Analysis of Cosmic Muons Measured in CMS Drift Chambers

Why do you study physics?" Which student of that subject does not know this question asked by a friend or acquaintance not being involved in scientific research? A typical answer starts with the native curiosity of men and ends with the Theory of Everything, which unfortunatly still has to be developed even though there already are auspicious approaches. Usually the next question from that person is "And what is that all good for?" Typical replies from the scientist to-be are shrugged shoulders and a lack of understanding for such a question. But let us start from scratch: Ever since the dawn of civilisation people recognised certain rules and patterns within their environment, such as night and day or the change of the seasons, and started to think of mystic explanations for these observations. Later in the ancient world first theories arose about the composition of matter: Demokrit's idea of atoms and Aristoteles' thesis of four elements. Both suggestions had in common that they tried to reduce a broad spectrum of matter properties to a compact set of constituents. But rightly, these persons are regarded as philosophers and not as physicists simply because they did not make predictions that could be compared to reality. Physics from a modern point of view started when theories began to quantify expectations and were tested through experiments for their validity. With the publication of Newton's theory of motion and gravitation, his Principia Mathematica, physics entered a new age in which nature decided about success or failure of an explanation. As history shows, many long time accepted theories later were proven to be inaccurate, as experiments became able to test their predictions on new scales, which resulted in modifications of the models used or sometimes even in completely new ideas. The presumably greatest leaps that followed that way were Maxwell's theory about electromagnetic phenomena, Einstein's theories of relativity and quantum theory, developed by a number of now legendary scientists. The common aim of all these ideas is the reduction of the complex impression of the world to as few basic elements as possible, perhaps one day to a single fundamental principle. But as that aim could not be reached until now it is appropriate to divide the wide world of physics into some major fields, each with a different emphasis, of which one is particle physics. Ratios of chemical reactions gave the first hints that matter consists of tiny lumps. Later on it was discovered by Thomson that these atoms are not elementary and scattering experiments with electrons by Lenard and with alpha particles by Geiger, Marsden and Rutherford turned out that atoms are composed of electrons carrying a unit of negative charge which surround a positively charged nucleus. A new era with particle accelerators, allowing studies such as the structure of atomic nuclei, revealed that protons and neutrons build up the atomic core. Furthermore, physicists detected a large quantity of new, exotic particles being produced at high energies, first by cosmic rays and later also in accelerator experiments. But it became clear that this initial confusion is explainable by the existence of a few kinds of quarks being combined following certain rules. The quarks are regarded as elementary until today. The present state of particle physics is desribed by the so called Standard Model containing not only these particles but also the forces that let them interact. This theory already made a lot of predictions which could be confirmed by experiments. But one of the main hypotheses is still left to be examined: the existence of the predicted Higgs particle could only be excluded for masses smaller than 114 GeV/c2. To answer the question if it does exist after all, and to look for the presence of phenomena beyond the Standard Model, new, unevitably huge setups are required. Right now a new particle accelerator called Large Hadron Collider, abbreviated as LHC, and its two major detectors Compact Muon Solenoid (CMS) and A Toroidal LHC Apparatus (ATLAS) are under construction at the research centre CERN near Geneva. One part of the first mentioned CMS detector is a complex system for the detection of particles called muons. This installation has been designed to be able to measure muons being produced at the collision of accelerated particles and to recognise the signature from the decay of possibly produced Higgs particles into four muons. The contribution of the III. Phys. Inst. of RWTH Aachen University mainly consists of the development, production and subsequent testing of drift chambers as a part of the muon system. This diploma thesis concerns the analysis of data taken from drift chambers in a test setup with cosmic muons with a first emphasis on the quality control of the production and a second on the properties of just these cosmic particles as far as measurable. A major part of this work was the development of a software that transforms the recorded data into particle track descriptions from which the quality of a muon chamber can be deduced. As a side effect in succession it was tried to confirm already known characteristics of cosmic muons. Now my trial to answer the question from above, what all this is good for, apart from satisfying the curiosity to see how the world can be described: I don't know. Maybe the technology and the knowledge gained by the challenge of finding the Higgs particle will turn out to be useful in some way we do not think of now, as it has already happened with earlier experiments. But I am not a prophet...