Expected measurement of the Z production rate with the CMS detector and simulation of the tracker laser alignment system [Elektronische Ressource] / vorgelegt von Maarten Thomas

Maarten Thomas

Sujets

• Physik

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2009
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 44 Mo

Extrait

Expected measurement of theZ production rate
with the CMS detector and simulation of the
Tracker Laser Alignment System
Von der Fakult¨at fur¨ Mathematik, Informatik und Naturwissenschaften der RWTH
Aachen University zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften genehmigte Dissertation
vorgelegt von
von
Diplom-Physiker Maarten Thomas
aus Heerlen, die Niederlande
Berichter: Apl. Professor Dr. F.A. Raupach
Universit¨atsprofessor Dr. St. Schael
Tag der mundlic¨ hen Prufung:¨ 16. Juni 2009
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek verfugbar.¨iiContents
Introduction 1
1 The Standard Model: Basic concepts and their application 3
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.2 Spontaneous symmetry breaking, particle masses and the Higgs mech-
anism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.3 Higgs production at proton-proton colliders ............... 7
1.2 Parton distribution functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Massive lepton pair production in hadron collisions 11
2 The Large Hadron Collider and CMS experiment 15
2.1 The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 The CMS experiment ............................... 18
2.2.1 The magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.2 The inner tracking system . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.2.1 The pixel tracker......................... 20
2.2.2.2 The strip tracker 21
2.2.2.3 Performance of the tracker ................... 24
2.2.2.4 The Laser Alignment System . . . . . . . . . . . . . . . . . . 28
2.2.3 The electromagnetic calorimeter ..................... 30
2.2.4 The hadron calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2.5 The muon system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2.6 The CMS trigger system and data acquisition system . . . . . . . . . 37
2.2.7 The luminosity measurement . . . . . . . . . . . . . . . . . . . . . . . 38
2.2.8 The CMS software and computing .................... 38
3 Simulation and Reconstruction Software for the Laser Alignment System 41
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2 Simulation of the Laser Alignment System 41
3.3 Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3.1 Alignment Algorithms ........................... 48
3.3.2 Laser Tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4 Data Quality Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5 Analysis of the TEC+ sector test data . . . . . . . . . . . . . . . . . . . . . . 58
4 Hadron collider physics: measuring the luminosity using the Z production rate 71
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.2 Monte Carlo at NLO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.3 Reconstruction of the signal candidates ..................... 78
4.4 Background events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.5 E!ciencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.5.1 The “tag & probe” method . . . . . . . . . . . . . . . . . . . . . . . . 94
iiiContents
4.5.2 Muon reconstruction e!ciency . . . . . . . . . . . . . . . . . . . . . . 94
4.5.3 Isolation e!ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.4 Trigger e!ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.5 Detector acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.5.6 E!ciency of the used selection criteria . . . . . . . . . . . . . . . . . . 100
4.5.7 Total e!ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4.6 Systematic uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4.6.1 Parton distribution functions . . . . . . . . . . . . . . . . . . . . . . . 102
4.6.2 Underlying event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.6.3 Muon and tracker misalignment...................... 103
4.6.4 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.6.5 Final remarks on systematic uncertainties ................ 106
4.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Conclusions 109
A Software for the Laser Alignment System 111
A.1 Simulation options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A.2 Reconstruction options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
A.3 Data Quality Monitoring options . . . . . . . . . . . . . . . . . . . . . . . . . 115
B Data from the TEC+ sector test 117
B.1 Sector 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
B.2 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
B.3 Sector 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
B.4 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
B.5 Sector 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
B.6 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
B.7 Sector 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
B.8 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
C Muon reconstruction in CMS 159
D Analytical functions used to fit the invariant mass distributions 161
D.1 Relativistic Breit-Wigner function . . . . . . . . . . . . . . . . . . . . . . . . 161
D.2 and Gaussian ..................... 161
E Bootstrap methods 163
E.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
E.2 The algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
E.3 Confidence Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
E.4 Example: systematic uncertainty due to misalignment . . . . . . . . . . . . . 165
F Formula for error propagation 167
F.1 Width of the Z boson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
F.2 Error of the background to signal ratios f . . . . . . . . . . . . . . . . . . . . 168i
F.3 Error of the muon reconstruction e!ciency ................... 169
F.3.1 Standalone muon e!ciency . . . . . . . . . . . . . . . . . . . . . . . . 169
F.3.2 Tracker e!ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
F.3.3 Matching e!ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
F.4 Error of the isolation e!ciency .......................... 170
ivContents
F.5 Error of the acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
List of Figures 173
List of Tables 177
Bibliography 179
Lebenslauf 189
vContents
viIntroduction
In the past four decades many discoveries of new phenomena in particle physics have led to
the formation of a theory, which provides a microscopic description of all known forces except
gravity. This theory is known as the Standard Model. Despite the success of the Standard
Model, the theory is not yet complete. For example, the lack of an explanation for the origin
of the particle masses illustrates the shortfalls of the Standard Model.
From Summer 2009 on the Large Hadron Collider (LHC) at the European Center for
Nuclear Research (CERN) will provide proton-proton collisions at a center of mass energy of
14TeV. The high energy, never before reached in a particle collider, allows for the search of
the missing parts in our current knowledge of particle physics and for the discovery of new
phenomena.
In order to measure the properties of the particles created in the proton-proton collisions,
four large experiments have been constructed. One of these is named the Compact Muon
Solenoid (CMS) experiment. The CMS detector is build out of several subsystems, each
serving di"erent purposes. The so called tracking devices measure the momentum of charged
particles. The superconducting magnet of the CMS detector provides a strong magnetic field
allowing for a good momentum resolution within a compact detector volume.
The alignment of the tracking devices is an important issue in achieving an accurate track
reconstruction. TheCMStrackeristhereforeequippedwithaLaser Alignment System (LAS)
allowing for the alignment of the larger substructures of the CMS tracker and for the moni-
toring of the sensor position during data taking.
Apart from an aligned detector and accurate reconstruction of the particles created in
the proton-proton collisions, a precise measurement of the luminosity delivered by the Large
Hadron Collider to the experiments is needed in order to measure the cross sections of newly
discovered phenomena. In the present study the production of muon pairs via the Drell-Yan
mechanism, whichistheoreticallywellunderstood, isusedtomeasuretheluminosity. Besides
the important determination of the luminosity by means ofZ bo