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In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb −1 , and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e + e − → WW process of 3.67 −0.85 +0.97 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44 (stat.) ± 0.09 (syst.) ± 0.03 (LEP) GeV/ c 2 . Alternatively, if m W is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV (V ≡ γ, Z) couplings.
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This letter describes a measurement of one of the anomalous triple gauge boson couplings using the first data recorded by the OPAL detector at LEP2. A total of 28 W-pair candidates have been selected for an integrated luminosity of 9.89±0.06 pb −1 recorded at a centre-of-mass energy of 161 GeV. We use these data to place constraints upon the coupling parameter α W φ . We analyse the predicted variation of the total cross-section for all observed channels and the distribution of kinematic variables in the semileptonic decay channels. We measure α W φ to be −0.61 −0.61 0.73 ±0.35, which is consistent with the Standard Model expectation of zero.
ALPHA-W-PHI is the triple gauge boson couplings (TGC). For definition see 'Physics at LEP2', Ed. G. Altarelli, CERN 96-01 (1996), vol. 1.
The total cross section and the forward-backward asymmetry for the process e + e − → μ + μ − ( nγ ) are measured in the energy range 20–136 GeV by reconstructing the effective centre-of-mass energy after initial state radiation. The analysis is based on the data recorded with the ALEPH detector at LEP between 1990 and 1995, corresponding to a total integrated luminosity of 143.5 pb −1 . Two different approaches are used: in the first one an exclusive selection of events with hard initial state radiation in the energy range 20–88 GeV is directly compared with the Standard Model predictions showing good agreement. In the second one, all events are used to obtain a precise measurement of the energy dependence of σ 0 and A FB 0 from a model independent fit, enabling constraints to be placed on models with extra Z bosons.
Exlclusive analysis from events with hard ISR.
Inclusive analysis from evvents with no specific selection of hard ISR.
Measurements of helicity density matrix elements have been made for the φ(1020), D*± and B* vector mesons in multihadronic Z0 decays in the OPAL experiment at LEP. Results for inclusive φ produced with high energy show evidence for production preferentially in the helicity zero state, with ρ00 = 0.54 ± 0.08, compared to the value of 1/3 expected for no spin alignment. The corresponding element for the D*± has a value of 0.40 ± 0.02, also suggesting a deviation from 1/3. The B* result, with ρ00 = 0.36 ± 0.09, is consistent with no spin alignment. Off-diagonal elements have been measured for the f and D* mesons; for the D* the element Re ρ1−1 is non-zero, indicating non-independent fragmentation of the primary quarks.
Helicity density matrices elements. Helicity beam frame is used.
Charge conjugated states are understood.
Helicity density matrices elements. Charge conjugated states are understood.
Using the CLEO detector at the Cornell $e~+e~-$ storage ring, CESR, we study the two-photon production of $\Lambda \overline{\Lambda}$, making the first observation of $\gamma \gamma \to \Lambda \overline{\Lambda}$. We present the cross-section for $ \gamma \gamma \to \Lambda \overline{\Lambda}$ as a function of the $\gamma \gamma$ center of mass energy and compare it to that predicted by the quark-diquark model.
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Using data collected with the CLEO II detector at the Cornell Electron Storage Ring, we determine the ratio R(chrg) for the mean charged multiplicity observed in Upsilon(1S)->gggamma events, to the mean charged multiplicity observed in e+e- -> qqbar gamma events. We find R(chrg)=1.04+/-0.02+/-0.05 for jet-jet masses less than 7 GeV.
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A measurement of the spectral functions of non-strange τ vector current final states is presented, using 124 358 τ pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two- and four-pion τ decay channels are compared to published results of e+e- annihilation experiments via isospin rotation. A combined fit of the pion form factor from τ decays and e+e- data is performed using different parametrizations. The mass and the width of the ρ±(770) and the ρ0(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be Mρ±(770) - Mρ0(770) = (0.0 ± 1.0) MeV/c2 and Γρ±(770) - Γρ0(770) = (0.1 ± 1.9) MeV/c2.
Invariant mass-squared distribution of the $\tau^- \to h^- \pi^0 \nu_{\tau}$ decay. The error has been set to zero if it is smaller than the point size. A dash indicates a data point lying outside the plot range.
Invariant mass-squared distributions of the $h^- 3\pi^0 \nu_{\tau}$ decay channel. The error has been set to zero if it is smaller than the point size.
Invariant mass-squared distribution of the $2h^- h^+ \pi^0 \nu_{\tau}$ decay channel. The error has been set to zero if it is smaller than the point size.
Measurements of the pp spin correlation coefficients Axx, Ayy, and Axz and analyzing power Ay for pp elastic scattering at 197.8 MeV over the angular range 4.5°–17.5° have been carried out. The statistical accuracy is approximately ±0.01 for Amn and ±0.004 for Ay, while the corresponding scale factor uncertainties are 2.4% and 1.3%, respectively. The experiment makes use of a polarized hydrogen gas target internal to a proton storage ring (IUCF Cooler) and a circulating beam of polarized protons. The target polarization (Q=0.79) is switched in sign and in direction (x,y,z) every 2 s by reversing a weak guide field (about 0.3 mT). The forward-scattered protons are detected in two sets of wire chambers and a scintillator, while recoil protons are detected in coincidence with the forward protons by silicon strip detectors placed 5 cm from the proton beam. The background rate from scattering by the walls of the target cell is (0.2±0.2)% of the good event rate. Analysis methods and comparisons with pp potential models and pp partial wave analyses are described.
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