Etude et impact du bruit de fond corrÃ©lÃ© pour la mesure de l'angle ...

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which is few MeV for electrons and few hundreds MeV for muons, light is emitted on a cone centered on the lepton trajectory. The typical water Cerenkov detector is composed of a huge water tank equipped with an array of phototubes mounted on its wall used to record the Cerenkov light. If the lepton stops inside the detector, the amount of Cerenkov light is used to determine the energy of the lepton, and hence of its neutrino parent. Moreover muons and electrons can be separated by the shape of their Cerenkov rings, giving in this way also the flavor of 30 the primary neutrino. 2. Neutrino physics tel-00821629, version 1 - 11 May 2013 Figure Figure 1.8: 2.8: SuperKamiokande The ⌫ e and ⌫ µ results[24]. fluxes are measured The neutrino as a function fluxes areofmeasured the zenithin bins of the zenith angle angle and✓ divided and divided with respect in two categories, to the lepton muon energy. events Black created points byrepresent a ⌫ µ interaction, and electron data, events, green histogram created by represent a ⌫ e interaction. MC expectation A further with oscillation division is hypothesis done according to the energy andof red thehistogram lepton. represent MC expectation in case of no oscillations [96]. The larger detector of this type is SuperKamiokande[24], a 50 kton water Cerenkov detector. In addition to the solar neutrinos SuperKamiokande observes atmospheric neutrinos, phase is of the order of 1, which represent the best condition to measure oscillation. separating the neutrino flux for di erent directions (see figure 1.8). The experiment counts The oscillation parameters are measured through ⌫ ⌫ e and ⌫ µ in bins of the zenith angle ✓ (cos ✓ = 1 for µ disappearance, P (⌫ the neutrinos coming µ ! from the zenith ⌫ and cos µ )=1 P (⌫ ✓ = 1 if µ ! ⌫ they x ), comparing the ⌫ come from the nadir). µ flux observed at SK with the unoscillated flux measured by a 1 kton water Cherenkov detector placed at The experimental result, first presented in about 300 m from the neutrino source. Results from K2K are reported in [32]. 20 Another important experiment is MINOS, placed in the Sudan mine, at 735 km from a neutrino pulsed beam produced at Fermilab. The neutrino energy is higher than K2K as to obtain an oscillation phase of the order of 1. Like K2K, the initial flux is measured by a near detector and compared with the flux at the far detector to observe ⌫ µ disappearance. Both near and far detectors are steel-scintillator sampling calorimeters made of alternating planes of magnetised steel and plastic scintillators. Disappearance measurements of ⌫ µ determined ✓ 23 and m 2 23 in agreement with SK [24]. The beam capability to switch between ⌫ µ to ⌫ µ allows to measure oscillation parameters in case of ⌫ µ disappearance [26]. MINOS can also detect ⌫ e interaction through compact electromagnetic showers and attempt measurement of ⌫ µ ! ⌫ e oscillation, thus ✓ 13 [23]. The Opera detector, installed at LNGS, instead of measuring oscillation parameters via ⌫ µ disappearance, is designed to explicit detect ⌫ ⌧ appearance. Direct observation of ⌫ ⌧ would confirm the interpretation of SK results in
2.4 Measuring neutrino oscillation parameters 31 Figure 2.9: Result from MINOS for ⌫ µ (left) and ⌫ µ (right) disappearance. The reconstructed neutrino energy is compared with expected spectrum in the non oscillation hypothesis and the best oscillation fit [24] [26]. The mixing angle ✓ 13 is the smallest angle of the PMNS matrix. For this reason the related oscillations have been the most di cult to observe. Direct and indirect bounds on its value were set in the past by CHOOZ [36], MINOS [23] and from the analysis of sub-leading e↵ects in the solar and atmospheric oscillation, as shown in Fig. 2.10 [91]. However, such bounds were not sensitive enough to exclude a zero value of ✓ 13 . The value of ✓ 13 become accessible just recently thanks to the new generation of reactor and accelerator experiments, which provide sensitivities to small mixing angle of about one order of magnitude better than previous limits. The Tokai to Kamioka experiment (T2K) uses a muon neutrino beam produced at the J-PARC accelerator facility, a segmented near detector with a tracking system to precisely measure the non-oscillated flux and the well known SK detector in order to directly measure the appearance of ⌫ e .The ⌫ µ beam is directed 2-3 degree away from the SK baseline of about 295 km. This o↵-axis configuration lower the neutrino flux but provide a narrow energy spectrum peaked at about 600 MeV. In summer 2011 T2K reported the observation of six ⌫ e in the SK detector, with an expected background level of 1.5±0.5 (sys.) events, providing a sigtel-00821629, version 1 - 11 May 2013 term of ⌫ µ ! ⌫ ⌧ oscillation. The ⌫ µ beam, with a mean energy of about 17 GeV, is produced from a pulsed proton beam at the CERN SPS, about 730 km from Gran Sasso. The ⌧ lepton produced by ⌫ ⌧ charged current interaction is detected through the topology of its decay in nuclear emulsion films. The expected signal statistics is not very high, 2 ⌫ ⌧ have been observed (2.1 events expected and 0.2 expected background) since data taking started in 2008 [9]. 2.4.3 Experimental determination of ✓ 13
Page 1 and 2: UNIVERSITÉ DENANTES FACULTÉ DES S
Page 3 and 4: tel-00821629, version 1 - 11 May 20
Page 5 and 6: Abstract tel-00821629, version 1 -
Page 7 and 8: Acknowledgments Since so many peopl
Page 9 and 10: Contents 1 Introduction 13 tel-0082
Page 11 and 12: CONTENTS 11 tel-00821629, version 1
Page 13 and 14: Chapter 1 Introduction tel-00821629
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Page 17 and 18: Chapter 2 Neutrino physics tel-0082
Page 19 and 20: 2.2 Neutrino history in brief 19 ma
Page 21 and 22: 2.3 Neutrino oscillation, the theor
Page 23 and 24: 2.4 Measuring neutrino oscillation
Page 25 and 26: 3-flavour oscillations The dominant
Page 29: After the Sun, the other main natur
Page 35 and 36: 2.5 The problem with the neutrino m
Page 37 and 38: 2.6 Summary and open questions 37 s
Page 39 and 40: In the next future, reactor experim
Page 41 and 42: Chapter 3 The Double Chooz experime
Page 43 and 44: 3.1 The Double Chooz detector 43 to
Page 45 and 46: 3.1 The Double Chooz detector 45 te
Page 47 and 48: 3.1 The Double Chooz detector 47 it
Page 49 and 50: 3.1 The Double Chooz detector 49 te
Page 51 and 52: 3.2 The detector read-out 51 40 m o
Page 53 and 54: 3.3 The online system 53 IV trigger
Page 55 and 56: 3.3 The online system 55 tions as s
Page 57 and 58: 3.3 The online system 57 tel-008216
Page 59 and 60: 3.4 The calibration system 59 tel-0
Page 61 and 62: loosing their kinetic energy 3 and
Page 63 and 64: 3.5 Reactor neutrino flux simulatio
Page 69 and 70: 3.8 Data reconstruction 69 A dedica
Page 71 and 72: Regarding the pulse information, th
Page 73 and 74: 3.8 Data reconstruction 73 tel-0082
Page 75 and 76: 3.8 Data reconstruction 75 Gain (ch
Page 77 and 78: 3.9 Conclusions 77 tel-00821629, ve
Page 79 and 80: Chapter 4 Measurement of ✓ 13 wit
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4.1 Data sample 81 create a signal
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4.2 ¯⌫ e signal selection 83 Liv
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4.2 ¯⌫ e signal selection 85 Pro
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4.2 ¯⌫ e signal selection 87 Neu
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4.3 Backgrounds 89 energy spectrum
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4.3 Backgrounds 91 tel-00821629, ve
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4.4 Selection e ciencies and system
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4$&14+#':"'$"$468'#21%$;' ! $"$468'
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4.4 Selection ! e ciencies and syst
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4.5 Data analysis summary 99 4.4.3
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4.6 Final fit and measurement of
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4.6 Final fit and measurement of
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4.7 Summary and Conclusions 105 tel
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Chapter 5 Correlated background tel
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5.1 Measuring correlated background
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5.2 High energy analysis 111 in a l
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5.2 High energy analysis 113 tel-00
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5.3 OV Tag analysis 115 The t cut v
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5.4 Fast Neutrons analysis 117 bigg
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5.4 Fast Neutrons analysis 119 5.4.
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5.4 Fast Neutrons analysis 121 tel-
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5.4 Fast Neutrons analysis 123 esti
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5.4 Fast Neutrons analysis 125 Corr
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5.4 Fast Neutrons analysis 129 Prom
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5.4 Fast Neutrons analysis 131 lect
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5.4 Fast Neutrons analysis 133 mari
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5.5 Stopping Muon analysis 139 5.5.
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5.5 Stopping Muon analysis 141 tel-
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5.5 Stopping Muon analysis 143 tel-
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5.5 Stopping Muon analysis 145 Sour
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5.5 Stopping Muon analysis 147 belo
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5.5 Stopping Muon analysis 149 The
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5.6 Estimation of correlated backgr
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5.7 Conclusion 157 5.7 Conclusion t
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Chapter 6 Conclusions tel-00821629,
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161 • The SM analysis could be im
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Chapter 7 Contributions to Double C
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165 from this study and from [64] f
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List of Figures tel-00821629, versi
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LIST OF FIGURES 169 tel-00821629, v
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List of Tables 3.1 Mean energy rele
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Bibliography [1] [2] tel-00821629,
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BIBLIOGRAPHY 183 [31] J.K. Ahn et a
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BIBLIOGRAPHY 185 [61] W. Hampel et
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BIBLIOGRAPHY 187 [92] A. Stueken et
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