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We present a method to align between sections of a particle tracking detector exploiting the fact that most of the tracks in an event originate from a common spatial point. The method optimizes the reconstruction of interaction vertices of high energy particle collisions and is particularly useful for aligning sections of a detector which cover different ranges of the 4 [Pi] solid angle. A fast algorithm, suitable for online use, is derived. We demonstrate this method for the P238 vertex detector and present results with data and simulation.

The Pierre Auger Observatory will study cosmic rays with energy exceeding [10.sup.19] eV. The experiment will measure properties of extensive air showers with a hybrid detector consisting of a surface array and an atmospheric fluorescence telescope. This paper presents the characteristics and performance of the optical system for the fluorescence detector prototype. The system adopts a Schmidt camera design with a diaphragm to remove coma aberration. A large spherical mirror (approximately 3.6 x 3.6 m, with radius of curvature 3.47 m), segmented in 49 trapezoidal elements, is supported by a mechanical structure, where segments are positioned on the meridians of the spherical cap. At the diaphragm, an absorption filter is installed to preferentially transmit the nitrogen fluorescence light. The construction technique, image characteristics, and results of tests performed on the system are discussed. Index Terms--Fluorescence detectors, mirror system, ultra high energy cosmic rays, UV glass filter.

The Fluorescence Detector of the Pierre Auger Cosmic Ray Observatory will provide a measurement of the parameters of extensive air showers with energy [is greater than] 1019 eV. The mirror of the Fluorescence Detector prototype has dimension ~ 3.6 x 3.6 [m.sup.2], and is composed of 49 trapezoidal segments of approximately 50 x 50 [cm.sup.2]. Each segment is curved using a steel mold in which the glass sags in a controlled environment. The glass is then aluminized under vacuum and coated with oxide ([Al.sub.2][O.sub.3]). The oxide thickness is chosen to maximize the reflectivity in the wavelength range of fluorescence light (300 nm [is less than] [Lambda] [is less than] 400 nm). The 49 mirror segments, plus eight spare ones, are now ready for installation. In this paper, we discuss the production technique of the segments for the Torino prototype mirror.