pm 0.0014.$$ Within the framework of the Standard Model, and including our measurements of the $$Z \to b\bar b$$ forward-backward asymmetry and partial decay width, we derive an effective electroweak mixing angle of $$sin^2 \bar \theta _W = 0.2326 \pm 0.0012$$ . We obtain an estimate for the strong coupling constant, αS=0.142 ± 0.013 and for the top-quark mass,m t =158 −40 +32 ±19(Higgs) GeV, where the second error arises due to the uncertainty in the Higgs-boson mass.

The results of the searches for neutral Higgs boson production in the process e+e− → Z∗ H0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z0 decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e+e− → Z∗h0 are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state.

We have searched for anomalous Z → γγγ events with the L3 detector at LEP. No significant deviations from the expected QED e+e− → γγγ events are observed. The branching ratio upper limit for a compoite Z decaying directly into three photons is found to be 1.0 × 10−5 at 95% C.L. The branching ratio upper limits for the process Z → γX, X → γγ are in the range of 0.4 to 1.3 × 10−5, depending on the mass and width of the scalar particle X. In the context of a model with magnetic monopoles coupling to the Z, we find BR(Z → γγγ) < 0.8 × 10−5 at 95% C.L.; this results in a lower mass limit of 510 GeV for a magnetic monopole.

The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reaction ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\gamma}*\ensuremath{\gamma}*\ensuremath{\rightarrow}${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\gamma}\ensuremath{\gamma}, where X is a narrow resonance with mass between 100 and 3000 MeV. Formation of ${\ensuremath{\pi}}^{0}$, \ensuremath{\eta}, and \ensuremath{\eta}' mesons is observed, and the following meson partial widths are obtained: ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{\ensuremath{\pi}}0\mathrm{\ensuremath{\Gamma}}0\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$=7.7\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.5 eV, ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{\ensuremath{\eta}}\mathrm{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}}$=0.514\ifmmode\pm\else\textpm\fi{}0.017\ifmmode\pm\else\textpm\fi{}0.035 keV, and ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{\ensuremath{\eta}}\mathcal{'}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$=4.7\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.5 keV. No other narrow resonances are observed, and upper limits are given for the product ${\ensuremath{\Gamma}}_{X\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$${B}_{X\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$. .AE

We have performed a high-statistics measurement of Bhabha scattering and of the production of hadrons in electron-positron annihilation at PETRA energies ($12 \mathrm{GeV}&lt;~\sqrt{s}&lt;~36.7 \mathrm{GeV}$). Combining the results with measurements of ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ production enables us to compare our results with electroweak theory. We find ${{sin}^{2}\ensuremath{\theta}}_{w}=0.27\ifmmode\pm\else\textpm\fi{}0.08$. This is in good agreement with the value obtained from neutrino experiments which were carried out in entirely different kinematic regions.

By combining results from the MARK-J at PETRA on Bhabha scattering, μ+μ- and τ+τ- production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants gV and gA in the framework of electroweak models containing a single Z0. In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin2θW=0.24±0.11.

Recent theories propose that quantum gravity effects may be observable at LEP energies via gravitons that couple to Standard Model particles and propagate into extra spatial dimensions. The associated production of a graviton and a photon is searched for as well as the effects of virtual graviton exchange in the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No evidence for this new interaction is found in the data sample collected by the L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1 TeV on the scale of this new scenario of quantum gravity are set.

The hadronic photon structure function Fγ2 is studied in the reaction e+e−→e+e−hadrons at LEP with the L3 detector. The data, collected from 1991 to 1995 at a centre-of-mass energy s≃91 GeV, correspond to an integrated luminosity of 140 pb−1. The photon structure function Fγ2 is measured in the Q2 interval 1.2 GeV2 ≤Q2≤9.0 GeV2 and the x interval 0.002<x<0.2. Fγ2 shows a linear growth with lnQ2. The value of the slope α−1dFγ2(Q2)/dlnQ2 is measured to be 0.079±0.011±0.009.

The production of c and b quarks in gamma-gamma collisions is studied with the L3 detector at LEP with 410 pb^-1 of data, collected at centre-of-mass energies from 189 GeV to 202 GeV. Hadronic final states containing c and b quarks are identified by detecting electrons or muons from their semileptonic decays. The cross sections sigma(e+e- -> e+e- c c~ X) and sigma(e+e- -> e+e- b b~ X) are measured and compared to next-to-leading order perturbative QCD calculations. The cross section of b production is measured in gamma-gamma collisions for the first time. It is in excess of the QCD prediction by a factor of three.

Final results of the search for the Standard Model Higgs boson are presented for the data collected by the L3 detector at LEP at centre-of-mass energies up to about 209 GeV. These data are compared with the expectations of Standard Model processes for Higgs boson masses up to 120 GeV. A lower limit on the mass of the Standard Model Higgs boson of 112.0 GeV is set at the 95 % confidence level. The most significant high mass candidate is a Hnunu event. It has a reconstructed Higgs mass of 115 GeV and it was recorded at root(s)=206.4 GeV.

The e+e−→e+e−KS0K±π∓ and e+e−→e+e−ηπ+π− final states are studied with the L3 detector at LEP using data collected at centre-of-mass energies from 183 GeV up to 202 GeV. The mass spectrum of the K0SK±π∓ final state shows an enhancement around 1470 MeV, which is identified with the pseudoscalar meson η(1440). This state is observed in γγ collisions for the first time and its two-photon width is measured to be Γγγ(η(1440))×BR(η(1440)→KK̄π)=212±50 (stat.)±23 (sys.) eV. Clear evidence is also obtained for the formation of the axial vector mesons f1(1420) and f1(1285). In the ηπ+π− channel the f1(1285) is observed, and upper limits for the formation of η(1440) and η(1295) are obtained.

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies between 189 and 209GeV, corresponding to an integrated luminosity of 629.4/pb. Decays into a charm and a strange quark or into a tau lepton and its neutrino are considered. No significant excess is observed and lower limits on the mass of the charged Higgs boson are derived at the 95% confidence level. They vary from 76.5 to 82.7GeV, as a function of the H->tv branching ratio.

We present a study of the structure of hadronic events recorded by the L3 detector at center-of-mass energies of 130 and 136 GeV. The data sample corresponds to an integrated luminosity of 5 pb−1 collected during the high energy run of 1995. The shapes of the event shape distributions and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed O(αs2) QCD calculations, we determine the strong coupling constant to be αs(133 GeV) = 0.107 ± 0.005(exp) ± 0.006(theor).

We have searched for the neutral Higgs boson produced in the decays of the Z0 through the processes Z0→H0μ+μ−, Z0→H0e+e− and Z0→H0νν. The data sample analysed corresponds to about 50 200 Z0→hadrons. Combining the results of all three processes we exclude a minimal standard model Higgs boson in the mass range 2<MH0<32 GeV at the 95% confidence level.

We present a study of energy-energy correlations based on 83 000 hadronic Z0 decays. From this data we determine the strong coupling constant αs to second order QCD: αs(91.2 GeV)=0.121±0.004(exp.)±0.002(hadr.)−0.006+0.009(scale)±0.006(theor.) from the energy-energy correlation and αs(91.2 GeV)=0.115±0.004(exp.)−0.004+0.007(hadr.)−0.000+0.002(scale)−0.005+0.003 (theor.) from its asymmetry using a renormalization scale μ1=0.1 s. The first error (exp.) is the systematic experimental uncertainly, the statistical error is negligible. The other errors are due to hadronization (hadr.), renormalization scale (scale) uncertainties, and differences between the calculated second order corrections (theor.).

We have measured the partial widths of the Z0 into lepton pairs, and the forward-backward charge asymmetry for the process e+e−→μ+μ− using the L3 detector at LEP. We obtain an average Γℓℓ of 83.0±2.1±1.1 MeV.From this result and the asymmetry measurement, we extract the values of the vector and axial vector couplings of the Z0 to leptons: grmv=−0.066−0.027+0.046 and grmA= −0.495−0.007+0.007.

This paper reports the results of a study of hadron production in e+e− collisions at c.m. system energies of 33, 35, and 35.8 GeV. Production of a new quark flavor has been sought. The measured values of the total cross section, the thrust distributions, and the study of inclusive muon production show no evidence for the production of a new charge-23e quark near threshold. In addition, during an energy scan in the region 29.9<~√s<~31.6 GeV, no hadron resonance indicating the existence of a bound state composed of charge-23e quarks has been found.Received 1 April 1980DOI:https://doi.org/10.1103/PhysRevLett.44.1722©1980 American Physical Society

We report on the measurement of the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ with a large---solid-angle electromagnetic shower detector at center-of-mass energies $\sqrt{s}=13 \mathrm{and} 17$ GeV. Comparison of our results with predictions of quantum electrodynamics shows excellent agreement in both the angular distribution and energy dependence. Values of cutoff parameters are also given.

We report the first measurement of the ratio R=(σe+e−→hadrons)(σe+e−→μ+μ−) (with negligible τ-lepton contribution) at a center-of-mass energy s=13 GeV and s=17 GeV, from the just finished electron-positron colliding-beam facility PETRA. The detector, MARK-J, has an approximately 4π solid angle and measures γ, e, μ, and charged and neutral hadrons simultaneously. Our results yield R(s=17 GeV)=4.9±0.6 (statistical) ±0.7 (systematic error), and R(s=13 GeV)=4.6±0.5 (statistical) ±0.7 (systematic error). The ratio R(s=17 GeV)R(s=13 GeV) is 1.08±0.18.Received 6 February 1979DOI:https://doi.org/10.1103/PhysRevLett.42.1113©1979 American Physical Society

Bose-Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various parametrizations. A good description is achieved using a L\'evy stable distribution in conjunction with a model where a particle's momentum is correlated with its space-time point of production, the \taumodel. Using this description and the measured rapidity and transverse momentum distributions, the space-time evolution of particle emission in two-jet events is reconstructed. However, the elongation of the particle emission region previously observed is not accommodated in the \taumodel, and this is investigated using an \adhoc/ modification.

This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).

In this work, we undertake a comprehensive reformulation, modification, and extension of Smith and Spiegelhalter's (1980) and (1982) Bayes Factor work within the evolving subject of Objective Bayes Factors. Our primary focus centers on defining and computing empirical and theoretical bounds for the Intrinsic Bayes Factor (IBF) across various models, including normal, exponential, Poisson, geometric, linear, and ANOVA. We show that our new bounds are useful, feasible, and change with the amount of information. We also propose a methodology to construct the least favorable (for the null model) intrinsic priors that result in the lower and upper bounds of the Intrinsic Bayes Factors under certain conditions. Notably, our lower bounds exhibit superior performance compared to the well-known -ep log(p) bound proposed by Sellke et al. (2001) (Sellke et al., 2001) based on p-values.

Extra spatial dimensions are proposed by recent theories that postulate the scale of gravity to be of the same order as the electroweak scale. A sizeable interaction between gravitons and Standard Model particles is then predicted. Effects of these new interactions in boson and fermion pair production are searched for in the data sample collected at centre-of-mass energies above the Z pole by the L3 detector at LEP. In addition, the direct production of a graviton associated with a Z boson is investigated. No statistically significant hints for the existence of these effects are found and lower limits in excess of 1 TeV are derived on the scale of this new theory of gravity.

The K0s K0s final state in two-photon collisions is studied with the L3 detector at LEP. The mass spectrum is dominated by the formation of the f_2'(1525) tensor meson in the helicity-two state with a two-photon width times the branching ratio into K Kbar of 76 +- 6 +- 11 eV. A clear signal for the formation of the f_J(1710) is observed and it is found to be dominated by the spin-two helicity-two state. No resonance is observed in the mass region around 2.2 GeV and an upper limit of 1.4 eV at 95% C.L. is derived for the two-photon width times the branching ratio into K0s K0s for the glueball candidate xi(2230).

The reaction e+e− → e+e−γ∗γ∗ → e+e− hadrons is analysed using data collected by the L3 detector during the LEP runs at s = 130−140 GeV and s = 161 GeV. The cross sections σ(e+e− → e+e− hadrons) and σ(γγ → hadrons) are measured in the interval 5 ≤ Wγγ ≤ 75 GeV. The energy dependence of the σ(γγ → hadrons) cross section is consistent with the universal Regge behaviour of total hadronic cross sections.

Single and multi-photon events with missing energy are analysed using data collected with the L3 detector at LEP at a centre-of-mass energy of 189 GeV, for a total of 176 pb^{-1} of integrated luminosity. The cross section of the process e+e- -> nu nu gamma (gamma) is measured and the number of light neutrino flavours is determined to be N_\nu = 3.011 +/- 0.077 including lower energy data. Upper limits on cross sections of supersymmetric processes are set and interpretations in supersymmetric models provide improved limits on the masses of the lightest neutralino and the gravitino. Graviton-photon production in low scale gravity models with extra dimensions is searched for and limits on the energy scale of the model are set exceeding 1 TeV for two extra dimensions.

Measurements of the two-photon interaction e+e− → e+e− + hadrons at s≃ 91GeV and s≃ 183GeV are presented. The double-tag events, collected with the L3 detector, correspond to interated luminosities of 140 pb−1 at 91 GeV and 52 pb−1 at 183 GeV. The cross-section of γ∗γ∗ collisions has been measured at 〈Q2〉 = 3.5 GeV2 and 〈Q2〉 = 14 GeV2. The data agree well with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data.

The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4 pb−1, collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4% and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W→hadrons)=67.50±0.42(stat.)±0.30(syst.)%, in agreement with the Standard Model. Differential cross sections as a function of the W− production angle are also measured for the semi-leptonic channels qqeν and qqμν.

A search, in e^+e^- collisions, for chargino, neutralino, scalar lepton and scalar quark pair-production is performed, without assuming R-parity conservation in decays, in the case that only one of the coupling constants lambda_ijk or lambda''_ijk is non-negligible. No signal is found in data up to a centre-of-mass energy of 208GeV. Limits on the production cross sections and on the masses of supersymmetric particles are derived.

From the analysis of the reactions e+e−→l+l−(nγ) (l=e,μ,τ) we observe four events, one e+e−γγ and three μ+μ−γγ, with the invariant mass of the photon pairs close to 60 GeV. These events were selected from a data sample collected in the L3 detector corresponding to 950 000 produced Z0's. More data are necessary to ascertain the origin of these events.

We have searched for lepton flavour violation in Z boson decays into lepton pairs using all data collected with the L3 detector during the 1990, 1991 and 1992 runs on an event sample corresponding to 1 500 000 Z's produced. At the 95% confidence level the upper limits on the branching ratio for Z→eμ is 0.6×10−5 and for Z→μτ this is 1.9×10−5.

We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the L3 detector in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded.

We report a measurement of Rb= ΓbbΓhad from Z→qq events at LEP. Z→bb events are identified using a multidimensional analysis based on a neural network approach. We obtain 60% sample purity with an efficiency of 35%. Our measured value of Rb is 0.222±0.003±0.007.

The process e+e−→W+W−γ is studied using the data collected by the L3 detector at LEP. New results, corresponding to an integrated luminosity of 427.4 pb−1 at centre-of-mass energies from 192 to 207 GeV, are presented. The W+W−γ cross sections are measured to be in agreement with Standard Model expectations. No hints of anomalous quartic gauge boson couplings are observed. Limits at 95% confidence level are derived using also the process e+e−→νν̄γγ.

The evolution of the electromagnetic coupling, alpha, in the momentum-transfer range 1800GeV^2 < -Q^2 < 21600GeV^2 is studied with about 40000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energies 189-209GeV. The running of alpha is parametrised as: alpha(Q^2) = alpha_0/(1-C Delta alpha(Q^2)), where alpha_0=\alpha(Q^2=0) is the fine-structure constant and C=1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e+e- ->e+e- process for scattering angles in the range |cos theta|<0.9 excludes the hypothesis of a constant value of alpha, C=0, and validates the QED prediction with the result: C = 1.05 +/- 0.07 +/- 0.14, where the first uncertainty is statistical and the second systematic.

We have measured the cross section for e+e−→hadrons over the center of mass energy range of the Z0 peak, from 88.22 to 95.03 GeV. We determine the Z0 mass Mz=91.164±0.013 (experiment) ±0.030 (LEP) GeV. Within the framework of the standard model we determine the invisible width, Γinvisible=0.502±0.018 GeV, and the number of light neutrino species, Nν=3.01±0.11. We exclude the existence of a supersymmetric scalar neutrino having a mass less than 31.4 GeV, at the 95% confidence level. We performed a model independent combined fit to the e+e−→hadrons and e+e−→μ+μ− data to determine total width, leptonic width and hadronic width of the Z0.

The results are reported of a search for excited muons (${\ensuremath{\mu}}^{*}$) and electrons (${e}^{*}$) and for a stable charged heavy lepton by measurements of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}$, and $\ensuremath{\gamma}\ensuremath{\gamma}$ final states. Excluded are large regions of the $\ensuremath{\lambda}$ (coupling constant), $M$ (mass) planes for spin-\textonehalf{} ${\ensuremath{\mu}}^{*}$ and ${e}^{*}$, and a new stable charged heavy lepton with mass 14 GeV.

We have measured both the rates and the forward-backward asymmetry of ℓ+ℓ− from Z0→ℓ+ℓ− (where ℓ=μ, τ) with the L3 detector. We obtained Γℓℓ=88±4±3 MeV and the vector neutral current coupling constant, gv=0.00±0.07 and the axial vector neutral current coupling constant, gA=−0.515±0.015.

We have used our measurements of final states from e+e− containing an isolated muon and a hadronic or electron shower to search for new spin 0 charged particles. We exclude (95% CL) a supersymmetric partner of the τ with a mass less than 14 GeV/c2. We obtain upper limits on the branching ratio to τvτ for charged Higgs particles or technipions with masses up to 14 GeV/c2. This disagrees with some technicolor model predictions.

The reaction e+e−→e+e−γ∗γ∗→e+e−hadrons for quasi-real photons is studied using data from s=183 GeV up to 202 GeV. Results on the total cross sections σ(e+e−→e+e−hadrons) and σ(γγ→hadrons) are given for the two-photon centre-of-mass energies 5 GeV⩽Wγγ⩽185 GeV. The total cross section of two real photons is described by a Regge parametrisation. We observe a steeper rise with the two-photon centre-of-mass energy as compared to the hadron–hadron and the photon–proton cross sections. The data are also compared to the expectations of different theoretical models.

We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb−1, we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigmaWW = 2.89−0.70+0.81(stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: MW = 80.80−0.42+0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.

A search for the Standard Model Higgs boson has been performed with the L3 detector at LEP. The data sample was collected at three centre-of-mass energies, 161.3, 170.3 and 172.3 GeV with integrated luminosities of 10.8, 1.0 and 9.2 pb, respectively. No Higgs signal is observed. In combination with previous data taken at the Z resonance, a lower Higgs mass limit, MH > 69.5 GeV, is obtained at 95% confidence level.

We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z decays with the L3 detector at LEP. The analysis is performed in three dimensions in the longitudinal center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of $0.81\pm 0.02 ^{+0.03}_{-0.19}$.

The search for an additional heavy gauge boson Z′ is described. The models considered are based on either a superstring-motivated E6 or on a left-right symmetry and assume a minimal Higgs sector. Cross sections and asymmetries measured with the L3 detector in the vicinity of the Z resonance during the 1990 and 1991 running periods are used to determine limits on the Z-Z′ gauge boson mixing angle and on the Z′ mass. For Z′ masses above the direct limits, we obtain the following allowed ranges of the mixing angle, θM at the 95% confidence level: −0.004 ⪕ θM⪕ 0.015 for the χ model, −0.003 ⪕ θM⪕ 0.020 for the ψ model, −0.029 ⪕ θM⪕ 0.010 for the η model, −0.002 ⪕ θM⪕ 0.020 for the LR model,

Total and differential cross sections for the process e+e− → γγ(γ), and the total cross section for the process e+e− → γγγ, are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron me∗>146GeV and on the QED cut-off parameters Λ+ > 149 GeV and Λ_ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ, π° and ηγ of 5.2 × 10−5, 5.2 × 10−5 and 7.6 × 10−5 respectively. The reactions e+e− → ℓ+ℓ−nγ (ℓ = e, μ, τ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.

Results are presented from a study of the structure of high energy hadronic events recorded by the L3 detector at sqrt(s)>192 GeV. The distributions of several event shape variables are compared to resummed O(alphaS^2) QCD calculations. We determine the strong coupling constant at three average centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements, combined with previous L3 measurements at lower energies, demonstrate the running of alphaS as expected in QCD and yield alphaS(mZ) = 0.1227 +- 0.0012 +- 0.0058, where the first uncertainty is experimental and the second is theoretical.

We have searched for direct leptoquark production in Z0 decays from a scan of the Z0 resonance, in the energy range 88.2 ⩽ √s ⩽ 94.2 GeV, using 5.2 pb−1 of data. We exclude the existence of scalar leptoquarks with masses less than 41 to 44 GeV, depending on the charge assignments, at the 95% confidence level.

Anomalous couplings of the Higgs boson are searched for through the processes e^+ e^- -> H gamma, e^+ e^- -> e^+ e^- H and e^+ e^- -> HZ. The mass range 70 GeV < m_H < 190 GeV is explored using 602 pb^-1 of integrated luminosity collected with the L3 detector at LEP at centre-of-mass energies sqrt(s)=189-209 GeV. The Higgs decay channels H -> ffbar, H -> gamma gamma, H -> Z\gamma and H -> WW^(*) are considered and no evidence is found for anomalous Higgs production or decay. Limits on the anomalous couplings d, db, Delta(g1z), Delta(kappa_gamma) and xi^2 are derived as well as limits on the H -> gamma gamma and H -> Z gamma decay rates.

The L3 detector at LEP has been used to determine the number of light neutrino families by measuring the cross section of single photon even in e+e− collisions at energies near the Z0 resonance. We have observed 61 single photon candidates with more than 1.5 GeV of deposited energy in the barrel electromagnetic calorimeter, for a total integrated luminosity of 3.0 pb−1. From a likelihood fir to the single photon cross sections, we determin Nν=3.24 ± 0.46 (statistical) ±0.22 (systematic).

The inclusive photon spectrum in hadronic decays of the $\ensuremath{\Upsilon}(2S)$ is measured with the Crystal Ball detector at DORIS II. Four well separated photon lines, which are consistent with the decay hypothesis $\ensuremath{\Upsilon}(2S)\ensuremath{\rightarrow}\ensuremath{\gamma}+^{3}P_{2,1,0}$ and $^{3}P_{2,1}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\Upsilon}(1S)$, are observed. The energies of the lines from the primary transitions are ${E}_{\ensuremath{\gamma}1}=110.4\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}2.2$ MeV, ${E}_{\ensuremath{\gamma}2}=130.6\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}2.4$ MeV, and ${E}_{\ensuremath{\gamma}3}=163.8\ifmmode\pm\else\textpm\fi{}1.6\ifmmode\pm\else\textpm\fi{}2.7$ MeV; the branching fractions are (5.8\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}1.0)%, (6.5\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}1.2)%, and (3.6\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}0.9)%, respectively. The secondary transitions center at $〈{E}_{\ensuremath{\gamma}}〉\ensuremath{\simeq}430$ MeV with a combined branching fraction of (3.6\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}0.5)%.

We have measured the forward-backward asymmetry in Z0→bb decays using hadronic events containing muons and electrons. The data sample corresponds to 118 200 hadronic events at √s≈Mz. From a fit to the single and dilepton p and P⊥ spectra, we determine Abb=0.130−0.042+0.044 including the correction for B0−B0 mixing.

This paper reports on the first results of the study of e+e collisions at 4's =27.4 GeV and vs = 27.7 GeV at PETRA, using the 47'-sr electromagnetic and calorimetric detector MARK-J.We obtain an average A=a(e+e hadrons)/o(e+e p+p ) = 8.8+0.3 (statis- tical) + 0.6 (systematic) and a relative R = 1.0+ 0.2 between the two energies.The R values, the measured thrust distribution, and average spherocity show no evidence for the production of new quark flavors.

We report on the results of the study of e+e− collisions at the highest PETRA energy of √s = 31.57 GeV, using the 4π sr, electromagnetic and calorimetric detector Mark J. Based on 88 hadron events, and an integrated luminosity of 243 nb−1 we obtain R = σ(e+e− → hadrons)/σ(e+e− → μ+μ−) = 4.0 ± 0.5 (statistical) ± 6 (systematic). The R value, the measured thrust distribution and average spherocity show no evidence for the production of new quark flavors.

The K0SK±π∓ final state in two-photon collisions is studied with the L3 detector at LEP at e+e− centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6 pb−1. The η(1475) and f1(1420) mesons are observed and their contribution is separated by measuring the formation rates as a function of the photon virtuality Q2. The η(1475) is found to be dominant for Q2 ⩽ 0.01GeV2 and its two-photon width is measured to be 0.23±0.05 (stat.) ±0.05 (sys.) keV. At higher Q2, the f1(1420) is formed and decays to K*(892)K. The γγ coupling and form factor parameters of this state are measured to be Γγγ = 3.2±0.6 (stat.) ±0.7 (sys.) keV and Λ1 = 926±72 (stat.) ±32 (sys.) MeV, respectively.

We present a study of the structure of hadronic events recorded by the L3 detector at LEP at the center of mass energies of 161 and 172 GeV. The data sample corresponds to an integrated luminosity of 21.25 pb−1 collected during the high energy runs of 1996. The distributions of event shape variables and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed O(αs2) QCD calculations, we determine the strong coupling constant at the two energies. Combining this with our earlier measurements we find that the strong coupling constant decreases with increasing energy as expected in QCD.