| 1 |
– |
\section{Introduction} |
| 2 |
– |
\label{ref:intro} |
| 1 |
|
|
| 2 |
|
This note presents a search for the production of supersymmetric (SUSY) stop quark pairs in events with a |
| 3 |
|
single isolated lepton, several jets, missing transverse energy, and large transverse mass. We use the full |
| 14 |
|
\end{itemize} |
| 15 |
|
|
| 16 |
|
Both of these signatures contain high transverse momentum (\pt) jets including two b-jets, and missing transverse |
| 17 |
< |
energy (\MET) due to the invisible $\chi^0_1$ lightest SUSY particles (LSP's). In addition, the presence of |
| 17 |
> |
energy (\met) due to the invisible $\chi^0_1$ lightest SUSY particles (LSP's). In addition, the presence of |
| 18 |
|
two W bosons leads to a large branching fraction to the single lepton final state. Hence we require the presence |
| 19 |
< |
of exactly one isolated, high \pt electron or muon, which provides significant suppression of several backgrounds |
| 19 |
> |
of exactly one isolated, high \pt\ electron or muon, which provides significant suppression of several backgrounds |
| 20 |
|
that are present in the all-hadronic channel. The largest backgrounds for this signature are semi-leptonic \ttbar\ |
| 21 |
|
and \wjets. These backgrounds contain a single leptonically-decaying W boson, and the transverse mass (\mt) |
| 22 |
< |
of the lepton-neutrino system has a kinematic endpoint requiring \mt $<$ $M_W$. For signal stop quark events, |
| 23 |
< |
the presence additional LSP's in the final states allows the \mt to exceed $M_W$. Hence we search for an excess |
| 22 |
> |
of the lepton-neutrino system has a kinematic endpoint requiring \mt\ $<$ $M_W$. For signal stop quark events, |
| 23 |
> |
the presence of additional LSP's in the final states allows the \mt\ to exceed $M_W$. Hence we search for an excess |
| 24 |
|
of events with large \mt. The dominant background in this kinematic region is dilepton \ttbar\ where one of the |
| 25 |
|
leptons is not identified, since the presence of two neutrinos from leptonically-decaying W bosons allows the |
| 26 |
|
\mt\ to exceed $M_W$. Backgrounds are estimated from Monte Carlo (MC) simulation, with careful validation |
| 28 |
|
|
| 29 |
|
The expected stop quark pair production cross section (see Fig.~\ref{fig:stopxsec}) varies between O(10) pb |
| 30 |
|
for $m_{\tilde{t}}=200$~GeV and O(0.01) pb for $m_{\tilde{t}}=500$~GeV. The critical challenge of this analysis |
| 31 |
< |
is due to the fact that for light stop quarks with a mass close to the top quark, the production cross section is |
| 32 |
< |
large but the kinematic distributions, in particular \mt, are very similar to SM \ttbar\ production, such that it becomes very |
| 31 |
> |
is due to the fact that for light stop quarks ($m_{\tilde{t}} \approx m_t$), the production cross section is |
| 32 |
> |
large but the kinematic distributions, in particular \mt, are very similar to SM \ttbar\ production. In this regime |
| 33 |
> |
it becomes very |
| 34 |
|
difficult to distinguish the signal and background. For large stop quark mass the kinematic distributions differ |
| 35 |
|
from those in SM \ttbar\ production, but the cross section decreases rapidly, reducing the signal-to-background |
| 36 |
|
ratio. |
| 37 |
|
|
| 38 |
|
\begin{figure}[hbt] |
| 39 |
|
\begin{center} |
| 40 |
< |
\includegraphics[width=0.4\linewidth]{plots/stop.pdf} |
| 40 |
> |
\includegraphics[width=0.5\linewidth]{plots/total_scale_pdf_LHC-eps-converted-to.pdf} |
| 41 |
|
\caption{ |
| 42 |
|
\label{fig:stopxsec}\protect |
| 43 |
|
The stop quark pair production cross section in pb, as a function of the stop quark mass.} |
