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.
No description provided.
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 spin asymmetry in deep inelastic scattering of longitudinally polarised muons by longitudinally polarised protons has been measured in the range 0.01<×<0.7. The spin dependent structure function g 1 ( x ) for the proton has been determined and, combining the data with earlier SLAC measurements, its integral over x found to be 0.126±0.010(stat.)±0.015(syst.), in disagreement with the Ellis-Jaffe sum rule. Assuming the validity of the Biorken sum rule, this result implies a significant negative value for the integral of g 1 for the neutron. These integrals lead to the conclusion, in the naïve quark parton model, that the total quark spin constitutes a rather small fraction of the spin of the nucleon. Results are also presented on the asymmetries in inclusive hadron production which are consistent with the above picture.
THE MEAN Q**2 FOR EACH OF THE 10 VALUES OF X BELOW ARE 3.5,4.5,6.0, 8.010.3,12.9,15.2,18.0,22.5,29.5.
No description provided.
No description provided.
Results are presented on the inclusive photoproduction of λ and λ for incident photon energies between 25 and 70 GeV. The slope parameter of the p T 2 distribution is found to be 2.83±0.1 GeV −2 for λ and 3.28±0.25 GeV −2 for λ . The x F distributions, measured in the range −0.2 to 0.7, show that while λ are produced centrally, λ production extends to more negative values of x F ; the shapes show no energy dependence and are similar to those in pion-induced reactions. The polarization of the produced λ is less than 10%. The results are discussed in terms of vector dominance and quark fusion models.
No description provided.
No description provided.
No description provided.
Results are presented on vector meson production in the hypercharge exchange reactions: π + p → K ∗+ (890) Y + and K − p→ ρ − Y + where Y + is either Σ + or Y ∗+ (1385). These reactions have been studied at 7 GeV/ c and 11.5 GeV/ c using the SLAC Hybrid Facility. Total and differential cross sections, hyperon polarization, and vector meson decay angular distributions are presented. We find that reactions with Σ + production are dominated by natural parity exchange. The Y ∗ (1385) reactions are consistent with substantial natural parity exchange contributions but also show significant unnatural parity exchange. The differential cross sections and polarization measurements for the vector meson production are compared to the pseudoscalar production reactions.
Axis error includes +- 20/20 contribution.
Axis error includes +- 20/20 contribution.
Axis error includes +- 20/20 contribution.
We have studied hypercharge exchange in two pairs of line-reversed reactions at 7 GeV/ c incident beam momentum in a triggered bubble chamber experiment at the SLAC Hybrid Facility. The experiment was carried out with the particular object of testing the predictions of exchange degeneracy using the same apparatus. We present differential and total cross sections for the reactions π + p → K + Σ + , K − p →π − Σ + and π + p → K + Y ∗+ (1385), K − p →π − Y ∗+ (1385) from a π + exposure of sensitivity 150 events/μb and a K − exposure of 100 events/μb. In each case we have measured the polarization of the final-state hyperon for | t |<1.0 (GeV/ c ) 2 by direct observation of its decay in the bubble chamber. We present results from an amplitude analysis of the Y ∗ (1385) reactions and find agreement with the predictions of the additive quark model. The Σ + polarization data are consistent with weak exchange degeneracy but the predicted equality of the differential cross section is not observed.
Axis error includes +- 10/10 contribution.
Axis error includes +- 10/10 contribution.
INCREASED STATISTICS OVER EARLIER RESULTS REPORTED IN P. A. BAKER ET AL., PRL 40, 678 (1978).
The polarization of the Σ+ has been measured for the line-reversed reactions π+p→K+Σ+ and K−p→π−Σ+ at 7 and 11.6 GeV/c using the SLAC Hybrid Facility. Since the Σ+ decay is observed in the bubble chamber, the trigger of the flash lamps on a fast K+(π−) did not bias the polarization measurements. We find that the Σ+ polarizations from the two reactions have opposite signs but similar magnitudes and are in much better agreement with the predictions of weak exchange degeneracy than previous lower-energy comparisons.
No description provided.
Cross sections, differential cross sections, and hyperon polarization results are presented for the reactions K¯0p→Λπ+ and K¯0p→Σ0π+ in the momentum interval 1 to 12 GeV/c. Emphasis is placed on the comparison of Λ and Σ channels, and on the momentum dependences of the data. In particular, the Λ polarization data are consistent with being independent of energy above 2 GeV/c; and the slopes of the forward cross sections are found to increase toward the slope values for the line-reversed reactions πp→K(Λ,Σ) as energy increases.
No description provided.
No description provided.
RESONANCE REGION CROSS SECTIONS.
We observe an energy-dependent polarization of the Σ+ produced in the reaction π+n→K0Σ+ at incident beam momenta between 1.1 and 2.4 GeV/c. These data form a significant source of information on the Σ− polarization in the charge-symmetric reaction π−p→K+Σ−.
INTEGRATED OVER ALL PRODUCTION ANGLES.
No description provided.
The elastic scattering of 600-MeV protons from light nuclei has been studied at the National Aeronautics Space Administration Space Radiation Effects Laboratory (SREL) synchrocyclotron. Differential cross sections have been obtained for the scattering of protons from hydrogen, deuterium, helium-3, and helium-4. Polarization was measured for deuterium and He4 nuclei. The p−p cross-section data are in excellent agreement with the predictions from the Livermore phase shifts. Small-angle p−D, p−He3 elastic scattering data are compared with calculations based on the multiple-scattering theories of Watson and Glauber.
No description provided.
No description provided.
No description provided.
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