Detection and reconstruction of short-lived particles produced by
neutrino interactions in emulsion
Uiterwijk, J.W.H.M.
Citation
Uiterwijk, J. W. H. M. (2007, June 12). Detection and reconstruction of short-lived particles
produced by neutrino interactions in emulsion. Retrieved from
https://hdl.handle.net/1887/12079
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License: Leiden University Non-exclusive license
Downloaded from: https://hdl.handle.net/1887/12079
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Detection and reconstruction of short-lived
particles produced by neutrino interactions
in emulsion
Proefschrift
ter verkrijging van
de graad van Doctor aan de Universiteit Leiden,
op gezag van de Rector Magnificus Prof. Mr. P.F. van der Heijden, volgens besluit van het College voor Promoties
te verdedigen op dinsdag 12 juni 2007 klokke 15:00 uur
door
Johannes Wilhelmus Edmond Uiterwijk
geboren te Maastricht in 1969
promotor: Prof. Dr. M. de Jong co-promotor: Dr. J. Panman
referent: Prof. Dr. E. Koffeman
promotiecommissie: Prof. Dr. A. Ach´ucarro Prof. Dr. P.J. van Baal Prof. Dr. J.M. van Ruitenbeek Dr. J.L. Visschers
The work described in this dissertation is part of the research program of ’het Nation- aal Instituut voor Kernfysica en Hoge-Energie Fysica (NIKHEF)’ in Amsterdam, the Netherlands. The Author was financially supported by ’de Stichting voor Fundamenteel Onderzoek der Materie (FOM)’ and the European Center for Nuclear Research (CERN) in Geneva, Switzerland. FOM is funded by ’de Nederlandse Organisatie voor Fundame- teel Onderzoek der Materie (NWO)’
ISBN: 978-90-8666-034-6
iii
Contents
Introduction vii
1 Neutrino masses and oscillations 1
1.1 Neutrino history . . . 2
1.1.1 The electron neutrino . . . 2
1.1.2 The muon neutrino . . . 2
1.1.3 The tau neutrino . . . 3
1.2 The standard model . . . 4
1.2.1 Particles and forces . . . 4
1.2.2 Parameters and constants . . . 6
1.2.3 Neutrinos . . . 6
1.2.4 Neutrino–matter interactions and cross-sections . . . 7
1.2.5 Beyond the standard model . . . 10
1.3 Neutrino masses and oscillation . . . 10
1.3.1 Direct mass measurements . . . 10
1.3.2 Neutrino oscillation . . . 11
1.3.3 Oscillation detection methods . . . 14
1.4 Neutrino oscillation hints . . . 15
1.4.1 Cosmology . . . 15
1.4.2 Solar neutrinos . . . 16
1.4.3 Atmospheric neutrinos . . . 20
1.4.4 The 1998 Super-Kamiokande result . . . 22
1.5 TheCHORUSoscillation search . . . 23
1.5.1 Motivation . . . 23
1.5.2 Excluded parameter space . . . 24
1.6 Current neutrino experiments . . . 25
1.6.1 Super-Kamiokande . . . 26
1.6.2 SNO . . . 29
1.6.3 KamLAND . . . 30
1.7 Status of oscillation research . . . 31
1.7.1 Atmospheric neutrinos . . . 31
1.7.2 Solar and reactor neutrinos . . . 35
1.7.3 Accelerator experiments . . . 40
1.7.4 Cosmic neutrinos . . . 42
1.7.5 Three-flavour oscillation . . . 43
1.8 Discussion and outlook . . . 43
iv contents
2 The CHORUS experiment 47
2.1 Detection principle . . . 48
2.1.1 Tau identification in emulsion . . . 48
2.1.2 Background processes . . . 50
2.2 Neutrino beam . . . 51
2.3 Experimental setup overview . . . 54
2.4 Emulsion target and electronic tracking detectors . . . 55
2.4.1 Emulsion target considerations . . . 55
2.4.2 Interfacing emulsion and electronic tracking detectors . . . 58
2.4.3 Tracking detector . . . 59
2.4.4 Target region experimental setup . . . 60
2.5 Trigger . . . 62
2.6 Downstream detectors . . . 64
2.6.1 Hadron spectrometer . . . 64
2.6.2 Streamer-tubes and honeycomb detector . . . 65
2.6.3 Calorimeter . . . 66
2.6.4 Muon spectrometer . . . 66
2.7 Online monitoring . . . 68
2.8 Track reconstruction and scanning predictions . . . 70
2.9 Emulsion and scanning techniques . . . 71
2.9.1 Hybrid experiments and automatic scanning . . . 71
2.9.2 Emulsion characteristics . . . 72
2.9.3 Scanning microscopes . . . 76
2.9.4 Automatic track recognition . . . 76
2.10 Reconstructing tracks and vertices in emulsion . . . 77
2.10.1 Alignment . . . 77
2.10.2 Interaction location by scan-back . . . 79
2.10.3 Vertex reconstruction with net-scan . . . 82
3 Honeycomb tracker 85 3.1 Motivation and requirements . . . 86
3.2 Detection principle . . . 87
3.3 Design and mechanical construction . . . 88
3.3.1 Monolayer . . . 89
3.3.2 Honeycomb module . . . 91
3.3.3 Honeycomb tracker . . . 92
3.3.4 Prototype measurements . . . 93
3.4 Data-acquisition and read-out electronics . . . 95
3.4.1 The bit-stream principle . . . 95
3.4.2 Chambercards . . . 96
3.4.3 Clockcard . . . 100
3.5 Read-out system . . . 101
3.5.1 Read-out protocol . . . 103
3.5.2 Read-out program . . . 104
3.5.3 Data compression . . . 106
contents v
3.6 Tracking . . . 106
3.6.1 Drift-time calibration . . . 107
3.6.2 Track finding per module . . . 108
3.6.3 Reconstructing 3-Dtracks . . . 109
3.7 Performance and discussion . . . 111
3.7.1 Resolution . . . 111
3.7.2 Read-out electronics . . . 111
3.7.3 Conclusion . . . 112
4 Track finding in emulsion 113 4.1 Introduction . . . 114
4.1.1 Microscope optics and stages . . . 115
4.1.2 Tracking input characteristics . . . 118
4.1.3 Algorithm restrictions and requirements . . . 118
4.1.4 Toolkit abstraction . . . 119
4.2 Multi-dimensional ordering containers . . . 119
4.2.1 Find-in-range algorithm . . . 119
4.2.2 Search trees . . . 120
4.2.3 Hash table . . . 123
4.2.4 Implementation . . . 124
4.2.5 Timing performance . . . 127
4.3 Track-finding algorithm . . . 129
4.3.1 Concept . . . 130
4.3.2 Implementation . . . 133
4.3.3 Tracking time . . . 137
4.4 Tracking efficiency for simulated data . . . 140
4.4.1 Hit generators . . . 141
4.4.2 Acceptance criteria . . . 143
4.4.3 Efficiency criteria . . . 145
4.4.4 Results and discussion . . . 145
4.5 The track trigger . . . 149
4.5.1 Concept . . . 149
4.5.2 Implementation . . . 149
4.6 Application inCHORUSemulsion scanning . . . 150
4.6.1 Tracking configuration . . . 151
4.6.2 Prediction matching on the interface sheets . . . 152
4.6.3 Local-alignment procedure . . . 153
4.6.4 Tracking results . . . 154
4.7 Conclusion and discussion . . . 156
5 D∗+ production 157 5.1 Introduction . . . 158
5.2 Charm-quark production and fragmentation . . . 158
5.3 Vertex reconstruction and charm sample selection . . . 161
5.4 Event selection ofD∗+ → D0π+ . . . 163
vi contents
5.4.1 D0 secondary vertex selection . . . 163
5.4.2 Primaryπ+ selection . . . 163
5.4.3 Monte-Carlo simulation . . . 164
5.4.4 Signal extraction . . . 165
5.5 Efficiency and background evaluation . . . 167
5.5.1 Background evaluation . . . 167
5.5.2 Detection efficiency . . . 168
5.6 Results and conclusion . . . 168
Bibliography 171
Summary 184
Samenvatting 186
Acknowledgments 188
Curriculum Vitae 190
vii
Introduction
Several experiments have detected discrepancies in the fluxes of solar and atmospheric neutrinos. Neutrino oscillations provide a possible explanation for the measured differ- ences. This dissertation presents one of the first generation, specific, neutrino-oscillation experiments using a man-made neutrino source, thechorus experiment at the European laboratory for particle physics (cern)1.
Chorus was designed to look for νμ → ντ oscillation. Such oscillations can only happen if the neutrino eigenstates of the weak interaction do not coincide with the mass eigenstates. In the standard model of elementary particles and interactions, the neutrinos are assumed to be massless. However, there is no fundamental reason why neutrinos would be the only elementary fermion with no mass.
In 1998, the Super-Kamiokande experiment published clear evidence for neutrino os- cillation [86]. That result unfortunately implied that chorus would not observe any oscillation signal. Since then, the emphasis of the chorus data analysis has shifted to exploiting the unique potential of the large number (about 100,000) recordedνμ interac- tions in the emulsion to analyse in detail the production and decay of charmed particles.
In Chapter 1, the key aspects of neutrino masses and oscillations are discussed. A description of the role of thechorus experiment is given, followed by an overview of the current status of neutrino-oscillation experiments. Chapters 2 and 3 describe the layout of thechorus experiment and the design of one particular sub-detector, the honeycomb tracker. The algorithms for reconstructing particle tracks contained in the emulsion images and their implementation are the subjects of Chapter 4. The last chapter, Chap- ter 5, reproduces a published charmed-meson production study. An introduction to the phenomenology of charm-quark production and fragmentation is given. This chapter highlights the possibilities of emulsion and current-day scanning techniques to recon- struct neutrino-interaction vertices and subsequent decay of short-lived particles.
As a final note, in this dissertation all particle masses, branching ratios, and other particle characteristics have been taken from the Particle Data Group review of 2004 [1].
1The abbreviation stands for ‘Conseil Europ´een pour la Recherche Nucl´eaire’, the original committee that proposed to built thecern laboratory
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