The reactions e + e − → e + e − e + e − and e + e − → e + e − μ + μ − , in a single tag configuration, are studied at LEP with the L3 detector. The data set corresponds to an integrated luminosity of 93.7 pb −1 at s =91 GeV. Differential cross sections are measured for 1.4 GeV 2 ≤Q 2 ≤7.6 GeV 2 . The leptonic photon structure function F γ 2 and azimuthal correlations are measured for e + e − → e + e − μ + μ − . The related structure functions F γ A and F γ B , which originate from interference terms of the scattering amplitudes, are determined for the first time.
The systematic and statistical errors added in quadrature. F2(NAME=FA) AND F2(NAME=FB) are related structure functions FA and FB, which originate from inerference terms of the scattering amplitudes. See text for exact definition and details.
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 Z 0 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 α s (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.
Measured EEC distribution corrected for detector effects and photon radiation. Errors are combined statistical and systematic uncertainties.
Measured average jet multiplicities for the K_PT algorithm. All numbers are corrected for detector effects and photon radiation. Errors are combined statistical and systematic uncertainties.
Value of strong coupling constant, alpha_s, determined from the data. First error is experimental, the second is theoretical.
We present measurements of the hadronic photon structure functionF2γ(x), in twoQ2 ranges with mean values of 5.9 GeV2 and 14.7 GeV2. The data were taken by the OPAL experiment at LEP, with\(\sqrt s\) close to theZ0 mass and correspond to an integratede+e− luminosity of 44.8 pb−1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon hasQ2>4 GeV2. Our measurements extend to lower values ofx than any previous experiment, and no increase ofF2γ(x) is observed.
Additional overall systematic error 5.9% not included.
Additional overall systematic error 5.9% not included.
The strong coupling constant, αs, has been determined in hadronic decays of theZ0 resonance, using measurements of seven observables relating to global event shapes, energy correlatio
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
We describe the sample of energetic single-photon events ( E γ > 15 GeV) collected by L3 in the 1991–1993 LEP runs. The event distributions agree with expectations from the Standard Model. The data are used to constrain the ZZ γ coupling and to set an upper limit of 4.1 × 10 −6 , μ B (90% C.L.) on the the magnetic moment of the τ neutrino.
The number of events expected from Standard Model is 8.2. Here UNSPEC is 'invisible' particle.
90 PCT C.L. limit on an anomalous magnetic moment for tau-neutrino from '1GAMMA + nothing' events. Magnetic moment in Bohr magnetons.
The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reactionγγ→π0π0π0 in theπ0π0π0 invariant mass range from 850 MeV/c2 to 2600 MeV/c2. An enhancement around 1750 MeV/c2 is attributed to theπ2(1670) resonance. The observedπ0π0 invariant mass distribution and theπ0 angular distributions are consistent with those expected for the decay chainπ2→π0f2(1270)→π0π0π0. From our measurements we find the following resonance parameters: two photon partial width\(\Gamma _{\pi _2 }^{\gamma \gamma }= (1.41 \pm 0.23 \pm 0.28)keV\), massM(π2)=(1742±31±49)MeV/c2. and total width\(\Gamma _{\pi _2 }^{tot}= (236 \pm 49 \pm 36)MeV\).
Data read from graph.
Cross section times branching ratio to 3pi0 assuming the decay chain pi2 --> pi0f2 --> 3pi0.
We study the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-\gamma$, with a hard photon radiated from the initial state. About 60,000 fully reconstructed events have been selected from 89 $fb^{-1}$ of BaBar data. The invariant mass of the hadronic final state defines the effective \epem center-of-mass energy, so that these data can be compared with the corresponding direct $e^+e^-$ measurements. From the $4\pi$-mass spectrum, the cross section for the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-$ is measured for center-of-mass energies from 0.6 to 4.5 $GeV/c^2$. The uncertainty in the cross section measurement is typically 5%. We also measure the cross sections for the final states $K^+ K^- \pi^+\pi^-$ and $K^+ K^- K^+ K^-$. We observe the $J/\psi$ in all three final states and measure the corresponding branching fractions. We search for X(3872) in $J/\psi (\to\mu^+\mu^-) \pi^+\pi^-$ and obtain an upper limit on the product of the $e^+e^-$ width of the X(3872) and the branching fraction for $X(3872) \to J/\psi\pi^+\pi^-$.
Measured PI+ PI- PI+ PI- cross sections. The errors are statistical only.
Measured K+ K- PI+ PI- cross sections. The errors are statistical only.
Measured K+ K- K+ K- cross sections. The errors are statistical only.
The hadronic photon structure function F γ 2 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 F γ 2 is measured in the Q 2 interval 1.2 GeV 2 ≤ Q 2 ≤9.0 GeV 2 and the x interval 0.002< x <0.2. F γ 2 shows a linear growth with ln Q 2 . The value of the slope α −1 d F γ 2 ( Q 2 )/dln Q 2 is measured to be 0.079±0.011±0.009.
No description provided.
No description provided.
No description provided.
Using data collected with the L3 detector near the Z resonance, corresponding to an integrated luminosity of 150pb-1, the branching fractions of the tau lepton into electron and muon are measured to be B(tau->e nu nu) = (17.806 +- 0.104 (stat.) +- 0.076 (syst.)) %, B(tau->mu nu nu) = (17.342 +- 0.110 (stat.) +- 0.067 (syst.)) %. From these results the ratio of the charged current coupling constants of the muon and the electron is determined to be g_mu/g_e = 1.0007 +- 0.0051. Assuming electron-muon universality, the Fermi constant is measured in tau lepton decays as G_F = (1.1616 +- 0.0058) 10^{-5} GeV^{-2}. Furthermore, the coupling constant of the strong interaction at the tau mass scale is obtained as alpha_s(m_tau^2) = 0.322 +- 0.009 (exp.) +- 0.015 (theory).
First DSYS error is experimental, the second is from theory.
New measurements at a centre-of-mass energy s ≃183 GeV of the hadronic photon structure function F γ 2 ( x ) in the Q 2 interval, 9 GeV 2 ≤ Q 2 ≤30 GeV 2 , are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb −1 . Combining with the data taken at a centre-of-mass energy of 91 GeV, the evolution of F γ 2 with Q 2 is measured in the Q 2 range from 1.2 GeV 2 to 30 GeV 2 . F γ 2 shows a linear growth with ln Q 2 ; the value of the slope α −1 d F γ 2 ( Q 2 )/dln Q 2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted.
Measured values of F2/ALPHA as a function of x. The second systematic error (DSYS) is that due to the model dependence and is the difference between the results obtained with PHOJET and TWOGAM. The full systematic error is the quadrature sum of the two systematic errors.
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