Comparison of Iron and Tungsten Absorber Structures for an Analog Hadron Calorimeter

169 Pages·2015·38.74 MB·English

Comparison of Iron and Tungsten
Absorber Structures for an Analog
Hadron Calorimeter
Dissertation
zur Erlangung des Doktorgrades
des Department Physik
der Universit(cid:228)t Hamburg
vorgelegt von
Clemens G(cid:252)nter
aus Hamburg
Hamburg
2014
2
Gutachter der Dissertation: Prof. Dr. Erika Garutti
Dr. Felix Sefkow
Gutachter der Disputation: Prof. Dr. Eckhard Elsen
Prof. Dr. Johannes Haller
Datum der Disputation: 04.02.2015
Vorsitzender des Pr(cid:252)fungsausschusses: Dr. Georg Steinbr(cid:252)ck
Vorsitzende des Promotionsausschusses: Prof. Dr. Daniela Pfannkuche
Dekan der MIN-Fakult(cid:228)t: Prof. Dr. Heinrich Graener
Leiter des Department Physik: Prof. Dr. Peter Hauschildt
3
Abstract
Future electron-positron-collider experiments will require unprecedented jet-energy resolu-
tion to complete their physics programs. This can only be achieved with novel approaches
to calorimetry. One of these novel approaches is the Particle Flow Algorithm, which uses
thebestsuitedsub-detectortomeasuretheenergyoftheparticlesproducedbytheelectron-
positron collision. The CALICE Collaboration evaluates di(cid:27)erent read-out technologies for
Particle Flow Calorimeters. This thesis describes the comparison of two di(cid:27)erent absorber
materials, iron and tungsten, for the CALICE Analog Hadron Calorimeter. It is described
how testbeam data, that has been recorded in the range from 2 GeV to 10 GeV with the
Analog Hadron Calorimeter is calibrated, and how samples are selected containing showers
from just one particle type. The data is then compared to simulations and the remaining
disagreement between data and simulation is discussed. The validated simulations are then
used to decompose the showers into di(cid:27)erent fractions. These fractions are compared for
the two absorber materials to understand the impact of the absorber material choice on
the calorimeter performance.
4
Zusammenfassung
Zuk(cid:252)nftige Elektron-Positron-Collider Experimente erfordern eine nie zuvor erreichte Jet-
Energie Au(cid:29)(cid:246)sung f(cid:252)r ihre Physik Programme. Dies kann nur mit neuen Ans(cid:228)tzen f(cid:252)r
die Kalorimeter erreicht werden. Einer dieser neuen Ans(cid:228)tze ist der Particle Flow Algo-
rithmus, der den jeweils bestgeeigneten Unterdetektor nutzt, um die Energie von den in
der Elektron-Positron Kollision produzierten Teilchen zu messen. Die CALICE Kollab-
oration evaluiert verschiedene Auslesetechnologien f(cid:252)r Particle Flow Kalorimeter. Diese
Arbeit beschreibt, den Vergleich von zwei verschiedenen Absorbermaterialien, Eisen und
Wolfram, f(cid:252)r das CALICE Analoge Hadron Kalorimeter. Es wird beschrieben, wie Test-
beamdaten, die bei Energien von 2 GeV bis 10 GeV mit dem Analogen Hadron Kalorimeter
aufgenommen wurden, kalibriert werden und wie Datens(cid:228)tze, die nur Schauer von einer
Teilchenart enthalten, selektiert werden. Die Daten werden mit Simulationen verglichen
und die verbleibenden Unterschiede zwischen Daten und Simulationen werden diskutiert.
Die validierten Simulationen werden dann genutzt um die Schauer in verschiedene Kompo-
nenten zu zerlegen. Diese Komponenten werden zwischen den beiden Absorbermaterialien
verglichen, um zu verstehen, welchen Ein(cid:29)uss die Wahl des Absorbermaterials auf die
Kalorimeterleistung hat.
CONTENTS 5
Contents
Introduction 9
1 Future Linear Collider Experiments 13
1.1 The International Linear Collider . . . . . . . . . . . . . . . . . . . . . . . 14
1.2 The Compact Linear Collider . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.3 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 Particle Showers and Calorimetry 21
2.1 Electromagnetic Cascades . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Charged heavy Particles traversing Matter . . . . . . . . . . . . . . . . . . 24
2.3 Hadron Showers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Calorimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5 Particle Flow concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3 The CALICE AHCAL Physics Prototype 33
3.1 The Active Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2 Read-out Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.1 Silicon Photomultiplier . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.2 Very-frontend Electronics . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.3 The Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.4 The Calibration and Monitoring Boards . . . . . . . . . . . . . . . 39
3.3 The Absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4 The Testbeam Setups 43
4.1 The FNAL 2008 and 2009 Testbeams . . . . . . . . . . . . . . . . . . . . . 43
4.2 The CERN 2010 Testbeam . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6 CONTENTS
5 Physics Simulation 49
5.1 Hadron Cascade Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.1.1 Cascade Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.1.2 String Parton Models . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1.3 Chiral Invariant Phase-space Model . . . . . . . . . . . . . . . . . . 52
5.1.4 LEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2 GEANT4 Pre-compound and De-excitation Models . . . . . . . . . . . . . 53
5.3 Physics Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4 Precision Neutron Calculations . . . . . . . . . . . . . . . . . . . . . . . . 54
6 Detector Calibration and Characterization 55
6.1 O(cid:31)ine Calibration of the Temperature Sensors . . . . . . . . . . . . . . . . 56
6.2 Pedestal Subtraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.3 Gain Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.4 Inter-Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.5 Saturation Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.6 Cell Equalization with Muons . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.7 Identi(cid:28)cation of Bad Channels . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.8 Noise after Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.9 Inter-tile Crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7 Event Selection 77
7.1 Beam Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.2 Events with LED (cid:29)ashes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
7.3 Empty Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
7.4 Upstream Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.5 Additional Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.6 Particle Identi(cid:28)cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.7 Multi-Particle Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.8 Selection of the Tungsten Data Samples . . . . . . . . . . . . . . . . . . . 85
7.9 Selection of the Iron Data Samples . . . . . . . . . . . . . . . . . . . . . . 86
8 Detector Simulation 91
8.1 Simulation of the Physics Processes . . . . . . . . . . . . . . . . . . . . . . 91
8.2 Simulation of the Detector Response . . . . . . . . . . . . . . . . . . . . . 92
8.3 Beam Pro(cid:28)les . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
8.4 Simulation of the Detector Noise . . . . . . . . . . . . . . . . . . . . . . . 95
8.5 Hadron Shower Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . 97
CONTENTS 7
9 Validation of the Simulation 101
9.1 Detector Validation with Muons . . . . . . . . . . . . . . . . . . . . . . . . 101
9.2 Detector Validation with Electron Showers . . . . . . . . . . . . . . . . . . 104
9.3 Validation of the Pion Shower Simulation . . . . . . . . . . . . . . . . . . . 110
10 Comparison 121
10.1 The First Hadronic Interaction and the Electromagnetic Fraction . . . . . 121
10.2 Comparison of Shower Pro(cid:28)les . . . . . . . . . . . . . . . . . . . . . . . . . 124
10.3 Time evolution of the Shower . . . . . . . . . . . . . . . . . . . . . . . . . 125
10.4 Comparison of the Shower Components for di(cid:27)erent Physics Lists . . . . . 128
10.5 Comparison of the Calorimeters . . . . . . . . . . . . . . . . . . . . . . . . 131
11 Summary and Outlook 139
A Data Sets and Calibration 145
B Event Selection Parameters 147
C Simulation Parameters 153
D Additional Results 155
Bibliography 163
Acknowledgements 169
8 CONTENTS
CONTENTS 9
Introduction
Roughly a century after the beginning of modern physics with the discovery of quantum
theory and relativity, particle physics has formed a theoretical model, which can explain
the overwhelming majority of all measurement results: the Standard Model of particle
physics [1, 2, 3]. The Standard Model describes the constituents of matter as twelve
fermions, six quarks, which form the hadrons, and six leptons. For each of the particles,
there is an anti-particle, having the same mass, but opposite quantum numbers. Hadrons
likeprotons,neutrons,pionsandothersareformedfromeithercombinationsofthreequarks
or quark-anti-quark pairs. The twelve fermions are further divided into three generations,
where the properties of the generations are similar, except for the mass. The gauge bosons
of the strong and electroweak interaction mediate the forces between these fermions. All
these particles have been observed in experiments. Not included in the standard model of
particle physics is the gravitational force, which can typically be neglected in the quantum
regime due to the small involved masses.
The standard model particles have zero mass in this theory, which obviously contradicts
the measured masses of these particles. This shortcoming of the standard model can be
overcome by breaking of the electroweak symmetry, which can be done by adding a new
scalar (cid:28)eld, the Higgs (cid:28)eld. The Higgs-(cid:28)eld generates the particle masses by its couplings
to the standard model particles [4, 5, 6]. By the introduction of this (cid:28)eld a new parti-
cle, the Higgs particle is also introduced. The search for this particle lasted for several
decades without success and the possible mass of the Higgs, which is not (cid:28)xed by theory,
was already severely constrained by earlier experiments at the LEP and Tevatron colliders
(and other experiments). However, a new boson with a mass around 125 GeV, that is so
far consistent with this Standard Model Higgs, has recently been discovered by both the
ATLAS and CMS collaborations at the Large Hadron Collider at CERN [7, 8].
Despite the enormous success of the standard model to explain experimental results,
it is clear, that the standard model has limitations. At the moment it is not clear, how
neutrino masses, that are measured in neutrino oscillation experiments can be consistent
with the experimental absence of right-handed neutrinos (and left handed anti-neutrinos).
Another example that can point at physics beyond the standard model are the measured
rotational spectra of galaxies and larger cosmological objects, that are not in agreement
with the visible matter distributions of these objects. The additional matter needed to
explain the rotational spectra is called dark matter, since it underlies gravity but is not
visible in the electromagnetic spectrum. A possible candidate for this matter is one or
more unknown particles.
10 CONTENTS
ThecapabilityoftheLargeHadronColliderforprecisionmeasurementsofthisnewpar-
ticle,andothersthatmightbefoundinthefuture,islimited,sincethecollisionsparameters
are not well de(cid:28)ned due to the compound nature of the collided protons and the strong
backgrounds from proton collisions. Therefore, a next generation of electron-positron col-
liders, which have the capability for precision measurements of the Higgs particle, has been
developed and proposed. Besides precision measurements of the Higgs-like particle, these
physics programs also foresee searches for physics beyond the Standard Model, precision
measurements of th top quark mass and many others [9, 10].
Besidesnewacceleratortechnologythathastobedevelopedforthenextgenerationcol-
liders to achieve the desired collision energy and collision rate, the precision requirements
set also unprecedented performance goals for the detectors that record the collisions. The
required jet-energy resolution of a few percent at around 100 GeV (to distinguish W-boson
and Z-boson decays), can only be achieved with new detector concepts as the Particle Flow
concept. This concept aims to measure each collision product with the sub-detectors which
o(cid:27)ers the best measurement. It is used in a simple version, called energy (cid:29)ow, at the CMS
detector. It requires optimized sub-detectors as tracking systems and calorimeters, with
high granularity to disentangle the signals from the individual collision products. The
CALICE collaboration has developed several high-granular calorimeter prototypes with
di(cid:27)erent read-out technologies: Digital, semi-digital and analog high-granular sandwich
calorimeters. However, the choice of the absorber material is not (cid:28)xed by the read-out
technology. Therefore this thesis will investigate the di(cid:27)erences of hadron showers in an
analogue high-granular sandwich calorimeter equipped with either tungsten or iron ab-
sorber plates.
Chapter 1 will give a brief introduction to the two most advanced next generation
electron-positron collider projects and their detectors.
Chapter 2 will introduce the physics of particle showers and the underlying mechanisms for
di(cid:27)erent particles. This chapter will also give a summary on the most important principles
in calorimetry and an introduction into the principles of Particle Flow calorimetry, which
is the design paradigm of the detectors for the next generation of electron-positron linear
colliders.
Chapter 3 is a description of the Analog Hadron Calorimeter used to record the data which
is evaluated in this thesis. It is one of the CALICE collaboration prototype calorimeters
and constructed as a sandwich calorimeter with layers of scintillator tiles which are read
out by Silicon Photomultipliers. These active layers are interleaved with metal absorber
layers which induce particle showers. The active layers are described in detail as well as
the two di(cid:27)erent absorber materials used and the read-out electronics needed to record
shower data.
The shower data which is evaluated in this thesis has been recorded during two di(cid:27)erent
testbeam campaign at the Fermi National Accelerator Laboratory and at CERN. The two
experimental setups are described in chapter 4.
The recorded data is compared with di(cid:27)erent hadron shower simulations. Chapter 5 gives
a brief overview on the di(cid:27)erent hadrons physics simulations from the GEANT4 software
framework, which are used for the thesis.