The Michel parameters ϱ, η, ξ, and ξδ, the chirality parameter ξ h and the τ polarization P τ are measured using 32012 τ pair decays. Their values are extracted from the energy spectra of leptons and hadrons in τ − → l − ν l ν τ and τ − → π − ν τ decays, the energy and decay angular distributions in τ − → ϱ − ν τ decays, and the correlations in the energy spectra and angular distributions of the decay products. Assuming universality in leptonic and semileptonic τ decays, the results are ϱ = 0.794±0.039±0.031, η = 0.25±0.17±0.11, ξ = 0.94±0.21±0.07, ξδ = 0.81±0.14±0.06, ξ h = −0.970±0.053±0.011, and P τ = −0.154±0.018±0.012. The measurement is in agreement with the V-A hypothesis for the weak charged current.
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The polarization of Λ baryons from Z decays is studied with the Aleph apparatus. Evidence of longitudinal polarization of s quarks from Z decay is observed for the first time. The measured longitudinal Λ polarization is P L Λ = −0.32 ± 0.07 for z = p p beam > 0.3 . This agrees with the prediction of −0.39 ± 0.08 from the standard model and the constituent quark model, where the error is due to uncertainties in the mechanism for Λ production. The observed Λ polarization is diluted with respect to the primary s quark polarization by Λ baryons without a primary s quark. Measurements of the Λ forward-backward asymmetry and of the correlation between back-to-back Λ Λ pairs are used to check this dilution. In addition the transverse Λ polarization is measured. An indication of transverse polarization, more than two standard deviations away from zero, is found along the normal to the plane defined by the thrust axis and the Λ direction.
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The Λ b polarization in hadronic Z decays is measured in semileptonic decays from the average energies of the charged lepton and the neutrino. In a data sample of approximately 3 million hadronic Z decays collected by the ALEPH detector at LEP between 1991 and 1994, 462 ± 31 Λ b candidates are selected using ( Λπ + )-lepton correlations. From this event sample, the Λ b polarization is measured to be P Λ b = −0.23 −0.20 +0.24 (stat.) −0.07 +0.08 (syst.).
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We have searched for signatures of polarization in hadronic jets from $Z~0 \rightarrow q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95\% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}
Polarized E- beam. Events were classified as being of light or heavy flavors based on impact parameters of charged tracks measured in the vertex detector. Jet handedness are measured for helicity-based and chirality-based analysis (seetext). C=95PCT CL indicates the upper limits at the 95 PCT C.L. on the magnitudes.
A complete set of polarization-transfer observables has been measured for quasifree (p→,n→) reactions on H2, C12, and Ca40 at a bombarding energy of 495 MeV and a laboratory scattering angle of 18°. The data span an energy-loss range from 0 to 160 MeV, with a corresponding momentum transfer range of qc.m.=1.7–1.9 fm−1. The laboratory observables are used to construct partial cross sections proportional to the nonspin response and three orthogonal spin responses. These results are compared to the transverse spin response measured in deep inelastic electron scattering and to nuclear responses based on the random phase approximation. The polarization observables for all three targets are remarkably similar and reveal no evidence for an enhancement of the spin-longitudinal nuclear response relative to the spin-transverse response. These results suggest the need for substantial modifications to the standard form assumed for the residual particle-hole interaction.
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The polarization of τ leptons produced in the reaction e + e − → τ + τ − at the Z resonance has been measured using the τ decay modes e ν e ν τ , μν μ ν τ , πν τ , ϱν τ , and a 1 ν τ . The mean value obtained is P τ = −0.152±0.045, indicating that parity is violated in the neutral current process e + e − → τ + τ − . The result corresponds to a ratio of a neutral current vector and axial vector coupling constants of the τ lepton g V τ (M 2 Z ) g A τ (M 2 Z ) = 0.076±0.023 and a value of the electroweak mixing parameter sin 2 θ w ( M 2 Z ) = 0.2302 ± 0.0058.
Results are for both TAU+ and TAU- decay. Final combined result contains statistical and systematic errors added in quadrature.
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We have measured the polarization of D*, the energy dependence of the polarization, and the spin-density matrix of D* in e+e− annihilation at a center-of-mass energy of 29 GeV using the Time Projection Chamber detector at the SLAC storage ring PEP. In 147 pb−1 of data we see no strong evidence for polarization, alignment, or final-state interactions in this fragmentation process.
Polarization is the factor alpha(z) in the expression d width (D*-->D pi)/domega = C(1+alpha(z)cos(theta)**2).
Spin density matrices for D* --> D0 pi+.
The vector analyzing power has been measured for π+d elastic scattering at 0.74 GeV/c in the angular range of thetac.m.=40?(de–105°, using a polarized deuteron target in a large aperture spectrometer. A comparison with calculations based on the Glauber model was made.
Data read from graph. Statistical errors only.
The neutron polarization asymmetry in neutron-deuteron scattering has been measured from 44.5° to 160° (c.m.) neutron angle. The results display quantitatively the same structure as proton-deuteron polarization data, but discrepancies appear for angles corresponding to those near the minimum of the differential cross section. In this region the polarization is considerably more negative than in the proton-deuteron case, and both are more negative than current theoretical predictions.
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