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Jan 6, 2009, 4:05:06 PM (16 years ago)
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Xavier Rouby
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visualisation and conclusion and bibliogrpahy modified

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    39 \title{\textsc{Delphes}, a framework for fast simulation \\of a general purpose \textsc{lhc} detector}
    40 \author{S. Ovyn and X. Rouby\thanks{Now in Physikalisches Institut, Albert-Ludwigs-Universit\"at Freiburg} \\
    41         Center for Particle Physics and Phenomenology (CP3)\\ Universit\'e catholique de Louvain \\ B-1348 Louvain-la-Neuve, Belgium \\ \\
    42         \textit{severine.ovyn@uclouvain.be, xavier.rouby@cern.ch} \\
     39%\title{\textsc{Delphes}, a framework for fast simulation \\of a general purpose \textsc{lhc} detector}
     40\title{\textsc{Delphes}, a framework for fast simulation \\of a generic collider experiment}
     41\author{S. Ovyn and X. Rouby$^\textrm{a}$\\
     42        \small{Center for Particle Physics and Phenomenology (CP3)}\\
     43        \small{Universit\'e catholique de Louvain}\\
     44        \small{B-1348 Louvain-la-Neuve, Belgium}\\ \\
     45        \texttt{severine.ovyn@uclouvain.be, xavier.rouby@cern.ch} \\
    4346}
    4447\date{}
    4548
     49
    4650\begin{document}
    4751
    4852\twocolumn[
    4953\maketitle
     54
     55\begin{center}
     56\includegraphics{DelphesLogoSml}
     57\end{center}
     58
     59
    5060\begin{abstract}
    5161Knowing whether theoretical predictions are visible and measurable in a high energy experiment is always delicate, due to the
    … …  
    5666The simulation of detector response takes into account the detector resolution, and usual reconstruction algorithms for complex objects, like \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.
    5767An overview of \textsc{Delphes} is given as well as a few use-cases for illustration.
    58 \vspace{1cm}
     68\vspace{0.5cm}
    5969
    6070\noindent
    6171\textit{Keywords:} \textsc{Delphes}, fast simulation, \textsc{lhc}, smearing, trigger, \textsc{FastJet}, \textsc{Hector}, \textsc{Frog}
    62 \vspace{1cm}
     72\vspace{1.5cm}
     73
    6374\end{abstract}
     75\small{$^\textrm{a}$ Now in Physikalisches Institut, Albert-Ludwigs-Universit\"at Freiburg}
    6476]
    65 \saythanks
     77%\saythanks
    6678
    6779\section{Introduction}
    … …  
    99111%The 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.
    100112
    101 Three formats of input files can currently be used as input in \textsc{Delphes}\footnote{\texttt{[code] }See the \texttt{HEPEVTConverter}, \texttt{LHEFConverter} and \texttt{STDHEPConverter} classes.}. In order to process events from many different generators, the standard Monte Carlo event structure \mbox{\textsc{s}td\textsc{hep}} 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 \textbf{h2root} utility from the \textsc{root} framework~\cite{bib:Root}.
     113Three formats of input files can currently be used as input in \textsc{Delphes}\footnote{\texttt{[code] }See the \texttt{HEPEVTConverter}, \texttt{LHEFConverter} and \texttt{STDHEPConverter} classes.}. In order to process events from many different generators, the standard Monte Carlo event structure \mbox{\textsc{s}td\textsc{hep}} 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 \texttt{h2root} utility from the \textsc{root} framework~\cite{bib:Root}.
    102114%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.
    103115
    104 The output of \textsc{Delphes} contains a copy of the generator level data (\textsc{gen} tree), the analysis data objects after reconstruction (\mbox{\textsc{A}nalysis} tree), and possibly the results of the trigger emulation (\mbox{\textsc{T}rigger} tree). The program is driven by input cards. The detector card (\texttt{data/DataCardDet.dat}) allows a large spectrum of running conditions by modifying basic detector parameters, including calorimeter and tracking coverage and resolution, thresholds or jet algorithm parameters. The trigger card (\texttt{data/trigger.dat}) lists the user algorithms for the simplified online preselection.\\
     116\textsc{Delphes} uses the \texttt{ExRootAnalysis} utility~\cite{bib:ExRootAnalysis} to create output data in a \texttt{*.root} file format.
     117This output contains a copy of the generator level data (\textsc{gen} tree), the analysis data objects after reconstruction (\mbox{\textsc{A}nalysis} tree), and possibly the results of the trigger emulation (\mbox{\textsc{T}rigger} tree). The program is driven by input cards. The detector card (\texttt{data/DataCardDet.dat}) allows a large spectrum of running conditions by modifying basic detector parameters, including calorimeter and tracking coverage and resolution, thresholds or jet algorithm parameters. The trigger card (\texttt{data/trigger.dat}) lists the user algorithms for the simplified online preselection.\\
    105118
    106119
    … …  
    335348\begin{enumerate}[start=4]
    336349 
    337 \item {\it Longitudinally invariant $k_t$ jet}:
     350\item {\it Longitudinally invariant $k_t$ jet}~\cite{bib:ktjet}:
    338351\begin{equation}
    339352\begin{array}{l}
    … …  
    343356\end{equation}
    344357 
    345 \item {\it Cambridge/Aachen jet}:
    346  
     358\item {\it Cambridge/Aachen jet}~\cite{bib:aachen}:
    347359\begin{equation}
    348360\begin{array}{l}
    … …  
    352364\end{equation}
    353365 
    354 \item {\it Anti $k_t$ jet}: where hard jets are exactly circular
    355  
     366\item {\it Anti $k_t$ jet}~\cite{bib:antikt}: where hard jets are exactly circular
    356367\begin{equation}
    357368\begin{array}{l}
    … …  
    381392
    382393
    383 \subsection{$\tau$ identification}
     394\subsection{\texorpdfstring{$\tau$}{\texttau} identification}
    384395
    385396Jets originating from $\tau$-decays are identified using an identification procedure consistent with the one applied in a full detector simulation~\cite{bib:cmstaus}.
    … …  
    427438\includegraphics[width=\columnwidth]{Tau2}
    428439\caption{Distribution of the electromagnetic collimation $C_\tau$ variable for true $\tau$-jets, normalised to unity. This distribution is shown for associated $WH$ photoproduction~\cite{bib:whphotoproduction}, where the Higgs boson decays into a $W^+ W^-$ pair. Each $W$ boson decays into a $\ell \nu_\ell$ pair, where $\ell = e, \mu, \tau$.
    429 Events generated with MadGraph/MadEvent~\cite{bib:mgme}.
     440Events generated with \textsc{MadGraph/MadEvent}~\cite{bib:mgme}.
     441Final state hadronisation is performed by \textsc{Pythia}~\cite{bib:pythia}.
    430442Histogram entries correspond to true $\tau$-jets, matched with generator level data. }
    431443\label{fig:tau2}
    … …  
    533545The majority of interesting processes at the \textsc{lhc} contain jets in the final state. The jet resolution obtained using \textsc{Delphes} is therefore a crucial point for its validation. Even if \textsc{Delphes} contains six algorithms for jet reconstruction, only the jet clustering algorithm (\textsc{jetclu}) with $R=0.7$ is used to validate the jet collection.
    534546
    535 This validation \textcolor{red}{employs} $pp \rightarrow gg$ events produced with \textsc{mg/me} and hadronised using \textsc{Pythia}~\cite{bib:mgme,bib:pythia}. The events were arranged in $14$ bins of gluon transverse momentum $\hat{p}_T$. In each $\hat{p}_T$ bin, every jet in \textsc{Delphes} is matched to the closest jet of generator-level particles, using the spatial separation between the two jet \textcolor{red}{axes}
     547This validation \textcolor{red}{employs} $pp \rightarrow gg$ events produced with \textsc{MadGraph/MadEvent} and hadronised using \textsc{Pythia}~\cite{bib:mgme,bib:pythia}. The events were arranged in $14$ bins of gluon transverse momentum $\hat{p}_T$. In each $\hat{p}_T$ bin, every jet in \textsc{Delphes} is matched to the closest jet of generator-level particles, using the spatial separation between the two jet \textcolor{red}{axes}
    536548\begin{equation}
    537549\Delta R = \sqrt{ \big(\eta^\textrm{rec} - \eta^\textrm{MC} \big)^2 +  \big(\phi^\textrm{rec} - \phi^\textrm{MC} \big)^2}<0.25.
    … …  
    572584The samples used to study the \textsc{met} performance are identical to those used for the jet validation.
    573585It is worth noting that the contribution to $E_T^\textrm{miss}$ from muons is negligible in the studied sample.
    574 \textcolor{red}{The\footnote{je n'ai pas tout compris. Ce que j'ai devin\'e est en rouge.} input samples are divided in five bins of scalar $E_T$ sums $(\Sigma E_T)$. This sum, called \textit{total visible transverse energy}, is defined as the scalar sum of transverse energy in all towers.}
     586\textcolor{red}{The\footnote{\textcolor{red}{je n'ai pas tout compris. Ce que j'ai devin\'e est en rouge.}} input samples are divided in five bins of scalar $E_T$ sums $(\Sigma E_T)$. This sum, called \textit{total visible transverse energy}, is defined as the scalar sum of transverse energy in all towers.}
    575587The quality of the \textsc{met} reconstruction is checked via the resolution on its horizontal component $E_x^\textrm{miss}$.
    576588
    … …  
    598610The same quantity obtained by \textsc{Delphes} is in excellent agreement with the expectations of the general purpose detector, as $\alpha = 0.68$.
    599611
    600 \subsection{$\tau$-jet efficiency}
     612\subsection{\texorpdfstring{$\tau$}{\texttau}-jet efficiency}
    601613Due to the complexity of their reconstruction algorithm, $\tau$-jets have also to be checked.
    602614Table~\ref{tab:taurecoefficiency} lists the reconstruction efficiencies for the hadronic $\tau$-jets in the \textsc{cms} experiment and in \textsc{Delphes}. Agreement is good enough to validate this reconstruction.
    603615
    604 ~\cite{bib:cmstauresolution}.
    605 
    606616\begin{table}[!h]
    607617\begin{center}
    608 \caption{Reconstruction efficiencies of $\tau$-jets in decays from $Z$ or $H$ bosons.\vspace{0.5cm}}
     618\caption{Reconstruction efficiencies of $\tau$-jets in decays from $Z$ or $H$ bosons, in \textsc{Delphes} and in the \textsc{cms} experiment~\cite{bib:cmstauresolution}.\vspace{0.5cm}}
    609619\begin{tabular}{lll}
    610620\hline
    … …  
    624634\section{Visualisation}
    625635
     636When performing an event analysis, it can be usefull to convey informations about the detector layout or the event topology in a simple way. With this aim in view, a visualisation tool can be of great interest. Hence, the Fast and Realistic OpenGl Displayer \textsc{frog} has been interfaced in \textsc{Delphes} allowing an easy display of the defined detector configuration\footnote{\texttt{[code] } To prepare the visualisation, the \texttt{FLAG\_frog} parameter should be equal to $1$.}.
     637 
    626638\begin{figure}[!h]
    627639\begin{center}
    628640\includegraphics[width=\columnwidth]{Detector_Delphes_1}
    629 \caption{Layout of the generic detector geometry assumed in \textsc{Delphes}. The innermost layer, close to the interaction point, is a central tracking system (pink). 
    630 It is surrounded by a central calorimeter volume (green) with both electromagnetic and hadronic sections. 
    631 The outer layer of the central system (red) consist of a muon system. In addition, two end-cap calorimeters (blue) extend the pseudorapidity coverage of the central detector. 
     641\caption{Layout of the generic detector geometry assumed in \textsc{Delphes}. The innermost layer, close to the interaction point, is a central tracking system (pink).
     642It is surrounded by a central calorimeter volume (green) with both electromagnetic and hadronic sections.
     643The outer layer of the central system (red) consist of a muon system. In addition, two end-cap calorimeters (blue) extend the pseudorapidity coverage of the central detector.
    632644The actual detector granularity and extension is defined in the user-configuration card. The detector is assumed to be strictly symmetric around the beam axis (black line). Additional forward detectors are not depicted.}
    633645\label{fig:GenDet}
    634646\end{center}
    635647\end{figure}
    636 
    637 
     648 
     649For the purpose of publication and talks, the two and three-dimentional representation of the used detector configuration can be used as it clearly show the geometric coverage of the different detector subsystems. An an illustration, the obtained representation of the generic detector geometry assumed in \textsc{Delphes} is shown in Fig.\ref{fig:GenDet} and \ref{fig:GenDet2}  As pointed before, the detector is assumed to be strictly symmetric around the beam axis. The extention in pseudorapidity of the central tracking system, the central calorimeters are displayed.  In addition, the two end-cap calorimeters ad defined in the Datacard extend the pseudorapidity coverage of the central detector until $|\eta|=5$. Nevertheless, it should be noticed that only the geometry coverage is represented and that the calorimeter segmentation is not taken into account in the draw  of the detector. Morevocer, the radius as well as the length of the different sub-detectors are insignifiant
     650 
    638651\begin{figure}[!h]
    639652\begin{center}
    … …  
    643656\end{center}
    644657\end{figure}
    645 
    646 
    647 As an illustration, an associated photoproduction of a $W$ boson and a $t$ quark is shown in Fig.~\ref{fig:wt}. This corresponds to a $pp \rightarrow Wt \ +  \ p  \ + \ X$ process, where the $Wt$ couple is induced by an incoming photon emitted by one interacting proton. This leading proton survives from the photon emission and subsequently from the $pp$ interaction, and is present in the final state. The experimental signature is a lack of hadronic activity in one forward hemisphere, where the surviving proton escapes. The $t$ quark decays into a $W$ and a $b$. Both $W$ bosons decay into leptons ($W \rightarrow \mu \nu_\mu$ and $W \rightarrow \tau \nu_\tau$).
    648 
     658 
     659A more deep understanding of interesting physics processes is obtained using the display of the events. The visibility of each set of objects (e.g. electrons, muons, taus, jets, transverse missing energy) is enhanced by a color coding. Moreover, each object is toggled on by a simple mouse action allowing to access its four-momentum infomration. As an illustration, an associated photoproduction of a $W$ boson and a $t$ quark is shown in Fig.~\ref{fig:wt}. This corresponds to a $pp \rightarrow Wt \ +  \ p  \ + \ X$ process, where the $Wt$ couple is induced by an incoming photon emitted by one interacting proton. This leading proton survives from the photon emission and subsequently from the $pp$ interaction, and is present in the final state. The experimental signature is a lack of hadronic activity in one forward hemisphere, where the surviving proton escapes. The $t$ quark decays into a $W$ and a $b$. Both $W$ bosons decay into leptons ($W \rightarrow \mu \nu_\mu$ and $W \rightarrow \tau \nu_\tau$).
     660 
    649661\begin{figure}[!h]
    650662\begin{center}
    … …  
    655667\end{figure}
    656668
    657 
    658 
    659 
    660669\section{Conclusion and perspectives}
    661670
     671\subsection{version 1}
     672We have described here the major features of the \textsc{Delphes} framework, introduced for the fast simulation of a collider experiment.
     673It has already been used for several phenomenological studies, in particular in photon interactions at the \textsc{lhc}.
     674
     675\textsc{Delphes} takes the output of event generators, in various formats, and yields analysis object data.
     676The simulation applies the resolutions of central and forward detectors by smearing the kinematical properties of final state particles.
     677It yields tracks in a solenoidal magnetic field and calorimetric towers.
     678Realistic reconstruction algorithms are run, including the \textsc{FastJet} package, to produce collections of $e^\pm$, $\mu^\pm$, jets and $\tau$-jets. $b$-tag and missing transverse energy are also evaluated.
     679The output is validated by comparing to the \textsc{cms} expected performances.
     680A trigger stage can be emulated on the output data.
     681At last, event visualisation is possible through the \textsc{Frog} 3D event display.
     682
     683
     684\textsc{Delphes} has been developped using the parameters of the \textsc{cms} experiment but can be easily extended to \textsc{atlas} and other non-\textsc{lhc} experiments, as at Tevatron or at the \textsc{ilc}. Further developments include a more flexible design for the subdetector assembly and possibly the implementation of an event mixing module for pile-up event simulation.
     685\textcolor{red}{c'est complet, mais ca ressemble fort a l'abstract et a l'intro.}
     686
     687
     688\subsection{version 2}
     689We have described here the major features of the \textsc{Delphes} framework, introduced for the fast simulation of a collider experiment. This framework is a tool meant for feasibility studies in phenomenology, probing the observability of models in collider experiments. It has already been used for several analyses, in particular in photon interactions at the \textsc{lhc}.
     690
     691\textsc{Delphes} takes the output of event generators and yields analysis object data.
     692The simulation includes central and forward detectors to produce realistic observables using standard reconstruction algorithms.
     693Moreover, the framework allows trigger emulation and 3D event visualisation.
     694
     695\textsc{Delphes} has been developped using the parameters of the \textsc{cms} experiment but can be easily extended to \textsc{atlas} and other non-\textsc{lhc} experiments, as at Tevatron or at the \textsc{ilc}. Further developments include a more flexible design for the subdetector assembly and possibly the implementation of an event mixing module for pile-up event simulation.
     696
     697
     698
     699\section*{Acknowledgements}
     700\addcontentsline{toc}{section}{Acknowledgements}
     701The author would like to thank Vincent Lemaitre, Muriel Vander Donckt and David d'Enterria for useful discussions and comments, and Loic Quertenmont for support in interfacing \textsc{Frog}.
     702Part of this work was supported by the Belgian Federal Office for Scientific, Technical and Cultural Affairs through the Interuniversity Attraction Pole P6/11.
     703
     704
    662705\begin{thebibliography}{99}
     706\addcontentsline{toc}{section}{References}
    663707 
    664708\bibitem{bib:Delphes} \textsc{Delphes}, hepforge:
    665 \bibitem{bib:FastJet} \textsc{Fast-Jet},
    666 \bibitem{bib:SIScone} A practical Seedless Infrared-Safe Cone jet algorithm, G.P. Salam, G. Soyez, JHEP0705:086,2007.
    667 \bibitem{bib:Hector} \textsc{Hector},
     709\bibitem{bib:Root} %\textsc{Root}, \textit{An Object Oriented Data Analysis Framework},
     710R. Brun, F. Rademakers, Nucl. Inst. \& Meth. in Phys. Res. A 389 (1997) 81-86.
     711\bibitem{bib:ExRootAnalysis} %\textit{The} \textsc{ExRootAnalysis} \textit{analysis steering utility},
     712P. Demin, (2006), unpublished. Now part of \textsc{MadGraph/MadEvent}.
     713\bibitem{bib:Hector} %\textsc{Hector}, \textit{a fast simulator for the transport of particles in beamlines},
     714X. Rouby, J. de Favereau, K. Piotrzkowski, JINST 2 P09005 (2007).
     715\bibitem{bib:FastJet} %\textit{The} \textsc{FastJet} \textit{package},
     716M. Cacciari, G. Salam, Phys. Lett. B 641 (2006) 57.
     717\bibitem{bib:SIScone} %\textsc{SIScone}, \textit{A practical Seedless Infrared-Safe Cone jet algorithm},
     718G.P. Salam, G. Soyez, JHEP0705:086 (2007).
     719\bibitem{bib:ktjet} S. Catani, Y. L. Dokshitzer, M. H. Seymour and B. R. Webber, Nucl. Phys. B 406 (1993) 187. S. D. Ellis and D. E. Soper, Phys. Rev. D 48 (1993) 3160.
     720\bibitem{bib:aachen} Y.L. Dokshitzer, G.D. Leder, S. Moretti and B.R. Webber, JHEP 9708 (1997) 001. M. Wobisch and T. Wengler, arXiv:hep-ph/9907280.
     721\bibitem{bib:antikt} %\textit{The anti-kt jet clustering algorithm},
     722M. Cacciari, G. P. Salam and G. Soyez, JHEP 0804 (2008) 063.
     723\bibitem{bib:cmstaus} Tau reconstruction in CMS
     724\bibitem{bib:pdg} C. Amsler et al. (Particle Data Group), PL B667, 1 (2008).
     725\bibitem{bib:whphotoproduction} S. Ovyn
     726\bibitem{bib:mgme} %\textsc{MadGraph/MadEvent v4}, \textit{The New Web Generation},
     727J. Alwall, P. Demin, S. de Visscher, R. Frederix, M. Herquet, F. Maltoni, T. Plehn, D.L. Rainwater, T. Stelzer, JHEP 0709:028 (2007).
     728\bibitem{bib:pythia} %\textsc{Pythia 6.4}, \textit{Physics and Manual},
     729T. Sjostrand, S. Mrenna and P. Skands, JHEP 05 (2006) 026.
     730\bibitem{bib:cmsjetresolution} CMS IN 2007/053.
     731\bibitem{bib:cmstauresolution} %\textit{Study of $\tau$-jet identification in CMS},
     732R. Kinnunen, CMS NOTE 1997/002.
    668733\bibitem{bib:Frog} \textsc{Frog},
    669 \bibitem{bib:cmsjetresolution} CMS IN 2007/053
    670 \bibitem{bib:Root} \textsc{Root} - An Object Oriented Data Analysis Framework, R. Brun and F. Rademakers, Nucl. Inst. \& Meth. in Phys. Res. A 389 (1997) 81-86, \url{http://root.cern.ch}
    671 \bibitem{bib:cmstaus} Tau reconstruction in CMS
    672 \bibitem{bib:whphotoproduction} WH photoproduction, S. Ovyn
    673 \bibitem{bib:mgme} Madgraph/Madevent version xx.yy
    674 \bibitem{bib:pythia} \textsc{Pythia} version xx.yy
    675 \bibitem{bib:pdg} C. Amsler et al. (Particle Data Group), PL B667, 1 (2008) (URL: http://pdg.lbl.gov)
    676 \bibitem{bib:cmstauresolution} R. Kinnunen, \textit{Study of $\tau$-jet identification in CMS}, CMS NOTE 1997/002.
    677734\end{thebibliography}
    678735
    … …  
    9571014 
    9581015\end{document}
     1016
     1017%[25] ATLAS Collaboration, Detector and Physics Performance Technical Design
     1018%     Report, Vols. 1 and 2, CERN–LHCC–99–14 and CERN–LHCC–99–15.
     1019%[26] CMS Collaboration, CMS Physics Technical Design Report, CERN/LHCC
     1020%     2006–001.
     1021%[27] A. Djouadi, J. Lykken, K. Monig, Y. Okada, M. J. Oreglia and S. Yamashita,
     1022%     International Linear Collider Reference Design Report Volume 2: PHYSICS
     1023%     AT THE ILC, arXiv:0709.1893 [hep-ph].
     1024
     1025% personnes qui pourraient être intéressées:
     1026% Alice, Benjamin
     1027% auteurs de arXiv:0801.3359
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