Measurements of top quark decay properties Page: 3 of 9
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1 14 DO Preliminary
-100 a 12
50 4 95% C.L.
2 68% C.L.
R = 1.06+g 0.27....I.. 0.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0. ' '. ' ' B(t -> Wb)/B(t -> Wq)
S 0.5 1 1.5 2
Figure 1: Results of measurements of R (defined in the text) at CDF (left) and DO (right). The standard
model predicts R 1. The DO analysis performs a simultaneous measurement of R and the tt production
quark generations this restriction would be lifted, allowing a greater rate of t -> Wq where q/ is a
d or s quark. This can be tested by using the finite B hadron lifetime to identify jets arising from b
quarks and measuring the ratio:
BR(t - Wb) +BR(t - Wq/) (3.1)
The distribution of jets identified as b jets depends on R as follows:
Pn(tt) = R2Pn (tt-> bb +X) (3.2)
+2R (1 - R) Pn (tt-> qib+X )
+(1 -R2) Pn (tt -> qic+X )
where Pn (tt) is the overall probability to observe n = 0,1 or 2 b-tagged jets, Pn (t - bb +X) is
the probability to observe n tagged jets when both top quarks decay to Wb, Pn (tt -> qb +X) is the
probability to observe n tagged jets when one top quark decays to Wb and the other decays to Wq/,
and Pn (tt -> qcq,+X) is the probability to observe n tagged jets when both top quarks decay to
Wq/. The Pn depend upon the efficiencies for b and light quark jets to satisfy the b tagging criteria,
which are measured in data control samples.
The distribution of f+jets and dilepton events with zero, one, and two tagged b jets in 160pb-1
of CDF data is consistent with standard model expectations, as shown in Table 1. A maximum
likelihood fit to this distribution (shown in Fig. 1) yields R = 1.12+02(stat.) 13(stat.). This
is equivalent to R having a lower limit of 0.61 at 95% C.L. using the Feldman-Cousins technique.
DO performs a simultaneous measurement of the tt production cross section and R by fitting
the number of events with 0, 1, and 2 b-tagged jets in 230 pb-1 of data. The preliminary result of
the fit is shown in Fig. 1. G is found to be 7.9i j7(stat. + syst.) 0.5(lumi.) pb, and R is measured
Measurements of top quark decay properties
Erich W. Varnes
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Varnes, Erich W. & U., /Arizona. Measurements of top quark decay properties, article, April 1, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc883225/m1/3/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.