the logarithm of the jet measure, $y_{32}$. []{data-label="fig:top_parton"}](figure_2b)

To study the impact of the POWHEG style correction on top quark decays, parton level $e^+ e^- \rightarrow t \bar{t}$ events were simulated and analysed as in [@Hamilton:2006ms]. Events were generated at a centre-of-mass energy close to the $t \bar{t}$ threshold, $\sqrt{s} =360 {\,\mathrm{GeV}}$, to minimize the effects of radiation from the initial-state shower. Unless otherwise stated, in this study we use the default set of tuned perturbative and non-perturbative parameters, or *event tune*, in  version 2.6 [@Arnold:2012fq]. Final-state partons were clustered into three jets using the [@Cacciari:2011ma] implementation of the $k_T$ algorithm. The $W$ bosons were decayed leptonically and their decay products excluded from the jet clustering. Events were discarded if they contained a jet with $p_{T}<10 {\,\mathrm{GeV}}$ or the minimum jet separation[^4], $\Delta R$ , did not satisfy $ \Delta R \geq 0.7$. Using events that passed these selection criteria, differential distributions were plotted of $ \Delta R $ and $\log \left(y_{32}\right)$, where $y_{32}$ is the value of the jet resolution parameter[^5] at which a three jet event is classified as a two jet event. The resulting distributions are shown in the left and right-hand plots in Fig. \[fig:top\_parton\]. Distributions 