Comparison of Measured and Simulated Light Yield in Plastic ...

UNIVERSITY OF ZURICH

Comparison of Measured and Simulated Light Yield in Plastic Scintillators

by Markus Baumgartner

Bachelor-Thesis Supervisor Prof. Dr. Ulrich Straumann Roman Gredig

in the Faculty of Science Physik-Institut

November 2013

”No. Try not. Do... or do not. There is no try.”

Master Yoda

UNIVERSITY OF ZURICH

Abstract Faculty of Science Physik-Institut Bachelor-Thesis by Markus Baumgartner

We present the results of experimental studies on the physical coherency of the fibre simulation tool-kit for the Mu3e experiment developed with Geant4 [1]. The goal was to investigate different aspects of the simulation i.e. surface properties and wrapping and to check the simulation for overall comparable results with the experimental setup. To achieve this the simulation was modified in different aspects to match the experimental setup i.e. geometry of the scintillation material, scintillating and optical properties of the experiment. Different simulations were carried out and the results compared to experimental measurements from the newly calibrated Mu3e test setup.

Acknowledgements At this point I want to thank several people who made this thesis possible. First of all I want to thank Prof. Ulrich Straumann, Roman Gredig and Dr. Peter Robmann who made it possible to write this paper in the Mu3e-Group. A special thank goes to Roman Gredig who was always willing to support my work with his expertise in programming and experimental knowledge. But I also want to thank the people of the office I was allowed to work in, Nicolas Chiapolini, Christian Elsasser, Arno Gadola, Marco Tresch and Roman Gredig for thier support and the atmosphere, it has been a great time.

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Contents Abstract

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Acknowledgements

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1 Introduction 2 Mu3e Experiment 2.1 Theoretical Background 2.2 The Experiment . . . . 2.3 The Detector . . . . . . 2.4 The scintillating Fibres .

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3 Simulation 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . 3.2 Estimations . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Energy deposition . . . . . . . . . . . . . . 3.2.2 Photon yield . . . . . . . . . . . . . . . . . 3.3 Modifications to the Simulation tool-kit . . . . . . 3.3.1 Geometry . . . . . . . . . . . . . . . . . . . 3.3.2 Materials . . . . . . . . . . . . . . . . . . . 3.3.3 Scintillating photons and surface-properties 3.3.4 90 Sr-Source . . . . . . . . . . . . . . . . . . 3.4 Simulation Data . . . . . . . . . . . . . . . . . . . 3.4.1 General Analysis Overview . . . . . . . . . 3.4.2 90 Sr-Source vs. Mono-energetic Source . . . 3.4.3 Roughness” and Wrapping . . . . . . . . . 3.4.4 Second Scintillator . . . . . . . . . . . . . .

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4 Experiment 4.1 Experimental Setup . . . . . . . . . . . . . . . . . . . 4.2 Data Acquisition . . . . . . . . . . . . . . . . . . . . . 4.3 Experimental Data . . . . . . . . . . . . . . . . . . . . 4.3.1 Analysis Overview . . . . . . . . . . . . . . . . 4.3.2 Reproducibility of the measurement . . . . . . 4.3.3 Optical coupling of the scintillator to the PMT 4.3.4 Wrapping . . . . . . . . . . . . . . . . . . . . .

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Contents 4.3.5

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5 Results 5.1 Reproducibility of the measurement 5.2 Optical coupling . . . . . . . . . . . 5.3 Surface Properties . . . . . . . . . . 5.4 Simulation vs. Reality . . . . . . . . 5.5 Wrapping . . . . . . . . . . . . . . . 5.5.1 Simulation . . . . . . . . . . 5.5.2 Experimental Results . . . .

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6 Conclusion

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Bibliography

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Chapter 1

Introduction The standard model is currently the theoretical basis of particle physics. Several experiments are at the moment under development to search for physics beyond the wellestablished standard model. The proposed Mu3e-experiment is one of these experiments, searching for the lepton flavour violating decay µ+ → e+ e− e+ with a proposed sensitivity of 10−16 . Since the branching ratio is so small a high muon rate is needed to carry out the experiment. The πE5 beam-line at Paul Scherer Institut (PSI) in Villingen Switzerland provides one of the worlds highest muon-rate and a new muon beam-line will be established within the next ∼10 years. The Mu3e experiment is developed by groups of the University of Heidelberg, University of Geneva, PSI, ETH Zuerich and University of Zuerich. Due to very small branching ratio high spatial and timing resolution is needed for the detector. The proposed system contains a fibre tracking detector to establish a time resolution of