| 22 |
|
(i) $t\bar{t} \to \ell $+ jets, and (ii) $t\bar{t} \to \ell^+ \ell^-$ where one of the two |
| 23 |
|
leptons is not found by the second-lepton-veto (here the second lepton can be a hadronically |
| 24 |
|
decaying $\tau$). |
| 25 |
< |
For a reasonable $M_T$ cut, say $M_T >$ 150 GeV, the dilepton background is approximately 80\% of |
| 25 |
> |
For a reasonable $M_T$ cut, say $M_T >$ 150 GeV, the dilepton background is approximately 70\% of |
| 26 |
|
the total. This is because in dileptons there are two neutrinos from $W$ decay, thus $M_T$ |
| 27 |
|
is not bounded by $M_W$. This is a very important point: while it is true that we are looking in |
| 28 |
|
the tail of $M_T$, the bulk of the background events end up there not because of some exotic |
| 46 |
|
% Sophisticated fully ``data driven'' techniques are not really needed. |
| 47 |
|
|
| 48 |
|
One general point is that in order to minimize systematic uncertainties, the MC background |
| 49 |
< |
predictions are whenever possible normalized to the bulk of the $t\bar{t}$ data, i.e., events passing all of the |
| 49 |
> |
predictions are whenever possible normalized to the bulk of the $t\bar{t}$ data, i.e. events passing all of the |
| 50 |
|
requirements but with $M_T \approx 80$ GeV. |
| 51 |
|
This (mostly) removes uncertainties |
| 52 |
|
due to $\sigma(t\bar{t})$, lepton ID, trigger efficiency, luminosity, etc. |
| 74 |
|
|
| 75 |
|
|
| 76 |
|
For $W +$ jets the ability of the Monte Carlo to model this ratio |
| 77 |
< |
($R_{wjet}$) is tested in a sample of $\ell +$ jets enriched in |
| 77 |
> |
($R_{wjet}$) is validated in a sample of $\ell +$ jets enriched in |
| 78 |
|
$W +$ jets by the application of a b-veto. |
| 79 |
< |
The equivalent ratio for top events ($R_{top}$) is validated in a sample of well |
| 79 |
> |
The equivalent ratio for top events ($R_{top}$) is tested in a sample of well |
| 80 |
|
identified $Z \to \ell \ell$ with one lepton added to the \met\ |
| 81 |
< |
calculation. |
| 81 |
> |
calculation. |
| 82 |
|
This sample is well suited to testing the resolution effects on |
| 83 |
|
the $M_T$ tail, since off-shell effects are eliminated by the $Z$-mass |
| 84 |
< |
requirement. |
| 84 |
> |
requirement. However, this test is unfortunately statistically |
| 85 |
> |
limited and its usefulness is limited to |
| 86 |
> |
event selections with modest \met\ |
| 87 |
> |
requirements. |
| 88 |
|
|
| 89 |
|
Note that the fact that the ratios are different for |
| 90 |
|
$t\bar{t}$/single top and $W +$ jets introduces a systematic |
