M. Cerrada

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017<sin(2)2θ(13)<0.16.

The L3 experiment is one of the six large detectors designed for the new generation of electron-positron accelerators. It is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons. By not attempting to identify hadrons, L3 has been able to provide an order of magnitude better resolution for electrons, muons and photons. Vertices and hadron jets are also studied. The construction of L3 has involved much state of the art technology in new principles of vertex detection and in new crystals for large scale electromagnetic shower detection and ultraprecise muon detection. This paper presents a summary of the construction of L3.

The Double Chooz experiment has observed 8,249 candidate electron antineutrino events in 227.93 live days with 33.71 GW-ton-years (reactor power × detector mass × livetime) exposure using a 10.3 m 3 fiducial volume detector located at 1050 m from the reactor cores of the Chooz nuclear power plant in France.The expectation in case of θ13= 0 is 8,937 events.The deficit is interpreted as evidence of electron antineutrino disappearance.From a rate plus spectral shape analysis we find sin 2 2θ13 = 0.109 ± 0.030(stat) ± 0.025(syst).The data exclude the no-oscillation hypothesis at 99.8% CL (2.9σ).

The Double Chooz experiment presents improved measurements of the neutrino mixing angle $\theta_{13}$ using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the $\bar\nu_{e}$ signal has increased. The value of $\theta_{13}$ is measured to be $\sin^{2}2\theta_{13} = 0.090 ^{+0.032}_{-0.029}$ from a fit to the observed energy spectrum. Deviations from the reactor $\bar\nu_{e}$ prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of $\theta_{13}$ is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the $\theta_{13}$ measurement despite the observed distortion.

The cross-section for e+e− → hadrons in the vicinity of the Z boson peak has been measured with the ALEPH detector at the CERN Large Electron Positron collider, LEP. Measurements of the Z mass, Mz = (91.174±0.070) GeV, the Z width Γz=(2.68±0.15) GeV, and of the peak hadronic cross-section, σhadpeak=(29.3±1.2) nb, are presented. With the constraints of the standard electroweak model, the number of light neutrino species is found to be Nv=3.27±0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.

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.

Neutrinos were assumed to be massless particles until the discovery of the neutrino oscillation process. This phenomenon indicates that the neutrinos have non-zero masses and the mass eigenstates (ν1, ν2, ν3) are mixtures of their flavour eigenstates (νe, νμ, ντ). The oscillations between different flavour eigenstates are described by three mixing angles (θ12, θ23, θ13), two differences of the squared neutrino masses of the ν2/ν1 and ν3/ν1 pairs and a charge conjugation parity symmetry violating phase δCP. The Double Chooz experiment, located near the Chooz Electricité de France reactors, measures the oscillation parameter θ13 using reactor neutrinos. Here, the Double Chooz collaboration reports the measurement of the mixing angle θ13 with the new total neutron capture detection technique from the full data set, yielding sin2(2θ13) = 0.105 ± 0.014. This measurement exploits the multidetector configuration, the isoflux baseline and data recorded when the reactors were switched off. In addition to the neutrino mixing angle measurement, Double Chooz provides a precise measurement of the reactor neutrino flux, given by the mean cross-section per fission 〈σf〉 = (5.71 ± 0.06) × 10−43 cm2 per fission, and reports an empirical model of the distortion in the reactor neutrino spectrum. The Double Chooz collaboration reports the neutrino oscillation parameter θ13 from a measurement of the disappearance of reactor anti-electron neutrinos with the total neutron capture technique.

The Double Chooz experiment has determined the value of the neutrino oscillation parameter θ13 from an analysis of inverse beta decay interactions with neutron capture on hydrogen. This analysis uses a three times larger fiducial volume than the standard Double Chooz assessment, which is restricted to a region doped with gadolinium (Gd), yielding an exposure of 113.1 GW-ton-years. The data sample used in this analysis is distinct from that of the Gd analysis, and the systematic uncertainties are also largely independent, with some exceptions, such as the reactor neutrino flux prediction. A combined rate- and energy-dependent fit finds sin22θ13=0.097±0.034 (stat.)±0.034 (syst.), excluding the no-oscillation hypothesis at 2.0σ. This result is consistent with previous measurements of sin22θ13.

The forward-backward muon detector of the L3 experiment is presented. Intended to be used for LEP 200 physics, it consists of 96 self-calibrating drift chambers of a new design enclosing the magnet pole pieces of the L3 solenoid. The pole pieces are toroidally magnetized to form two independent analyzing spectrometers. A novel trigger is provided by resistive plate counters attached to the drift chambers. Details about the design, construction and performance of the whole system are given together with results obtained during the 1995 running at LEP.

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.

Nearly 200 000 examples of the diffractive process K−p → K−π−π+p at 63 GeV have been obtained using a two magnet spectrometer equipped with Čerenkov counters for secondary particle identification. In addition some 2000 examples of the process K−p → ωK−p have been obtained. The Kππ data have been subjected to partial-wave analysis. The dominant JP = 1+ system couples to K∗π, in both S and D waves, ϱK, κπ and εK. The data confirm the existence of two JP = 1+ Q mesons and their masses, widths and branching ratios are given. The ifωK data show that the couplings of the Q mesons to ωK are approximately equal to the couplings to ϱ0K. The two 1+ nonets expected in the quark model are discussed in the light of this and other recent experiments. There is strong evidence for a broad JP = 0− resonance at about 1.46 GeV. At higher masses, structure in the JP = 2− partial waves establishes the existence of at least one JP = 2− L meson.

The π+π− partial waves are studied up to the F-wave in the mass region from 580 to 1780 MeV/c2 at low four-momentum transfer. The study is based on a previous hydrogen target experiment and a more recent polarized target experiment. Using the results of both experiments for 0.01 ⩽ |t| ⩽ 0.20 GeV2/c2, a partial-wave analysis is performed in each mass bin (Δm = 40 MeV/c2) independently. For the first time a model-independent analysis has been possible, which enables us to check the assumptions made in previous studies. In general we find a unique solution determining the exact intensity of each partial wave. The uniqueness of our solution is related to the Barrelet zeros being real in the mass region where their imaginary part were supposed to produce ambiguities. We observe a non-π exchange contribution even in the helicity m = 0 amplitudes.

Diffractive production of the 3π system has been studied at 63 and 94 GeV using a two magnet spectrometer with high, uniform acceptance. The total number of events used in the analysis is ∼600 000. The A2 meson is shown to be diffractively produced. The existence of a resonant component in both the 1+ and 2− enhancements is established and resonance parameters for the corresponding A1 and A3 mesons are given. There are several indications in the data of states which would correspond to radial excitations in the quark model.

The Double Chooz experiment presents improved measurements of the neutrino mixing angle θ13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the ν¯¯¯e signal has increased. The value of θ13 is measured to be sin2 2θ13 = 0.090+ 0.032− 0.029 from a fit to the observed energy spectrum. Deviations from the reactor ν¯¯¯e prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of θ13 is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the θ13 measurement despite the observed distortion.

The Double Chooz collaboration presents a measurement of the neutrino mixing angle θ 13 using reactor $$ \overline{\nu_{\mathrm{e}}} $$ observed via the inverse beta decay reaction in which the neutron is captured on hydrogen. This measurement is based on 462.72 live days data, approximately twice as much data as in the previous such analysis, collected with a detector positioned at an average distance of 1050 m from two reactor cores. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties. Accidental coincidences, the dominant background in this analysis, are suppressed by more than an order of magnitude with respect to our previous publication by a multi-variate analysis. These improvements demonstrate the capability of precise measurement of reactor $$ \overline{\nu_{\mathrm{e}}} $$ without gadolinium loading. Spectral distortions from the $$ \overline{\nu_{\mathrm{e}}} $$ reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin2 2θ 13 = 0.095 − 0.039 + 0.038 (stat+syst) is obtained from a fit to the observed event rate as a function of the reactor power, a method insensitive to the energy spectrum shape. A simultaneous fit of the hydrogen capture events and of the gadolinium capture events yields a measurement of sin2 2θ 13 = 0.088 ± 0.033(stat+syst).

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.

The two-loop massive operator matrix elements for the fermionic local twist-2 operators with external massive fermion lines in Quantum Electrodynamics (QED) are calculated up to the constant terms in the dimensional parameter ε=D−4. We investigate the hypothesis of Berends et al. (1988) [1] that the 2-loop QED initial state corrections to e+e− annihilation into a virtual neutral gauge boson, except power corrections of O((mf2/s)k), k⩾1, can be represented in terms of these matrix elements and the massless 2-loop Wilson coefficients of the Drell–Yan process.

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.

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.

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 $$\sin ^2 \bar \theta _W = 0.2315 \pm 0.0025$$ .

The Double Chooz Reactor Neutrino Experiment in France plans to quickly measure the neutrino mixing angle theta-13, or limit it to sin^2 2-theta_13 less than 0.025. The physics reach, experimental site, detector structures, scintillator, photodetection, electronics, calibration and simulations are described. The possibility of using Double Chooz to explore the possible use of a antineutrino detector for non-proliferation goals is also presented.

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.

PETRA, the e+e− collider, has operated at a maximum CM energy of 46.78 GeV. We update our previous results on new particle searches and set significantly better mass limits on some.

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

We present a search for Lorentz violation with 8249 candidate electron antineutrino events taken by the Double Chooz experiment in 227.9 live days of running. This analysis, featuring a search for a sidereal time dependence of the events, is the first test of Lorentz invariance using a reactor-based antineutrino source. No sidereal variation is present in the data and the disappearance results are consistent with sidereal time independent oscillations. Under the Standard-Model Extension, we set the first limits on 14 Lorentz violating coefficients associated with transitions between electron and tau flavor, and set two competitive limits associated with transitions between electron and muon flavor.Received 26 September 2012DOI:https://doi.org/10.1103/PhysRevD.86.112009© 2012 American Physical Society

The oscillation results published by the Double Chooz collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle $\theta_{13}$ by including 7.53 days of reactor-off data. A global fit of the observed neutrino rates for different reactor power conditions is performed, yielding a measurement of both $\theta_{13}$ and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields $\sin^2(2\theta_{13})=$ 0.102 $\pm$ 0.028(stat.) $\pm$ 0.033(syst.). The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of $\theta_{13}$ that does not depend on a background model.

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.

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.

In partial wave analyses of the (π−π−π+) system, substantial shape changes of the 1+S (ϱπ) intensity as a function of t, and relative phase changes of ≈ 90°, provide compelling evidence for a resonant A1 of mass ≈ 1280 MeV and width ≈ 300 MeV.

The reaction π−p→π+π−n has been measured in a high-statistics experiment on a transversely polarized proton target at 17.2 GeV, and unexpectedly large nucleon polarization effects have been observed. Combining the results of this experiment with a measurement on a hydrogen target allows a model-independent partial-wave analysis in terms of the “nucleon transversity” amplitudes. Unique or at most twofold ambiguous solutions are obtained. In particular we find a high lower limit (⪆30%) of the spin non-flip unnatural exchange amplitudes at low |t|. These amplitudes, interpreted as being due to the exchange of an object with the quantum numbers of the A1, have been assumed to be absent in previous analyses. In checking the consequences of this finding on the old results, we test the validity of the rank-two assumotions for the density matrix. We find a small but significant deviation, which shows the need for a new phase-shift analysis including the A1 exchange contribution.

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.

The inclusive reactions h+p→φ+X, (h=π±,,K±,p±), are studied for 0⪅xF⪅0.3 and p⊥ ⩽ 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp⊥2 anddσ/dxF are presented and are compared with predictions of the naive parton model.

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 design and operation of precision drift chambers with multisampling as well as the concepts and methods for reaching an extraordinary degree of precision in mechanics and calibration are described. Specific instruments were developed for this purpose. The concept of reproducible positioning and the implementation to 30 μm accuracy, showing stability over three years, is given. Calibration and analysis with UV-laser and cosmic test measurements are outlined with the critical results. The experience of calibration and reliability of the large system in an actual L3 running experiment is analyzed. The resolution under “battle conditions” at LEP resulted in Δpp = (2.50±0.04)% at 45.6 GeV and will be presented in detail. The concept is well suited for future TeV energies.

A precise quantitative measurement of the effect of low magnetic fields in Hamamatsu R7081 photomultipliers has been performed. These large-area photomultipliers will be used in the Double Chooz neutrino experiment. A magnetic shielding has been developed for these photomultipliers. Its design and performance is also reported in this paper.

A study of the inclusive production of π−, η, ϱ0, ω ad f mesons in pp annihilation at 0.7 GeV/c is presented. Topological and channel cross sections are determined. Longitudinal and transversal momentum distributions of non-strange mesons are studied. It is deduced that nearly 48% of all negative pions arise from the decay of η, ϱ0, ω and f mesons.

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.

We have searched for neutralinos produced via the reactions e+e− → χχ′ and e+e−→ χ′χ′, where the next-to lightest neutralino, χ′, decays into the lightest neutralino, χ, and either a photon or a fermion pair. Based on 1.8 × 106 hadronic Z decays collected with the L3 detector at LEP, no signal has been observed. We present upper limits of a few times 10−5 on the branching ratios Z → χχ′ and Z → χ′χ′. In the framework of the Minimial Supersymmetric Standard Model, we exclude a lightest χ with mχ less than 18 GeV, if either tan β > 2 or the gluino mass m≈g > 100 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.

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.

Abstract This article describes the setup and performance of the near and far detectors in the Double Chooz experiment. The electron antineutrinos of the Chooz nuclear power plant were measured in two identically designed detectors with different average baselines of about 400 m and 1050 m from the two reactor cores. Over many years of data taking the neutrino signals were extracted from interactions in the detectors with the goal of measuring a fundamental parameter in the context of neutrino oscillation, the mixing angle $$\theta _{13}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>θ</mml:mi> <mml:mn>13</mml:mn> </mml:msub> </mml:math> . The central part of the Double Chooz detectors was a main detector comprising four cylindrical volumes filled with organic liquids. From the inside towards the outside there were volumes containing gadolinium-loaded scintillator, gadolinium-free scintillator, a buffer oil and, optically separated, another liquid scintillator acting as veto system. Above this main detector an additional outer veto system using plastic scintillator strips was installed. The technologies developed in Double Chooz were inspiration for several other antineutrino detectors in the field. The detector design allowed implementation of efficient background rejection techniques including use of pulse shape information provided by the data acquisition system. The Double Chooz detectors featured remarkable stability, in particular for the detected photons, as well as high radiopurity of the detector components.

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 use the reaction e+ e p, + p, , in the Mark J detector at the DESY high-energy e+ e col- lider PETRA, to test the standard electroweak theory and find good agreement.We also set limits on the parameters of several extended gauge theories.

We report mass limits on the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{Z}}^{0}$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}}^{\ifmmode\pm\else\textpm\fi{}}$, supersymmetric partners of the ${Z}^{0}$ and ${W}^{\ifmmode\pm\else\textpm\fi{}}$, respectively, using the MARK-J detector at PETRA. The experimental signatures in both cases are acoplanar lepton pairs with missing energy. For the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}}^{\ifmmode\pm\else\textpm\fi{}}$, an additional signature is a single energetic lepton. No evidence is found for either the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{Z}}^{0}({M}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{Z}}^{0}}&lt;35\mathrm{GeV})$ or the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}}^{\ifmmode\pm\else\textpm\fi{}}({M}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{W}}&lt;25\mathrm{GeV})$.

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.

We have searched for resonances in the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadrons}, \ensuremath{\gamma}\ensuremath{\gamma}, \ensuremath{\mu}\ensuremath{\mu}, \mathrm{and} \mathrm{ee}$, in the energy range $39.79&lt;\sqrt{s}&lt;45.52$ GeV, using the Mark J detector at PETRA. We obtain stringent upper limits on the production of toponium and particles postulated to explain ${Z}^{0}\ensuremath{\rightarrow}\mathrm{lepton}\mathrm{pair}+\ensuremath{\gamma}$ events observed at the CERN $\stackrel{-}{p}p$ collider. We also set limits on the mass and coupling constant of excited electrons.

Using our high-statistics data from the πp → ππn reaction, we have remade a model-independent partial-wave analysis in finer mass bins at low four-momentum transfer. The Breit-Wigner fits to the leading waves yield mρ = (777.4 ± 2.0) MeV and Γρ = (160P+4.1−4.0) MeV, as well as mf = (1273.3 ± 2.3) MeV, Γf = (179.2 +6.9−6.6) MeV and xf = (84.9 ± 2.5)%. The last two parameters yield Γ(f → ππ) = (152.1 ± 7.3) MeV, a value which is higher than the one resulting from fits to the decays of the JPC = 2++ mesons. On the basis of a smaller discrepancy, Rosner has speculated about a non-qq admixture (possibly gg) in the f(1270), i.e. |f(1270)〉 = |qq〉cos θ + |gg〉sin θ. Repeating his fits with more recent data we obtain a considerably more significant effect with sin2θ = 0.18 ± 0.04. This sets a mass of an orthogonal state |fT〉 = − |qq〉sinθ + |gg 〉cosθ between 1420 and 1620 MeV. The fT could be identified with a 1440 MeV state seen in some KK experiments, A1 exchange being a possible production mechanism. A fit to our polarized target K+K− data at ∼ 18 GeV/c yields m(fT) = (1445 +20−19) MeV and Γ (fT = (81+52−25) MeV.

The JPC = 2−+ partial wave intensities and their large phase changes prove the resonant nature of the A3 meson (mass ≈ 1670 MeV, width ≈ 210 MeV). The decay modes are f0π, ϱ0π, and ϵ0π. Evidence is found for a further 2− enhancement.

Double Chooz is unique among modern reactor-based neutrino experiments studying $\bar \nu_e$ disappearance in that data can be collected with all reactors off. In this paper, we present data from 7.53 days of reactor-off running. Applying the same selection criteria as used in the Double Chooz reactor-on oscillation analysis, a measured background rate of 1.0$\pm$0.4 events/day is obtained. The background model for accidentals, cosmogenic $\beta$-$n$-emitting isotopes, fast neutrons from cosmic muons, and stopped-$\mu$ decays used in the oscillation analysis is demonstrated to be correct within the uncertainties. Kinematic distributions of the events, which are dominantly cosmic-ray-produced correlated-background events, are provided. The background rates are scaled to the shielding depths of two other reactor-based oscillation experiments, Daya Bay and RENO.

The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.

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,