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Changeset 476 in svn for trunk/paper/notes.tex


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Timestamp:
Jul 13, 2009, 5:28:00 PM (15 years ago)
Author:
Xavier Rouby
Message:

uniformisation avec le CommPhysComp + resolution MET atlas

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  • trunk/paper/notes.tex

    r441 r476  
    2828  \graphicspath{{all_png/}}
    2929  \pdfinfo{
    30    /Author (S. Ovyn, X. Rouby, V. Lemaitre)
     30   /Author (S. Ovyn, X. Rouby)
    3131   /Title  (Delphes, a framework for fast simulation of a generic collider experiment)
    3232   /Subject ()
    … …  
    3838
    3939\title{\textsc{Delphes}, a framework for fast simulation \\of a generic collider experiment}
    40 \author{S. Ovyn, X. Rouby$^\textrm{a}$ and V. Lema\^itre\\
     40\author{S. Ovyn$^*$ and X. Rouby$^\textrm{a}$\\
    4141        \small{Center for Particle Physics and Phenomenology (CP3)}\\
    4242        \small{Universit\'e catholique de Louvain}\\
    4343        \small{B-1348 Louvain-la-Neuve, Belgium}\\ \\
    4444        \texttt{severine.ovyn@uclouvain.be, xavier.rouby@cern.ch} \\
    45         \texttt{vincent.lemaitre@uclouvain.be} \\
    4645}
    4746\date{}
    … …  
    6362a general-purpose experiment. The simulation includes a tracking system, embedded into a magnetic field, calorimetry and a muon
    6463system, and possible very forward detectors arranged along the beamline.
    65 The framework is interfaced to standard file formats (e.g.\ Les Houches Event File  or \texttt{HepMC}) and outputs observable objects for analysis, like missing transverse energy and collections of electrons or jets.
     64The framework is interfaced to standard file formats (e.g.\ Les Houches Event File or \texttt{HepMC}) and outputs observable objects for analysis, like missing transverse energy and collections of electrons or jets.
    6665The simulation of detector response takes into account the detector resolution, and usual reconstruction algorithms, such as \textsc{FastJet}. A simplified preselection can also be applied on processed data for trigger emulation. Detection of very forward scattered particles relies on the transport in beamlines with the \textsc{Hector} software. Finally, the \textsc{Frog} 2D/3D event display is used for visualisation of the collision final states.
    6766An overview of \textsc{Delphes} is given as well as a few \textsc{lhc} use-cases for illustration.
    … …  
    7170\textit{Keywords:} \textsc{Delphes}, fast simulation, trigger, event display, \textsc{lhc}, \textsc{FastJet}, \textsc{Hector}, \textsc{Frog}\\
    7271\href{http://www.fynu.ucl.ac.be/delphes.html}{http://www.fynu.ucl.ac.be/delphes.html}\\
     72\textit{PACS:}  29.85.-c ~~~ 07.05.Tp ~~~ 29.90.+r ~~~ 29.50.+v\\
    7373\textit{Preprint:} \texttt{CP3-09-01}
    7474\vspace{1.5cm}
    7575
    7676\end{abstract}
     77\small{$^{*}$ Corresponding author: +32.10.47.32.29.}
    7778\small{$^\textrm{a}$ Now in Physikalisches Institut, Albert-Ludwigs-Universit\"at Freiburg}
    7879]
    … …  
    115116Although this kind of approach yields much realistic results than a simple ``parton-level" analysis, a fast simulation comes with some limitations. Detector geometry is idealised, being uniform, symmetric around the beam axis, and having no cracks nor dead material. Secondary interactions, multiple scatterings, photon conversion and bremsstrahlung are also neglected.
    116117
    117 Four datafile formats can be used as input in \textsc{Delphes}\footnote{\texttt{[code] }See the \texttt{HEPEVTConverter}, \texttt{HepMCConverter}, \texttt{LHEFConverter} and \texttt{STDHEPConverter} classes.}. In order to process events from many different generators, the standard Monte Carlo event structure \texttt{StdHEP}~\cite{bib: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}~\cite{bib:lhe}) and \textsc{root} files obtained from \textsc{.hbook} using the \texttt{h2root} utility from the \textsc{root} framework~\cite{bib:Root}.
     118Four datafile formats can be used as input in \textsc{Delphes}\footnote{\texttt{[code] }See the \texttt{HEPEVTConverter}, \texttt{HepMCConverter}, \texttt{LHEFConverter} and \texttt{STDHEPConverter} classes.}. In order to process events from many different generators, the standard Monte Carlo event structures \texttt{StdHEP}~\cite{bib:stdhep} and \texttt{HepMC}~\cite{bib:hepmc} can be used as an input. Besides, \textsc{Delphes} can also provide detector response for events read in ``Les Houches Event Format'' (\textsc{lhef}~\cite{bib:lhe}) and \textsc{root} files obtained from \textsc{.hbook} using the \texttt{h2root} utility from the \textsc{root} framework~\cite{bib:Root}.
    118119%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.
    119120
    … …  
    331332
    332333\subsubsection*{Electrons and photons}
    333 Electron ($e^\pm$) and photon candidates are reconstructed if they fall into the acceptance of the tracking system and have a transverse momentum above a threshold (default $p_T > 10~\textrm{GeV}/c$). A calorimetric tower will be seen in the detector, an electrons will leave in addition a track. Subsequently, electrons and photons create a candidate in the jet collection.
     334Electron ($e^\pm$) and photon candidates are reconstructed if they fall into the acceptance of the tracking system and have a transverse momentum above a threshold (default $p_T > 10~\textrm{GeV}/c$). A calorimetric tower will be seen in the detector, as electrons will leave in addition a track. Subsequently, electrons and photons create a candidate in the jet collection.
    334335Assuming a good measurement of the track parameters in the real experiment, the electron energy can be reasonably recovered. In \textsc{Delphes}, electron energy is smeared according to the resolution of the calorimetric tower where it points to, but independently from any other deposited energy is this tower. This approach is still conservative as the calorimeter resolution is worse than the tracker one.
    335336
    … …  
    498499\subsubsection*{Tracking isolation}
    499500
    500 The tracking isolation for the $\tau$ identification requires that the number of tracks associated to particles with significant transverse momenta is one and only one in a cone of radius $R^\textrm{tracks}$ (3-prong $\tau$s are dropped).
     501The tracking isolation for the $\tau$ identification requires that the number of tracks associated to particles with significant transverse momenta is one and only one in a cone of radius $R^\textrm{tracks}$ ($3-$prong $\tau$-jets are dropped).
    501502This cone should be entirely incorporated into the tracker to be taken into account. Default values of these parameters are given in Tab.~\ref{tab:tauRef}.
    502503
    … …  
    625626\begin{center}
    626627\includegraphics[width=\columnwidth]{resolutionETmis}
    627 \caption{$\sigma(E^\textrm{miss}_{x})$ as a function on the scalar sum of all towers ($\Sigma E_T$) for $pp \rightarrow gg$ events.}
     628\includegraphics[width=\columnwidth]{resolutionETmis_atlas}
     629\caption{$\sigma(E^\textrm{mis}_{x})$ as a function on the scalar sum of all towers ($\Sigma E_T$) for $pp \rightarrow gg$ events, for a \textsc{cms}-like detector (top) and an \textsc{atlas}-like detector (bottom), for dijet events produced with MadGraph/MadEvent and hadronised with Pythia.}
    628630\label{fig:resolETmis}
    629631\end{center}
    … …  
    636638where the $\alpha$ parameter depends on the resolution of the calorimeters.
    637639
    638 The \textsc{met} resolution expected for the \textsc{cms} detector for similar events is $\sigma_x = (0.6-0.7) ~ \sqrt{E_T} ~ \mathrm{GeV}^{1/2}$ with no pile-up\footnote{\textit{Pile-up} events are extra simultaneous $pp$ collision occurring at high-luminosity in the same bunch crossing.}~\cite{bib:cmsjetresolution}, which compares very well with the $\alpha = 0.68$ obtained with \textsc{Delphes}.
     640The \textsc{met} resolution expected for the \textsc{cms} detector for similar events is $\sigma_x = (0.6-0.7) ~ \sqrt{E_T} ~ \mathrm{GeV}^{1/2}$ with no pile-up\footnote{\textit{Pile-up} events are extra simultaneous $pp$ collision occurring at high-luminosity in the same bunch crossing.}~\cite{bib:cmsjetresolution}, which compares very well with the $\alpha = 0.68$ obtained with \textsc{Delphes}. Similarly, for an \textsc{atlas}-like detector, a value of $0.57$ is obtained by \textsc{Delphes} for the $\alpha$ parameter, while the experiment expects it in the range $[0.53~ ;~0.57]$~\cite{bib:ATLASresolution}.
    639641
    640642\subsection{\texorpdfstring{$\tau$}{\texttau}-jet efficiency}
    … …  
    10961098~~~Particle & generator particles from \textsc{hepevt}     & {\verb GenParticle }\\
    10971099\multicolumn{3}{l}{}\\
    1098 {\bf Trigger tree } & &\\
     1100{\bf Trigger \textsc{tree} } & &\\
    10991101~~~TrigResult & Acceptance of different trigger-bits       & {\verb TRootTrigger }\\
    11001102\multicolumn{3}{l}{}\\
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