Our tasks, responsibility and preliminary status quo
The main goal of the
experiment is looking for the experimental
evidence of Higgs particle and the investigation of the properties of
matter in the region 1 TeV (physics beyond Standard Model, MSSM,
SUSY). This last point after HERA results is more actual and attractive.
Calorimeters will play a crucial role at
LHC. In contrast to other
detectors their intrinsic resolution improves with energy, which
makes them very suitable detectors at high energy machines. An
important aspect of the
Hadronic End-Cap (HEC) is its ability to detect muons, and to
measure any radiative energy loss.
The Hadronic End-Cap is designed to provide coverage for hadronic
showers in the range 1.55 < eta < 3.2. The HEC detector elements are
located in the
at either end of the ATLAS tracking
volume. It is a liquid argon (LAr) sampling calorimeter with
copper-plate absorber (with the thickness 25/50 mm).
This technology was selected as it allows
a simple mechanical design to be produced that is radiation
resistant and covers the required area in a cost-effective way.
The gaps between the copper plates (8.5 mm) are instrumented with
structure forming an electrostatic transformer (EST), see fig 1.
|Figure 1: Hadronic
end-cap EST (cell)
optimizes the signal-to-noise ratio while reducing the high-voltage
requirements and ionization pile-up, and limiting the effect of failure
modes such as high-voltage sparks and shorts.
The signals are amplified and summed employing the concept of
"active pads": the signals from two consecutive pads are fed into
separate amplifiers (based on GaAs electronics) and summed to read-out
channels. The use of cryogenic GaAs preamplifiers provides the optimum
signal-to-noise ratio for the HEC.
The boards with the GaAs chips are mounted on the outer
radius of the HEC. The use of cryogenic GaAs preamplifiers provides
the optimum signal-to-noise ratio for the HEC.
Our primary goal in ATLAS experiment is the proposal and
the development of the calibration system for HEC
Our responsibilities can be described by the following way:
In 1996 was signed Interim Memorandum of Understanding for ATLAS
experiment (period two years 1996-1997) and in July 1998 was signed
Memorandum of Understanding (MoU) for ATLAS experiment up to 2005.
These two acts represent the basic juridical background of our present
activities in ATLAS experiment.
According to MoU of the
experiment, which from our side
was signed by the secretary of the Ministry of education of Slovak
republic, our financial obligations during whole time period of the
detector construction are following:
- core expenses: 100 000,- CHF
(today we reimbursed 6 x 12 500,- CHF)
- core expenses expressed as in-kind invoices: 100 000,- CHF
(today we reimbursed by cash 5 000,- CHF)
- hardware contribution into liquid argon subdetectors, especially
into the construction of the hadronic end-cap calorimeter:
304 000,- CHF
The proposal and the development of the calibration system for HEC
calorimeter is serious and difficult task. HEC is make up from
two symmetric calorimeters in the wheel structure HEC1 and HEC2,
each wheel has 32 modules, see fig. 2, where the one module of HEC
Hadronic end-cap module
One wheel has roughly 4 x 7 m size. On the fig. 3 you can see the first
from four HEC wheels
One wheel of HEC
Pad structure defines lateral segmentation
in (eta, phi) = 0.1 x 0.1. LAr gap is instrumented with 1 PAD board and
2 EST boards. From the electronic point of view HEC has 92 160 full
independent read-out channels, which is approximately two-time more
than in the up today largest liquid argon calorimeter which is used
in H1 in
Our project from the view on the development and realization of the
calibration procedures for HEC is possible to divide into three
parts, which in the present time status quo is following:
We continued in the development and testing
of the calibration system
for the modules assembled in five different laboratories
The calibration system was developed and tested in 1999-2000
test runs. In fig. 4 you can see the calibration signal (left) and
the prediction for the ionization signal (right) together with the
residuals with the respects to the fit (lower figures).
The calibration signal (left) and
the prediction for the ionization signal (right) together with the
residuals with the respects to the fit (lower figures)
We participate also on the design and laboratory tests of the Front
End Board (FEB) for Atlas experiment. The FEB, see fig. 5,
|Figure 5: The view on
is going to be
used for the EM and HEC part of the Atlas calorimeter. As described
of the liquid argon (LAr) calorimeter, the FEBs contain
the electronics for amplifying, shaping, sampling, pipeling, and
digitizing the LAr calorimeter signals. The FEB electronics e..g. must
handle the signal dynamic range of about 16 bits without
contributing more than 0.2%.
We have produced also a set of print boards with the different patterns
for the wiring of the final modules of HEC. Parameters of the board
divided a calibration signal on 3 pads are crucial for the accuracy
calibration signal distribution. A dividing ratio of the front
calibration distribution board for all channels is shown in figure
Dividing ratio of the Front Module
Calibration Distribution Boards of HEC
We finished HV and signal boards production. All these elements are the
parts of HEC modules and this year also the first of four large wheels
of the HEC calorimeter has been successfully assembled and rotated into
its final position on schedule - see fig. 3. To assemble a wheel have
been taken modules that have already been cold tested, do the final
electrical testing and locate them onto the HEC wheel assembly table.
All mechanical and electrical tests have been
successfully passed, it means also Košice elements are satisfied.
In period 2001-2002 we began start the filter box production,
see fig. 7,
all needed quality criteria.
The filter boxes will be used in all ATLAS calorimeters, e.g. on the
ATLAS barrel cryostat
the ATLAS barrel cryostat with our filter boxes (see
fig. 9 in more detail) is shown.
Detail view: the filter box in the ATLAS barrel cryostat
In 1998 the Cleland method for the noise suppression in the calorimeter
readout was successfully applied. The improvement of the signal/noise
ratio can be seen in fig. 10.
The noise reduction for 100 GeV electron
deposits in HEC module 0 a) before and b) after filter applying|
In fig. 11 is shown the linearity in the four different impact points in
the test modules with the points corresponding to uncalibration and calibration data for the various electrons energies. The improvement is markant.
|Figure 11: Response linearity of
module 0 in four different impact points. The full points -
before and, triangle - after calibration|
The new function describing the response of the whole testing
electronics for various signal's types (e..g. calibration one or
signal from particle) had been calculated and implemented, which
also using less number of free parameters the measured signals
describes very well.
In Košice now we have full present in stand-alone mode the ATLAS
software, which is based on OO-object oriented software.
We take participation
in Monte-Carlo simulation of HEC beam set-up, in the cluster
reconstruction in LAr using standard
Athena ATLAS tool and in this
time we try to use last GEANT4 version for the missing ET/jets physics
in HEC, e.g. in fig. 12 the comparision between GEANT3.21 and GEANT4
simulation has been shown.
The energy resolution of electrons in EMBarrel
Into generator PYTHIA6.2 has been putted new process with the
production two top quarks and we began the analyze with two top
production including background calculation.