Muon Identification in Hadron Calorimeter at DELPHI and Muons as P robes of Particle Interactions

The presented dissertation consists of the papers [A.1, A.2, A.3, A.4, A.5, A.6, A.7] on DELPHI hadron calorimeter (HAC) [B.1]. These papers deal with signal simulations, performance and major upgrade of HAC after the period LEP1 (production of Z 0 around the resonance peak). This upgrade resulted from extensive tests of streamer tube1 prop- erties and studies of possible utilisation of tube signals for data analysis. The aim was to improve the capabilities of HAC for the second period of the LEP collider operation, so called LEP200 program when the energy of e+ and e− beams has been gradually increased up to the energy 104 GeV per beam. The above mentioned studies led to the conclusion, that with the constraints imposed by HAC construction, the upgrade can improve signif- icantly the muon identification of DELPHI [A.7] and on this ground the upgrade project has been defended and realized in the years 1994-1996. The muon identification has been used in standard analyses (part 3.1). However, it turned out that HAC upgrade brings benefits not foreseen previously. These features have been employed in searches for particles predicted by some supersymmetry models in topologies which are very difficult from the point of view of trigger and background suppression [A.8, A.9]. The large volume of HAC with good muon identification capability led naturally to increased interest in cosmic muons. DELPHI has adopted a cosmic trigger which led to regular cosmic muon detection even during data taking at LEP operation. The regis- tered data initiated study which resulted in proposal to use muon identification to unfold the dynamics of cosmic ray interactions at very high energies [A.10, A.11, B.5]. This method cannot be used in collider experiments and it increases potential of muon identi- fication beyond its standard use like Drell-Yan pair detection, b or c quark identification, semileptonic or leptonic decays of various particles etc.