Setup of a Drift Tube Muon Tracker and Calibration of Muon ...

essential for vetoing these events.Cosmic muons created in the atmosphere have the ability to penetrate the Earthto significant depths. They are hard to shield and a disturbance to measurementswith most particle detectors. Placing the experiment underground helps to reducethe muon flux. However, even at a depth of a few thousand meters water equivalentcosmic muons still cannot be neglected. It is thus of importance to effectively tagthese muons to be able to veto their induced signals.To veto events from cosmogenic induced nuclei, the intersection of a cylinderaround the incident muon track and a sphere around the position of the capture ofthe knocked out neutron are taken off the fiducial volume for a few half-lives of the11 C. A good resolution of the muon tracking thus is a key feature to prevent largefractions of the detector being blinded by this method. In Borexino, muon tracks arereconstructed by investigating the arrival time patterns at the PMTs. For a precisedetermination of the tracking resolution, the true muon track coordinates have tobe known.The compact muon tracker (CMT) presented in this work is capable of a threedimensional reconstruction of muon tracks with a spatial resolution of better than300ñm and an angular resolution of approximately 5 mrad. It is based on the drifttube technology developed for the Precision Tracker (PT) of the OPERA experiment.Whereas the PT only reconstructs 2D projections of muon tracks, the CMT has beenmodified so that a three dimensional tracking is possible. After a commissioning inHamburg it is now operated at the Borexino experiment at the LNGS undergroundlaboratory in the Abruzzo region in Italy. Although the CMT only covers a smallfraction of the Borexino detector, muon tracks reconstructed in the detector canbe used as a reference sample for the internal Borexino muon tracking. Thus, theCMT data can be used to determine the resolution of the internal Borexino muontracking. Comparing the tracks as reconstructed by the CMT with high precisionto the Borexino reconstruction can help to identify possible systematic errors of thelatter, and to improve its performance and hence the 11 C tagging.Within this thesis, the setup and commissioning of the CMT were performedand are described here. Its application to the Borexino experiment is presented andthe resolution of the Borexino muon tracking is determined.Following the introduction, Chapter 2 of this work deals with the physics ofneutrinos. After a brief overview of the history of neutrino physics in Section 2.1,the basics of neutrino oscillations are presented. An emphasis on solar neutrinos inparticular is given in Section 2.3, followed by a look at other neutrino sources andopen questions in neutrino physics.The general setup of the CMT is described in Chapter 3. After an introductionto the working principle of drift tubes, the setup of the individual components suchas the drift tube modules, the gas supply, and the electronics is described. This isfollowed by a description of the data taking procedure. The CMT data are processedwith the software package cmtrack which was developed within this thesis and isthen introduced. The reconstruction algorithms are described in detail. Finally, thecalibration and alignment of the detector is introduced and the first commissioningof the detector in Hamburg is presented.Chapter 4 gives an overview of the Borexino experiment. The detection methodfor neutrinos in liquid scintillators is described and the general setup of the Borexino2