COMP/CSA06DOC/analysisdemo.tex

\section {Analysis Demonstrations}


Different physics groups prepared some analysis codes to extract
physics results by running on skimmed files at Tier-2s.

\subsection {Calibration}

\subsection {Allignment}

\subsection {Physics Analysis Exercises}

\subsubsection {Effect of tracker misalignment on track reconstruction performances}

The alignment uncertainties of the CMS Tracker detector, made of a huge amount of independent silicon sensors with an excellent position resolution, affect the performances of the track reconstruction and track parameters measurement. 
The analysis exercise performed by the team at Bari during the CSA06 had the purpose of study the effect of the CMS tracker misalignment on the performances of the track reconstruction \cite{misalignment}. Realistic estimates for the expected displacements of the tracking systems were supplied in different scenarios as specified in the following: 
 
\begin{itemize}
\item the ideal scenario with a perfect tracker geometry;
\item the short term misalignment scenario supposed to reproduce the mis-alignment conditions during the first 
data taking when the uncertainties on the position of the sub-structures of the CMS
tracker will be between $10 \, \mu$ for pixel detectors and $400 \, \mu$ for microstrip silicon detectors in 
the endcaps. Detector position and errors are read
 from the offline database at CERN by caching the needed information locally via frontier/squid
software \cite{frontier}.

\item the long term scenario when the alignment uncertainties are supposed to be a factor 10 smaller because of the
improvement obtained by using aligmnent algorithms with a high statistics of tracks.
 
\item the CSA06 aligned scenario by using the tracker module position and errors as obtained by the output of the
 alignment procedure that was run at CERN Tier-0 to verify the efficiency of the alignment procedure on the track
reconstruction. The refit of tracks is performed also in this case.
 
\end{itemize}


Track reconstruction is based on the Kalman Filter formalism \cite{Kalman} for trajectory building, cleaning and smoothing steps and uses hits from pixel detector as seeds to provide initial trajectory candidates. Because of the misalignment the analysis requires to refit tracks with a misaligned tracker geometry.

Global efficiency of track recostruction and track parameter resolutions for muons and fake rate were
compared in all the cases. 
                                                                                                                  
Muons from $Z\rightarrow \mu \mu $ sample in a large $p_T$ spectrum were used to extract the results. The 
$t\bar{t}$ sample was used to compute the rate of fake tracks.


\begin{2figures}{hbtp}
  \resizebox{\linewidth}{!}{\includegraphics{figs/Eff_eta.eps}} &
  \resizebox{\linewidth}{!}{\includegraphics{figs/Residual_mZ_mu.eps}} \\
  \caption{Global track reconstrution efficiency vs pseudorapidity for muons coming from Z decay in the case of perfect 
tracker geometry and in short-term and long term misalignment scenarios when the APE is not used.}
  \label{eff} &
  \caption{Residual of Z mass obtained as the invariant mass of muons coming from Z decay in the case of perfect
tracker geometry and in short-term and long term misalignment scenarios.}
  \label{mz} \\
\end{2figures}
                                                                                                                                   
Some preliminary results were derived. The global efficiency of track reconstruction of muons coming from
Z decay is shown in Fig.~\ref{eff} as a function of the pseudorapidity in the tracker acceptance;
the effect of misalignment is relevant in the short term scenario and causes a partial inefficiency of the
track reconstruction; that can be recovered if the intrinsic position resolution of the tracker
 detector is combined with the alignment uncertainties to make larger the error on the position of the
reconstructed hit (called alignment position error, APE) so improving the track fit at the
expence of a larger rate of fake tracks.
                                                                                                                                   
The residual of Z mass obtained as the invariant mass of muons coming from Z decay in the case of perfect
tracker geometry and in short-term and long term misalignment scenarios is shown in Fig.~\ref{mz}; the Z mass
resolution is degradated of a factor 2 because of the tracker misalignment in the short term scenario.
                                                                                                                          
                                                                                                                                   
Revision:	1.3
Committed:	Tue Nov 28 23:18:36 2006 UTC (18 years, 5 months ago) by ndefilip
Content type:	application/x-tex
Branch:	MAIN
Changes since 1.2:	+59 -0 lines
Log Message:	Misalignment analysis
#	User	Rev	Content
1	fisk	1.1	\section {Analysis Demonstrations}
2
3	ndefilip	1.3
4			Different physics groups prepared some analysis codes to extract
5			physics results by running on skimmed files at Tier-2s.
6
7	fisk	1.1	\subsection {Calibration}
8
9			\subsection {Allignment}
10
11			\subsection {Physics Analysis Exercises}
12
13	ndefilip	1.2	\subsubsection {Effect of tracker misalignment on track reconstruction performances}
14
15	ndefilip	1.3	The alignment uncertainties of the CMS Tracker detector, made of a huge amount of independent silicon sensors with an excellent position resolution, affect the performances of the track reconstruction and track parameters measurement.
16			The analysis exercise performed by the team at Bari during the CSA06 had the purpose of study the effect of the CMS tracker misalignment on the performances of the track reconstruction \cite{misalignment}. Realistic estimates for the expected displacements of the tracking systems were supplied in different scenarios as specified in the following:
17
18			\begin{itemize}
19			\item the ideal scenario with a perfect tracker geometry;
20			\item the short term misalignment scenario supposed to reproduce the mis-alignment conditions during the first
21			data taking when the uncertainties on the position of the sub-structures of the CMS
22			tracker will be between $10 \, \mu$ for pixel detectors and $400 \, \mu$ for microstrip silicon detectors in
23			the endcaps. Detector position and errors are read
24			from the offline database at CERN by caching the needed information locally via frontier/squid
25			software \cite{frontier}.
26
27			\item the long term scenario when the alignment uncertainties are supposed to be a factor 10 smaller because of the
28			improvement obtained by using aligmnent algorithms with a high statistics of tracks.
29
30			\item the CSA06 aligned scenario by using the tracker module position and errors as obtained by the output of the
31			alignment procedure that was run at CERN Tier-0 to verify the efficiency of the alignment procedure on the track
32			reconstruction. The refit of tracks is performed also in this case.
33
34			\end{itemize}
35
36
37			Track reconstruction is based on the Kalman Filter formalism \cite{Kalman} for trajectory building, cleaning and smoothing steps and uses hits from pixel detector as seeds to provide initial trajectory candidates. Because of the misalignment the analysis requires to refit tracks with a misaligned tracker geometry.
38
39			Global efficiency of track recostruction and track parameter resolutions for muons and fake rate were
40			compared in all the cases.
41
42			Muons from $Z\rightarrow \mu \mu $ sample in a large $p_T$ spectrum were used to extract the results. The
43			$t\bar{t}$ sample was used to compute the rate of fake tracks.
44
45
46			\begin{2figures}{hbtp}
47			\resizebox{\linewidth}{!}{\includegraphics{figs/Eff_eta.eps}} &
48			\resizebox{\linewidth}{!}{\includegraphics{figs/Residual_mZ_mu.eps}} \\
49			\caption{Global track reconstrution efficiency vs pseudorapidity for muons coming from Z decay in the case of perfect
50			tracker geometry and in short-term and long term misalignment scenarios when the APE is not used.}
51			\label{eff} &
52			\caption{Residual of Z mass obtained as the invariant mass of muons coming from Z decay in the case of perfect
53			tracker geometry and in short-term and long term misalignment scenarios.}
54			\label{mz} \\
55			\end{2figures}
56
57			Some preliminary results were derived. The global efficiency of track reconstruction of muons coming from
58			Z decay is shown in Fig.~\ref{eff} as a function of the pseudorapidity in the tracker acceptance;
59			the effect of misalignment is relevant in the short term scenario and causes a partial inefficiency of the
60			track reconstruction; that can be recovered if the intrinsic position resolution of the tracker
61			detector is combined with the alignment uncertainties to make larger the error on the position of the
62			reconstructed hit (called alignment position error, APE) so improving the track fit at the
63			expence of a larger rate of fake tracks.
64
65			The residual of Z mass obtained as the invariant mass of muons coming from Z decay in the case of perfect
66			tracker geometry and in short-term and long term misalignment scenarios is shown in Fig.~\ref{mz}; the Z mass
67			resolution is degradated of a factor 2 because of the tracker misalignment in the short term scenario.
68
69