pdgLive

${{\mathit \tau}}$-DECAY PARAMETERS

$\rho ({{\mathit e}}$ or ${{\mathit \mu}}$) PARAMETER

INSPIRE JSON (beta) PDGID:

($\mathit V−\mathit A$) theory predicts $\rho $ = $0.75$.

VALUE

EVTS

DOCUMENT ID

TECN

COMMENT

$\bf{ 0.745 \pm0.008}$

OUR FIT

$\bf{ 0.749 \pm0.008}$

OUR AVERAGE

$0.742$ $\pm0.014$ $\pm0.006$

81k

ALEP

1991--1995 LEP runs

$0.775$ $\pm0.023$ $\pm0.020$

36k

DLPH

1992--1995 runs

$0.781$ $\pm0.028$ $\pm0.018$

46k

OPAL

1990--1995 LEP runs

$0.762$ $\pm0.035$

54k

L3

$1991 - 1995$ LEP runs

$0.731$ $\pm0.031$

ARG

${\it{}E}^{\it{}ee}_{\rm{}cm}$= $9.5 - 10.6$ GeV

$0.72$ $\pm0.09$ $\pm0.03$

SLD

1993--1995 SLC runs

$0.747$ $\pm0.010$ $\pm0.006$

55k

CLEO

${\it{}E}^{\it{}ee}_{\rm{}cm}$= $10.6$ GeV

$0.79$ $\pm0.10$ $\pm0.10$

3732

MAC

${\it{}E}^{\it{}ee}_{\rm{}cm}$= 29 GeV

$0.71$ $\pm0.09$ $\pm0.03$

1426

CLEO

${{\mathit e}^{+}}{{\mathit e}^{-}}$ near ${{\mathit \Upsilon}{(4S)}}$

• • We do not use the following data for averages, fits, limits, etc. • •

$0.735$ $\pm0.013$ $\pm0.008$

31k

CLEO

Repl. by ALEXANDER 1997F

$0.794$ $\pm0.039$ $\pm0.031$

18k

L3

Repl. by ACCIARRI 1998R

$0.732$ $\pm0.034$ $\pm0.020$

8.2k

ARG

${\it{}E}^{\it{}ee}_{\rm{}cm}$= $9.5 - 10.6$ GeV

$0.738$ $\pm0.038$

ARG

Repl. by ALBRECHT 1998

$0.751$ $\pm0.039$ $\pm0.022$

ALEP

Repl. by HEISTER 2001E

$0.742$ $\pm0.035$ $\pm0.020$

8000

ARG

${\it{}E}^{\it{}ee}_{\rm{}cm}$= $9.4 - 10.6$ GeV

¹

Combined fit to ARGUS tau decay parameter measurements in ALBRECHT 1998, ALBRECHT 1995C, ALBRECHT 1993G, and ALBRECHT 1994E. ALBRECHT 1998 use tau pair events of the type ${{\mathit \tau}^{-}}$ ${{\mathit \tau}^{+}}$ $\rightarrow({{\mathit \ell}^{-}}{{\overline{\mathit \nu}}_{{{{{\mathit \ell}}}}}}{{\mathit \nu}_{{{\tau}}}})({{\mathit \pi}^{+}}{{\mathit \pi}^{0}}{{\overline{\mathit \nu}}_{{{\tau}}}}$), and their charged conjugates.

²	ABE 1997O assume $\eta $ = 0 in their fit. Letting $\eta $ vary in the fit gives a $\rho $ value of $0.69$ $\pm0.13$ $\pm0.05$.

³	Value is from a simultaneous fit for the $\rho $ and $\eta $ decay parameters to the lepton energy spectrum. Not independent of ALBRECHT 1990E $\rho ({{\mathit e}}$ or ${{\mathit \mu}}$) value which assumes $\eta $ = 0. Result is strongly correlated with ALBRECHT 1995C.

⁴	Combined fit to ARGUS tau decay parameter measurements in ALBRECHT 1995C, ALBRECHT 1993G, and ALBRECHT 1994E.

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