Measurement of the D*± meson cross section and extraction of the charm contribution, F_1hnc_1tn2(x,Q_1hn2), to the proton structure in deep inelastic ep scattering with the H1 detector at HERA [Elektronische Ressource] / vorgelegt von Andreas Werner Jung

De
INAUGURAL - DISSERTATIONzurErlangung der Doktorwurde˜derNaturwissenschaftlich - MathematischenGesamtfakult˜ atder Ruprecht - Karls - Universit˜ atHeidelbergvorgelegt vonDipl.-Phys. Andreas Werner Jungaus Dortmund (Nordrhein - Westfalen)Tag der mundlic˜ hen Prufung:˜ 14. Januar 2009⁄§Measurement of the D Meson Cross Sectionandc 2Extraction of the Charm Contribution, F (x;Q ), to2the Proton Structurein Deep Inelastic ep Scattering withthe H1 Detector at HERAGutachter: Prof. Dr. Hans-Christian Schultz-CoulonProf. Dr. Norbert HerrmannKurzfassung⁄Die Produktion von D -Mesonen in tiefunelastischer Streuung bei HERA wurde mit Datenuntersucht, die mit dem H1-Detektor in den Jahren 2004-2007 aufgezeichnet wurden. Diese¡1Daten entsprechen einer integrierten Luminosit˜ at von 347 pb , welches eine Steigerung derverfugbaren˜ Statistik um den Faktor acht, verglichen mit der vorherigen H1-Publikation,2darstellt. Der sichtbare Bereich dieser Messung deckt Photonvirtualit˜ aten von 5 < Q <2 ⁄100 GeV und einen erweiterten Inelastizit˜ atsbereich von 0:02 < y < 0:70 ab. Das D -Meson⁄wird dabei im Transversalimpulsbereich ab p (D ) > 1.5 GeV in einem Pseudorapidit˜ ats-T⁄bereich vonj·(D )j < 1.5 gemessen. Einfach- und doppeltdifierentielle Verteilungen werdenmit perturbativen QCD Vorhersagen in fuhrender˜ und n˜ achstfuhrender˜ Ordnung verglichen.Der systematische Fehler der Messung ist entscheidet verringert worden.
Publié le : jeudi 1 janvier 2009
Lecture(s) : 28
Tags :
Source : ARCHIV.UB.UNI-HEIDELBERG.DE/VOLLTEXTSERVER/VOLLTEXTE/2009/8977/PDF/DISS_AWJUNG.PDF
Nombre de pages : 213
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INAUGURAL - DISSERTATION
zur
Erlangung der Doktorwurde˜
der
Naturwissenschaftlich - Mathematischen
Gesamtfakult˜ at
der Ruprecht - Karls - Universit˜ at
Heidelberg
vorgelegt von
Dipl.-Phys. Andreas Werner Jung
aus Dortmund (Nordrhein - Westfalen)
Tag der mundlic˜ hen Prufung:˜ 14. Januar 2009⁄§Measurement of the D Meson Cross Section
and
c 2Extraction of the Charm Contribution, F (x;Q ), to2
the Proton Structure
in Deep Inelastic ep Scattering with
the H1 Detector at HERA
Gutachter: Prof. Dr. Hans-Christian Schultz-Coulon
Prof. Dr. Norbert HerrmannKurzfassung
⁄Die Produktion von D -Mesonen in tiefunelastischer Streuung bei HERA wurde mit Daten
untersucht, die mit dem H1-Detektor in den Jahren 2004-2007 aufgezeichnet wurden. Diese
¡1Daten entsprechen einer integrierten Luminosit˜ at von 347 pb , welches eine Steigerung der
verfugbaren˜ Statistik um den Faktor acht, verglichen mit der vorherigen H1-Publikation,
2darstellt. Der sichtbare Bereich dieser Messung deckt Photonvirtualit˜ aten von 5 < Q <
2 ⁄100 GeV und einen erweiterten Inelastizit˜ atsbereich von 0:02 < y < 0:70 ab. Das D -Meson
⁄wird dabei im Transversalimpulsbereich ab p (D ) > 1.5 GeV in einem Pseudorapidit˜ ats-T
⁄bereich vonj·(D )j < 1.5 gemessen. Einfach- und doppeltdifierentielle Verteilungen werden
mit perturbativen QCD Vorhersagen in fuhrender˜ und n˜ achstfuhrender˜ Ordnung verglichen.
Der systematische Fehler der Messung ist entscheidet verringert worden. Der Beitrag von
c 2charm-Quarks zur Protonstruktur, F (x;Q ), wird in zwei verschiedenen QCD Evolution-2
⁄sschemata aus den gemessenen D -Meson Wirkungsquerschnitten bestimmt und mit pQCD
Vorhersagen in n˜ achst-fuhrender˜ Ordnung verglichen. Dabei wird eine, verglichen mit der
letzten H1-Publikation, 18fach h˜ ohere Statistik genutzt.
Die vorliegende Arbeit umfa…t ebenfalls ein erfolgreich beendetes Hardwareprojekt: Die In-
betriebnahme und Optimierung der dritten Stufe des schnellen Spurtriggers (FTT) bei H1,
die Anfang 2006 erfolgreich abgeschlossen wurde. Der FTT ist in die ersten drei Stufen des
zentralen H1-Triggersystems integriert und stellt eine verbesserte Selektivit˜ at fur˜ die Identi-
flzierung von Ereignissen mit geladenen Teilchen zur Verfugung.˜ Die dritte Stufe des FTT
fuhrt˜ innerhalb von 100 „s eine spurbasierte Ereignisrekonstruktion aus und ist als Comput-
erfarm, bestehend aus PowerPC Karten, realisiert. Au…erdem wurde die FTT Simulation in
die Simulation des H1-Triggersystems integriert.
Abstract
⁄Inclusive production of D mesons in deep inelastic scattering at HERA is studied using
data taken with the H1 detector in the years 2004 to 2007 corresponding to an integrated
¡1 2 2luminosity of 347 pb . The measurement covers the region 5 < Q < 100 GeV in pho-
ton virtuality and the increased region 0:02 < y < 0:70 in the inelasticity of the scattering
⁄process. The visible range of the D meson is restricted in transverse momentum and pseudo-
⁄ ⁄rapidity to p (D ) > 1.5 GeV and j·(D )j < 1.5. The present measurement is based on anT
eightfold increased statistics compared to the previous H1 publication and provides a signif-
icantly reduced systematic error. Single and double-difierential cross sections are compared
to leading and next-to-leading order perturbative QCD predictions. The charm contribution,
c 2F (x;Q ), to the proton structure in difierent QCD evolution schemes is derived from the2
⁄D cross sections and compared to next-to-leading order perturbative QCD predictions. This
cF measurement is performed using a factor of 18 more data compared to the previous H12
publication.
The present thesis additionally describes a successfully completed hardware project: The
commissioning and optimisation of the third level of the H1 Fast Track Trigger (FTT), which
was fully operational from 2006 onwards. The FTT is integrated in the flrst three levels of the
H1 trigger system and provides enhanced selectivity for events with charged particles. The
third trigger level of the FTT performs a track-based event reconstruction within a latency
of about 100 „s. The third trigger level of the FTT is realised by a farm of PowerPC boards.
Furthermore, the FTT simulation is now incorporated into the H1 trigger simulation.6Contents
Contents
1 Introduction 1
1.1 Motivation of the present Measurement . . . . . . . . . . . . . . . . . . . 2
⁄I Measurement of the D Meson Production Cross Section and Extrac-
c 2tion of F (x;Q ) 7
2
2 Deep Inelastic electron-proton Scattering 8
2.1 Kinematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 QCD based Model of Deep Inelastic Scattering . . . . . . . . . . . . . . . 12
2.3 Heavy Quark Production Mechanisms in ep Scattering . . . . . . . . . . . 17
2.4 The Charm Structure Function and the Connection to the Gluon Density . 21
3 HERA and the H1 Detector 23
3.1 The LAr Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 The SPACAL Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3 The Central Tracking System . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 The Luminosity Measurement . . . . . . . . . . . . . . . . . . . . . . . . 31
3.5 The Trigger Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4 Event Generators 36
4.1 Leading-order Monte Carlo Generators . . . . . . . . . . . . . . . . . . . 36
4.2 Next-to-leading Order Calculations . . . . . . . . . . . . . . . . . . . . . 39
4.3 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5 Open Charm Tagging and Experimental Methods 42
5.1 On-line Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.2 Signal Extraction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.3 Unfolding of Detector Efiects . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4 Reconstruction Methods for the Event Kinematics . . . . . . . . . . . . . 52
6 Run and Event Selection 60
6.1 Ofi-line Event . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
7 Control Distributions for DIS Events 65
7.1 Control for Electron Quantities . . . . . . . . . . . . . . . . 66
⁄7.2 Distributions for D Meson Events . . . . . . . . . . . . . . . . . 68
8 Cross Section Determination 73
8.1 Correction of Detector Efiects . . . . . . . . . . . . . . . . . . . . . . . . 73
8.2 Co of next-to-leading Order QED Contributions . . . . . . . . . . 84
8.3 Correction due to Re ections . . . . . . . . . . . . . . . . . . . . . . . . 87
iContents
9 Systematic Uncertainties 90
9.1 Uncorrelated . . . . . . . . . . . . . . . . . . . . . . . . . . 90
9.2 Correlated . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
9.3 Fragmentation Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . 105
10 Cross Section Results 109
10.1 The total Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
10.2 Single-difierential Cross Section Distributions . . . . . . . . . . . . . . . . 111
10.3 Double-difierential Cross . . . . . . . . . . . . . . . 117
11 The Charm Contribution to the Proton Structure 122
11.1 Phase Space Coverage & Extrapolation . . . . . . . . . . . . . . . . . . . 123
11.2 Theoretical Uncertainties of the Extrapolation Procedure . . . . . . . . . . 125
11.3 The Charm Contribution to the Proton Structure . . . . . . . . . . . . . . 131
12 Phase Space Extension of the Measurement 134
12.1 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
12.2 Matrix Unfolding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
12.3 Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
12.4 The Charm Contribution to the Proton Structure . . . . . . . . . . . . . . 144
13 Conclusion & Outlook 148
II The H1 Fast Track Trigger 151
14 The Fast Track Trigger System 152
14.1 The FTT Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
14.2 The Post-processing for H1 Monte Carlo Production . . . . . . . . . . . . 156
15 The Level three system 158
15.1 The Hardware Implementation . . . . . . . . . . . . . . . . . . . . . . . . 159
15.2 Input Data & Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
15.3 The Readout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
15.4 Physics Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
15.5 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
15.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
A Cross Section Tables 185
B List of Abbreviations 191
Bibliography 202
Danksagung 203
ii1. Introduction
The standard model of particle physics is a very successful theory, which predicts and
explains most of the phenomena observed in elementary particle physics. It consists of
three gauge theories for the strong, weak and electromagnetic interaction. In addition
there is the gravitational force dominant at very large distances, where up to now a
theoretical framework similar to the formulation of the standard model is missing.
In the standard model matter is built from elementary particles out of three so-called
families { I., II., and III. {, which incorporate six leptons and six quarks and the charge
conjugated (c:c:) states. Moreover the families possess very difierent mass scales from a
+few MeV for up- and down-quarks to 180 GeV for the top-quark [Y 06]. In that sense
a classiflcation of the quarks into light (uds) quarks and heavy (sct) quarks is obvious
and useful for later discussions. The standard model describes the three fundamental
forces between the 12 fermions (spin 1=2-particles) via the exchange of gauge bosons
(spin 1-particles) for the strong, weak and electromagnetic interactions. These are
known as gluons g for the strong force, as W and Z bosons for the weak force and as
? boson for the electromagnetic force.
For the theory of the strong interactions (quantum chromodynamics, QCD) one of the
ideal experimental setups is deep inelastic scattering of leptons on nucleons where the
photon (? ) is utilised as a probe of the nucleon. Deep inelastic scattering experiments
played a major role for the measurement of the nucleon structure, which is dominated
by QCD efiects. These experiments started as flxed target experiments at low centre-
of-mass energies. Due to the flxed-target setup the available centre-of-mass energy
1increased only slowly for these kind of experiments. HERA , where an electron and a
proton beam have been collided, allowed the access of much higher energies that would
not have been possible with flxed target experiments. For these an electron beam
energy of 50 TeV would have been needed to reach the HERA centre-of-mass energy
of 320 GeV which is even nowadays far from trivial. Moreover HERA has conflrmed
many aspects of the standard model and in particular of QCD with a high experimental
precision. One of the highlights are the precise structure function data utilised by
global analyses for the determination of proton parton density functions (PDF). These
structure function data is only indirectly sensitive to the gluon density of the proton.
A precise knowledge of the parton density distributions is of great importance for the
Large Hadron Collider where two collimated proton beams or basically two highly
collimated parton beams are collided at highest centre-of-mass energies of 14 TeV.
Many new phenomena are expected at an energy scale of a few TeV because of certain
shortcomings of the standard model that concern for instance the very high energy
behaviour, the origin of matter, the origin of mass & families. To overcome these
problems a variety of extensions to the standard model exist, which are expected to be
2observable at a scale the LHC is able to reach.
1Hadron-Elektron-Ring-Anlage
2Large Hadron Collider
11. Introduction
1.1. Motivation of the present Measurement
The measurement of heavy a vor or charm production in deep inelastic scattering
(DIS) at the electron-proton collider HERA is of particular interest for dedicated tests
of perturbative QCD (pQCD). Experimentally heavy charm-quarks are identifled via
⁄the decay of the D meson into charged particles, which allows the measurement of
⁄the production cross section of D mesons. The large charm mass provides a hard
scale for reliable pQCD predictions, although di–culties arise from the additional hard
2scales, which are provided by the photon virtuality Q and the transverse momentum
⁄p (D ). However, in the context of the present analysis one can distinguish betweenT
two strategies: a precise experimental cross section restricted to a detector acceptance
confronted with a theoretical prediction, which inherits large errors from the phase
space restriction during the calculation; the other strategy is to extrapolate the experi-
mental measurement to the full phase space, which involves large uncertainties usually
assigned to the experimental error. However, a precise theoretical prediction is calcu-
lable for the full phase space. These two strategies have been pursued in the present
analyses and are discussed shortly in the following.
⁄High statistic D Cross Sections
⁄TheD cross section data in DIS provides a scale, which is in between the two difierent
3heavy a vor schemes where either the charm-quarks are treated completely massless
2 2 2 2valid forQ ?m (c) (ZM-VFNS) or massive most applicable at thresholdQ .m (c)
4(FFNS) and thus ideally suited to study pQCD predictions in a certain scheme . In or-
der to get a handle on these various theoretical schemes for the heavy a vor treatment
⁄in pQCD difierential or double-difierentialD cross section measurements as presented
in this analysis are helpful to further understand the underlying threshold and mass
efiects. The full available HERA II data statistics allows the determination of precise
ZEUS
3.5
4 a) d) b) ep e+D*+X33
-1ZEUS (prel.) 162 pb
2.5
3 HVQDIS
2
2 1.5
11
H1 Data
1
CASCADE 0.50.5
HVQDIS
00 -1.5 -1 -0.5 0 0.5 1 1.5
-1.5 -1 -0.5 0 0.5 1 1.5 (D*)
⁄ ⁄Figure 1.1.: The D cross section as a function of ·(D ) as measured by H1 using
the luminosity of the whole HERAI data taking (left) and from ZEUS as
+measured using the luminosity of the years 2003¡ 2005 (right) [Z 07].
cross section data. These are utilised to further understand regions of the phase space
3These schemes are also applicable to b- and t-quarks.
4In addition there exist schemes with interpolating features known as GM-VFNS which give good
descriptions of photoproduction data.
2
hshhsshhfih
d /d [nb]
vis
d /d (D*) (nb)

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