10 - H1 - Desy

3.2 H1 detector 47
cell size in the electromagnetic stack ranges between 5 × 5 cm 2 in the forward and 7 × 13
cm 2 in the central wheels.
Figure 3.8: Longitudinal (a) and transversal (b) cross section of the Liquid Argon
calorimeter illustrating the granulity of the readout system.
The energy resolution of the LAr calorimeter, determined in the test beam measurements
[102,103] is
σ el (E)
E = 12%
√ ± 1% (3.4)
E/GeV
for the electromagnetic section and
for hadronic showers.
σ had (E)
E
=
50%
√
E/GeV
± 2% (3.5)
During the reconstruction process, the readout cells of the LAr firstly undergo the noise
suppression algorithm and later are assigned to clusters, which are contiguous formations
of cells that are likely to contain the cascade of a single incident particle.
In the backward part of the H1 detector, the SPACAL [104] is used with the main purpose
of detection of the electron scattered under the polar angles 153 ◦ < θ < 177.5 ◦ . This
coverage corresponds to the measurements in the kinematic range of 4 < Q 2 < 150 GeV 2 .
Like the LAr calorimeter, SPACAL is a sampling calorimeter with an inner electromagnetic
and outer hadronic section. Both parts are fabricated of long scintillating fibres
placed parallel to the beam axis and embedded in the lead absorber material. Charged
shower particles in the induced showers are detected by the excitation of molecules in the
scintillator material, which trigger light impulses in the fibres. The light is transmitted to
photomultiplier tubes at the backward end of the fibres, where the impulses are converted
into electrical signals. In this analysis SPACAL is used to veto low Q 2 DIS events.
3.2.3 Luminosity system and electron tagger
The H1 luminosity system (LUMI) [105] make use of the Bethe-Heitler process ep → epγ
predicted in QED with high accuracy. Both electron and photons are mostly scattered