K. Ackerstaff et al., AN IMPROVED MEASUREMENT OF R-B USING A DOUBLE TAGGING METHOD, Zeitschrift fur Physik. C, Particles and fields, 74(1), 1997, pp. 1-17
This paper describes an update of the double tagging measurement of th
e fraction, R-b, of Z(0) --> <b(b)over bar> events in hadronic Z(0) de
cays, with statistics improved by including the data collected in 1994
. The presence of electrons or muons from semileptonic decays of botto
m hadrons and the detection of bottom hadron decay vertices were used
together to obtain an event sample enriched in Z(0) --> <b(b)over bar>
decays. The efficiency of the <b(b)over bar> event tagging was obtain
ed from the data by comparing the numbers of events having a bottom si
gnature in either one or both thrust hemispheres. Efficiency correlati
ons between opposite event hemispheres are small (< 0.5%) and well und
erstood through comparisons between the real and simulated data sample
s. A value of R-b = 0.2175 +/- 0.0014 +/- 0.0017 was obtained, where t
he first error is statistical and the second systematic. The uncertain
ty on the decay width Gamma(Z(0) --> <c(c)over bar>) is not included i
n these errors. The result depends on R-c as follows: Delta R-b/R-b =
-0.084 Delta R-c/R-c, where Delta R-c is the deviation of R-c from the
value 0.172 predicted by the Standard Model.