Are additional heavy quarks necessary to explain the observed behavior of R(s)?
Kuz'min V.A. , Tavkhelidze A.N. , Chetyrkin K.G.
The sum rules obtained by Krasnikov and Chetyrkin (1977) at finite energies for R(s) = σ(β ~e +hadrons) /cr(e ~e +—>μ~μ+) are compared with experiment. It is found that the four-quark model agrees satisfactorily with the experimental data (with the heavy lepton taken into account.). It is shown that the five-quark model (with Q5 = —1/3) describes the experimental results in the best manner.