10 - H1 - Desy

3.2 H1 detector 45
3.2.2 Calorimetry
Calorimeters are detector components providing the energy measurement for both charged
and neutral particles. H1 calorimetry system consists of four separate calorimeters, with
the main one, being the Liquid Argon (LAr) calorimeter covering the forward and central
region of the detector. Energy leaking out of the LAr is measured by the tail
catcher installed in the instrumented iron. The plug calorimeter and Spaghetti calorimeter
(SPACAL) provide energy measurements in the forward and backward detector regions
respectively.
The LAr calorimeter [98] is the most important subdetector used in the current analysis.
It provides the identification of prompt photons as well as measures energy of hadronic
final state particles. Due to its vital importance it is described below in some more details.
Figure 3.6 shows a longitudinal cross section of the LAr calorimeter. It is geometrically
divided into eight wheels, listed from the backward direction these are the Backward
Barrel (BBE), three Central Barrels (CB1, CB2 and CB3), two Forward Barrels (FB1
and FB2) and Inner and Outer Forward module (IF and OF). Except of BBE, which is
purely electromagnetic and OF, which is purely hadronic, all the wheels are equipped
with electromagnetic and hadronic sections. In addition to the wheel segmentation, LAr
calorimeter is divided into eight octants along the azimuthal angle φ. Between octants
and wheels, there are insensitive calorimeter regions, which are referred later on as to
φ-cracks and z-cracks, respectively. The LAr has an asymmetric polar angle coverage of
4 ◦ < θ < 154 ◦ .
Figure 3.6: Longitudinal cross section of the Liquid Argon calorimeter showing its
segmentation into eight wheels.
The LAr is a sampling calorimeter composed of alternating absorber layers and liquid
argon filled gaps. The electromagnetic section consists of 2.4 mm thick lead absorber
plates separated with 2.35 mm wide liquid argon sampling layers. The liquid argon acts
as an active material between the high voltage and readout cells which are mounted
on the absorber plates. Shower particles crossing the sampling layer induce a signal
by the ionisation of liquid argon atoms. The total depth of the absorber material in