# ${{\boldsymbol \tau}}$ MAGNETIC MOMENT ANOMALY

The $\mathit q{}^{2}$ dependence is expected to be small providing no thresholds are nearby.

# ${{\boldsymbol \mu}_{{\tau}}}/({{\boldsymbol e}}\hbar{}/2{{\boldsymbol m}_{{\tau}}})−$1 = (${{\boldsymbol g}_{{\tau}}}−$2)/2 INSPIRE search

For a theoretical calculation [(${\mathit g}_{{{\mathit \tau}}}−$2)/2 = 117$~721(5){\times }10^{-8}$], see EIDELMAN 2007 .
VALUE CL% DOCUMENT ID TECN  COMMENT
$\bf{ \text{>-0.052 and <0.013}}$ OUR LIMIT
$\text{>-0.052 and <0.013}$ 95 1
 2004 K
DLPH ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at LEP2
• • • We do not use the following data for averages, fits, limits, etc. • • •
$<0.107$ 95 2
 2004 G
L3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at LEP2
$\text{>-0.007 and <0.005}$ 95 3
 2000
RVUE ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ and ${{\mathit W}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \nu}_{{\tau}}}$
$\text{>-0.052 and <0.058}$ 95 4
 1998 E
L3 1991--1995 LEP runs
$\text{>-0.068 and <0.065}$ 95 5
 1998 N
OPAL 1990--1995 LEP runs
$\text{>-0.004 and <0.006}$ 95 6
 1997
RVUE ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at LEP
$<0.01$ 95 7
 1993
RVUE ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at LEP
$<0.12$ 90
 1991
RVUE ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \tau}}{{\mathit \tau}}{{\mathit \gamma}}$ at LEP
$<0.023$ 95 8
 1983
RVUE ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ at PETRA
1  ABDALLAH 2004K limit is derived from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ total cross-section measurements at $\sqrt {s }$ between 183 and 208 GeV. In addition to the limits, the authors also quote a value of $-0.018$ $\pm0.017$.
2  ACHARD 2004G limit is derived from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ total cross-section measurements at $\sqrt {s }$ between 189 and 206 GeV, and is on the absolute value of the magnetic moment anomaly.
3  GONZALEZ-SPRINBERG 2000 use data on tau lepton production at LEP1, SLC, and LEP2, and data from colliders and LEP2 to determine limits. Assume imaginary component is zero.
4  ACCIARRI 1998E use ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit \gamma}}$ events. In addition to the limits, the authors also quote a value of $0.004$ $\pm0.027$ $\pm0.023$.
5  ACKERSTAFF 1998N use ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}{{\mathit \gamma}}$ events. The limit applies to an average of the form factor for off-shell ${{\mathit \tau}}$'s having $\mathit p{}^{2}$ ranging from ${{\mathit m}^{2}}_{{{\mathit \tau}}}$ to ($\mathit M_{{{\mathit Z}}}-{\mathit m}_{{{\mathit \tau}}}){}^{2}$.
6  ESCRIBANO 1997 use preliminary experimental results.
7  ESCRIBANO 1993 limit derived from $\Gamma\mathrm {( {{\mathit Z}} \rightarrow {{\mathit \tau}^{+}} {{\mathit \tau}^{-}} )}$, and is on the absolute value of the magnetic moment anomaly.
8  SILVERMAN 1983 limit is derived from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \tau}^{+}}{{\mathit \tau}^{-}}$ total cross-section measurements for $\mathit q{}^{2}$ up to (37 GeV)${}^{2}$.
References:
 ABDALLAH 2004K
EPJ C35 159 Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
 ACHARD 2004G
PL B585 53 Muon Pair and ${{\mathit \tau}}$ Pair Production in Two Photon Collisions at LEP
 GONZALEZ-SPRINBERG 2000
NP B582 3 Model Independent Bounds on the ${{\mathit \tau}}$ Lepton Electromagnetic and Weak Magnetic Moments
 ACCIARRI 1998E
PL B434 169 Measurement of the Anomalous Magnetic and Electric Dipole Moments of the ${{\mathit \tau}}$ Lepton
 ACKERSTAFF 1998N
PL B431 188 An Upper Limit on the Anomalous Magnetic Moment of the ${{\mathit \tau}}$ Lepton
 ESCRIBANO 1997
PL B395 369 Improved Bounds on the Electromagnetic Dipole Moments of the ${{\mathit \tau}}$ Lepton
 ESCRIBANO 1993
PL B301 419 New Bounds on the Magnetic and Electric Moments of the ${{\mathit \tau}}$ Lepton
 GRIFOLS 1991
PL B255 611 Electromagnetic Properties of the ${{\mathit \tau}}$ Lepton from ${{\mathit Z}^{0}}$ Decay
 SILVERMAN 1983
PR D27 1196 Limits on the Composite Structure of the ${{\mathit \tau}}$ Lepton and Quarks from Anomalous Magnetic Moment Measurements in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation