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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}}}
- \begin{frame}[c]%{\phantom{title page}}
- \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}
- \begin{column}{0.53\textwidth}
- \includegraphics[height=1.3cm]{uzh-transp}
- \end{column}
- \end{columns}
-
- \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
-
- \end{frame}
-
- \backupend
-
- \end{document}