Changeset 816

Timestamp:

05/30/01 13:49:36 (24 years ago)

Author:

harald

Message:

intermediate

File:

• trunk/ICRC_01/mccontrib.tex (modified) (12 diffs)

trunk/ICRC_01/mccontrib.tex

@@ -40 +40 @@
 \section{Introduction}
 
-In this year the construction of the $17~\mathrm{m}$ diameter
-Che\-ren\-kov telescope called MAGIC \cite{mc98}
-will be finished. The aim of this
+The $17~\mathrm{m}$ diameter
+Che\-ren\-kov telescope called MAGIC 
+is presently in the construction stage \cite{mc98}. 
+The aim of this
 detector is the observation of $\gamma$-ray sources in the 
-energy region above $\approx 10~\mathrm{GeV}$. 
-The size of the telesope mirrors will be around $250~\mathrm{m^2}$.
+energy region above $\approx 30~\mathrm{GeV}$ in its first phase. 
 The air showers induced by cosmic ray particles (hadrons and gammas) 
-will be detected with a "classical" camera consisting of 577
+will be detected with a "classical" camera consisting of 576
 photomultiplier tubes (PMT). The analog signals of these PMTs will 
 be recorded by a FADC system running with a frequency of 
@@ -55 +55 @@
 different trigger levels. 
 
-The goal of the trigger system is to reject the hadronic cosmic ray
-background from the gamma rays, for which the lowest threshold 
-is aimed. 
+The primary goal of the trigger system is the selction of showers, 
 For a better understanding of the MAGIC telescope and its different 
 systems (trigger, FADC) a detailed Monte Carlo (MC) study is 
 neccessary. Such an study has to take into account the simulation
-of air showers, the effect of absorption in the atmosphere, the 
+of the air showers, the effect of absorption in the atmosphere, the 
 behaviour of the PMTs and the response of the trigger and FADC
 system.
  
-For a big telescope like MAGIC there is an additional source of 
-noise, which is the light of the night sky. As a rude assumption
-there will be around 50 stars with magnitude $m \le 9$ in the 
+An important issue for a big telescope like MAGIC 
+is the light of the night sky. 
+There will be around 50 stars with magnitude $m \le 9$ in the 
 field of view of the camera. 
-Investigations are neccessary to invent methods which allows to 
-reduce the effect of the light from stars. The methods can be
-tested before the MAGIC telescope exists by using monte carlo
-data. 
+Methods have to be developed which allow to 
+reduce the biases introduced by the presence of stars. 
+The methods can be tested by using Monte Carlo data. 
 
 
@@ -79 +76 @@
 \section{Generation of MC data samples} 
 
-The simulation of the MAGIC telescope is seperated in a 
-subsequent chain of smaller simulation parts. First the 
+The simulation is done in several steps: 
+First the 
 air showers are simulated with the 
 CORSIKA program \citep{hk95}. 
@@ -87 +84 @@
 Then the behaviour of the PMTs is simulated and the
 response of the trigger and FADC system is generated. 
-In the following subsections you find a more precise 
-description of all the programs. 
+In the following subsections 
+the various steps are described in more details. 
 
 \subsection{Air shower simulation}
@@ -94 +91 @@
 The simulation of gammas and of hadrons is done with
 the CORSIKA program, version 5.20. 
-For the simulation of hadronic 
+For the simulation of had\-ro\-nic 
 showers we use the VENUS model. We simulate showers 
 for different zenith angles 
 ($\Theta = 0^\circ, 5^\circ, 10^\circ, 15^\circ, 
-20^\circ, 25^\circ $). 
-Gammas where simulated like a point source
-whereas the hadrons are simulated isotropic around
-the given zenith angle. 
-The trigger probality for hadronic showers with 
-a big impact parameter $I$ is not negliable. 
+20^\circ, 25^\circ $) at fixed azimuth angel $\Phi$. 
+Gammas are assumed to originate from point sources 
+in the direction ($\Theta,\Phi$)
+whereas the hadrons are simulated isotropically
+around the given ($\Theta,\Phi$) direction. 
+The trigger probability for hadronic showers with 
+a big impact parameter $I$ is not Englisch negligible. 
 Therefore we 
 simulate hadrons with $I < 400~\mathrm{m}$ and gammas
@@ -134 +132 @@
 %
 For each simulated shower all
-Cherenkov photons hitting the ground at observation level 
+Cherenkov photons hitting a horizontal plane at observation level 
 close to the telescope position are stored.
 
-\subsection{atmospheric and mirror simulation}
-
-The output of the air shower simualition is used 
-as the input to the mirror simulation. 
+\subsection{Atmospheric and mirror simulation}
+
+The output of the air shower simulation is used 
+as the input to this step. 
 First the absorption in the atmosphere is taken into
 account. 
 By knowing the height of production and the 
-wavelength of each Cherenkov photen it is possible
-to calculate the effect of Rayleigh and Mie scattering. 
-The second step is the simulation of the mirror dish. 
+wavelength of each Cherenkov photon the effect of Rayleigh 
+and Mie scattering is calculated.
+Next the reflection at the mirrors is simulated.  
 We assume a reflectivity of the mirrors of around 90\%. 
-Each Cherenkov photon hitting one mirror is tracked back
+Each Cherenkov photon hitting one mirror is propagated 
 to the camera plane of the telescope. This procedure 
 depends on the orientation of the telescope to the 
 shower axis. 
 All Cherenkov photons reaching the camera plane will be
-keeped for the next simulation program.  
-
-\subsection{camera simulation}
-
-The camera simulates the behaviour of the PMTs and the
-electronics of the trigger and FADC system. After the 
-pixelisation we take the wavelength dependent quantum
+kept for the next simulation step. 
+
+\subsection{Camera simulation}
+
+The simulation comprises the behaviour of the PMTs and the
+electronics of the trigger and FADC system. 
+We take the wavelength dependent quantum
 efficiency (QE) for each PMT into account. 
 In figure \ref{fig_qe} 
@@ -176 +174 @@
 %
 %
-For each photo electron (PE) leaving the photo cathod we
-generate a "standard" response function that we add to 
-the analog signal of that PMT - seperatly for the 
+For each photo electron (PE) leaving the photo cathode we
+use a "standard" response function to generate  
+the analog signal of that PMT - separatly for the 
 trigger and the FADC system. 
-At the present these response function are gaussians with
-a given width. 
-The amplitude of the response function is randomized 
-by using the distribution of figure \ref{fig_ampl}. 
+At present these response functions are gaussians with
+a given width in time. 
+The amplitude of the response function is chosen randomly
+according to the distribution of figure \ref{fig_ampl}
+ .
+ 
 By superimposing all photons of one pixel and by taking
-the arrival time into account the response 
+the arrival times into account the response 
 of the trigger and FADC system for that pixel is generated
 (see also figure \ref{fig_starresp}). 
 This is done for all pixels in the camera. 
 
-Then the simulation of the trigger electronic is applied. 
-We look in the generated analog signal if the discriminator
-threshold is achieved. In that case a digital output
+The simulation of the trigger electronic starts by checking 
+whether the generated analog signal exceeds the discriminator 
+level. 
+In that case a digital output
 signal of a given length (We use in that study a gate length of 6
 nsec.)
-for that pixels. 
+for that pixels is generated. 
 By checking next neighbour conditions (NN) at a given time
 the first level trigger is simulated. 
@@ -209 +210 @@
  \includegraphics[width=8.3cm]{ampldist.eps} % .eps for Latex,
                                             % pdfLatex allows .pdf, .jpg, .png and .tif
- \caption{The distibution of amplitude of the standard response function.}
+ \caption{The distibution of the amplitude of the standard response
+ function to single photo electrons.}
  \label{fig_ampl}
 \end{figure}
@@ -216 +218 @@
 %
 
-\subsection{starlight simulation}
-
-Due to the big mirror surface the light from the stars around 
-the position of an expected gamma ray source is contributing to 
-the noise in the camera. We developed a program that allows us
+\subsection{Starlight simulation}
+
+Due to the big mirror area MAGIC will be sensitive up to 
+$10^m$ stars. 
+These stars will contribute locally to the noise in the 
+camera and have to be taken into account. 
+We developed a program that allows us
 to simulate the star light together with the generated showers. 
-This program takes all stars in the field of view of the camera
-around chosen sky region. The light of these stars is track up to 
-the camera taking the frequency of the light into account.
+This program considers all stars in the field of view of the camera
+around a chosen direction. The light of these stars is traced up to 
+the camera taking the wavelength of the light into account.
 After simulating the response of the photo cathode, we
 get the number of emitted photo electrons per pixel and 
 time.
 
-These number is used to generate a noise signal for all the pixels. 
+These number are used to generate a noise signal for all the pixels. 
 %
 %
@@ -247 +251 @@
 %
 In figure \ref{fig_starresp} the response of the trigger and the 
-FADC system can be seen for one pixel with a star of 
+FADC system can be seen for a pixel with a star of 
 magnitude $m = 7$.
 These stars are typical, because there will 
-be always one $7^m$ star in the trigger area of the camera.
+be on average one $7^m$ star in the trigger area of the camera.
 
 
@@ -259 +263 @@
 \subsection{Trigger studies}
 
-The MC data produced are used to calculate some important
-parameter of the MAGIC telescope on the level of the 
-trigger system. 
-The trigger system build up will consist of different 
-trigger levels. The discriminator of each channel is called the 
-zero-level-trigger. For a given signal each discriminator will 
-produce a digital output signal of a given length. So the important
-parameters of such an system are the threshold of each discriminator
-and the length of the digital output. 
+The trigger system will consist of different 
+trigger levels. 
+The discriminator of each channel is called the 
+zero-level-trigger. 
+If a given signal exceeds the discriminator threshold 
+a digital output signal of a given length is produced. 
+So the important parameters of such a system are the 
+threshold of each discriminator and the length of the 
+digital output. 
 
 The first-level-trigger is looking in the digital output of the 
@@ -275 +279 @@
 overlapping time. 
 
+
+The MC data produced are used to calculate some important
+parameter of the MAGIC telescope on the level of the 
+trigger system. 
+
 The second-level-trigger of the MAGIC telescope will be a 
 pattern-recognition method. This part is still in the design 
 phase. All results presented here are based on studies of the
 first-level-trigger.
+
  
 \subsubsection{Collection area}