Aligning the CMS Muon Endcap Detector with a System of Optical Sensors

The positions and orientations of one sixth of 468 large cathode strip chambers in the endcaps of the CMS muon detector are directly monitored by several hundred sensors including 2-D optical sensors with linear CCDs illuminated by cross-hair lasers. Position measurements obtained by photogrammetry and survey under field-off conditions show that chambers in the +Z endcap have been placed on the yoke disks with an average accuracy of $\approx 1$ mm in all 3 dimensions. We reconstruct absolute Z$_{CMS}$ positions and orientations of chambers at B=0T and B=4T using data from the optical alignment system. The measured position resolution and sensitivity to relative motion is about 60 $\mu m$. The precision for measuring chamber positions taking into account mechanical tolerances is \mbox{$\approx 270 \mu m$}. Comparing reconstruction of optical alignment data and photogrammetry measurements at B=0T indicates an accuracy of $\approx$ 680 $\mu m$ currently achieved with the hardware alignment system. Optical position measurements at B=4T show significant chamber displacements of up to 13 mm due to yoke disk deformation

Design and performance of the alignment system for the CMS muon endcaps

The alignment system for the CMS Muon Endcap detector employs several hundred sensors such as optical 1-D CCD sensors illuminated by lasers and analog distance- and tilt-sensors to monitor the positions of one sixth of 468 large Cathode Strip Chambers. The chambers mounted on the endcap yoke disks undergo substantial deformation on the order of centimeters when the 4T field is switched on and off. The Muon Endcap alignment system is required to monitor chamber positions with 75-200 {micro}m accuracy in the R? plane, {approx}400 {micro}m in the radial direction, and {approx}1 mm in the z-direction along the beam axis. The complete alignment hardware for one of the two endcaps has been installed at CERN. A major system test was performed when the 4T solenoid magnet was ramped up to full field for the first time in August 2006. We present the overall system design and first results on disk deformations, which indicate that the measurements agree with expectations

Design and Performance of the Alignment System for the CMS Muon Endcaps

The alignment system for the CMS Muon Endcap detector employs several hundred sensors such as optical 1-D CCD sensors illuminated by lasers and analog distance- and tilt-sensors to monitor the positions of one sixth of 468 large Cathode Strip Chambers. The chambers mounted on the endcap yoke disks undergo substantial deformation on the order of centimeters when the 4T field is switched on and off. The Muon Endcap alignment system is required to monitor chamber positions with \mbox{75-200 $\mu$m} accuracy in the R$\phi$ plane, $\approx$400 $\mu$m in the radial direction, and $\approx$1 mm in the z-direction along the beam axis. The complete alignment hardware for one of the two endcaps has been installed at CERN. A major system test was performed when the 4T solenoid magnet was ramped up to full field for the first time in August 2006. We present the overall system design and first results on disk deformations, which indicate that the measurements agree with expectations

Measurement of the hadronic photon structure function F(2)(gamma) with the L3 detector at LEP

The photon is one of the basic components of our present understanding of elementary particles and their interactions. The theory of Quantum Electrodynamics describes this object as being the mediator of the electromagnetic force between charged particles. Contrary to earlier assumptions the photon turns out to have a "structure" due to quantum fluctuations into fermion anti-fermion pairs that can further interact with other particles. In this case the photon reveals its structure. The structure of the photon can be described by the concept of photon structure functions, which are studied at high energy accelerators like the Large Electron Positron Collider at the European Center for Particle Physics. With the large amount of data (L = 608 pb-1) collected with the L3 detector at center-of-mass energies 189 GeV < s < 209 GeV and the analysis method used in this dissertation, a measurement of the hadronic structure function F2gamma (x,Q2)/alpha is obtained with better precision than previous measurements. The evolution of F2 gamma/alpha as a function of x and Q2 is studied in the 11 GeV2 < Q2 < 34 GeV2 and 0.006 < x < 0.556 intervals. Due to the precision of this measurement it is possible for the first time to demonstrate that the results of the higher-order GRV parametrization of the structure function are in good agreement with the data and give a correct description of the physical processes involved