Date

Measurement of the Michel parameters and the average tau-neutrino helicity from tau decays in e+ e- ---> tau+ tau-

The L3 collaboration Acciarri, M. ; Adam, A. ; Adriani, O. ; et al.
Phys.Lett.B 377 (1996) 313-324, 1996.
Inspire Record 418417 DOI 10.17182/hepdata.47587

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.

1 data table

No description provided.


Measurement of Lambda polarization from Z decays

The ALEPH collaboration Buskulic, D. ; De Bonis, I. ; Decamp, D. ; et al.
Phys.Lett.B 374 (1996) 319-330, 1996.
Inspire Record 415745 DOI 10.17182/hepdata.47830

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.

3 data tables

No description provided.

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Measurement of Lambda(b) polarization in Z decays

The ALEPH collaboration Buskulic, D. ; Casper, D. ; De Bonis, I. ; et al.
Phys.Lett.B 365 (1996) 437-447, 1996.
Inspire Record 402895 DOI 10.17182/hepdata.48060

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.).

1 data table

No description provided.


A Search for jet handedness in hadronic Z0 decays

The SLD collaboration Abe, K. ; Abt, I. ; Ahn, C.J. ; et al.
Phys.Rev.Lett. 74 (1995) 1512-1516, 1995.
Inspire Record 378343 DOI 10.17182/hepdata.19666

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.}

1 data table

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.


Measurement of the polarization of tau leptons produced in Z decays

The ALEPH collaboration Decamp, D. ; Deschizeaux, B. ; Goy, C. ; et al.
Phys.Lett.B 265 (1991) 430-444, 1991.
Inspire Record 316781 DOI 10.17182/hepdata.29377

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.

2 data tables

Results are for both TAU+ and TAU- decay. Final combined result contains statistical and systematic errors added in quadrature.

No description provided.


Measurements of the Polarization of Protons from Deuteron Photodisintegration

Liu, F.F. ; Lundquist, D.E. ; Wiik, B.H. ;
Phys.Rev. 165 (1968) 1478-1482, 1968.
Inspire Record 944944 DOI 10.17182/hepdata.26514

The polarization of the proton produced by the photodisintegration of the deuteron has been measured at several angles for photon energies between 170 and 450 MeV. The polarization is found to be around -0.20 (Basel convention) for 90° c.m. and photon energies between 200 and 300 MeV. This is in reasonable agreement with a calculation by D. George based upon the Austern model. However, the calculation fails to explain the strong increase in polarization with increasing photon energies. At a photon energy of 450 MeV and 90° c.m. the proton polarization is as large as -0.60.

1 data table

No description provided.


Positive-Pion Production Asymmetry with Polarized Bremsstrahlung Near Second Resonance

Liu, F.F. ; Vitale, S. ;
Phys.Rev. 144 (1966) 1093-1100, 1966.
Inspire Record 50917 DOI 10.17182/hepdata.26643

The azimuthal asymmetry Σ=(σ⊥−σII)(σ⊥+σII) in π+ photoproduction by linearly polarized bremsstrahlung was measured at photon energies from 475 to 750 MeV at 90° and 135° in the center-of-mass system. The experimental results show that even in this energy region, π+ are produced predominantly in the plane of the magnetic vector.

2 data tables

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Charged-Pion Photoproduction from Deuterium with Polarized Bremsstrahlung

Liu, F.F. ; Drickey, D.J. ; Mozley, R.F. ;
Phys.Rev. 136 (1964) B1183-B1186, 1964.
Inspire Record 1186786 DOI 10.17182/hepdata.26721

Measurements have been made on the ratio of pion-production cross sections at right angles to and along the photon electric-field vector. The positive and negative pions were first momentum-analyzed and counted by means of a counter telescope. Data have been taken at 45, 90, and 135° in the c.m. system, and at proton energies of 225, 330, and 450 MeV. A comparison of the data is made with the dispersion-relation calculation of McKinley.

2 data tables

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