bbtautau: Why the had-had channel is best
There is more ttbar background in the lep-had, because you have W->lnu decays
ttbar: had had : 3/5**2 (1/9)**2 = 3/5**2 (1/9)**2 = 0.004 lep had: 2 * 2*(1.2/9) * 3/5 *1./9 = 4.8 * (1/9)2 = 4 x 3/5 x 1.2 x 1/9**2 = 0.036
bbtautau: had had : 3/5**2 = 0.36 lep had: 2 * 0.8 * 2 * 0.2 = 0.82 = 0.64x