Changes between Version 13 and Version 14 of Private/RefereeComments/Section_2

Timestamp:

Oct 3, 2013, 12:12:31 PM (11 years ago)

Author:

Michele Selvaggi

Comment:

--

Private/RefereeComments/Section_2

@@ -196 +196 @@
 content is not related whatsoever to the information in this bullet.
 
+>>> the discussion about hits is not present anymore.
+
 PAGE 5
 
@@ -201 +203 @@
 even by experts. The suggestion is to work the text out and come with a
 clearer version.
+
+>>> this part has been completely re-written. 
 
 First bullet :
@@ -218 +222 @@
 electron and a neutron point to the same HCAL tower, the e ID is smart
 enough to detect it, is almost correct for most detector designs.
+
+ 
 
 Second bullet:
@@ -256 +262 @@
 If the momentum resolution of the tracking system is higher than the energy resolution of calorimeters, it can be convenient to use the tracking information within the tracker acceptance for estimating the charged particles momenta. In real experiments, the tracker resolution will be better than the calorimeter resolution only up to some energy threshold. In \DELPHES, we assume it is always convenient to estimate charged particle momenta via the the tracker.
 
-The particle-flow algorithm produces two collections of 4-vectors --- particle-flow tracks and particle-flow towers --- that will serve later as input for reconstructing jets and missing transverse energy with a higher resolution. 
-For each calorimeter cell, the algorithm counts: 
+The energy-flow algorithm produces two collections of 4-vectors --- \emph{energy-flow tracks} and \emph{energy-flow towers} --- that will serve later as input for reconstructing jets and missing transverse energy with a higher resolution. 
+For each calorimeter tower, the algorithm counts: 
+
 \begin{itemize}
-\item $N_{calo}$, the total number of hits that originate from all long-lived standard model particles propagating within the calorimeter acceptance, provided that at least one among $f_{ECAL}$ and $f_{HCAL}$ is non-zero.~\footnote{Muons, neutrinos and neutralinos do not deposit any energy in the calorimeters.} Each time the calorimeter cell is reached by such a particle, $N_{calo}$ is incremented by 1. Similarly we define $N_{calo-HCAL}$ ($N_{calo-ECAL}$) which gets incremented if a particle with $f_{HCAL}>0$ ($f_{ECAL}>0$) reaches the calorimeter cell.
-
-\item $N_{trk}$, the number of hits that originate from a reconstructed track. Due to tracking inefficiencies, some charged particles will not be reconstructed as tracks, but will produce a hit in a calorimeter cell. By construction $N_{trk} \leq N_{calo}$. We also define $N_{trk-HCAL}$ ($N_{trk-ECAL}$) which is incremented if a charged particle reconstructed as a track with $f_{HCAL}>0$ ($f_{ECAL}>0$) reaches the calorimeter cell.
-
+\item $E_{ECAL}$ and $E_{HCAL}$, the total energy deposited respectively in ECAL and HCAL. 
+\item $E_{ECAL,trk}$ and $E_{HCAL,trk}$, the total energy deposited respectively in ECAL and HCAL originating from charged particles for which the tracks have been reconstructed. The charged components $E_{ECAL,trk}$ and $E_{HCAL,trk}$ can be 
+asserted if one assumes perfect charged particle identification. 
 \end{itemize}
+
+We then define
+
+\begin{equation}
+\Delta_{ECAL} =E_{ECAL} - E_{ECAL,trk}\,,
+\qquad
+\Delta_{HCAL} =E_{HCAL} - E_{HCAL,trk}\,,
+\label{eq:efexcess}
+\end{equation}
+
+and,
+
+\begin{equation}
+E^{e-flow}_{Tower} =  max(0,\Delta_{ECAL}) + max(0,\Delta_{HCAL})
+\label{eq:eftower}
+\end{equation}
+
+The energy-flow proceeds then as follows: 
+
+\begin{itemize}
+\item each reconstructed track will result in an \emph{energy-flow track}
+\item if $E^{e-flow}_{Tower}>0$, an \emph{energy-flow tower} is created with energy $E^{e-flow}_{Tower}$
+\end{itemize}
+
+To illustrate the energy-flow algorithm in \DELPHES, here are a few simple examples:
+
+\begin{itemize}
+\item a single charged pion particle is reconstructed as a track with energy E_{HCAL,trk} and deposits some energy $E_{HCAL} in the HCAL. If $E_{HCAL} \leq E_{HCAL,trk}$ only an energy-flow track with energy E_{HCAL,trk} is produced. If $E_{HCAL} >  E_{HCAL,trk}$, an energy-flow track with energy $E_{HCAL,trk}$ and an energy-flow tower with energy $E_{HCAL}$ are produced. This case is analogous to that of a single electron depositing energy in the ECAL and being reconstructed as a track. 
+\item 
+\end{itemize}
+
+
+Due to tracking inefficiencies, some charged particles will not be reconstructed as tracks, but will produce a hit in a calorimeter cell. 
+Therefore, in most cases, $E_{ECAL,trk} \leq E_{ECAL}$ and $E_{HCAL,trk} \leq E_{HCAL}$. The algorithm comap
+
+
 
 The following two scenarios may occur, $N_{calo}=N_{trk}$ and $N_{calo}>N_{trk}$. 
@@ -279 +321 @@
 The output of the particle-flow algorithm consists in two collections of objects. The particle-flow tracks contain charged particles estimated with a good resolution. The particle-flow towers contain in general a combination of charged and neutral particles, and are characterized by a lower resolution. As will be shown in sections~\ref{sec:jets} and~\ref{sec:pus}, besides producing high-resolution inputs for jets and missing transverse energy, the particle-flow approach can be pretty useful for addressing pile-up subtraction. 
 While very simple when compared to what is actually required in real experiments, the algorithm described above is shown to reproduce well the performance achieved at LHC later in section~\ref{sec:validation}.
-