%%    TEMPLATE for articles submitted to the full-tex econf proceedings
%%     
%%
%%     Please do not remove lines commented out with %+
%%           these are for the editors' use.
%%
%%     Questions?  Send email to :  mpeskin@slac.stanford.edu
%%   

\documentclass[12pt]{article}
\usepackage{epsfig}
\usepackage{lineno}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%  Do not change these:
\textwidth=6.0in  \textheight=8.25in

%%  Adjust these for your printer:
\leftmargin=-0.3in   \topmargin=-0.20in


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  personal abbreviations and macros
%    the following package contains macros used in this document:
\input econfmacros.tex
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  To include an item in the INDEX of the conference volume,
%           flag it with    \index{<item name>}
%  The use of this macro is illustrated in the text.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\Title#1{\begin{center} {\Large {\bf #1} } \end{center}}

\begin{document}


\Title{Search for Charged Higgs Bosons Decaying \\ via $H^{+} \rightarrow \tau\nu$ in 7\,TeV pp Collisions \\with the ATLAS Detector}

\bigskip\bigskip

%+\addtocontents{toc}{{\it D. Reggiano}}
%+\label{ReggianoStart}

\begin{raggedright}  

{\it Anna Kopp on behalf of the ATLAS Collaboration\index{Kopp, A.}\\
Physikalisches Institut, Albert-Ludwigs-Universit\"at Freiburg\\
Hermann-Herder-Str. 3a, 79104 Freiburg, Germany}
\bigskip\bigskip\\
\end{raggedright}




Charged Higgs bosons ($H^{+}, H^{-}$) are predicted by several non-minimal Higgs scenarios, such as the Minimal Supersymmetric Standard Model (MSSM),
and their discovery would be clear evidence for new physics beyond the Standard Model.
If the mass of the charged Higgs boson, $m_{H^{+}}$, is less than the top quark mass, the main
production mode at the LHC is via top quark decays, $t\rightarrow H^{+}b$ in $t\bar{t}$ production.
For values of $\tan\beta>2$, the decay mode $H^{+}\rightarrow\tau\nu$ is dominant in the MSSM.
Using 4.6 fb$^{-1}$ taken by the ATLAS detector \cite{Aad:2008zzm} at $\sqrt{s}=7$\,TeV in 2011, three different final states have been investigated \cite{Aad:2012tj}, taking into account various combinations
of leptonically or hadronically decaying $\tau$ leptons (arising from the charged Higgs boson decay) and $W$ boson decays (resulting from the second
top quark decay).
The three final states are the lepton+jets, the $\tau$+lepton and the $\tau$+jets channel.

In the lepton+jets channel, leptonically decaying $\tau$ leptons arising from the $H^{+}$ decay 
and hadronically decaying $W$ bosons are considered.
The background contribution from misidentified or non-isolated leptons is estimated in a data-driven
way using a matrix method. All other background contributions are estimated using simulation, with the
normalization of the $t\bar{t}$ background being taken from data.
A transverse mass \cite{Gross:2009wia} of the charged Higgs boson is used as final discriminating variable.

In the $\tau$+lepton channel, events containing hadronically decaying $\tau$ leptons originating 
from the $H^{+}$ decay and leptonically decaying $W$ bosons are considered.
The background contribution from misidentified or non-isolated leptons is estimated in the same way as for the lepton+jets channel. 
Events containing electrons and jets misidentified as $\tau$ leptons are estimated using their misidentification probabilities measured from data. 
Only the background contribution with true $\tau$ leptons is estimated using simulation.
Missing transverse momentum, $E_{T}^{\mathrm{miss}}$, is used as a final discriminating variable.

In the $\tau$+jets channel, both the $\tau$ lepton arising from the charged Higgs boson decay and the $W$ boson decay hadronically.
In this final state, all background contributions are estimated using data-driven methods. 
Electrons and jets misidentified as $\tau$ jets are estimated in the same way as in the $\tau$+lepton channel.
Multijet background events are estimated using a template fit in $E_{T}^{\mathrm{miss}}$.
The background contribution including true $\tau$ jets is estimated with an embedding method.
A transverse mass calculated from $E_{T}^{\mathrm{miss}}$, the transverse momentum of the $\tau$ jet and the angle between these two is used as final discriminating variable.

Data and background estimation agree well in all three channels, thus no
evidence for charged Higgs bosons is found. 
Exclusion limits at a 95\% confidence level \cite{Read:2002hq} 
are set on the branching ratio $B(t\rightarrow H^{+}b)$ assuming $B(H^{+}\rightarrow\tau\nu)=1$. 
For charged Higgs boson masses between 90 and 160$\,$GeV the limits range from 5\% to 1\% (Fig. \ref{fig:limits}, left). 
These limits are interpreted in the $m_{h}^{\mathrm{max}}$ scenario of the MSSM \cite{Carena:2002qg}
.
For $90<m_{H^{+}}<150$\,GeV, values of $\tan\beta$ between 1 and 2 and as much as between 1 and 6 are excluded and values of $\tan\beta$ above 26 to 12 are excluded (Fig. \ref{fig:limits}, right).


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%%   use this format to include an .eps figure into your paper
%%
\begin{figure}[htb]
\begin{center}
\epsfig{file=limit_combined.eps,height=4cm}
\epsfig{file=limit_mhmax.eps,height=4cm}
\caption{Exclusion limit on the branching ratio $B(t\rightarrow H^{+}b)$ assuming $B(H^{+}\rightarrow\tau\nu)=1$ for all three final states combined (left)
and interpretation in the $m_{H^{+}}-\tan\beta$-plane of the $m_{h}^{\mathrm{max}}$ scenario of the MSSM (right)\cite{Aad:2012tj}. \label{fig:limits}}
\end{center}
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



\begin{thebibliography}{99}

%%
%%  bibliographic items can be constructed using the LaTeX format in SPIRES:
%%    see    http://www.slac.stanford.edu/spires/hep/latex.html
%%  SPIRES will also supply the CITATION line information; please include it.
%%

%\cite{Aad:2008zzm}
\bibitem{Aad:2008zzm} 
  The ATLAS Collaboration,
  %``The ATLAS Experiment at the CERN Large Hadron Collider,''
  JINST {\bf 3}, S08003 (2008).
  %%CITATION = JINST,3,S08003;%%


\bibitem{Aad:2012tj} 
  The ATLAS Collaboration, 
  JHEP {\bf 1206}, 039 (2012)
  [arXiv:1204.2760 [hep-ex]].
  %%CITATION = ARXIV:1204.2760;%%


\bibitem{Gross:2009wia} 
  E.~Gross and O.~Vitells,
  %``Transverse mass observables for charged Higgs boson searches at hadron colliders,''
  Phys.\ Rev.\ D {\bf 81}, 055010 (2010)
  [arXiv:0907.5367 [hep-ph]].
  %%CITATION = ARXIV:0907.5367;%%

\bibitem{Read:2002hq} 
  A.~L.~Read,
  %``Presentation of search results: The CL(s) technique,''
  J.\ Phys.\ G G {\bf 28}, 2693 (2002).
  %%CITATION = JPHGB,G28,2693;%%

\bibitem{Carena:2002qg} 
  M.~S.~Carena, S.~Heinemeyer, C.~E.~M.~Wagner and G.~Weiglein,
  %``Suggestions for benchmark scenarios for MSSM Higgs boson searches at hadron colliders,''
  Eur.\ Phys.\ J.\ C {\bf 26}, 601 (2003)
  [hep-ph/0202167].
  %%CITATION = HEP-PH/0202167;%%




\end{thebibliography}

 
\end{document}

