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

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20 2. Neutrino physics The Fermi theory is now understood as low energy limit of a SM charged current interaction with the exchange of a W boson. In 1956 Cowan and Reines first detected antineutrino created in a nuclear reactor using the inverse -decay reaction [87]: p + ⌫ e ! n + e + (2.5) tel-00821629, version 1 - 11 May 2013 The detector was made of a tank containing 200 l water with about 40 kg of dissolved cadmium chloride, three layer of plastic scintillator and 110 5” photomultiplier tube. The positron from the inverse -decay quickly finds an electron and annihilates, rising gamma rays detectable in the scintillator. The neutron is captured by the Cadmium giving further gamma rays with a delay of about 5 µs. The second neutrino family was discovered in 1962 at Brookhaven National Laboratory [48]. A spark chamber detector was exposed to the first neutrino beam created by the decay of pions. Neutrinos were observed to create muons through charged current interaction in the detector, suggesting such neutrinos were of a di↵erent species with respect to the one observed by Cowan and Reines. When in 1975 the third family charged lepton, the ⌧, was discovered [83], it was postulated that a third type of neutrino, ⌫ ⌧ , would have to exist. The tau neutrino was finally directly observed in 2001 by the DONUT experiment at Fermilab [55]. The CERN experiments at LEP during the 1990s studied in detail the property of the W ± and Z bosons. The number of active neutrinos was precisely constrained to three families by measuring the Z decay width [10], which depends from the number of kinematically accessible decay channels: N ⌫ = inv SM ⌫ =2.9840 ± 0.0082 (2.6) where inv is the total Z with minus the measured individual contribution from charged fermions and SM ⌫ is the theoretical contribution of one neutrino flavour. It should be noted that the LEP measurement constrains only the numbers of active neutrinos, the ones for which the decay Z ! ⌫ x ⌫ x is kinematically allowed. The existence of a fourth sterile neutrino family with masses bigger than m Z /2 ' 45.5 GeV is not excluded. Within these experimental evidences, neutrinos are coupled with corresponding leptons in a flavour doublet and SM interactions conserve the lepton flavour quantum number (i.e. charged-current interactions transform the ⌫ l (⌫ l ) into the corresponding charged lepton l (antilepton l + )). Nevertheless, since the late 1960s several experiments observed some discrepancies between the number of neutrinos coming from the sun and the theoretical prediction. Such discrepancies known as the solar neutrino anomalies remained unsolved for about thirty years until being later understood
2.3 Neutrino oscillation, the theory 21 in terms of the so called neutrino oscillation mechanism. As explained with more details in the following sections, the oscillation mechanism requires the neutrino to have non-null mass and lepton flavour quantum numbers are no longer conserved. The SM is clearly not complete and requires extension to accommodate neutrino oscillation mechanism and its consequences. 2.3 Neutrino oscillation, the theory tel-00821629, version 1 - 11 May 2013 Neutrino oscillation were postulated in 1957 by Pontecorvo [86]. In analogy with K 0 $ K 0 oscillations, Pontecorvo suggested the possibility of neutrinoantineutrino oscillation ⌫ $ ⌫. When the second neutrino family where discovered, Maki, Nakagawa and Sakata proposed in 1962 the possibility of oscillation among the neutrino families introducing the concept of lepton flavour mixing [101]. The neutrino oscillation mechanism is based on the fact that if neutrino have a non-null mass, flavour states |⌫ ↵ i (interaction states) and mass states |⌫ i i (propagation states) could not coincide, in analogy to the mixing in the quark sector: |⌫ ↵ i = X i U ⇤ ↵,i|⌫ i i (2.7) where ↵ represent the flavour families (e, µ, ⌧), |⌫ i i the mass states of mass m i (with i =1, 2, 3) and U is the so called PMNS 1 unitary mixing matrix. Neutrinos are produced via weak interaction in a defined flavour eigenstate |⌫ ↵ i together with the corresponding lepton ↵. Assuming the neutrino is produced at time t = 0: |⌫(t = 0; L = 0)i = |⌫ ↵ i = X i U ⇤ ↵,i|⌫ i i (2.8) and propagates as a free particle following the Schrodinger equation, after atimet: |⌫ ↵ (t, L)i = X U↵,ie ⇤ i(E it pL) |⌫ i i (2.9) i assuming the three mass eigenstates propagate with the same momentum with relativistic energies (p ' E m): q E i = p 2 + m 2 i ' p + m2 i 2p ' E + m2 i (2.10) 2E Eq. 2.9 could be written, using natural units (c = ~ = 1), as: |⌫ ↵ (t, L)i = X i U ⇤ ↵,ie i m2 i 2E L |⌫ i i (2.11) 1 Pontecorvo-Maki-Nakagawa-Sakata matrix
Page 1 and 2: UNIVERSITÉ DENANTES FACULTÉ DES S
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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: 2.2 Neutrino history in brief 19 ma
Page 23 and 24: 2.4 Measuring neutrino oscillation
Page 25 and 26: 3-flavour oscillations The dominant
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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
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Regarding the pulse information, th
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3.8 Data reconstruction 73 tel-0082
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3.8 Data reconstruction 75 Gain (ch
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3.9 Conclusions 77 tel-00821629, ve
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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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