Measurement of the partial branching fraction for inclusive semileptonic B meson decays to light hadrons B→X_1tnulv  and an improved determination of the quark mixing matrix element V_1tnu_1tnb [Elektronische Ressource] / von Alexei Volk

Measurement of the partial branching fraction for inclusive semileptonic B meson decays to light hadrons B→X_1tnulv and an improved determination of the quark mixing matrix element V_1tnu_1tnb [Elektronische Ressource] / von Alexei Volk

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Measurement of the Partial Branching Fraction forInclusive Semileptonic B Meson Decays to Light HadronsB→ X l and an Improved Determination of the Quark-uMixing Matrix Element|V |ubDISSERTATIONzur Erlangung des akademischen GradesDoctor rerum naturalium(Dr. rer. nat.)vorgelegtder Fakultät Mathematik und Naturwissenschaftender Technischen Universität DresdenvonDiplom-Physiker Alexei Volkgeboren am 16. Februar 1978 in WinogradnojenGutachter :AbstractThis thesis presents an analysis of inclusive semileptonic B→ X e decays using approximatelyu e454 million (4S)→ BB decays collected during the years 1999 to 2008 with the BABAR detector.2The electron energy, E , and the invariant mass squared of the electron-neutrino pair, q , are recon-estructed, where the neutrino kinematics is deduced from the decay products of both B mesons. Thefinal hadronic state, X , consists of a sum of many hadronic channels, each of which contains at leastu2one u quark. The variables q and E are then combined to compute the maximum kinematicallyemaxallowed invariant mass squared of the hadronic system, s . Using these kinematic quantities, thehpartial branching fraction, B(B→ X l ), unfolded for detector effects, is measured to beumax 2 −4B(E > 2.0GeV,s < 3.52GeV )=(3.33± 0.18± 0.21)× 10e hin the (4S) andmax 2 −4˜ ˜B(E > 1.9GeV,s˜ < 3.5GeV )=(4.57± 0.24± 0.32)× 10e hin the B meson rest frames. The quoted errors are statistical and systematic, respectively.

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Measurement of the Partial Branching Fraction for
Inclusive Semileptonic B Meson Decays to Light Hadrons
B→ X l and an Improved Determination of the Quark-u
Mixing Matrix Element|V |ub
DISSERTATION
zur Erlangung des akademischen Grades
Doctor rerum naturalium
(Dr. rer. nat.)
vorgelegt
der Fakultät Mathematik und Naturwissenschaften
der Technischen Universität Dresden
von
Diplom-Physiker Alexei Volk
geboren am 16. Februar 1978 in Winogradnoje
nGutachter :Abstract
This thesis presents an analysis of inclusive semileptonic B→ X e decays using approximatelyu e
454 million (4S)→ BB decays collected during the years 1999 to 2008 with the BABAR detector.
2The electron energy, E , and the invariant mass squared of the electron-neutrino pair, q , are recon-e
structed, where the neutrino kinematics is deduced from the decay products of both B mesons. The
final hadronic state, X , consists of a sum of many hadronic channels, each of which contains at leastu
2one u quark. The variables q and E are then combined to compute the maximum kinematicallye
maxallowed invariant mass squared of the hadronic system, s . Using these kinematic quantities, theh
partial branching fraction, B(B→ X l ), unfolded for detector effects, is measured to beu
max 2 −4B(E > 2.0GeV,s < 3.52GeV )=(3.33± 0.18± 0.21)× 10e h
in the (4S) and
max 2 −4˜ ˜B(E > 1.9GeV,s˜ < 3.5GeV )=(4.57± 0.24± 0.32)× 10e h
in the B meson rest frames. The quoted errors are statistical and systematic, respectively. The CKM
˜matrix element|V | is determined from the measured B using theoretical calculation based onub
Heavy Quark Expansion. The result is
+0.26+0.26 −3|V |=(4.19± 0.18 )× 10 ,ub −0.20−0.25
where the errors represent experimental unceratinties, uncertainties from HQE parameters and
theoretical uncertainties, respectively.
Kurzfassung
In dieser Dissertation wird eine Analyse von inklusiven semileptonischen B→ X e Zerfällenu e
präsentiert. Die Daten wurden in den Jahren von 1999 bis 2008 mit dem BABAR Detektor
aufgezeichnet und entsprechen ungefähr 454 Millionen (4S)→ BB Zerfällen. Es werden die
Energie des Elektrons, E , und das Quadrat der invarianten Masse des Elektron-Neutrino-Systems,e
2q , rekonstruiert. Die Kinematik des Neutrinos wird aus den Zerfallsprodukten beider B-Mesonen
abgeleitet. Der hadronische Endzustand, X , ist eine Summe aus vielen hadronischen Zuständen,u
2von denen jeder mindestens ein u Quark enthält. Die Grössen q und E werden zu einer weit-e
maxeren Variable, s , kombiniert, die das Quadrat der invarianten Masse des hadronischen Systemsh
darstellt. Mit Hilfe dieser kinematischen Grössen wird das folgende partielle
Verzweigungsverhältnis, B(B→ X l ), gemessen:u
max 2 −4B(E > 2.0GeV,s < 3.52GeV )=(3.33± 0.18± 0.21)× 10e h
im (4S)- und
max 2 −4˜ ˜B(E > 1.9GeV,s˜ < 3.5GeV )=(4.57± 0.24± 0.32)× 10e h
in B-Ruhesystem. Die angegebene Fehler sind statistisch und systematisch. Das CKM-Matrixelement
˜|V | wird aus der Messung des partiellen Verzweigungsverhältnis, B, und einer Berechnung imub
Rahmen der Theorie der “Heavy Quark Expansion” bestimmt. Das Ergebnis ist
+0.26+0.26 −3|V |=(4.19± 0.18 )× 10 ,ub −0.20−0.25
wobei die angegebenen Fehler experimentelle Unsicherheiten, Unsicherheiten aus HQE-Parametern
und theoretische Unsicherheiten darstellen.
Dnn¡¡¡D¡nDDnDDDDContents
1 Introduction 1
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Theory and Motivation 3
2.1 The Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Symmetry Breaking and Mass Generation . . . . . . . . . . . . . 3
2.1.2 Weak Interactions and the CKM Matrix . . . . . . . . . . . . . . 4
2.2 Semileptonic B Meson Decays . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Exclusive Semileptonic Decays . . . . . . . . . . . . . . . . . . 7
2.2.2 Inclusive Semileptonic Decays . . . . . . . . . . . . . . . . . . . 10
2.2.2.1 Differential Decay Rates . . . . . . . . . . . . . . . . 11
22.3 The q − E Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15l
3 The BABAR Experiment 17
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 The BABAR Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.1 The Silicon Vertex Tracker (SVT) . . . . . . . . . . . . . . . . . 19
3.2.2 The Drift Chamber (DCH) . . . . . . . . . . . . . . . . . . . . . 19
3.2.3 The Cherenkov Detector (DIRC) . . . . . . . . . . . . . . . . . . 19
3.2.4 The Electromagnetic Calorimeter (EMC) . . . . . . . . . . . . . 21
3.2.5 The Instrumented Flux Return (IFR) . . . . . . . . . . . . . . . . 22
4 Analysis Strategy 25
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 Data Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3 Monte Carlo Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.3.1 Simulation of Signal Events . . . . . . . . . . . . . . . . . . . . 26
4.3.2 HQE parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.3.3 Background Simulation . . . . . . . . . . . . . . . . . . . . . . 30
4.4 Event Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4.1 Event Preselection . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4.2 Charged Track Selection . . . . . . . . . . . . . . . . . . . . . . 32
4.4.3 Neutral Candidate Selection . . . . . . . . . . . . . . . . . . . . 33
4.4.4 Selection of Composite Particle Candidates . . . . . . . . . . . . 34
4.4.5 Particle Identification . . . . . . . . . . . . . . . . . . . . . . . . 34
4.5 Neutrino Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . 35
∗4.6 Partial Reconstruction of B→ D ℓ Decays . . . . . . . . . . . . . . . . 36
4.6.1 Low-Momentum Pion Reconstruction . . . . . . . . . . . . . . . 38
i
nContents
∗4.6.2 Inclusive D Reconstruction . . . . . . . . . . . . . . . . . . . . 38
∗4.6.3 B→ D ℓ Veto Definition . . . . . . . . . . . . . . . . . . . . . 40
4.7 Continuum Subtraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.8 Optimization Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.8.1 Discriminating Variables . . . . . . . . . . . . . . . . . . . . . . 47
4.8.2 Optimization Technique . . . . . . . . . . . . . . . . . . . . . . 49
4.8.3 Optimization Results . . . . . . . . . . . . . . . . . . . . . . . . 51
4.9 Comparison Between Data and Simulation . . . . . . . . . . . . . . . . . 52
5 Control Sample 71
05.1 Selection of B→ D e events . . . . . . . . . . . . . . . . . . . . . . . 71e
5.2 Adjusting the Monte Carlo Efficiency . . . . . . . . . . . . . . . . . . . 72
5.3 Results of the Control Sample Studies . . . . . . . . . . . . . . . . . . . 75
6 Signal Extraction 83
6.1 Signal Extraction Procedure . . . . . . . . . . . . . . . . . . . . . . . . 83
7 Systematic Uncertainties 87
7.1 Evaluation Procedure for Systematic Uncertainties . . . . . . . . . . . . 87
7.2 Signal simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.3 Background simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.4 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.4.1 Track selection efficiency . . . . . . . . . . . . . . . . . . . . . 92
7.4.2 Neutrals selection efficiency . . . . . . . . . . . . . . . . . . . . 94
7.4.3 Particle identification . . . . . . . . . . . . . . . . . . . . . . . 94
07.4.4 Modeling of K Meson . . . . . . . . . . . . . . . . . . . . . . . 96L
7.4.5 Reconstruction of composite particles . . . . . . . . . . . . . . . 96
7.4.6 Bremsstrahlung . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.4.7 Final state radiation . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.5 Beam energy correction . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.6 B-meson counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.7 Summary of systematic uncertainties . . . . . . . . . . . . . . . . . . . . 101
8 Results 105
8.1 Measurement of B(B→ X e ) . . . . . . . . . . . . . . . . . . . . . . 105u e
8.2 Stability Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.3 Extraction of|V | and Outlook . . . . . . . . . . . . . . . . . . . . . . . 108ub
9 Summary and Conclusion 117
Bibliography 119
ii
nDnnList of Figures
2.1 The unitarity triangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 The global CKM fit results in the − plane . . . . . . . . . . . . . . . 6
2.3 Angles , , and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10l V
2.4 Semileptonic B meson decays . . . . . . . . . . . . . . . . . . . . . . . 11
22.5 Distribution of B→ X l and B→ X l decays in the q − E plane . . . 16c u l
3.1 Integrated luminosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 The PEP-II storage rings and the linear colider . . . . . . . . . . . . . . . 19
3.3 Schematic view of the BABAR detector . . . . . . . . . . . . . . . . . . . 20
3.4 Longitudinal section through the SVT . . . . . . . . . . . . . . . . . . . 21
3.5 Schematic view of the DCH . . . . . . . . . . . . . . . . . . . . . . . . 21
3.6 Schematic view of the DIRC . . . . . . . . . . . . . . . . . . . . . . . . 22
3.7 Longitudinal section through the EMC . . . . . . . . . . . . . . . . . . . 23
0 +4.1 Mass spectrum of X system for B and B decays in hybrid Monte Carlou
events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
0 +4.2 Electron energy spectrum for B and B decays in hybrid Monte Carlo events 29
2 0 +4.3 q spectrum for B and B decays in hybrid Monte Carlo events . . . . . 30
4.4 Generated B→ X e neutrino momentum|P | minus|P | as a func-u e ,true miss
tion of|P | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36miss
4.5 Generated B→ X e |P | minus corrected|P | neutrino momenta as au e ,true
function of|P | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
24.6 Distribution of signal B→ X e events for q resolution . . . . . . . . . 38u e
max min4.7 Distribution of E vs. E for slow neutral pions . . . . . . . . . . . . 38

∗4.8 Distribution of fully reconstructed D → D events in|P |−|P | plane . 39D
4.9 Propagation scheme of an Artificial Neural Network . . . . . . . . . . . . 41
4.10 Angle defined in the (4S) frame . . . . . . . . . . . . . . . . . . . 42BY
∗ ±4.11 Distributions of the neural network input variables for D → class . . 43
∗ 04.12 Distributions of the neural network input variables for D → class . . . 44
4.13 Linear correlation coefficients of NN input variables . . . . . . . . . . . 45
∗ ± ∗4.14 The normalized neural network output distributions for D → and D →
0 classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.15 Off-peak data and off-peak MC distributions . . . . . . . . . . . . . . . . 46
4.16 Lepton energy distribution for on-peak and off-peak data in the region
above 2.8 GeV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.17 Distribution for cos and cos for on-peak and scaled off-peak datamiss e−T
after applying the preselection requirement . . . . . . . . . . . . . . . . 48
4.18 Distributions of electron energy for simulated B→ X e signal events foru e
different values of SF parameters m and a . . . . . . . . . . . . . . . . . 50b
iii
QQcpnprpn¡nQqpppngngnnnnqnhList of Figures
4.19 Optimization of the event selection using cos and cos variables 52miss e−T
4.20 Optimization of the event selection using neural net output and E −miss
|P | variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53miss
max4.21 Optimization of event selection using E and s variables . . . . . . . . 54e h
4.22 Refined selection requirement for cos and cos obtained as amiss e−T
function of parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.23 Refined selection requirements for neural network outputs, E −|P |,miss miss
maxE and s obtained as a function of parameter . . . . . . . . . . . . . 57e h
4.24 Data and MC distributions for |P | after applying the preselection andmiss
the refined selection requirements . . . . . . . . . . . . . . . . . . . . . 59
4.25 Data and MC distributions for|P | after applying the preselection and the
refined selection requirements . . . . . . . . . . . . . . . . . . . . . . . 60
4.26 Data and MC distributions for E after applying the preselection and themiss
refined selection requirements . . . . . . . . . . . . . . . . . . . . . . . 61
4.27 Data and MC distributions for E −|P | after applying the preselectionmiss miss
and the refined selection requirements . . . . . . . . . . . . . . . . . . . 62
4.28 Data and MC distributions for cos after applying the preselection andmiss
the refined selection requirements . . . . . . . . . . . . . . . . . . . . . 63
4.29 Data and MC distributions for cos after applying the preselection ande−T
the refined selection requirements . . . . . . . . . . . . . . . . . . . . . 64
±
4.30 Data and MC distributions for NN after applying the preselection andmax
the refined selection requirements . . . . . . . . . . . . . . . . . . . . . 65
0
4.31 Data and MC distributions for NN after applying the preselection andmax
the refined selection requirements . . . . . . . . . . . . . . . . . . . . . 66
24.32 Data and MC distributions for q after applying the preselection and the
refined selection requirements . . . . . . . . . . . . . . . . . . . . . . . 67
4.33 Data and MC distributions for E after applying the preselection and thee
refined selection requirements . . . . . . . . . . . . . . . . . . . . . . . 68
max4.34 Data and MC distributions for s after applying the preselection and theh
refined selection requirements . . . . . . . . . . . . . . . . . . . . . . . 69
0 05.1 Distribution of cos and invariant mass of D e system in the B→ D e XBY e
control sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
0 05.2 D mass spectra for data and simulation in the B→ D e X control sample 74e
05.3 Data and MC distributions for|P | and E in the B→ D e X controlmiss miss e
sample after applying the refined selection requirements . . . . . . . . . . 77
05.4 Data and MC distributions for|P | and E −|P | in the B→ D e Xmiss miss e
control sample after applying the refined selection requirements . . . . . 78
05.5 Data and MC distributions for cos and cos in the B→ D e Xmiss e−T e
control sample after applying the refined selection requirements . . . . . 79
± 0 05.6 Data and MC distributions for NN and NN in the B→ D e X con-emax max
trol sample after applying the refined selection requirements . . . . . . . 80
max 05.7 Data and MC distributions for E and s in the B→ D e X controle eh
sample after applying the refined selection requirements . . . . . . . . . . 81
iv
npnnprnQnnQQprQQpQQnnnQQList of Figures
2 05.8 Data and MC distributions for q in the B→ D e X control sample aftere
applying the refined selection requirements . . . . . . . . . . . . . . . . 82
26.1 Distribution of generated B→ X e events in true q − E plane . . . . . 84u e e
7.1 Error ellipse of the HQE parameters and . . . . . . . . . . . . . . . 881
7.2 Distribution of form factor weight for B→ Dℓ decays . . . . . . . . . . 92
7.3 Comparison of various true distrubutions of B→ Dℓ decays for PHOTOS
on/off scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.4 Comparison of various true distrubutions of B→ X l decays for the PHO-u
TOS on/off scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
8.1 Stability scans of the extracted results I . . . . . . . . . . . . . . . . . . 110
8.2 Stability scans of the extracted results II . . . . . . . . . . . . . . . . . . 111
8.3 Stability scan versus cos . . . . . . . . . . . . . . . . . . . . . . . . 112e−T
8.4 Stability scans versus E . . . . . . . . . . . . . . . . . . . . . . . . . . 113e
max8.5 Stability scans versus s . . . . . . . . . . . . . . . . . . . . . . . . . 114h
8.6 Comparison between inclusive|V | determinations . . . . . . . . . . . . 115ub
v
nnlQnnnL