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8 CHAPTER 1. INTRODUCTION Displaced Vertex: Often it is important to identify charged particles that originate at points a short distance from the collision point rather than at the collision point itself (B-, D- or τ-tagging). This is achieved with high spatial resolution detectors placed around the collision point. Neutrinos: The presence of the not directly detectable neutrinos can be infered through momentum conservation. A particle will not be evident until it either interacts with the detector in a measurable fashion, or decays into detectable particles. Despite their differences the detector types that were just described all rely on the same basic principles. Particle detectors make visible the effects that the particles have on their surroundings. In the next section we will give a brief summary of the different ways in which particles interact with matter. 1.2 Interactions of Particles with Matter In the last section we mentioned that a particle detector has to be able to reveal the presence of eight particles (and their corresponding antiparticles): electrons, muons, protons, neutrons, photons, charged pions, charged kaons and neutral kaons. These particles leave characteristic trails as they lose energy when they travel through a material, be it a gas, a liquid or a solid. This energy loss can be of different forms: • Electrically charged particles lose energy by ’colliding’ with atomic electrons of the material (excitation, ionization) and by the emission of bremsstrahlung when they scatter off the nuclei. • Strongly interacting particles can in addition lose energy through hadronic interactions (inelastic nuclear collisions, nuclear excitation, splitting). • Photons lose energy by Compton scattering with atomic electrons or they disappear completely in the processes of Photo Electric Effect and pair production. In this section the basic interaction mechanisms of particles with matter are summarized briefly. The energy loss of charged particles due to ionization and excitation is fundamental to most particle detectors – and the RPC, that is the topic of this <strong>thesis</strong> – and is therefore described in more detail.
1.2. INTERACTIONS OF PARTICLES WITH MATTER 9 1.2.1 Energy Loss due to Ionization and Excitation We consider a relativistic charged particle scattering on atomic electrons, e.g. µ + + atom → µ + + atom + + e − . If the distance of closest approach is large compared to the size of the atom (a distant collision), the atom will react ’as a whole’ to the variable electromagnetic field of the charged particle. The result can be excitation or ionization of the atom. If the distance of closest approach is of the order of the atomic dimensions, (a close collision) the interaction involves the passing particle and one of the atomic electrons. As a consequence, the electron is ejected from the atom with considerable energy (knock-on electrons). We define [15] distant collisions: Any collision resulting in the ejection of an electron of energy smaller than a predetermined value ν. close collisions: Any collision resulting in the ejection of an electron of energy larger than ν. If ν is sufficiently large (and the corresponding impact parameter sufficiently small) we can treat all close collisions by considering the atomic electrons as free particles. A limiting energy ν of 10 to 100 keV simultaneously satisfies the two conditions specified above for practically all cases of importance in the field of high energy phenomena. The Differential Collision Cross Section We note the atomic differential cross section that a particle with energy E loses an energy between E ′ and E ′ +dE ′ in a collision with an atom Then dσ dE ′ ⏐ ρ NA A ⏐ col dσ dE ′ ⏐ . (1.1) ⏐ col (1.2) is the average number of collisions with an energy loss between E ′ and E ′ + dE ′ per unit length in a material with density ρ [g/cm 3 ] and atomic number A [g/mol]. NA [1/mol] is Avogadro’s number. This leads to the average energy loss per length dx
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2.5. STREAMERS 59 Figure 2.20: A me
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2.6. SUMMARY 61 per cluster follows
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Chapter 3 Monte Carlo Avalanche Sim
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3.1. THE 1-D MODEL 65 Avalanche Siz
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3.2. THE 1.5-D MODEL 67 3. The prim
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3.2. THE 1.5-D MODEL 69 Here l(z
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3.2. THE 1.5-D MODEL 71 charge [pC]
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3.2. THE 1.5-D MODEL 73 a) b) induc
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3.2. THE 1.5-D MODEL 75 number of c
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3.3. THE 2-D MODEL 77 where δt is
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3.3. THE 2-D MODEL 79 Er(r, z, r
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3.3. THE 2-D MODEL 81 y r E Er θ x
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3.4. THE 3-D MODEL 83 The charge in
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3.4. THE 3-D MODEL 85 Electrons a)
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Chapter 4 Geometries and Typical Op
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RPC gas q [mm] g [mm] εr EW [/mm]
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The values shown in Table 4.3 are r
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Chapter 5 Results Obtained with the
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5.1. EFFICIENCY AND TIME RESOLUTION
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5.2. CHARGE-TO-TIME CORRELATION 97
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6.1. SIGNAL RISE TIME 101 induced c
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6.2. CHARGE SPECTRA 103 counts 10 3
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6.2. CHARGE SPECTRA 105 charges/ste
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6.2. CHARGE SPECTRA 107 The differe
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6.2. CHARGE SPECTRA 109 counts/35fC
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6.2. CHARGE SPECTRA 111 charges/ste
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6.3. OPERATIONAL MODE OF RPCS 113 t
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6.4. CHARGE-TO-TIME CORRELATION 115
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6.5. AVALANCHES IN PURE ISOBUTANE 1
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6.6. STREAMERS 121 a) b) electrons
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7.1. COMPARISON OF THE DIFFERENT MO
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7.2. AVALANCHES IN C2F4H2/ I-C4H10/
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7.4. SUMMARY 151 (e) The total elec
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7.4. SUMMARY 153 contracted at thei
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Chapter 8 Conclusions and Outlook C
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Appendix A Differential Collision C
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A.4. SCATTERING OF MASSIVE SPIN 1 P
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Appendix B Überblick Widerstandspl
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B.1. MOTIVATION FÜR DIE ARBEIT 163
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B.2. DETEKTORPHYSIK VON RPCS 165 i(
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B.4. SCHLUSSFOLGERUNG UND AUSBLICK
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Bibliography [1] W. Riegler, R. Vee
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BIBLIOGRAPHY 171 [29] V. Parchomchu
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BIBLIOGRAPHY 173 [59] E. Keil. The
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BIBLIOGRAPHY 175 [88] P. Fonte. App
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Danksagung Während der Dissertatio
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Curriculum Vitae Persönliche Infor
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