10 - H1 - Desy

44 The H1 experiment at HERA
resolution in the rφ plane is based on a drift-time measurement of the ionisation electrons,
while the z-coordinate is obtained from charge division. The hit position is measured with
an accuracy of 170 µm in the rφ plane and 3 cm along the z-axis. The z resolution can be
improved by employing the Central Inner Proportional (CIP) chamber [91] and Central
Outer Z (COZ) chamber [92], which leads to an improvement of the z measurement
resolution up to typically 300µm.
The CIP chamber (see figure 3.5) is a multiwire proportional chamber (MWPC) which
consist of five cylindrical detector layers with cathode pad readout. It is located between
15 < r < 20 cm and has a total active length of 2.2 m. The chamber is segmented into
16 azimuthal sectors and 93-119 (depending on the layer) pads along the z direction.
Multiwire proportional chambers are characterised by a very fast response to ionising
particles. A typical value for intrinsic time resolution is 10 ns. and for that reason, the
CIP chamber provides the information used already on the level one trigger level (see
section 3.2.5).
Figure 3.5: The structure of the CIP chamber.
The FTD [93] is a set of drift chambers designed to detect forward tracks in the polar
angle range 5 ◦ < θ < 25 ◦ . It consists of three identical supermodules aligned along the
z-axis. Each of the supermodules contains a planar drift chamber and a proportional
chamber.
The Backward Proportional Chamber (BPC) [94] covers the polar angle in range 153 ◦ <
θ < 174 ◦ and is used to enhance the angle measurement of the scattered electron at low
Q 2 .
The innermost part of the tracking system is composed of the silicon detectors, the Backward
Silicon Detector (BST), the Central Silicon Detector (CST) and the Forward Silicon
Detector (FST). The BST [95] has an acceptance coverage of 164 ◦ < θ < 176 ◦ and a
resolution σ r = 22 µm in r-direction. It is used to identify the scattered electron at
small polar angles. The CST [96] consists of two layers of silicon strip detectors, arranged
parallel to the beam pipe. The polar angle acceptance range is 30 ◦ < θ < 150 ◦ and the
resolution is σ z = 12 µm in z and σ rφ = 22 µm in both r and φ. It is used for a precise
reconstruction of the interaction vertex. The FST [97] consists of five planes of silicon
strip detector covering the polar angle 8 ◦ < θ < 16 ◦ and having resolution similar to the
BST.