We refer the reader to the 1982 version of the PDG [27]
for a critical discussion of the wealth of experimental information on
. Here we content ourselves with a short summary.
-experiments
The 
values obtained are fairly consistent. The average values are
-experiments
The result by Donaldson et al. [28]
dominates the statistics in the 
case. The 
value
(3.23) is consistent with the 
value (3.22).
However, the situation concerning the slope 
is rather unsatisfactory, as the following (chronological) list illustrates.
The 
fit to the 
data yields 
,
with a 
[27, p.76,]!
The situation in the charged mode 
is slightly better [27].
