Optimized Dark Matter Searches in Deep Observations of Segue 1 with MAGIC Ph.D. Dissertation Universitat Autonoma` de Barcelona Jelena Aleksic´ [email protected] May 2013 Suprvised by Dr. Manel Martinez Rodriguez Dr. F.Javier Rico Castro Dr. Enrique Fernandez´ Sanchez´ Contents Introduction 3 Introducti´on 5 1 Dark Matter Paradigm 7 1.1 Observational Evidence . 8 1.1.1 Dynamics of Galaxies and Galaxy Clusters . 8 1.1.2 Gravitational Lensing . 9 1.2 Λ Cold Dark Matter Model . 10 1.2.1 The Λ Cold Dark Matter Formalism . 11 1.2.2 Cosmic Microwave Background . 12 1.2.3 Large Structure Formation . 14 1.2.4 Challenges to the ΛCDM.......................... 15 1.2.5 Alternative Cosmologies . 16 1.3 Dark Matter Candidates . 17 1.3.1 Weakly Interacting Massive Particles . 17 1.3.1.1 Supersymmetric Dark Matter . 19 1.3.1.2 Universal Extra Dimensions . 21 1.3.1.3 Other WIMP Candidates . 21 1.3.2 Non-WIMP Dark Matter . 22 1.3.2.1 Sterile Neutrinos . 22 1.3.2.2 SuperWIMPs . 22 1.3.2.3 Axions . 23 1.3.2.4 Hidden Dark Matter . 23 2 Dark Matter Searches 25 2.1 Production at Particle Colliders . 26 2.2 Direct Detection . 27 2.3 Indirect Detection . 29 2.3.1 Messengers for Indirect Dark Matter Searches . 29 2.3.2 Photon Flux from Dark Matter . 31 2.3.2.1 Dark Matter Density Profile . 32 2.3.2.2 Annihilation Cross Section and Decay Time . 34 2.3.2.3 The Photon Spectrum . 35 2.3.3 Review of the Observational Targets . 38 2 Contents 2.3.4 Indirect Search with Gamma-ray Experiments . 41 2.3.4.1 Gamma-ray Satellites . 42 2.3.4.2 Imaging Air Cherenkov Telescopes . 43 3 The MAGIC Telescopes 49 3.1 Technical Description . 50 3.1.1 Mount, Drive and Mirrors . 50 3.1.2 Camera and Calibration System . 52 3.1.3 Readout System . 53 3.1.3.1 Pre-Upgrade . 53 3.1.3.2 Post-Upgrade . 54 3.1.4 Trigger . 55 3.2 Data Taking Procedure . 56 3.2.1 Source Pointing Models . 56 3.2.2 Types of Data . 57 3.3 Data Analysis . 57 3.3.1 Data Calibration . 58 3.3.2 Image cleaning and parametrization . 61 3.3.3 Data Selection . 62 3.3.4 Data Merger and Stereo Parameter Reconstruction . 63 3.3.5 Event Characterization . 64 3.3.5.1 γ/hadron Separation . 64 3.3.5.2 Arrival Direction Estimation . 65 3.3.5.3 Energy Estimation . 66 3.3.6 Signal Estimation . 66 3.3.7 Higher Level Products . 68 3.3.7.1 Response Function . 68 3.3.7.2 Skymap . 70 3.3.7.3 Spectra . 71 3.3.7.4 Light Curve . 71 3.3.7.5 Upper Limits . 71 3.3.8 Systematic Uncertainties . 72 3.3.9 Accessibility of the Analysis Results . 73 3.3.9.1 FITS File Format . 73 3.3.9.2 FITS Format for MAGIC Data . 73 3.3.9.3 MAGIC Data at the Virtual Observatory . 74 4 Full Likelihood Method 77 4.1 The Method . 78 4.1.1 Conventional Analysis Approach . 78 4.1.2 Full Likelihood Method . 78 4.1.2.1 Full vs. Conventional Likelihood Approach . 79 4.2 Characterization . 80 4.2.1 The setup . 81 4.2.1.1 Response Functions . 81 4.2.1.2 Spectral Functions . 81 4.2.1.3 Improvement Factor . 82 3 4.2.1.4 Experimental conditions . 83 4.2.2 Bias . 83 4.2.3 Optimization of the Integration Range . 83 4.2.3.1 Line . 84 4.2.3.2 Power Law . 84 4.2.4 Improvement Factor for different signal models . 86 4.2.4.1 Line . 86 4.2.4.2 Power Law . 86 4.2.4.3 Additional Features . 86 4.2.5 Stability . 90 4.2.6 Robustness . 91 4.2.7 Background . 92 4.3 Overview of the Full Likelihood Method . 93 5 Dark Matter Searches in Dwarf Spheroidal Galaxy Segue 1 with MAGIC 95 5.1 Segue 1 as Target for Dark Matter Searches . 96 5.1.1 Introduction to Dwarf Spheroidal Galaxies . 96 5.1.2 Dwarf Spheroidal Galaxies as the Dark Matter Candidates . 98 5.1.3 Segue 1 . 99 5.2 Observations and Data Reduction . 101 5.2.1 Sample A: 2011 Data . 101 5.2.2 Sample B: 2012 Data . 104 5.2.2.1 Sample B1: Pre-March Data . 105 5.2.2.2 Sample B2: Post-March Data . 106 5.2.3 Sample C: 2012-2013 Data . 107 5.3 Analysis . 108 5.3.1 Cuts Optimization . 109 5.3.2 Results of the Standard Analysis . 110 5.3.3 Response Function . 112 5.3.4 Background Modeling . 112 5.3.5 Signal . 116 5.3.6 Analysis Technicalities . 118 5.4 Results . 119 5.4.1 Secondary photons from annihilation into SM particles . 119 5.4.2 Gamma-ray Line . 127 Conclusions 129 References 130 Introduction There is an impressive amount of evidence, on all scales, favouring the existence of dark matter – an invisible, non-baryonic component of the Universe that accounts for almost 85% of its total mass density. Although its existence was for the first time postulated more than 80 years ago, the nature of dark matter still remains a mystery. Finding and understanding the answer to this question is one of the most important and exciting tasks of modern science. In the context of our current cosmological view of the Universe, dark matter is considered to be a new type of massive particle, that interacts weakly with ordinary matter and radi- ation. In addition, this new particle is most likely cold, non-baryonic, produced thermally in the early Universe and stable on cosmological scales. Our search for dark matter particle is carried out in parallel by three different approaches: detection of dark matter produced in colliders, direct detection of dark matter scattering off ordinary matter in underground experiments, and indirect search with space and ground-based observatories for Standard Model particles created in dark matter annihilation or decay. This last strategy is the subject of this Thesis. Results presented here are from indirect searches for dark matter in dwarf spheroidal galaxy Segue 1, carried out with the Imaging Air Cherenkov Telescopes called MAGIC. The objective is to recognize highly energetic photons, produced in annihilation or decay of dark matter particles, by some characteristic spectral features unique for gamma rays of dark matter origin. An dedicated analysis approach, called the full likelihood method, has been developed to optimize the sensitivity of the analysis for such dark matter signatures. The outline of the Thesis could be summarized as follows: O Chapter 1 introduces the dark matter paradigm: what are the astrophysical and cos- mological evidence supporting the existence of dark matter, and how can they be rec- onciled with our current image of the evolution of the Universe. The Chapter ends with review of some of the best motivated candidates for dark matter particle, with detailed discussion about those that are of particular interest for this work. O Chapter 2 is devoted to dark matter searches. It begins with presentation of different strategies currently employed by various.