A Classic Thesis Style - Johannes Gutenberg-Universität Mainz

2.4 kaos spectrometer
2.4 kaos spectrometer 29
Kaos was originally designed as a compact spectrometer for meson
detection in heavy ion collisions at the GSI facilities in Darmstat, and
was successfully operated during the 1990s. Positively charged particles
were focused vertically by a quadrupole magnet into the 20 cm
gap of the following analyzing pole shoe dipole. During May and
June 2003, Kaos magnets, together with associated electronics and
detectors, were brought to Mainz. For its conversion into a double
arm spectrometer dedicated to kaon electroproduction experiments,
the quadrupole was removed as it could not provide focusing for both
charge states. In addition, shortening the effective length of the magnetic
system resulted in a reduced flight path and a higher survival
probability 2 . During a first phase, and for the data analyzed in this
thesis, one of the existing spectrometers (B) was used for electron detection.
Positively charged particles at moderated angles were detected
with Kaos spectrometer. Fig. 13 shows the experimental hall of the A1
collaboration. The three large vertically deflecting spectrometers A, B
and C colored in red, blue and green respectively, can be freely rotated
for measurements at different angles. Kaos (in purple), at measurement
position, can be seen on the right hand side of the exit beam line
(metallic cone), sitting on a red platform. Some angular freedom is
given by a system of hydraulic positioning feet. The platform with the
spectrometer can be moved from a parking position to a measurement
position by means of a system of hydraulic pressure cylinders on
skid-tracks. The detector package of the spectrometer consists of two
multiwire proportional chambers for track determination, and two
scintillator walls for timing and triggering purposes (see Fig. 14). In
the next sections a complete description of Kaos magnet and detectors
will be provided.
2.4.1 Dipole magnet
Although force and acceleration are not parallel vectors in general for
relativistic particles as can be seen from:
�F = d�p
dt =
� �
m0�v
d √
1−v2 /c2 dt
=
� �
m0 d √
1−v2 /c2 dt
�v +
m0
� 1 − v 2 /c 2 �a
(where a term proportional to the velocity vector arises as a consequence
of the relativistic definition of linear momentum), if only
magnetic forces are responsible of the particle motion, the perpendicularity
of force and velocity expressed by the Lorentz force �F =
2 Recently, small angle coincidence experiments have been performed with two dipole
bending magnets bringing the electron beam into Kaos at zero degrees.