Search for anomalous weak dipole moments of the tau lepton

The anomalous weak dipole moments of the tau lepton are measured in a data sample collected by ALEPHfrom 1990 to 1995 corresponding to an integrated luminosity of 155pb-1. Tau leptons produced in the reaction e+e- -> tau+tau- at energies close to the Z mass are studied using their semileptonic decays to pi, rho, a_1 -> pi 2pi0 or a_1 -> 3 pi. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, Re,mu_tau, Im,mu_tau, Re, d_tau and Im, d_tau, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained 95% CL: |Re, mu_tau | < 1.14 x 10-3, |Im}, mu_tau | < 2.65 x 10-3, |Re}, d_tau | < 0.91 x 10-3, and |Im, d_tau | < 2.01 x 10-3.

Note:

22 pages, 6 figures Report-no: CERN-EP-2002-068

electron positron: colliding beams
electron positron: annihilation
Z0: electroproduction
tau: pair production
tau: moment
weak interaction: electric moment
weak interaction: magnetic moment
upper limit
tau: semileptonic decay
pi: multiple production

References(32)

Figures(8)

[1]

The Tau weak magnetic dipole moment

J. Bernabeu
(
- Valencia U.
)
,
G.A. Gonzalez-Sprinberg
(
- Valencia U.
)
,
M. Tung
(
- Valencia U.
)
,
J. Vidal
(
- Valencia U.
)

- Nucl.Phys.B 436 (1995) 474-486
•
e-Print:
- hep-ph/9411289
•
DOI:
- 10.1016/0550-3213(94)00525-J

[2]

CP Violation and Z Boson Decays

- Z.Phys.C 43 (1989) 117
•
DOI:
- 10.1007/BF02430617

[3]

Search for CP violation in Z ---> tau tau

ALEPH

Collaboration

•

D. Buskulic
(
- Annecy, LAPP
)

et al.

- Phys.Lett.B 297 (1992) 459-468
•
DOI:
- 10.1016/0370-2693(92)91285-H

[3]

Search for CP violation in the decay Z ---> tau+ tau-

ALEPH

Collaboration

•

D. Buskulic
(
- Annecy, LAPP
)

et al.

- Phys.Lett.B 346 (1995) 371-378
•
DOI:
- 10.1016/0370-2693(95)00093-Z

[4]

Test of CP invariance in e+ e- ---> Z0 ---> tau+ tau- and a limit on the weak dipole moment of the tau lepton

OPAL

Collaboration

•

P.D. Acton
(
- Brunel U.
)

et al.

- Phys.Lett.B 281 (1992) 405-415
•
DOI:
- 10.1016/0370-2693(92)91161-2

[4]

A Test of CP invariance in Z0 ---> tau+ tau- using optimal observables

OPAL

Collaboration

•

R. Akers

et al.

- Z.Phys.C 66 (1995) 31-44
•
DOI:
- 10.1007/BF01496578

[4]

Search for CP violation in Z0 ---> tau+ tau- and an upper limit on the weak dipole moment of the tau lepton

OPAL

Collaboration

•

K. Ackerstaff

et al.

- Z.Phys.C 74 (1997) 403-412
•
DOI:
- 10.1007/s002880050403

[5]

Measurement of the weak dipole moments of the tau lepton

L3

Collaboration

•

M. Acciarri

et al.

- Phys.Lett.B 426 (1998) 207-216
•
DOI:
- 10.1016/S0370-2693(98)00290-1

[6]

Measurement of tau branching ratios

ALEPH

Collaboration

•

D. Decamp
(
- Annecy, LAPP
)

et al.

- Z.Phys.C 54 (1992) 211-228
•
DOI:
- 10.1007/BF01566649

[7]

Tau leptonic branching ratios

ALEPH

Collaboration

•

D. Buskulic
(
- Annecy, LAPP
)

et al.

- Z.Phys.C 70 (1996) 561-578
•
DOI:
- 10.1007/s002880050133

[8]

Tau hadronic branching ratios

ALEPH

Collaboration

•

D. Buskulic
(
- Annecy, LAPP
)

et al.

- Z.Phys.C 70 (1996) 579-608
•
DOI:
- 10.1007/s002880050134

[9]

Measurement of the tau polarization at LEP

ALEPH

Collaboration

•

A. Heister
(
- Aachen, Tech. Hochsch.
)

et al.

- Eur.Phys.J.C 20 (2001) 401-430
•
e-Print:
- hep-ex/0104038
•
DOI:
- 10.1007/s100520100689

[10]

On the Lorentz structure of Z ---> tau tau

U. Stiegler
(
- Munich, Max Planck Inst.
)

- Z.Phys.C 58 (1993) 601-608
•
DOI:
- 10.1007/BF01553020

[11]

Measurement of the Z resonance parameters at LEP

ALEPH

Collaboration

•

R. Barate
(
- Annecy, LAPP
)

et al.

- Eur.Phys.J.C 14 (2000) 1-50
•
DOI:
- 10.1007/s100520000319

[12]

Measurement of the transverse spin correlations in the decay Z ---> tau+ tau-

ALEPH

Collaboration

•

R. Barate
(
- Annecy, LAPP
)

et al.

- Phys.Lett.B 405 (1997) 191-201
•
DOI:
- 10.1016/S0370-2693(97)00664-3

[13]

Optimal observable to measure the imaginary component of the tau anomalous weak-magnetic dipole moment

F. Sanchez
(
- Barcelona, Autonoma U.
)

- Phys.Lett.B 412 (1997) 137-142
•
DOI:
- 10.1016/S0370-2693(97)01051-4

[14]

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

[14]

The tau decay library TAUOLA: Version 2.4

S. Jadach
(
- CERN and
- Cracow, INP
)
,
Z. Was
(
- CERN and
- Cracow, INP
)
,
R. Decker
(
- Karlsruhe U.
)
,
Johann H. Kuhn
(
- Karlsruhe U.
)

- Comput.Phys.Commun. 76 (1993) 361-380
•
DOI:
- 10.1016/0010-4655(93)90061-G

[15]

Tau spin correlations at the Z peak: Aplanarities of the decay products

- Phys.Lett.B 257 (1991) 219-226
•
DOI:
- 10.1016/0370-2693(91)90885-T

[15]

Tau polarization at the Z peak from the acollinearity between both tau decay products

R. Alemany
(
- Barcelona, Autonoma U.
)
,
N. Rius
(
- Valencia U.
)
,
J. Bernabeu
(
- Valencia U. and
- CERN
)
,
J.J. Gomez-Cadenas
(
- CERN
)
,
A. Pich
(
- CERN
)

- Nucl.Phys.B 379 (1992) 3-23
•
DOI:
- 10.1016/0550-3213(92)90587-2

[16]

QED O (ALPHA**3) RADIATIVE CORRECTIONS TO THE REACTION E+ E- ---> TAU+ TAU- INCLUDING SPIN AND MASS EFFECTS. (ERRATUM)

S. Jadach
(
- Jagiellonian U.
)
,
Z. Was
(
- Jagiellonian U.
)

- Acta Phys.Polon.B 15 (1984) 1151,
- Acta Phys.Polon.B 16 (1985) 483 (erratum),
- Acta Phys. Pol. B16 ( 1985) 483. ( Acta Phys. Pol. B15 ( 1984) 1151)