Elliptic flow at different collision stages Andrea Dubla

202 Pages·2016·12.94 MB·English

Elliptic flow at different collision stages
Andrea Dubla
A catalogue record is available from Utrecht University Library
ISBN: 978-90-393-6524-3
Copyright c 2016 by A. Dubla All rights reserved. No part of this book
(cid:13)
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Elliptic flow at different collision stages
Elliptische stroming tijdens verschillende botsingsstadia
(met een samenvatting in het Nederlands)
Proefschrift
ter verkrijging van de graad van doctor aan de Universiteit Utrecht op
gezag van de rector magnificus, prof. dr. G.J. van der Zwaan, ingevolge
het besluit van het college voor promoties in het openbaar te verdedigen
op woensdag 6 april 2016 des middags te 2:30 uur
Andrea Dubla
geboren op 18 april 1985 te Turijn, Italië
Promotor: Prof.dr. R.J.M. Snellings
Copromotor: Dr. A. Grelli
And sometimes you close your eyes
and see the place where you used to live
when you were young...
To Simone, a person I truly madly deeply loved....

Contents
Introduction 1
1 Heavy Ion physics 3
1.1 Quantum ChromoDynamics . . . . . . . . . . . . . . . . . . 3
1.2 The QCD phase diagram . . . . . . . . . . . . . . . . . . . . 4
1.3 Evolution of the collision . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Different collision stages . . . . . . . . . . . . . . . . 6
1.4 Anisotropic flow as experimental observable . . . . . . . . . 8
1.4.1 Radial Flow . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.2 Elliptic Flow . . . . . . . . . . . . . . . . . . . . . . 11
1.5 Soft Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6 Hard Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.7 Electromagnetic Probes . . . . . . . . . . . . . . . . . . . . 24
2 The ALICE experiment 33
2.1 Detector design . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2 Inner Tracking System . . . . . . . . . . . . . . . . . . . . . 36
2.3 Time Projection Chamber . . . . . . . . . . . . . . . . . . . 40
2.4 Time of Flight . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.5 Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . 44
I
CONTENTS
2.6 VZERO detector . . . . . . . . . . . . . . . . . . . . . . . . 45
3 Flow analysis methodologies 47
3.1 Event plane method . . . . . . . . . . . . . . . . . . . . . . 48
3.1.1 Event plane with three sub-events resolution. . . . . 50
3.2 Scalar product method . . . . . . . . . . . . . . . . . . . . . 51
3.2.1 Scalar product with three sub-events . . . . . . . . . 53
3.3 Q-Cumulant and multi-particle correlation . . . . . . . . . . 53
4 Event selection 55
4.1 On-line and Off-line event selection . . . . . . . . . . . . . . 56
4.1.1 Additional event selection . . . . . . . . . . . . . . . 57
4.2 Centrality determination . . . . . . . . . . . . . . . . . . . . 59
4.2.1 Centrality flattening for the 2011 data . . . . . . . . 60
4.3 Event plane determination . . . . . . . . . . . . . . . . . . . 63
4.3.1 Further correction in most central collision . . . . . . 66
4.4 EMCal Trigger studies . . . . . . . . . . . . . . . . . . . . . 67
5 Elliptic flow of φ-mesons 73
5.1 Two particle resonance flow . . . . . . . . . . . . . . . . . . 74
5.2 φ-meson reconstruction . . . . . . . . . . . . . . . . . . . . . 76
5.2.1 Track selection . . . . . . . . . . . . . . . . . . . . . 76
5.2.2 Bayesian particle identification . . . . . . . . . . . . 78
5.2.3 Combinatorial background estimation . . . . . . . . 81
5.2.4 Signal extraction . . . . . . . . . . . . . . . . . . . . 84
5.3 Invariant mass fit method and vφ(p ) . . . . . . . . . . . . 90
2 T
5.4 Systematic studies on φ-meson v . . . . . . . . . . . . . . . 92
2
5.5 Results and discussion . . . . . . . . . . . . . . . . . . . . . 94
5.5.1 Comparison with other particle species . . . . . . . . 95
5.5.2 The meson-baryon scaling at LHC . . . . . . . . . . 97
5.5.3 Comparison with hydrodynamical model . . . . . . . 100
II
CONTENTS
6 Elliptic flow of heavy-flavour decay electrons 105
6.1 Inclusive electron identification . . . . . . . . . . . . . . . . 106
6.1.1 ITS–TOF–TPC . . . . . . . . . . . . . . . . . . . . . 107
6.1.2 TPC–EMCal . . . . . . . . . . . . . . . . . . . . . . 110
6.1.3 Inclusive electron purity . . . . . . . . . . . . . . . . 112
6.1.4 Inclusive electron v . . . . . . . . . . . . . . . . . . 119
2
6.1.5 Systematic uncertainties . . . . . . . . . . . . . . . . 120
6.2 Photonic electron background . . . . . . . . . . . . . . . . . 124
6.2.1 Invariant mass method . . . . . . . . . . . . . . . . . 124
6.2.2 Photonic electron reconstruction efficiency . . . . . . 127
6.2.3 (1 + R ) and systematic uncertainties . . . . . . . 131
SB
6.2.4 Background v . . . . . . . . . . . . . . . . . . . . . 134
2
6.2.5 Cocktail simulation method . . . . . . . . . . . . . . 136
6.2.6 Late photon conversions . . . . . . . . . . . . . . . . 139
6.3 Heavy-flavour decay electrons measurements . . . . . . . . . 143
6.3.1 Model comparison . . . . . . . . . . . . . . . . . . . 147
7 Elliptic flow of direct photons 149
7.1 Inclusive photon reconstruction . . . . . . . . . . . . . . . . 150
7.1.1 Electron identification . . . . . . . . . . . . . . . . . 150
7.1.2 Topological cut selection . . . . . . . . . . . . . . . . 151
7.1.3 Purity and efficiency . . . . . . . . . . . . . . . . . . 155
7.1.4 Inclusive photon v . . . . . . . . . . . . . . . . . . . 156
2
7.1.5 Systematic uncertainties . . . . . . . . . . . . . . . . 158
7.2 Photon conversion background . . . . . . . . . . . . . . . . 159
7.2.1 Photon background v . . . . . . . . . . . . . . . . . 159
2
7.2.2 Double ratio. . . . . . . . . . . . . . . . . . . . . . . 161
7.3 Direct photon measurements. . . . . . . . . . . . . . . . . . 162
7.3.1 Model comparison . . . . . . . . . . . . . . . . . . . 163
7.4 Ongoing and future activities . . . . . . . . . . . . . . . . . 165
Conclusion 169
Bibliography 174
III