hcalDoc/CalibNote/introduction.tex

\section{Introduction}

The purpose of the calibration of the Hadronic Calorimeter systems with
physics events is to derive response corrections (RC) and to establish a stable
hadronic energy scale. It is intended to improve on the calibration state of
the detector established with the available techniques and sources prior to
the start of collision data taking.

Before CMS assembly, a limited number of calorimeter modules were exposed to test beams of
pions with known energies to obtain reference calibrations.
The energy scale was later propagated to the remaining modules
in the assembled detector using Co60 radioactive sources.
Details of the test beam analysis and the wiresourcing can be found in
%Sect~\ref{S:testbeam}.
\cite{testbeam} and \cite{wiresource}, respectively.

The calibration of the detector was further improved using cosmic muons and splash events.
Both methods provided valuable information that allowed us to equalize the detector
response in the +/- sides of HB, and derive relative channel-to-channel corrections
in HB and HE. Splash events were also used in the identification of the most pronounced
"spikes" in HF.

%One of the deficiencies of the wiresource calibrations is that it does not account for
%the non-uniform dead material between the HCAL and ECAL.

The results with the above mentioned techniques have contributed to
the establishment of good reference points for the energy response of the HCAL
sub-detectors. However, they do not account for the effect of dead material
in front of the calorimeter towers as a function of their location.
Therefore, we need to employ additional techniques that can be applied throughout
the operation of CMS and account for the conditions applicable to particles produced
in collisions.


There are two components in the calibration:
\begin{itemize}
 \item{Equalize the response of the detector in $\eta$ and $\phi$
       (relative corrections)}
 \item{Set a reproducible global hadronic energy scale
       (absolute corrections)}
\end{itemize}

The corrections are derived with respect to the ``precalibrated'' conditions.

Due to the complex structure of the hadronic calorimeter, its large coverage
and different overlapping regions with other detector systems used in the calibration
procedure, these goals can only
be achieved through the use of multiple techniques and data samples.
Additional complications come from the non-linearity of the HCAL
energy response and the relatively large lateral size of hadronic showers.
Due to the nonlinear response of HCAL it is not possible to set an
absolute scale that is valid
for all energies of incident hadrons. We define the target absolute scale
to correspond to $E_{had}/p_{trk}$=1
for MIP-like charged hadrons with momentum 50~GeV in the barrel
($E_{had}$ measured in a tower cluster as described in Section~\ref{section:hcalIsoTracCalib}).
The criteria for this choice is that the energy is in a region where
the calorimeter response as a function of energy
is slowly changing and it can be set and tested directly.

In 2008 the HCAL DPG proposed a calibration workflow that includes several
techniques that covers the calibration of HB, HE and HF. It was targeted at
early data calibrations that can be performed with tens of $pb^{-1}$.
The calibration workflow includes the following steps:
\begin{itemize}
    \item{equalize the response in HB, HE, and HF within rings of
          constant $\eta$ (azimuthal symmetry corrections)}
    \item{equalize $\eta$ response in HB and part of HE using isolated
          tracks, obtain absolute energy corrections}
    \item{equalize $\eta$ response in HE and HF using di-jet events,
          obtain absolute scale corrections}
\end{itemize}

The calibration steps are not completely independent: the results of each step are used in the
subsequent one. A schematic view of the proposed calibration procedure is shown in
Figure~\ref{figure:hcalWorkflow}.

\begin{figure}[!Hhtb]
  \begin{center}
  \includegraphics*[width=12cm]{figs/hcalWorkflow08.eps}
  \caption{Schematic view of the HCAL calibration workflow proposed in CSA08.}
 \label{figure:hcalWorkflow}
 \end{center}
\end{figure}


This Note provides a description of the techniques and summarizes the results of the
feasibility studies for the proposed scheme with MC events.
It is restricted to the treatment of HB, HE, and HF.
The calibration of HO with collisions data is expected to
require much larger samples and will be treated separately. ZDC and Castor calibration with collisions
data are in the planning stages and are also excluded form this discussion.


Revision:	1.1
Committed:	Tue Jul 5 16:01:20 2011 UTC (13 years, 10 months ago) by anastass
Content type:	application/x-tex
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	Start from previous version of the note. A lot of updating needed.
#	Content
1	\section{Introduction}
2
3	The purpose of the calibration of the Hadronic Calorimeter systems with
4	physics events is to derive response corrections (RC) and to establish a stable
5	hadronic energy scale. It is intended to improve on the calibration state of
6	the detector established with the available techniques and sources prior to
7	the start of collision data taking.
8
9	Before CMS assembly, a limited number of calorimeter modules were exposed to test beams of
10	pions with known energies to obtain reference calibrations.
11	The energy scale was later propagated to the remaining modules
12	in the assembled detector using Co60 radioactive sources.
13	Details of the test beam analysis and the wiresourcing can be found in
14	%Sect~\ref{S:testbeam}.
15	\cite{testbeam} and \cite{wiresource}, respectively.
16
17	The calibration of the detector was further improved using cosmic muons and splash events.
18	Both methods provided valuable information that allowed us to equalize the detector
19	response in the +/- sides of HB, and derive relative channel-to-channel corrections
20	in HB and HE. Splash events were also used in the identification of the most pronounced
21	"spikes" in HF.
22
23	%One of the deficiencies of the wiresource calibrations is that it does not account for
24	%the non-uniform dead material between the HCAL and ECAL.
25
26	The results with the above mentioned techniques have contributed to
27	the establishment of good reference points for the energy response of the HCAL
28	sub-detectors. However, they do not account for the effect of dead material
29	in front of the calorimeter towers as a function of their location.
30	Therefore, we need to employ additional techniques that can be applied throughout
31	the operation of CMS and account for the conditions applicable to particles produced
32	in collisions.
33
34
35
36	There are two components in the calibration:
37	\begin{itemize}
38	\item{Equalize the response of the detector in $\eta$ and $\phi$
39	(relative corrections)}
40	\item{Set a reproducible global hadronic energy scale
41	(absolute corrections)}
42	\end{itemize}
43
44	The corrections are derived with respect to the ``precalibrated'' conditions.
45
46	Due to the complex structure of the hadronic calorimeter, its large coverage
47	and different overlapping regions with other detector systems used in the calibration
48	procedure, these goals can only
49	be achieved through the use of multiple techniques and data samples.
50	Additional complications come from the non-linearity of the HCAL
51	energy response and the relatively large lateral size of hadronic showers.
52	Due to the nonlinear response of HCAL it is not possible to set an
53	absolute scale that is valid
54	for all energies of incident hadrons. We define the target absolute scale
55	to correspond to $E_{had}/p_{trk}$=1
56	for MIP-like charged hadrons with momentum 50~GeV in the barrel
57	($E_{had}$ measured in a tower cluster as described in Section~\ref{section:hcalIsoTracCalib}).
58	The criteria for this choice is that the energy is in a region where
59	the calorimeter response as a function of energy
60	is slowly changing and it can be set and tested directly.
61
62	In 2008 the HCAL DPG proposed a calibration workflow that includes several
63	techniques that covers the calibration of HB, HE and HF. It was targeted at
64	early data calibrations that can be performed with tens of $pb^{-1}$.
65	The calibration workflow includes the following steps:
66	\begin{itemize}
67	\item{equalize the response in HB, HE, and HF within rings of
68	constant $\eta$ (azimuthal symmetry corrections)}
69	\item{equalize $\eta$ response in HB and part of HE using isolated
70	tracks, obtain absolute energy corrections}
71	\item{equalize $\eta$ response in HE and HF using di-jet events,
72	obtain absolute scale corrections}
73	\end{itemize}
74
75	The calibration steps are not completely independent: the results of each step are used in the
76	subsequent one. A schematic view of the proposed calibration procedure is shown in
77	Figure~\ref{figure:hcalWorkflow}.
78
79	\begin{figure}[!Hhtb]
80	\begin{center}
81	\includegraphics*[width=12cm]{figs/hcalWorkflow08.eps}
82	\caption{Schematic view of the HCAL calibration workflow proposed in CSA08.}
83	\label{figure:hcalWorkflow}
84	\end{center}
85	\end{figure}
86
87
88	This Note provides a description of the techniques and summarizes the results of the
89	feasibility studies for the proposed scheme with MC events.
90	It is restricted to the treatment of HB, HE, and HF.
91	The calibration of HO with collisions data is expected to
92	require much larger samples and will be treated separately. ZDC and Castor calibration with collisions
93	data are in the planning stages and are also excluded form this discussion.
94
95