Measurement of the tau lepton polarization and its forward - backward asymmetry from Z0 decays

We report on a measurement of the tau lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector. This measurement is based on analyses of the

\tau\to e\bar v_e v_\tau

,\tau\to \mu \bar v_\muv_\tau, τ→π(K)vτ and τ→ρvτ from a sample of 30663 e+e+→τ+τ- events collected during the years 1990 to 1992. Assuming that the tau lepton decays according to V-A theory, we measure the average τ polarization to be =(−14.9±1.9±1.3)% and the τ polarization forward-backward asymmetry to be ApolFB=(−8.9±2.2±0.9)%, where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality. When combined under the assumption of universality, our results can be interpreted as a measurement of sin2θefflept=0.2321±0.0023 within the context of the Standard Model.

electron positron: colliding beams
colliding beams: electron positron
electron positron: annihilation
annihilation: electron positron
Z0: electroproduction
electroproduction: Z0
Z0: leptonic decay
leptonic decay: Z0
tau: pair production
pair production: tau

References(31)

Figures(0)

Partial Symmetries of Weak Interactions

S.L. Glashow
(
- Copenhagen U.
)

- Nucl.Phys. 22 (1961) 579-588,
- Also in *Lai, C. H. (Ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 171-180
•
DOI:
- 10.1016/0029-5582(61)90469-2

A Model of Leptons

Steven Weinberg
(
- MIT, LNS
)

- Phys.Rev.Lett. 19 (1967) 1264-1266,
- Also in *Lichtenberg, D. B. (ed.), Rosen, S. P. (ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 157-159,
- In *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 185-187,
- In *Rosner, J. L. (ed.): New Particles*, 26-28
•
DOI:
- 10.1103/PhysRevLett.19.1264

Weak and Electromagnetic Interactions

Abdus Salam
(
- Imperial Coll., London and
- ICTP, Trieste
)

- Conf.Proc.C 680519 (1968) 367-377,
- Reprinted in *Lichtenberg, D. B. (ed.), Rosen, S. P. (ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 160-170, and in *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 188-198,
- Also in *Rosner, J.L. (ed.): New particles* 29-39,
- Also in *Ali, A. (ed.) et al.: Selected papers of Abdus Salam* 244-254
•
DOI:
- 10.1142/9789812795915_0034

Measurement of branching ratios and tau polarization from tau ---> e neutrino anti-neutrino , tau ---> mu neutrino anti-neutrino, and tau ---> pi (K) neutrino decays at LEP

OPAL

Collaboration

•

G. Alexander
(
- Tel Aviv U.
)

et al.

- Phys.Lett.B 266 (1991) 201-217
•
DOI:
- 10.1016/0370-2693(91)90768-L

A Combined Analysis of the Hadronic and Leptonic Decays of the $\Z^0$

OPAL

Collaboration

•

M.Z. Akrawy
(
- Queen Mary, U. of London
)

et al.

- Phys.Lett.B 240 (1990) 497-512
•
DOI:
- 10.1016/0370-2693(90)91137-Z

Measurement of the $Z^0$ line shape parameters and the electroweak couplings of charged leptons

OPAL

Collaboration

•

G. Alexander

et al.

- Z.Phys.C 52 (1991) 175-208

Precision measurements of the neutral current from hadron and lepton production at LEP

OPAL

Collaboration

•

P.D. Acton

et al.

- Z.Phys.C 58 (1993) 219-238
•
DOI:
- 10.1007/BF01560340

Improved measurements of the neutral current from hadron and lepton production at LEP

OPAL

Collaboration

•

R. Akers

et al.

- Z.Phys.C 61 (1994) 19-34
•
DOI:
- 10.1007/BF01641883

Decay Correlations of Heavy Leptons in e+ e- ---> Lepton+ Lepton-

Yung-Su Tsai
(
- SLAC
)

- Phys.Rev.D 4 (1971) 2821,
- Phys.Rev.D 13 (1976) 771 (erratum)
•
DOI:
- 10.1103/PhysRevD.13.771

Review of particle properties. Particle Data Group

et al.

- Phys.Rev.D 45 (1992) S1,
- Phys.Rev.D 46 (1992) 5210 (erratum)
•
DOI:
- 10.1103/PhysRevD.45.S1

Tau Polarization Measurements at LEP and SLC

Kaoru Hagiwara
(
- Durham U. and
- KEK, Tsukuba
)
,
Alan D. Martin
(
- Durham U.
)
,
D. Zeppenfeld
(
- Wisconsin U., Madison
)

- Phys.Lett.B 235 (1990) 198-202
•
DOI:
- 10.1016/0370-2693(90)90120-U

The OPAL detector at LEP

OPAL

Collaboration

•

K. Ahmet

et al.

- Nucl.Instrum.Meth.A 305 (1991) 275-319
•
DOI:
- 10.1016/0168-9002(91)90547-4

The Trigger system of the OPAL experiment at LEP

OPAL

Collaboration

•

M. Arignon
(
- Saclay
)

et al.

- Nucl.Instrum.Meth.A 313 (1992) 103-125
•
DOI:
- 10.1016/0168-9002(92)90087-K

The Detector simulation program for the OPAL experiment at LEP

OPAL

Collaboration

•

J. Allison
(
- Manchester U.
)

et al.

- Nucl.Instrum.Meth.A 317 (1992) 47-74
•
DOI:
- 10.1016/0168-9002(92)90593-S

The Monte Carlo program KORALZ, version 3.8, for the lepton or quark pair production at LEP / SLC energies

Stanislaw Jadach
(
- CERN
)
,
B.F.L. Ward
(
- Tennessee U. and
- SLAC
)
,
Zbigniew Was
(
- Cracow, INP
)

- Comput.Phys.Commun. 66 (1991) 276-292,
- Comput. Phys. Commun. 66 (1991) 276-292 and CERN Geneva - TH. 5994 (91/02,rec.May) 24 p
•
DOI:
- 10.1016/0010-4655(91)90077-X

TAUOLA: A Library of Monte Carlo programs to simulate decays of polarized tau leptons

- Comput.Phys.Commun. 64 (1990) 275-299,
- Comput. Phys. Commun. 64 (1990) 275-299 and CERN Geneva - TH. 5856 (90,rec.Oct.) 37 p
•
DOI:
- 10.1016/0010-4655(91)90038-M