Universit`a degli studi Roma Tre Measurement of the KL meson ...

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32 CHAPTER 3. THE KLOE DETECTOR The quadrupole calorimeter Two triplets of permanent quadrupoles for the beam final focus are located inside the detector starting from a distance of 46 cm from IP, and surrounding the beam pipe, as shown in Fig. 3.8. Figure 3.8: One side of the interaction region. Two permanent quadrupoles are shown together with the surrounding calorimeter (QCAL) corresponding to the shaded area, starting at a distance of 46 cm from the IP (the center of the sphere in the sketch). The quadrupoles of this low-beta insertion are equipped with two calorimeters made of lead plates and scintillator tiles of ∼5X0 thickness, called QCAL [34]. The task of QCAL is to identify photons from KL → π 0 π 0 π 0 decays that would mimic the CP-violating KL → π 0 π 0 decay if the photon would be absorbed by the quadrupoles. Each calorimeter consists of a sampling structure of lead and scintillator tiles arranged in 16 azimuthal sectors. The readout is done with plastic wavelength shifting (WLS) fibers coupled to mesh photomultipliers. The arrangement of the WLS fibers allows the measurement of the longitudinal z coordinate by time difference. Although the tiles are assembled in a way to optimize the efficiency for photons originated in KL decays, a high efficiency is in fact also obtained for photons coming from the IP. This allows to extend the calorimeter coverage of the solid angle down to cosθ = 0.99.
3.3. THE TRIGGER 33 3.3 The trigger Event rates at DAΦNE are high: at a luminosity of 10 32 cm −2 s −1 up to 300 φ decays and 30,000 Bhabha events are produced per second in the KLOE acceptance. The trigger design [35] is optimized to retain all φ decays. Moreover, all Bhabha and e + e − → γγ events produced at large polar angles are accepted for detector monitoring and calibration, as well as a downscaled fraction of cosmic rays, which cross the detector at a rate of 3000 Hz. Finally, the trigger provides efficient rejection of the two main sources of background: small angle Bhabha scattering events, and particle lost from the DAΦNE beams, resulting in very high photon and electron fluxes in the interaction region. Figure 3.9: KLOE trigger logical scheme. The trigger logic, shown in Fig. 3.9, rapidly recognizes event topologies and energy deposits of interest processing the signals from the DC and the EMC. Since φ decay events have a relatively high multiplicity, they can be efficiently selected by the EMC trigger by requiring at least two isolated energy deposits in the calorimeter (≥ 2 trigger sectors 1 ) above a given threshold. The threshold for most of the data was chosen 50 MeV in the barrel and 150 MeV in the endcaps. Events with only two trigger sectors in the same endcap are not accepted, because this topology is dominated by machine background. Events with charged particles give a large number of hits in the DC. The trigger uses the information from groups of DC drift cells requiring the presence of at least 15 hits within a time window of 250 ns from the beam crossing. An event satisfying at least one of the two above conditions generates a first level trigger, T1, which is produced with minimal delay and is synchronized with the DAΦNE RF clock. The T1 signal initiates the data conversion in the front-end 1 A trigger sector collects PM signals from adjacent columns of the calorimeter, see Ref. [35] for barrel and endcaps scheme.
Page 1: Università degli studi Roma Tre Di
Page 5 and 6: Contents 1 Neutral kaon physics wit
Page 7 and 8: Introduction The KLOE experiment ha
Page 9 and 10: Chapter 1 Neutral kaon physics with
Page 11 and 12: 1.2. MASS AND DECAY MATRICES 11 Γ
Page 13 and 14: 1.4. THE QUARK-MIXING MATRIX 13 rel
Page 15 and 16: 1.4. THE QUARK-MIXING MATRIX 15 s13
Page 17 and 18: 1.5. DETERMINATION OF THE |VUS| MAT
Page 19 and 20: Chapter 2 The DAΦNE collider DAΦN
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Page 25 and 26: 3.1. THE DRIFT CHAMBER 25 Figure 3.
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Page 29 and 30: 3.2. THE CALORIMETER 29 Figure 3.6:
Page 31: 3.2. THE CALORIMETER 31 Figure 3.7:
Page 35 and 36: 3.5. FILFO FILTERING 35 are associa
Page 37 and 38: 3.6. EVENT RECONSTRUCTION 37 • ca
Page 39 and 40: 3.6. EVENT RECONSTRUCTION 39 Figure
Page 41 and 42: Chapter 4 Data Sample and K L tag M
Page 43 and 44: 4.2. THE KL TAG 43 to GEANFI using
Page 45 and 46: 4.2. THE KL TAG 45 As explained in
Page 47 and 48: 4.2. THE KL TAG 47 while the good a
Page 49 and 50: Chapter 5 Data analysis 5.1 Introdu
Page 51 and 52: 5.1. INTRODUCTION 51 10 5 10 4 10 3
Page 53 and 54: 5.3. THE CONTROL SAMPLE KL → π +
Page 71 and 72: 5.4. KL → π 0 π 0 π 0 DECAY ID
Page 77 and 78: Chapter 6 Signal selection and back
Page 79 and 80: 6.1. BACKGROUND REJECTION 79 and N
Page 81 and 82: 6.2. NUCLEAR INTERACTIONS 81 Events
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6.2. NUCLEAR INTERACTIONS 83 Figure
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6.3. KL → KS REGENERATION 85 The
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Events / 1 MeV 6.4. NUCLEAR INTERAC
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Chapter 7 Fit results and errors 7.
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7.1. FIT TO THE KL PROPER TIME DIST
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7.2. CORRECTIONS AND SYSTEMATIC ERR
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Chapter 8 Conclusions A measurement
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By summarizing, the only correlated
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Bibliography [1] K. G. Vosburgh et
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BIBLIOGRAPHY 109 [31] M. Adinolfi e
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Universit`a degli studi Roma Tre Measurement of the KL meson ...

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