Abstract
Contents
1 Theoretical background 1
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 The Standard Model of particle physics . . . . . . . . . . . 2
2 Rare B0 → K∗0ℓ+ℓ− decays as probes for New Physics 13
2.1 Weak interactions as an Effective Field Theory . . . . . . . 13
2.2 The B0 → K∗0ℓ+ℓ− differential decay rate . . . . . . . . . 17
2.3 Conventional observables and experimental results in B0 →K∗0ℓ+ℓ− . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 Hunting for NP and compatibility with SM . . . . . . . . . 26
3 The LHCb detector at LHC 29
3.1 The large hadron collider at CERN . . . . . . . . . . . . . 29
3.2 The LHCb detector . . . . . . . . . . . . . . . . . . . . . . 30
4 Analysis strategy 51
4.1 Analysis overview . . . . . . . . . . . . . . . . . . . . . . . 55
5 Selecting B0 → K∗0ℓ+ℓ− decays 59
5.1 Data and simulation samples . . . . . . . . . . . . . . . . . 59
5.2 Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6 Corrections to simulation 97
6.1 Correction strategy . . . . . . . . . . . . . . . . . . . . . . 97
6.2 Particle identification corrections . . . . . . . . . . . . . . 99
6.3 Tracking corrections in electrons . . . . . . . . . . . . . . . 101
6.4 Trigger corrections . . . . . . . . . . . . . . . . . . . . . . . 103
6.5 Kinematic, multiplicity and reconstruction corrections . . . 110
6.6 Invariant mass resolution correction . . . . . . . . . . . . . 113
6.7 Impact of the correction chain on the distributions . . . . 116
7 Efficiency 121
7.1 Integrated and relative efficiency . . . . . . . . . . . . . . . 121
7.2 Effective acceptance . . . . . . . . . . . . . . . . . . . . . . 124
8 Invariant mass parametrization and yield extraction from fits 135
8.1 Fit generalities . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.2 Mass signal parametrization from simulation . . . . . . . . 137
8.3 Mass fits to B0 → K∗0ψn decays . . . . . . . . . . . . . . . 140
9 LFU cross-checks 153
9.1 LFU cross-checks on ratios of branching fractions . . . . . 153
9.2 LFU cross-check on the fit procedure: amplitude fits to B0 → K∗0J/ψ decays . . . . . . . . . . . . . . . . . . . . . 157
10 Amplitude fits to B0 → K∗0ℓ+ℓ− decays 171
10.1 Parametrization of the signal amplitude . . . . . . . . . . . 171
10.2 Parametrization of the backgrounds . . . . . . . . . . . . . 179
10.3 Constraint on the observed signal yield . . . . . . . . . . . 192
10.4 Amplitude fits to data . . . . . . . . . . . . . . . . . . . . 194
10.5 Statistical properties of the fit . . . . . . . . . . . . . . . . 203
10.6 Systematics . . . . . . . . . . . . . . . . . . . . . . . . . . 208
11 Conclusions and future prospects 213
12 Afterword 217
Appendices 219
A P-wave form factors in the narrow-width approximation 220
A.1 Form factors from LCRS and LQCD fits . . . . . . . . . . 221
B Long distance effects from analyticity 223
C Amplitude fits to B0 → K∗0J/ψ (→ ℓ+ℓ−) data candidates including partially reconstructed backgrounds 225
D S-wave form factors 232
E Improvements in the inclusion of the Kπ invariant mass lineshape 233
F Backgrounds modelling for B0 → K∗0ℓ+ℓ− 235
F.1 Double-semileptonic background . . . . . . . . . . . . . . . 235
F.2 Partially reconstructed B+ → K+
1 → (K+π+π−)e+e− decays 239
F.3 On the possibility of joining the parametrization of the combinatorial component . . . . . . . . . . . . . . . . . . . 242
G Blinded fit results to B0 → K∗0ℓ+ℓ− decay candidates 249
Bibliography 256
Atzeni, Michele