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Changeset 93 in svn for trunk/paper/notes.tex


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Timestamp:
Dec 9, 2008, 9:38:29 PM (16 years ago)
Author:
Xavier Rouby
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petit commit avant que je n'y touche

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  • trunk/paper/notes.tex

    r28 r93  
    1 \documentclass[a4paper,11pt,oneside]{article}
     1\documentclass[a4paper,11pt,oneside,twocolumn]{article}
    22\usepackage[english]{babel}
    33\usepackage[ansinew]{inputenc}
    … …  
    1616\usepackage{fancyhdr}
    1717\usepackage{verbatim}
    18 \addtolength{\textwidth}{4cm} \addtolength{\hoffset}{-2cm}
     18\addtolength{\textwidth}{2cm} \addtolength{\hoffset}{-1cm}
    1919\begin{document}
    2020
    2121\section*{Abstract}
     22
     23The \textsc{Delphes} software provides a framework for fast simulation of particle interactions in a generic high-energy physics collider detector containing a tracking system, electromagnetic and hadronic calorimeters, and a muon system. It is an object-oriented system writen using the C++ programming language. Using input files originating from a Monte-Carlo event generator such as \textsc{pythia} and \textsc{herwig}, \textsc{Delphes} creates ``high-level" analysis objects.\\
    2224
    2325\section{Introduction}
    … …  
    2628% - 2) relativement bonne prédiction en premiÚre approximation
    2729% - 3) permet de comparer
    28 Full simulation of the response of large detectors components to high energy particles requires a lot of computing resources. Moreover, a good knowledge of the exact geometry of subdetectors and dead material content is mandatory.
    29 
    30 Fast simulation can be a  powerful predictive tool for typical response of a large detector in high energy collider.
    31 
    32 The fast simulation of the detector response takes into account geometrical
    33 acceptance of sub-detectors and their finite energy resolution, no smearing is
    34 applied on particle direction. Charged particles, once are in the fiducial
    35 volume of the detector are assumed to be reconstructed with $100\%$ probability.
    36 The energy of each particle produced after hadronization, with a lifetime
    37 $c\tau$ bigger than $10~\textrm{mm}$ is then smeared according to detectors along
    38 particule's direction. For particles with a short lifetime such as the $K_s$,
    39 the fraction of electromagnetic or hadronic energy is determined according to
    40 its decay products. The calorimeter is assumed to cover the pseudorapidity range
    41 $|\eta|<3$ and consists in an electromagnetic and an hadronic part. The energy
    42 resolution is given by $\sigma_{E}/E=0.05/\sqrt{E} \oplus 0.25/E \oplus 0.0055$
    43 for the electromagnetic part and by $\sigma_{E}/E=0.91/\sqrt{E}\oplus 0.038$ for
    44 the hadronic part, where the energy is given in GeV. A very forward calorimeter
    45 is assumed to cover $3<|\eta|<5$ with an electromagnetic and hadronic energy
    46 resolution function given by $\sigma_{E}/E=1.5/\sqrt{E}\oplus 0.06$ and
    47 $\sigma_{E}/E=2.7/\sqrt{E}\oplus 0.13$ respectively.\\
     30
     31A fast simulation of a typical \textsc{lhc} multipurpose detector response can be used to obtain more realistic observables and fast approximate estimates of signal and background rates for specific channels. \textsc{Delphes} includes the most crucial detector apects as jet reconstruction, momentum/energy smearing for leptons, photons and hadrons and missing transverse energy. Starting from ``particle-level" information, the package provides reconstructed jets, isolated leptons, photons, reconstructed charged tracks, calorimeter towers and the expected transverse missing energy. Although this kind of approach yields much realistic results than a simple ``parton-level" analysis, a quick simulation comes at the expense of detector details. Therefore, the interactions not simulated in \textsc{Delphes} are: secondary interactions, multiple interactions, photon conversion, electron Bremsstrahlung, magnetic field effects, detector dead materials.\\
     32
     33The simulation package proceeds in two stages. The first part is executed on the generated events. ``Particle-level" informations are read from input files and stored in a {\it \textsc{gen}} \textsc{root} tree. Three varieties of input files can currently be used as input in \textsc{Delphes}. In order to process events from many different generators, the standard Monte Carlo event structure StdHep can be used as an input. Besides, \textsc{delphes} can also provide detector response for events read in "Les Houches Event Format" (\textsc{lhef}) and \textsc{root} files obtained using the {\bf h2root} converter program. This first stage is performed using three C++ classes: {\verb HEPEVTConverter }, {\verb LHEFConverter } and {\verb STDHEPConverter }. Afterwards, \textsc{delphes} performs a simple trigger simulation and reconstruct "high-level objects". These informations are organised in classes and each objects are ordered with respect to the transverse momentum. The output of the various C++ classes is stored in the {\it Analysis} tree. The program is driven by a datacard (data/DataCardDet.dat) which allow a large spectrum of running conditions by modifying basic detector parameters, including calorimeter and tracking coverage and resolution, thresholds or jet algorithm parameters.\\
     34
     35\section{Central detector simulation}
    4836
    4937\begin{figure}[!h]
    5038\begin{center}
    51 \includegraphics[width=0.7\textwidth]{detectorAng.eps}
     39\includegraphics[width=\columnwidth]{detectorAng.eps}
     40\caption{\small{detectorAng.eps}}
     41\label{fig:genDet}
     42\end{center}
     43\end{figure}
     44
     45The overall layout of the general purpose detector simulated by \textsc{Delphes} is shown in figure \ref{fig:GenDet}. A central tracking system surrounded by an electromagnetic (\textsc{ecal}) and a hadron calorimeter (\textsc{hcal}). A forward calorimeter ensure a larger geometric coverage for the measurement of the missing transverse energy. The fast simulation of the detector response takes into account geometrical acceptance of sub-detectors and their finite energy resolution. No smearing is applied on particle direction.\\
     46
     47Before starting to loop over events, the {\verb RESOLution } class loads all sub-detector resolutions and coverage from the detector parameter file. If no such file is provided, predifined values are used. The coverage of the various sub-systems used in the default configuration are summarized in table \ref{tab:defEta}.
     48
     49\begin{table}[!h]
     50\begin{center}
     51\begin{tabular}[!h]{lll}
     52\hline
     53Sub-system   & Card flag & $|\eta|^{max}$\\\hline
     54Tracking     & {\verb MAX_TRACKER } & 2.5\\
     55Calorimeters & {\verb MAX_CALO_CEN } & 3.0\\
     56             & {\verb MAX_CALO_FWD } & 5.0\\
     57Muon         & {\verb MAX_MU } & 2.4\\\hline
     58\end{tabular}
     59\label{tab:defEta}
     60\end{center}
     61\end{table}
     62
     63\subsection{Simulation of calorimeters response}
     64
     65The energy of all particle considered as stable in the generator particle list are smeared according to a resolution depending which sub-calorimeter is assumed to be used for the energy measurement. For particles with a short lifetime such as the $K_s$, the fraction of electromagnetic or hadronic energy is determined according to its decay products. The response of the each sub-calorimeter is parametrized as a function of the energy
     66\begin{equation}
     67\frac{\sigma}{E} = \frac{S}{\sqrt{E}} \oplus \frac{N}{E} \oplus C,
     68\end{equation}
     69where S is the stochastic term, N the noise and C the constant term.\\
     70
     71The response of the detector is applied to the electromagnetic and the hadronic particles through the {\verb SmearElectron }and {\verb SmearHadron } functions. The 4-momentum $p^\mu$ are smeared with a parametrisation directly derived from the detector techinal designs. In the default parametrisation, the calorimeter is assumed to cover the pseudorapidity range $|\eta|<3$ and consists in an electromagnetic and an hadronic part. Coverage between pseudorapidities of 3.0 and 5.0 is provided by a forward calorimeter. The response of this calorimeter can be different for electrons and hadrons. The default values of the stochastic, noisy and constant terms as well as the ``Card flag" names used in the configuration file are given in table \ref{tab:defResol}.\\
     72
     73\begin{table}[!h]
     74\begin{center}
     75\begin{tabular}[!h]{lclc}
     76\hline
     77\multicolumn{2}{c}{Resolution Term}   & Card flag & Value\\\hline
     78Central \textsc{ecal} & S & {\verb ELG_Scen }  & 0.05 \\
     79             & N & {\verb ELG_Ncen }  & 0.25 \\
     80             & C & {\verb ELG_Ccen }  & 0.0055 \\
     81Forward \textsc{ecal} & S & {\verb ELG_Sfwd }  & 2.084 \\
     82             & N & {\verb ELG_Nfwd }  & 0.0 \\
     83             & C & {\verb ELG_Cfwd }  & 0.107 \\
     84Central \textsc{hcal} & S & {\verb HAD_Shcal } & 1.5 \\
     85             & N & {\verb HAD_Nhcal } & 0.\\
     86             & C & {\verb HAD_Chcal } & 0.05\\
     87Forward \textsc{hcal} & S & {\verb HAD_Shf }   & 2.7\\
     88             & N & {\verb HAD_Nhf }   & 0. \\
     89             & C & {\verb HAD_Chf }   & 0.13\\
     90\hline
     91\end{tabular}
     92\label{tab:defResol}
     93\end{center}
     94\end{table}
     95
     96The energy of electron and photon particles found in the particle list are smeared using the \textsc{ecal} resolution terms. Charged and neutral final state hadrons interact with the \textsc{ecal}, \textsc{hcal} and the forward calorimeter. Some long-living particles, such as the $K_s$, possessing lifetime $c\tau$ smaller than 10~mma are considering as stable particles although they decay in the calorimeters. The energy smearing of such particles is performed using the expected fraction of the energy, determined according to their decay products, that whould be deposited into the \textsc{ecal} ($E_{ecal}$) and into the \textsc{hcal} ($E_{hcal}$). Defining $F$ as the fraction of the energy leading to a \textsc{hcal} deposit, the two energy values are given by
     97\begin{equation}
     98E_{hcal} = E \times F ~\mathrm{and}~ E_{ecal} = E \times (1-F),
     99\end{equation}
     100where $0 \leq F \leq 1$. The electromagnetic part is handled as the electrons, while the resolution terms used for the hadronic part are {\verb HAD_Shcal }, {\verb HAD_Nhcal } and {\verb HAD_Chcal }. The resulting final energy given after the application of the smearing is then $E = E_{hcal} + E_{ecal}$.\\
     101
     102
     103\subsection{Muon smearing}
     104
     105Muons candidates are searched
     106The smearing ot the muon 4-momentum $p^\mu$ is given by a Gaussian smearing of the $p_T$ function \texttt{SmearMuon}. Only the $p_T$ is smeared, but neither $\eta$ nor $\phi$.
     107
     108\subsection{Tracks reconstruction}
     109
     110All stable charged particles lying inside the fiducial volume of the tracking coverage provide a track. The reconstructio efficiency is manageable in the input datacard through the {\verb TRACKING_EFF } term. By default, a track is assumed to be reconstructed with $90\%$ probability.
     111
     112\subsection{Calorimetric towers}
     113
     114All undecayed particles, except muons and neutrinos are producing a calorimetric tower.  The same particles enter in the calculation of the missing transverse energy. \textit{what is used is the particle smeared momentum, not the calorimetric towers!}
     115
     116\subsection{Isolated lepton reconstruction}
     117
     118Photon and electron candidates are reconstructed if they fall into the acceptance of the tracking system and have a transverse momentum above the {\verb ELEC_pt } value (10~GeV by default). Muons candidates are searched
     119
     120Lepton isolation demands that there is no other charged particles with $p_T>2$~GeV within a cone of $\Delta R<0.5$ around the lepton.\\
     121
     122\section{``High-level" objects reconstruction}
     123
     124\subsection{Jet reconstruction}
     125
     126Jets are reconstructed using a cone algorithm with $R=0.7$ and make only use of the smeared particle momenta. The reconstructed jets are required to have a transverse momentum above 20~GeV and $|\eta|<3.0$. A jet is tagged as $b$-jets if its direction lies in the acceptance of the tracker, $|\eta|<0.5$, and if it is associated to a parent $b$-quark. A $b$-tagging efficiency of $40\%$ is assumed if the jet has a parent $b$ quark. For $c$-jets and light/gluon jets, a fake b-tagging efficiency of $10 \%$ and $1 \%$ respectively is assumed.\\
     127
     128\subsection{{\it b}tagging}
     129
     130The simulation of the b-tagging is based on the detector efficiencies assumed (1) for the tagging of a b-jet and (2) for the mis-identification of other jets as b-jets. This relies on the TAGGING\_B, MISTAGGING\_C and MISTAGGING\_L constants, for (respectively) the efficiency of tagging of a b-jet, the efficiency of mistagging a c-jet as a b-jet, and the efficiency of mistatting a light jet (u,d,s,g) as a b-jet. The (mis)tagging relies on the particle ID of the most energetic particle within a cone around the observed (eta,phi) region, with a radius CONERADIUS.
     131
     132\subsection{Tau identification}
     133
     134\begin{wrapfigure}{l}{0.5\columnwidth}
     135\includegraphics[width=0.5\columnwidth]{Tau.eps}
    52136\caption{\small{detectorAng.eps}}
    53137\label{h_WW_ss_cut1}
     138\end{wrapfigure}
     139
     140Jets originating from $\tau$-decay are identified using an identification procedure consistent with the one applied in a full detector simulation. The tagging rely on two tau properties. First, in roughly 75$\%$ of the time, the hadronic $\tau$-decay products contain only one charged hadron and a number of $\pi^0$. Second, the particles arisen from the $\tau$-lepton produce narrow jets in the calorimeter.
     141
     142\subsubsection*{Electromagnetic collimation}
     143
     144To use the narrowness of the $\tau$-jet, the \textit{electromagnetic collimation} ($C_{\tau}^{em}$) is defined as the sum of the energy in a cone with $\Delta R = ${\verb TAU_CONE_ENERGIE } around the jet axis divided by the energy of the reconstructed jet. The energy in the small cone is calculated using the towers objects. To be taken into account a calorimeter tower should have a transverse energy above a given threshold {\verb M_SEEDTHRESHOLD}. A large fraction of the jet energy, denominated here with {\verb TAU_EM_COLLIMATION } is expected in this small cone. The quantity is represented in figure \ref{fig:tau1} for the default values (see table \ref{tab:tauRef})
     145
     146\begin{figure}[!h]
     147\begin{center}
     148\includegraphics[width=0.8\columnwidth]{figures/Taujets1.eps}
     149\caption{\small{}}
     150\label{fig:tau1}
    54151\end{center}
    55152\end{figure}
    56153
    57 
    58 The acceptance cuts applied on leptons and jets used in this section are the
    59 following :\\
    60 
    61 \begin{itemize}
    62 
    63 \item Electrons and muons are reconstructed if they fall into the acceptance of
    64 the tracker, assumed to be $|\eta|<2.5$, and have to have a transverse momentum
    65 above 10~GeV (the energy resolution of muons is taken to be the same as for
    66 electrons). Lepton isolation demands that there is no other charged particles
    67 with $p_T>2$~GeV within a cone of $\Delta R<0.5$ around the lepton.\\
    68 
    69 \item Jets are reconstructed using a cone algorithm with $R=0.7$ and make only
    70 use of the smeared particle momenta. The reconstructed jets are required to have
    71 a transverse momentum above 20~GeV and $|\eta|<3.0$. A jet is tagged as $b$-jets
    72 if its direction lies in the acceptance of the tracker, $|\eta|<0.5$, and if it
    73 is associated to a parent $b$-quark. A $b$-tagging efficiency of $40\%$ is
    74 assumed if the jet has a parent $b$ quark. For $c$-jets and light/gluon jets, a
    75 fake
    76 b-tagging efficiency of $10 \%$ and $1 \%$ respectively is assumed.\\
    77 
    78 \item A jet is tagged as a $\tau$-jet if more than $90\%$ of its energy is
    79 localized in a cone of $\Delta R=0.15$ around its axis. Moreover, this jet must
    80 have its direction in the acceptance of the tracker and have exactly one charged
    81 particle with $p_{T}>2$~GeV within a cone $\Delta R<0.4$ around the jet axis.
    82 This procedure selects taus decaying hadronically with a typical efficiency of
    83 $60\%$. Moreover, the minimal $p_T$ of the $\tau$-jet is required to be
    84 10~GeV.\\
    85 
    86 \end{itemize}
    87 
    88 \section{implementation}
    89 \subsection{Electron smearing}
    90 The smearing of the electron 4-momentum $p^\mu$ is
    91  - if the electron is in the tracker ($\eta < MAX\_TRACKER$)
    92         Gaussian smearing with $\sigma = ELG_Ccen*E \oplus ELG_Ncen \oplus
    93 ELG_Scen*\sqrt{E}$
    94  - else Gaussian smearing with $\sigma = ELS_Cfwd*E \oplus ELG_Sfwd*\sqrt{E}$
    95 function \texttt{SmearElectron}
    96 Only the energy $E$ is smeared, but neither $\eta$ nor $\phi$.
    97 No negative values for the energy after smearing. If so, the $4$-momentum is set
    98 to $(0,0,0,0)$.
    99 \textbf{For the moment, electrons with $|\eta|> 5$ are also smeared !!!}
    100 
    101 \subsection{Muon smearing}
    102 The smearing ot the muon 4-momentum $p^\mu$ is given
    103 by a Gaussian smearing of the $p_T$
    104 function \texttt{SmearMuon}
    105 Only the $p_T$ is smeared, but neither $\eta$ nor $\phi$.
    106 No negative values for the energy after smearing. If so, the 4-momentum is set
    107 to $(0,0,0,0)$.
    108 
    109 \subsection{Hadron smearing}
    110 The energy of the hadron is smeared in the following ways:
    111  - if the hadron is in the central calorimeter (eta < MAX\_CALO\_CEN)
    112         Gaussian smearing with $\sigma = HAD_Chcal*E_{hcal} \oplus HAD_Nhcal
    113 \oplus HAD_Shcal*\sqrt{E_{hcal}}
    114                                        + HAD_Cecal*E_{ecal} \oplus HAD_Necal
    115 \oplus HAD_Secal*\sqrt{E_{ecal}}$
    116         where $E_{hcal} + E_{ecal} = E$. As some long-living particles decay in
    117 the calorimeters,
    118         some of them decay mostly in the ECAL, some mostly in the HCAL.
    119 $E_{hcal}$ and $E_{ecal}$ are
    120         given by $E_{hcal} = E \times F$ and $E_{ecal} = E times (1-F)$, where
    121 $F$ is a fraction
    122         $0 \leq F \leq 1$ describing each particles. By default, $F=1.$ but is
    123 $F=0.7$ for $K^0_S$ and $\Lambda$.
    124  - if the hadron is somewhere else (\textbf{even outside the forward
    125 calorimeters !!!})
    126         Gaussian smearing with $\sigma = HAD_Chf*E \oplus HAD_Nhf \oplus
    127 HAD_Shf*\sqrt{E}$
    128 
    129 Ainsi, pour les particules considérées comme stables par PYTHIA
    130 mais non stables dans un détecteur tel CMS ($c\tau < 4m$), les
    131 dépÃŽts laissés dans les différents détecteurs sont directement
    132 liés aux modes de désintégrations de ces particules. Les
    133 hypothÚses des dépÃŽts d'énergie sont données dans le tableau
    134 \ref{depot}.\newline
     154\subsubsection*{$\tau$ selection using tracks}
     155
     156\begin{figure}[!h]
     157\begin{center}
     158\includegraphics[width=0.8\columnwidth]{figures/Taujets2.eps}
     159\caption{\small{}}
     160\label{h_WW_ss_cut1}
     161\end{center}
     162\end{figure}
     163
     164The tracking isolation for the $\tau$ identification requires that the number of tracks associated to a particle with $p_T >$ {\verb PT_TRACK_TAU } is one and only one in a cone with $\Delta R =$ {\verb TAU_CONE_TRACKS }. This cone should be entirely included in the tracker to be taken into account. This procedure selects taus decaying hadronically with a typical efficiency of $60\%$. Moreover, the minimal $p_T$ of the $\tau$-jet is required to be {\verb TAUJET_pt }(default value: 10~GeV).\\
    135165
    136166\begin{table}[!h]
    137167\begin{center}
    138 \begin{tabular}{|c|c|c|c|c|c|}
    139 \hline
    140 \emph{Particules stables} & \emph{Stable} &\emph{Mode de}
    141 &$\Gamma_{i}/\Gamma$&\emph{Dépot}&\emph{Dépot}\\
    142 \emph{dans PYTHIA}&\emph{dans
    143 CMS}&\emph{desintégration}&&\emph{ECAL}&\emph{HCAL}\\\hline\hline
    144 $\pi^{\pm}$ & oui & & & 0 & 1 \\ \hline $K^{\pm}$ & oui & & & 0 &
    145 1 \\\hline $K^{0}_{S}$ & non & $\gamma\gamma\gamma\gamma$ & 0.31 &
    146 0.3 & 0.7\\
    147 & & $\pi^{+}\pi^{-}$& 0.69 &&\\\hline $K^{0}_{L}$ & oui & & & 0 &
    148 1\\\hline $\Lambda^{0}$ & non & $\pi^{-}p/\pi^{+}\overline{p}$ &
    149 0.64&
    150 0.3 & 0.7\\
    151 & & $n\pi^{0}$ & 0.36 & & \\\hline $\gamma$& oui & & & 1
    152 &0\\\hline
     168\begin{tabular}[!h]{llc}
     169\hline
     170Tau definition  & Card flag & Value\\\hline
     171$\Delta R^{for~em}$     & {\verb TAU_CONE_ENERGIE } & 0.15\\
     172min $E_{T}^{tower}$     & {\verb M_SEEDTHRESHOLD }  & 1.0~GeV\\
     173$C_{\tau}^{em}$         & {\verb TAU_EM_COLLIMATION } & 0.95.\\
     174$\Delta R^{for~tracks}$ & {\verb TAU_CONE_TRACKS } & 0.4\\
     175min $p_T^{tracks}$      & {\verb PT_TRACK_TAU } & 2 GeV\\\hline
    153176\end{tabular}
    154 \caption{HypothÚses des dépÃŽts d'énergie pour les particules les
    155 plus abondantes des jets.} \label{depot}
     177\label{tab:tauRef}
    156178\end{center}
    157179\end{table}
    158180
    159 
    160 function \texttt{SmearHadron}
    161 There is no ecal-hcal separation in the forward calorimeter.
    162 No negative values for the energy after smearing. If so, the 4-momentum is set
    163 to $(0,0,0,0)$.
    164 
    165 \subsection{Calorimetric towers}
    166 All final particles, which are neither muons nor neutrinos are produce a
    167 calorimetric tower.
    168 The same particles enter in the calculation of the missing transverse energy.
    169 \textit{what is used is the particle smeared momentum, not the calorimetric
    170 towers!}
    171 
    172 \subsection{Tracks}
    173 All final charged particles
    174 
    175 \subsection{Time of flight}
    176 Some subdetectors have the ability to measure the time of flight of the particle.
    177 This correspond to the delay after which the particle is observed in the detector, after the bunch crossing.
    178 The time of flight measurement of ZDC and FP420 detector is implemented here.
    179 For the ZDC, the formula is simply
     181\subsection{Transverse missing energy}
     182
     183\section{Very forward detectors simulation}
     184
     185Some subdetectors have the ability to measure the time of flight of the particle. This correspond to the delay after which the particle is observed in the detector, after the bunch crossing. The time of flight measurement of ZDC and FP420 detector is implemented here. For the ZDC, the formula is simply
    180186\begin{equation}
    181187 t_2 = t_1 + \frac{1}{v} \times \big( \frac{s-z}{\cos \theta}\big),
    … …  
    188194NB : for the moment, only neutrons and photons are assumed to be able to reach the ZDC. All other particles are neglected
    189195
    190 To fix the ideas, if the ZDC is located at $s=140~\textrm{m}$, neglecting $z$ and $\theta$, and assuming that $v=c$, one gets $t=0.47~\mu\textrm{s}$.
    191 
    192 \subsection{Tau identification}
    193 
    194 Two ways to identify a tau : using the energy inside a cone or the number of
    195 tracks in the cone.
    196 \begin{itemize}
    197 \item From the energy in the cone of radius TAU\_CONE\_ENERGY. To be taken into
    198 account, a calo tower should (1) have a transverse energy $E_T = \sqrt{E_X^2 +
    199 E_Y^2}$ above a given threshold M\_SEEDTHRESHOLD, (2) be inside a cone with a
    200 radius R and the axis defined by (eta,phi).
    201 \item From the number of tracks in the cone of radius TAU\_CONE\_TRACKS. To be
    202 taken into account, a track should (1) have a transverse momentum $ p_T =
    203 \sqrt{p_X^2 + p_Y^2} $ above a given threshold, (2) be inside a cone with a
    204 radius R and the axis defined by (eta,phi).
    205 \end{itemize}
    206 
    207 \begin{wrapfigure}{l}{0.3\textwidth}
    208 \includegraphics[width=0.3\textwidth]{Tau.eps}
    209 \caption{\small{detectorAng.eps}}
    210 \label{h_WW_ss_cut1}
    211 \end{wrapfigure}
    212 
    213 
    214 To identify a tau, one requires the \textit{electromagnetic collimation} and the
    215 \textit{tracking isolation}.
    216 The electromagnetic collimation is a kind of calorimetric isolation required
    217 around the jet axis.
    218 One requires that most of the energy of the cone is located in a small cone in
    219 the middle of the jet cone:
    220  \begin{equation}
    221    %C_{\tau}^{e.m.} = \frac{ \Sum E_T^{cell}(\Delta R= TAU\_CONE\_ENERGY)}{
    222 \sum E_T^{cell} (\Delta R= CONE\_RADIUS) > TAU\_EM\_COLLIMATION
    223  \end{equation}
    224  Typical values are TAU\_CONE\_ENERGY=0.15 ,  CONE\_RADIUS=0.7 and
    225 TAU\_EM\_COLLIMATION = 0.95.
    226 No further calorimetric isolation is required.
    227 
    228 The tracking isolation for the tau identification requires that the number of
    229 tracks associated to a particle with $p_T > PT\_TRACK\_TAU$ is one and only one
    230 in a cone with $\Delta R = TAU\_CONE\_TRACKS$. This cone should be entirely
    231 included in the tracker to be taken into account. Typical calues are
    232 $TAU\_CONE\_TRACKS = 0.4$ and $PT\_TRACK\_TAU = 2 GeV$.
    233 
    234 This means that the list of tau jet candidates includes the electron candidates.
    235 
    236 
    237 
    238 \subsection{B-tagging}
    239 The simulation of the b-tagging is based on the detector efficiencies assumed
    240 (1) for the tagging of a b-jet and (2) for the mis-identification of other jets
    241 as b-jets. This relies on the TAGGING\_B, MISTAGGING\_C and MISTAGGING\_L
    242 constants, for (respectively) the efficiency of tagging of a b-jet, the
    243 efficiency of mistagging a c-jet as a b-jet, and the efficiency of mistatting a
    244 light jet (u,d,s,g) as a b-jet. The (mis)tagging relies on the particle ID of
    245 the most energetic particle within a cone around the observed (eta,phi) region,
    246 with a radius CONERADIUS.
    247 
    248 \section{Validation}   
     196To fix the ideas, if the ZDC is located at $s=140~\textrm{m}$, neglecting $z$ and $\theta$, and assuming that $v=c$, one gets  $t=0.47~\mu\textrm{s}$.
     197
     198\section{Simulation physics validation}
     199
    249200\section{conclusion}
    250201
    251202\appendix
    252 Attention : in SmearUtil::NumTracks, the function arguments 'Eta' and 'Phi' have
    253 been switched. Previously, 'Phi' was before 'Eta', now 'Eta' comes in front.
    254 This is for consistency with the other functions in SmearUtil. Check your
    255 routines, when using NumTracks !
     203Attention : in SmearUtil::NumTracks, the function arguments 'Eta' and 'Phi' have been switched. Previously, 'Phi' was before 'Eta', now 'Eta' comes in front. This is for consistency with the other functions in SmearUtil. Check your routines, when using NumTracks !
    256204
    257205In the list of input files, all files should have the same type
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