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- \title{$\tau \rightarrow \mu \mu \mu$ at LHCb }
- \author{Marcin Chrzaszcz}
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- \date{\today}
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- \begin{document}
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- \institute{Institute of Nuclear Physics PAN}
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- \institute{IFJ PAN}
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- \section[Outline]{}
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- \section{Brief review of LHCb}
- \subsection{Introduction}
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- \begin{frame}\frametitle{Introduction}
- \begin{itemize}
- \item Fresh analysis! Approved less than 24hrs ago.
- \item Permission to speak only in general sense without going into any details.
- \item Will try to give a closed talk with as much information as possible.
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- \begin{block}{Apologise}
- All the details will be available on the FPCP conference so stay tuned!
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- \subsection{Detector}
- \begin{frame}\frametitle{LHCb detector}
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- \begin{frame}\frametitle{LHCb detector}
- Strong features of the LHCb detector:
- \begin{itemize}
- \item Good particle identification thanks to the RICH detectors.
- \item State of the art silicon strip detector provides good vertex resolution.
- \item High luminosity: currently operating $4 \times 10^{-32} cm^{-2}s^{-1}$; we target to get $1.5fb$ in 2012.
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- \subsection{Theoretical and experimental status}
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- Strong features of LHCb detector:
- \begin{itemize}
- \item LFV has been observed in neutrino oscillations.
- \item Never seen in the charged lepton sector.
- \item Depending on the model $\tau \rightarrow \mu\mu\mu$ can be dominant over $\tau \rightarrow \mu \gamma$.
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- \end{itemize}
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- SM prediction: BR $\sim 10^{-54}$
- \newline Best limits (90 \%CL):
- \newline BaBar: 3.3 x 10-8 ($468fb^{-1}$)
- \newline Belle: 2.1 x 10-8 ($782fb^{-1}$)
- \newline LHCb: X.Y ($1fb^{-1}$)
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- \includegraphics[scale=0.35]{sm.png}
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- \section{Analysis strategy}
- \subsection{General information}
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- \begin{frame}\frametitle{General information}
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- \begin{enumerate}
- \item Three separate likelihoods to discriminate background
- \begin{itemize}
- \item Geometry and topology
- \item Particle identification
- \item Three body invariant mass
- \end{itemize}
- \item Training done on MC samples:
- \begin{itemize}
- \item $\tau \rightarrow \mu \mu \mu$
- \item $b \bar{b} \rightarrow \mu \mu X$ and $c \bar{c} \rightarrow \mu \mu X$
- \end{itemize}
- \item Different input variables, MVA operators and training methods
- examined, choice: ~highest performance \& simplest
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- \end{enumerate}
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- \subsection{$\tau$ production}
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- \begin{frame}\frametitle{$\tau$ production}
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- \includegraphics[scale=0.35]{table.png}
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- MC signal sample generated with phase space distribution
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- \subsection{Binning optimisation}
- \begin{frame}\frametitle{Binning optimisation}
- The 3D plane(mass, kinematics, and geometry with topology) mentioned was divided into bins. The optimisation of that binning was done using CLs method.
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- \includegraphics[scale=0.15]{geolq.png}
- \includegraphics[scale=0.15]{pidlq.png}
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- $\Delta LQ = 2ln(Q_{SB})-2ln(Q_{B})$
- where,
- \newline $Q_{SB}= \prod \frac{P(s_{i}+b_{i},s_{i}+b_{i})}{P(s_{i}+b_{i},b_{i})}$
- \newline $Q_{SB}= \prod \frac{P(s_{i}+b_{i},s_{i}+b_{i})}{P(s_{i}+b_{i},b_{i})}$
- \newline $P(a,b)$ is the probability that the expected number of
- background a \newline fluctuates (by Poisson distribution) to b, and i is the bin number.
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- \subsection{MVA parameter space}
- \begin{frame}\frametitle{MVA parameter space}
- For the geometry and kinematics MVA is calibrated using $D_{s} \rightarrow \phi(\mu\mu) \pi$.
- \includegraphics[scale=0.35]{geo-out.pdf}
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- \subsection{Normalization}
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- $\tau$ BR was normalized to $D_{s} \rightarrow \phi(\mu\mu) \pi$
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- \includegraphics[scale=0.25]{alpha.png}
- \newline \includegraphics[scale=0.25]{ds.pdf}
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- \section{Background}
- \subsection{SM background}
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- \begin{frame}\frametitle{SM background}
- LHCb is not a B factory. We have irreducible background! And we have to live with it.
- \begin{center}
- \includegraphics[scale=0.23]{table2.png}
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- \end{center}
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- \subsection{SM background}
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- \begin{frame}\frametitle{$D_{s} \rightarrow (\eta \rightarrow \mu \mu \gamma) \mu \nu$}
- This decay was badly simulated in current version of MC. For proper simulation new method in EvtGen has been written.
- It takes into account of the factors from the NA60 experiment.
- \newline arXiv:1108.0968
- \begin{center}
- \includegraphics[scale=0.23]{old_new.png}
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- \end{center}
- For the purpose of this analysis 5M events were simulated in a private production in IFJ computing cloud.
- Many thanks to Mariusz Witek for the computing resources!
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- \subsection{Background extraction}
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- There are 3 possibilities to deal with the background.
- \begin{itemize}
- \item Treat it as normal combinatorical background.
- \item Veto the $\eta$.
- \item Parametrize the $\eta$ background and fit with combinatorical.
- \end{itemize}
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- \subsection{Results}
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- As mentioned before I can't give the number. Please see slides from FPCP conference.
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- \section{Summary}
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- \begin{itemize}
- \item LHCb is capable of performing $\tau \rightarrow \mu \mu \mu$ measurements.
- \item Method is completely different from that used in the B factories. We are cutting the phase space.
- \item Looking for particular model of decay could increase our sensitivity. Need MC generators for that.
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- Thank you for your attention.
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