Violation in Mixing

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Entries / 0.001 GeV 70 The BABAR Experiment 12000 10000 8000 6000 4000 2000 0 0.05 0.1 0.15 0.2 0.25 mγγ (GeV) Efficiency 1.0 0.8 0.6 0.4 0.2 0.0 ± e 0 1 2 Momentum (GeV/c) π ± 0.010 0.008 0.006 0.004 0.002 0.000 Figure 2-15. Left plot: invariant mass of two photon in �� events. The solid line is a fit to the data. Right plot: the electron efficiency and pion mis-identification probability as functions of the particle momentum. Left plot in fig. (2-15) shows the two-photon invariant mass in �� events: the reconstructed � mass is measured to be �� Å�Î� and is stable to better than over the full photon energy range. The width of �� Å�Î� agrees well with the prediction obtained from detailed Monte Carlo simulation. In low occupancy � � events, the width is slightly smaller, �� Å�Î� , for � energies below ��Î. The �Å� electron identification is based on the shower energy, lateral shower moments and track momentum to separate electrons from charged hadrons. In addition, the ��Ü energy loss in the ��À and the �ÁÊ� Čerenkov angle are required to be consistent with an electron. The most important variable for the discrimination of hadrons is the ratio of the shower energy to the track momentum (��Ô). Right plot in fig. (2-15) shows the efficiency for electron identification and the pion mis-identification probability as functions of momentum. The electron efficiency is measured using radiative Bhabha’s and � � � � � � � events, while the pion mis-identification for selected charged pions from Ã Ë decays and three-prong � decays: a tight selector results in an efficiency plateau at �� and a pion mis-identification probability of the order of � . 2.2.6 The magnet and the muon and neutral hadron detector Á�Ê. The Instrumented Flux Return (Á�Ê) was designed to identify muons with high efficiency and good purity and to detect neutral hadrons (mainly Ã Ä and neutrons) over a wide range of momenta and angles. Muon identification is important for the flavour tagging of the neutral � mesons via semileptonic decays, for the reconstruction of vector mesons (Â�� for instance) and for analyses of semileptonic and rare decays involving leptons of �s, �s and �s. Ã Ä detection allows the study of exclusive � decays (the golden mode Â��Ã Ä for example). The Á�Ê can also help in vetoing charm decays and improve the reconstruction of neutrinos. MARCELLA BONA
2.2 The BABAR detector. 71 The main requirements for the Á�Ê are large solid angle coverage, good efficiency and high background rejection for muons down to momenta below ��Î. For neutral hadrons, the most important requirements are high efficiency and good angular resolution. The momentum range in which the Á�Ê can work, starts from about �� Å�Î� (limit due to the barrel magnetic field: lower momentum particles cannot enter the Á�Ê), while in the forward and backward regions the lower limit is � Å�Î� . The upper limit is of order of some ��Î, but, since even direct muons cannot have momentum values higher than ��Î�, one can say that the Á�Ê does not have an upper limit for muons from § �Ë decays. H.V. Foam Bakelite Gas Bakelite Foam Figure 2-16. The Á�Ê detector and schematic representation of RPC components. Aluminum X Strips Insulator Graphite 2 mm 2 mm 2 mm Graphite Insulator Y Strips Spacers Aluminum 8-2000 8564A4 The Á�Ê uses the steel flux return of the magnet as muon filter and hadron absorber: the uniform magnetic field of �� Ì is generated by a superconducting solenoid and the large iron structure needed as magnet yoke is segmented and instrumented with Resistive Plate Chambers (RPCs) with two-coordinate readout. The RPCs are installed in the gaps of the finely segmented steel of the barrel and the end doors of the flux return (see fig. (2-16)). The steel segmentation has been chosen on the basis of Monte Carlo studies of muon penetration and charged and neutral hadron interactions: the steel is segmented into � plates increasing in thickness from Ñ for the inner nine plates to Ñ for the outermost plates. The nominal gap between the steel plates is �� Ñ in the inner layers of the barrel and � Ñ elsewhere. There are � RPC layers in the barrel and � in the end-caps. Each end-cap consists of hexagonal plates, divided vertically into two parts to allow opening of the detector and has a central hole for the beam components and the magnetic shields. In addition, two layer of cylindrical RPCs are installed between the �Å� and the magnet cryostat, in order to detect particle exiting the �Å�. RPCs detect streamers from ionizing particles via capacitive readout strips. The position resolution depends on the segmentation of the readout: a value of a few mm is achievable. A cross section of an RPC is shown schematically in fig.(2-16): the planar RPC consists of two bakelite sheets, ÑÑ thick and separated by a gap of ÑÑ. The gap width is kept uniform by policarbonate spaces that are glued to the bakelite, spaced THE BABAR EXPERIMENT
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ÍÒ�Ú�Ö×�Ø��
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Contents Introduction . ...........
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4 Strategy and Tools for Charmless
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7.2 Branching fraction � � �
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Introduction The main goal of the B
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1 �È Violation in the �� Sys
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1.2 Neutral � Mesons 7 Note, howe
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1.2 Neutral � Mesons 9 Applying t
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1.2 Neutral � Mesons 11 �È �
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1.2 Neutral � Mesons 13 ��
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1.2 Neutral � Mesons 15 � ¡�
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1.2 Neutral � Mesons 17 and � a
Page 25 and 26: 1.2 Neutral � Mesons 19 given tim
Page 27 and 28: 1.3 The Three Types of �È Violat
Page 33 and 34: 1.4 �È Violation in the Standard
Page 43 and 44: 1.5 Determination of « 37 1.5 Dete
Page 45 and 46: 1.5 Determination of « 39 Assuming
Page 47 and 48: 1.5 Determination of « 41 Figure 1
Page 49 and 50: 1.5 Determination of « 43 b q (a)
Page 51 and 52: 1.5 Determination of « 45 � �
Page 53 and 54: 2 The BABAR Experiment 2.1 Physics
Page 55 and 56: 2.1 Physics at � � B Factory op
Page 57 and 58: 2.2 The BABAR detector. 51 Integrat
Page 59 and 60: 2.2 The BABAR detector. 53 The dete
Page 61 and 62: 2.2 The BABAR detector. 55 two oute
Page 63 and 64: 2.2 The BABAR detector. 57 SVT Effi
Page 65 and 66: 2.2 The BABAR detector. 59 324 1015
Page 67 and 68: Efficiency 2.2 The BABAR detector.
Page 69 and 70: 2.2 The BABAR detector. 63 2.2.4 Th
Page 71 and 72: entries per mrad 2.2 The BABAR dete
Page 73 and 74: 2.2 The BABAR detector. 67 entries
Page 75: 2.2 The BABAR detector. 69 energies
Page 79 and 80: Efficiency 2.2 The BABAR detector.
Page 81 and 82: 2.2 The BABAR detector. 75 Table 2-
Page 83 and 84: 3 Ã Ë reconstruction and efficien
Page 85 and 86: 3.3 Studies on data 79 19.5° BINS
Page 87 and 88: 3.3 Studies on data 81 ¯ off-reson
Page 89 and 90: 3.3 Studies on data 83 0.504 0.502
Page 91 and 92: 3.3 Studies on data 85 0.03 0.025 0
Page 95 and 96: 3.3 Studies on data 89 N(π + π -
Page 99 and 100: 3.3 Studies on data 93 Figure 3-13.
Page 103 and 104: 4 Strategy and Tools for Charmless
Page 105 and 106: 4.2 Event selection 99 channel sele
Page 107 and 108: 4.2 Event selection 101 ÀÐ �
Page 109 and 110: 4.2 Event selection 103 Figure 4-2.
Page 111 and 112: 4.3 Background fighting 105 Figure
Page 113 and 114: 4.4 PID selection 107 In the case o
Page 115 and 116: 4.4 PID selection 109 θ c Cut Effi
Page 117 and 118: 4.5 Tracking Corrections 111 Ë�
Page 119 and 120: 4.6 Analysis methods 113 Ñ�Ë si
Page 121 and 122: 4.6 Analysis methods 115 Events/2.5
Page 123 and 124: 4.6 Analysis methods 117 Figure 4-1
Page 125 and 126: 4.6 Analysis methods 119 θ c radia
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5 Measurement of Branching Fraction
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5.2 Ã Ë reconstruction 123 1 0.8
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5.3 Analysis Strategy 125 0.35 0.3
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5.4 Background Suppression and PDF
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5.5 Maximum likelihood analysis 133
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5.6 Counting analysis 145 Table 5-1
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5.7 Determination of branching frac
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6 Measurement of Branching Fraction
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6.3 The maximum likelihood analysis
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6.4 Counting analysis 157 120 100 8
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6.5 Analysis choice 159 6.5 Analysi
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6.6 Results on the Run1 data-set 16
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6.7 Determination of the branching
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7 Analysis of the time-dependent
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7.3 Analysis strategy 167 Parameter
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7.4 Data samples and event selectio
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7.4 Data samples and event selectio
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7.5 Background characterization 173
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7.5 Background characterization 175
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7.8 Validation studies 185 Figure 7
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7.8 Validation studies 187 100 75 5
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7.8 Validation studies 189 Figure 7
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7.8 Validation studies 191 Paramete
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7.9 Results 193 Parameter Fit Resul
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7.9 Results 195 Events/2 MeV/c 2 Ev
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7.10 Systematic studies 197 Categor
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7.11 Summary 199 �Ã� Ë��
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7.11 Summary 201 �Ã� Ë��
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7.11 Summary 203 Variation �Ã�
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BIBLIOGRAFIA 205 Bibliografia Chapt
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BIBLIOGRAFIA 207 [38] J. Charles, P
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BIBLIOGRAFIA 209 Chapter 7 [67] D.
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