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\author{ {\fontspec{Trebuchet MS}Marcin Chrz\k{a}szcz} (Universit\"{a}t Z\"{u}rich)}
\institute{UZH}
\title[Searches for heavy long-lived particles at LHCb]{Searches for heavy long-lived particles at LHCb}
\date{25 September 2014}


\begin{document}
\tikzstyle{every picture}+=[remember picture]

{
\setbeamertemplate{sidebar right}{\llap{\includegraphics[width=\paperwidth,height=\paperheight]{bubble2}}}
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\begin{center}
\begin{center}
	\begin{columns}
		\begin{column}{0.75\textwidth}
			\flushright\fontspec{Trebuchet MS}\bfseries \LARGE {Searches for heavy long-lived particles at LHCb}
		\end{column}
                \begin{column}{0.02\textwidth}
                  {~}
                  \end{column}
                \begin{column}{0.23\textwidth}
                 % \hspace*{-1.cm}
                  \vspace*{-3mm}
                  \includegraphics[width=0.6\textwidth]{lhcb-logo}
                  \end{column}

	\end{columns}
\end{center}
	\quad
	\vspace{3em}
\begin{columns}
\begin{column}{0.44\textwidth}
\flushright \vspace{-1.8em} {\fontspec{Trebuchet MS} \Large Marcin Chrząszcz\\\vspace{-0.1em}\small \href{mailto:mchrzasz@cern.ch}{mchrzasz@cern.ch}}

\end{column}
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\includegraphics[height=1.3cm]{uzh-transp}
\end{column}
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\vspace{1em}
%		\footnotesize\textcolor{gray}{With N. Serra, B. Storaci\\Thanks to the theory support from M. Shaposhnikov, D. Gorbunov}\normalsize\\
\vspace{0.5em}
 \textcolor{normal text.fg!50!Comment}{SUSY 2015, Tahoe City, 23-29 August, 2015}

	
\end{center}
\end{frame}
}

\iffalse
\section[Outline]{}
\begin{frame}
%\tableofcontents
%FIXME!
\begin{enumerate}
\item Rare $\PB$ decays:
\begin{itemize}
\item $\PB^+ \to \PK^+ \Ppi^- \Ppi^+ \Pphoton$
\item $\PBs/\PBzero \to \mu^- \mu^+$.
\item $\PBzero \to \PKstar \Pmuon \APmuon$.
\end{itemize}

\end{enumerate}

\end{frame}
\fi

%-------------------------------------------------------------------
%                          Introduction
%-------------------------------------------------------------------
%
% Set the background for the rest of the slides.
% Insert infoline
%\setbeamertemplate{background}
% {\includegraphics[width=\paperwidth,height=\paperheight]{slide_bg}}
%\setbeamertemplate{footline}[bunsentheme]



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%\setbeamertemplate{background}
% {\includegraphics[width=\paperwidth,height=\paperheight]{slide_bg}}
%\setbeamertemplate{footline}[bunsentheme]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\section{LHCb detector}

%\begin{frame}\frametitle{LHCb detector}
%\begin{columns}
%\column{3.in}
%\begin{center}
%\includegraphics[width=0.98\textwidth]{det.jpg}
%\end{center}

%\column{2.0in}
%\begin{footnotesize}


 %     LHCb is a forward spectrometer:
 %       	\begin{itemize}
 %       	\item Excellent vertex resolution.
 %       	\item Efficient trigger.
 %       	\item High acceptance for $\Ptau$ and $\PB$.
 %       	\item Great Particle ID
 %       	\end{itemize}



%\end{footnotesize}
%\end{columns}

%\end{frame}

\section{Introduction}

\begin{frame}\frametitle{Why long-lived particles?}
\begin{columns}
\column{3in}
\begin{itemize}
\item We all know here that the SM is incomplete.
\item Unfortunately we do no know what is the scale of NP.
\item NP still can come from the Higgs sector $\Rightarrow$ not all properties are yet constrained.
\item There is a long list of theoretical models that predict the existence
of new particles that couple to the SM sector by mixing with the
Higgs.
\end{itemize}

\column{2in}
\includegraphics[width=0.9\textwidth]{susy/NP_couplings.png}


\end{columns}
\begin{itemize}

\item Inflaton, axion-like, dark matter mediator models also predict the
new boson to be light.
\item SUSY models also can have stable long living particles like $\Psquark$, $\Pslepton$.
\end{itemize}


\end{frame}

\begin{frame}
\only<1>{\frametitle{LHCb detector - tracking}
\begin{columns}
\column{3in}
\includegraphics[width=0.9\textwidth]{susy/1050px-Lhcbview.jpg}

\column{2in}
\includegraphics[width=0.95\textwidth]{susy/sketch.png}
\end{columns}
\begin{itemize}
\item Excellent Impact Parameter (IP) resolution ($20~\rm \mu m$).\\
$\Rightarrow$ Identify secondary vertices from heavy flavour decays
\item Proper time resolution $\sim~40~\rm fs$.\\
$\Rightarrow$ Good separation of primary and secondary vertices.
\item Excellent momentum ($\delta p/p \sim 0.4 - 0.6\%$) and inv. mass resolution.\\
$\Rightarrow$ Low combinatorial background.

\end{itemize}


}

\only<2>{\frametitle{LHCb detector - particle identification}
\begin{columns}
\column{3in}
\includegraphics[width=0.9\textwidth]{susy/1050px-Lhcbview.jpg}

\column{2in}
\includegraphics[width=0.95\textwidth]{susy/cher.png}
\end{columns}
\begin{itemize}
\item Excellent Muon identification $\epsilon_{\mu \to \mu} \sim 97\%$, $\epsilon_{\pi \to \mu} \sim 1-3\%$
\item Good $\PK-\Ppi$ separation via RICH detectors, $\epsilon_{\PK \to \PK} \sim 95\%$,  $\epsilon_{\Ppi \to \PK} \sim 5\%$.\\
$\Rightarrow$ Reject peaking backgrounds.
\item High trigger efficiencies, low momentum thresholds.
Muons: $p_T > 1.76 \GeV$ at L0, $p_T > 1.0 \GeV$ at HLT1,\\
$B \to \PJpsi X $: Trigger $\sim 90\%$.

\end{itemize}


}


\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}\frametitle{Data taken by LHCb}
\includegraphics[width=0.9\textwidth]{susy/data.png}

\begin{itemize}
\item In 2011 and 2012 LHCb has gathered $3~{\rm{fb^{-1}}}$ of $pp$ collisions.
\end{itemize}

\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}\frametitle{$\PB \to \PKstar \chi(\mu\mu)$ search}
\begin{itemize}
\item Search for displaced di-muon vertex coming form $\PB$ meson.
\end{itemize}
\begin{columns}
\column{2.5in}
\begin{Large}
$\PBzero \to \PKstar \chi( \Pmuon \APmuon)$
\end{Large}
\column{2.5in}
\includegraphics[width=0.9\textwidth]{susy/inflaton.png}
\end{columns}
\begin{itemize}
\item If $\chi$ mixes with the Higgs and it is light:
\begin{itemize}
\item $\Gamma(\PK \to \Ppi \chi) \propto m_t^4 \lambda^5$
\item $\Gamma(\PD \to \Ppi \chi) \propto m_b^4 \lambda^5$
\item $\Gamma(\PB \to \PK \chi) \propto m_t^4 \lambda^2$
\end{itemize}
\item In addition; $\PKstar \to \PK^+ \Ppi^-$ helps in vertex reconstruction.
\item High $\mathcal{B}(\chi \to \Pmuon \APmuon)$. 
\end{itemize}

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}\frametitle{$\PB \to \PKstar \chi(\mu\mu)$ motivation}
Discussed models:
\begin{enumerate}
\item \textbf{Inflaton:} \href{http://arxiv.org/abs/1403.4638}{{\color{blue}{Phys.Lett. B736 (2014) 494}}}
\begin{itemize}
\item $\tau_{\chi} = 10^{-8} - 10^{-10}~s$
\item $m_{\chi} ~\mathcal{O}(1~\GeV)$
\item $\mathcal{B}(\PB \to \PK \chi)~\sim 10^{-6}$
\item effective couplings to SM particles:
\begin{itemize}
\item $g_Y\frac{m_f}{v_{EW}},~g_Y=\sin \theta$
\end{itemize}
\end{itemize}
\item \textbf{Axion portal:} \href{http://arxiv.org/abs/0911.5355}{{\color{blue}{Phys.Rev.D81:034001,2010}}}
\begin{itemize}
\item Prompt decay.
\item Large allowed masses.
\item Axion decay constant: $f_{\chi} \sim 1-3~\TeV$
\begin{itemize}
\item Coupling $\propto \frac{m_f}{f_{\chi}}$.
\end{itemize}
\end{itemize}
\end{enumerate}

All those particles have width much smaller than resolution of LHCb detector.


\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Signal properties}
$\Rrightarrow$ Depending on the coupling of the hidden sector we can identify two lifetime regimes:\\{~}

\begin{columns}
\column{0.1in}
{~}
\column{2.5in}
\textbf{Long lifetime} ($>0.2~{\rm{ps}}$)
\begin{itemize}
\item Inflaton \href{http://arxiv.org/abs/0912.0390v2}{{\color{blue}{JHEP 1005:010}}}
\item Displaced vertex.
\item Almost background free.
\item Lower reconstruction efficiency.
\end{itemize}

\column{2.5in}
\textbf{Short lifetime} ($\leq0.2~{\rm{ps}}$)
\begin{itemize}
\item Dark matter mediator \href{http://arxiv.org/abs/1310.6752}{{\color{blue}{	Phys. Lett. B727 }}}
\item Axion \href{http://arxiv.org/abs/0911.5355}{{\color{blue}{Phys.Rev.D81}}}
\item Prompt decay.
\item Contaminated via SM decay.
\end{itemize}

\end{columns}
\begin{columns}
\column{0.1in}
{~}

\column{2.5in}
\includegraphics[width=0.95\textwidth]{susy/displaced.png}

\column{2.5in}
\includegraphics[width=0.95\textwidth]{susy/prompt.png}

\end{columns}

\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Selection}
\begin{itemize}
\item Trigger on muons.
\item Multivariate selection: ${\rm{\mu BDT}}$ \href{http://arxiv.org/abs/1305.7248}{JINST 8(2013)}
\begin{itemize}
\item ${\rm{\mu BDT}}$ ensures flat efficiency in lifetime of $\chi$.
\end{itemize}
\item Optimized on Punzi figure-of-merit:
\begin{align*}
P_a = \dfrac{S}{\frac{5}{2}+\sqrt{B}},
\end{align*}
with $S$ and $B$ are signal and background yields.
\item Factorize lifetime into two components: $\mathcal{L}=\mathcal{L}^{{\rm{prompt}}}  \bigotimes \mathcal{L}^{{\rm{displaced}}}$
\begin{itemize}
\item Prompt: $\tau < 3\sigma_{\tau}$\\
$\mapsto$ SM background of $\PBzero \to \PKstar \Pmuon \APmuon$
\item Displeased: $\tau > 3\sigma_{\tau}$\\
$\mapsto$ Almost background free.
\end{itemize}
\end{itemize}



\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Search strategy}
\begin{columns}

\column{0.05in}
{~}
\column{3.4in}
\begin{itemize}
\item $\PBzero$ mass constrained.
\item Di-muon mass resolution $\sigma_m  =1 -7~\MeV$.
\item Scan $m_{{\rm test}}$ in steps of $0.5~\sigma_m$.
\begin{itemize}
\item {\color{orange}{Wide resonances}} can't affect the search.
\item {\color{turtlegreen}{Narrows resonances}} we veto.
\end{itemize} 
\item Calculations performed in each $m_{test}$ window.
\end{itemize}
\column{1.6in}
\includegraphics[width=0.9\textwidth]{susy/williams.png}
\end{columns}


\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Results}

\includegraphics[width=0.95\textwidth]{susy/results.png}

$\Rrightarrow$ Grey regions correspond to vetoed regions where narrow resonances are expected.\\
$\Rrightarrow$ Largest deviation seen in $m_{\chi}=253~\MeV$.\\
$\rightarrowtail$ Not statistically significant: local p-value $=0.2$.\\

$\Rrightarrow$ \href{http://arxiv.org/abs/1508.04094}{\color{blue}{LHCb-PAPER-2015-036}} submited to PRL.   

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Branching fraction exclusion limit}

\includegraphics[width=0.95\textwidth]{susy/limit.png}

$\Rrightarrow$ No deviations from background only hypothesis is observed.
\begin{itemize}
\item We set a $95\%$ CL upper limit as function of mass and lifetime of the new particle (in the LHCb accessible range).
\item Lower lifetimes have better limit due to higher reconstruction efficiency.
\end{itemize}


\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Benchmark models}



$\Rrightarrow$ Interpretation of the results in two specific models:\\{~}\\

\includegraphics[width=1.05\textwidth]{susy/benchmarks.png}
\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Long living charged particles like $\PStau$}

$\Rrightarrow$ Long living particles can also be produced in the PV. \\
\begin{itemize}
\item This kind of particles would be produce in relatively low velocities and could be identified by their time -of-flight, $dE/dx$ or in Cherenkov detectors.
\end{itemize}
$\Rrightarrow$ LHCb performed a search for long living $\PStau$ particles.\\
$\Rrightarrow$ $\PStau^+ \PStau^-$ produced by Drell-Yan process. \\

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{$\PStau$ analysis strategy}
$\Rrightarrow$ Search performed $\PStau$ in mass range of $124-309~\GeV$.\\
$\Rrightarrow$ After the loose preselection to reduce normal Drell-Yan production.

\includegraphics[width=1.05\textwidth]{susy/stau.png}

$\Rrightarrow$ After the preselection an Neural Net is trained based on Cherenkov detectors to calculate to further suppress the remaining background.

\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{$\PStau$ results}
\begin{itemize}
\item No significant signal yield has been observed.
\item $95~\%$ upper limit has been set.
\end{itemize}
\includegraphics[width=0.8\textwidth]{susy/sps7.png}
\end{frame}



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Hidden valley searches}
\begin{itemize}
\item A possible extensions of the SM are models where the new particles have a small couplings to the SM particles.
\item Such models are:
\begin{itemize}
\item Lightest SUSY
\item B/LNV
\item Gravity mediated SUSY
\item Hidden Valleys
\end{itemize}
\item LHCb have performed a search for $\pi_{\nu}$ particles that are pair produced from Higgs like SM particle.
\item They have a long lifetime and decay to pair of jets.
\end{itemize}
\end{frame}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Analysis strategy}
\begin{itemize}
\item Efficient trigger for long living particles.
\item Reconstruction of two jets.
\item MVA used for vertex search.
%\item Remove interactions with material.

\item Search performed in different regions of displaced vertexes ($R_{xy}$).
\begin{itemize}
\item $0.4< R_{xy}<4\rm ~mm$, removes heavy flavour and material interaction backgrounds.
\end{itemize}
\end{itemize}
\begin{columns}



\column{0.5\textwidth}
\includegraphics[angle=-90,width=1.\textwidth]{images/Fig1a.pdf}

\column{0.5\textwidth}
\includegraphics[angle=-90,width=1.\textwidth]{images/Fig1b.pdf}

\end{columns}


\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Di-jet distribution}

\includegraphics[width=0.8\textwidth]{dijet.png}

\begin{itemize}
\item {\color{turtlegreen}{Signal component fit result}}, {\color{cyan}{Background component}}
\end{itemize}
\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Results}
\includegraphics[width=0.85\textwidth]{images/Fig4.pdf}


\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
\begin{frame}\frametitle{Conclusion}
\begin{itemize}
\item A search for a dark boson in the decay channel\\ $\PBzero \to \PKstar \Pmuon \APmuon$ has been presented.
\begin{itemize}
\item No deviations from SM observed.

\end{itemize}
\item Results are the most constraining exclusion limit on the process.
\item LHCb is suited for search for long lived particles.
\item Stay tuned, more searches like this are on they way.

\end{itemize}



\end{frame}


\backupbegin

\begin{frame}\frametitle{Backup}
\topline

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\backupend

\end{document}