Search for neutrinos from the direction of the Galactic Center with the IceCube neutrino telescope [Elektronische Ressource] / Jan-Patrick Hülß

Sujets

• Astronomie

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2011
• Nombre de lectures: 4
• Langue: English
• Poids de l'ouvrage: 14 Mo

Extrait

Search for Neutrinos from the Direction of the
Galactic Center with the IceCube Neutrino
Telescope
Von der Fakult¨at fu¨r Mathematik, Informatik und Naturwissenschaften der RWTH
Aachen University zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften genehmigte Dissertation
vorgelegt von
Diplom-Physiker Jan-Patrick Hu¨lß
aus Wuppertal
Berichter: Universit¨atsprofessor Dr. rer. nat. Christopher Wiebusch
Universitat¨ sprofessor Dr. rer. nat. Marek Kowalski
Tag der mu¨ndlichen Pru¨fung: 30. November 2010
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfu¨gbar.i
Abstract
The IceCube telescope located at the geographic South Pole is designed to detect neu-
trinos. Usually, IceCube uses the Earth as shield against the background of atmospheric
muon events. This restricts the eld of view to the Northern hemisphere. At high ener-
gies (PeV scale) the background fades away and the observation of the Southern sky is
possible, too. At lower energies, neutrino induced events from the Southern sky can be
identi ed if the interaction vertex is within the detector volume. For the reconstruction
and identi cation of the interaction vertex new algorithms are developed in this thesis.
The reconstruction algorithms are based on the spatial distribution of the hits in the de-
tector. These algorithms are utilized for a search for a neutrino signal from the direction of
the Galactic Center with IceCube in the 40 string con guration. In this region neutrinos
could be produced in interactions of accelerated Cosmic Ray protons or by the annihila-
tion or decay of Dark Matter particles from the Galactic halo. The analysis observes no
signi cant neutrino signal from the direction of the Center and limits are set to
constrain the neutrino ux and the properties of Dark Matter. Finally, an outlook to the
full IceCube Detector including DeepCore is presented. It is expected that the sensitivity
will increase signi cantly.iiCONTENTS iii
Contents
1 Introduction 1
2 Neutrino Astronomy 3
2.1 Cosmic Rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Multi Messenger Astronomy . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Sources for Cosmic Rays, Photons and Neutrinos . . . . . . . . . . . . . . . 6
2.3.1 Acceleration in Electromagnetic Fields . . . . . . . . . . . . . . . . . 6
2.3.2 Fermi Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.3 Candidate Sources for the Acceleration of Charged Particles . . . . . 9
2.3.4 Galactic Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.5 The Galactic Center Region . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Neutrinos from Dark Matter Halos . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.1 Evidence for Dark Matter . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.2 Particle Physics Indications for Dark Matter . . . . . . . . . . . . . 16
2.4.3 Expected Neutrino Signal . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.4 Cold Dark Matter Halo Models . . . . . . . . . . . . . . . . . . . . . 20
2.4.5 Recent Measurements related to Dark Matter . . . . . . . . . . . . . 22
3 Neutrino Telescopes 27
3.1 Detection Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.1 Cherenkov E ect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.2 Energy Loss and Decay of Leptons . . . . . . . . . . . . . . . . . . . 29
3.1.3 Signatures in a Detector . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2 IceCube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.1 Experimental Signals and Backgrounds . . . . . . . . . . . . . . . . 33
3.2.2 DeepCore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.3 The Ice Characteristics at the South Pole . . . . . . . . . . . . . . . 34
3.2.4 Measuring Neutrinos at the South Pole . . . . . . . . . . . . . . . . 36
3.2.5 Hard Local Coincidence . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.6 Triggering and Event Building . . . . . . . . . . . . . . . . . . . . . 37
3.3 Further Neutrino Telescopes . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4 Signal Hypotheses and Analysis Technique 41
4.1 Cosmic Neutrino Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.1 Neutrinos from Dark Matter in the Galactic Halo . . . . . . . . . . . 42
4.1.2 Galactic Center as a TeV Neutrino Source . . . . . . . . . . . . . . . 43
4.2 Analysis Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5 Reconstruction of Muon Tracks 47
5.1 Initial and Pattern Based Reconstruction . . . . . . . . . . . . . . . . . . . 47
5.1.1 LINEFIT Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . 47
5.1.2 Interaction Vertex and Stop Point . . . . . . . . . . . . . . . . . . . 48
5.2 Likelihood Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.2.1 Single Photo Electron Likelihood Function . . . . . . . . . . . . . . 50
5.2.2 Multi Photo Likelihood F . . . . . . . . . . . . . . . 51iv CONTENTS
5.3 The P -P based Reconstruction . . . . . . . . . . . . . . . . . . . . . . 51hit noHit
5.3.1 The P -P Likelihood Function . . . . . . . . . . . . . . . . . . 52hit noHit
5.3.2 Number of Expected Photons at a DOM . . . . . . . . . . . . . . . . 53
5.3.3 Reconstruction with the P -P likelihood . . . . . . . . . . . . . 54hit noHit
5.4 Energy reconstr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6 Simulation and Filtering 57
6.1 Simulated Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.1.1 Neutrino Event Generation . . . . . . . . . . . . . . . . . . . . . . . 57
6.1.2 Cosmic Ray simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1.3 Muon Simulation and Photon Propagation . . . . . . . . . . . . . . 59
6.1.4 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.2 The On-Line Filter at the South Pole . . . . . . . . . . . . . . . . . . . . . 60
6.3 Reconstruction and Data Filtering . . . . . . . . . . . . . . . . . . . . . . . 64
6.3.1 Muon Track Reconstruction . . . . . . . . . . . . . . . . . . . . . . . 64
6.3.2 Cleaning Selections to Remove Badly Reconstructed Events . . . . . 66
6.3.3 The Lowest Energy Events . . . . . . . . . . . . . . . . . . . . . . . 73
6.3.4 Signal Selections for High Energy Events . . . . . . . . . . . . . . . 77
6.4 Summary of the Selected Data Sample . . . . . . . . . . . . . . . . . . . . . 80
7 Sensitivity 83
7.1 Optimization of the Signal Region . . . . . . . . . . . . . . . . . . . . . . . 83
7.1.1 Optimization for a Signal from a Point-Like Source . . . . . . . . . . 83
7.1.2 for a from Dark Matter Particle Annihilations . 86
7.2 Amount of Background Events in the Signal Region . . . . . . . . . . . . . 86
7.3 Sensitivity for Neutrinos from Point-Like Sources . . . . . . . . . . . . . . . 89
7.4y for Dark Matter Annihilations in the Halo . . . . . . . . . . . . 91
8 Results 93
8.1 Measurement of Neutrinos from the Direction of the Galactic Center . . . . 93
8.2 The Six Events of the High Energy Data Set . . . . . . . . . . . . . . . . . 94
8.3 Limits on Neutrinos from the Dark Matter Halo . . . . . . . . . . . . . . . 103
8.3.1 Limits on Dark Matter Annihilation . . . . . . . . . . . . . . . . . . 103
8.3.2 on Dark Decay . . . . . . . . . . . . . . . . . . . . . . 106
8.3.3 Limits on the Dark Matter Halo by other Experiments . . . . . . . . 107
8.4 Limits on a Flux from a Point-Like Source . . . . . . . . . . . . . . . . . . . 111
8.5 Measurements of the Neutrino Flux by other Experiments . . . . . . . . . . 113
9 Outlook to the Full IceCube Detector with DeepCore 115
9.1 The new Veto Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
9.2 Sensitivity of the full IceCube Detector . . . . . . . . . . . . . . . . . . . . . 117
10 Summary and Conclusions 119
A HLC correction ICONTENTS v
B Angular Reconstruction III
B.1 Comparison of MPE and SPE likelihood . . . . . . . . . . . . . . . . . . . . III
B.2 Performance of the P -P likelihood . . . . . . . . . . . . . . . . . . . . IVnoHithitvi LIST OF FIGURES
List of Figures
1 Cosmic Ray Energy Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Propagation of di erent Particles in the Universe . . . . . . . . . . . . . . . 5
3 Fermi-acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 Hillas Plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Example -Ray and Neutrino Fluxes for Galactic Sources . . . . . . . . . . 13
6 The WMAP Three-Year Power Spectrum . . . . . . . . . . . . . . . . . . . 15
7 Example Rotation Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8 Line of Sight Parametrization . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9 Dark Matter Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10 Recent Measurements of the Self Annihilation Cross Section . . . . . . . . . 24
11tts of the Dark Matter Life Time . . . . . . . . . . . . . 25
12 Explanation of the Cherenkov e ect . . . . . . . . . . . . . . . . . . . . . . 28
13 Neutrino Signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . .