1 Latest results from the Double Chooz experiment with near and far detectors Masaki Ishitsuka (Tokyo University of Science) On behalf of the Double Chooz Collaboration September 11 th , 2019 16 th international Conference on Topics in Astroparticle and underground physics (TAUP) Toyama, Japan
Μ Reactor neutrinos β’ Reactor is a free and rich ! π # source β’ Ξ²-decays in a commercial fission reactor core produce 10 20 Ξ½/sec $ s are detected via inverse Ξ²-decay (IBD) reaction β’ Reactor ! π # β’ Cross-section is well known β’ Prompt signal: π ' + annihilation Ξ³βs ( πΉ ) β πΉsignal + 0.8MeV ) β’ Delayed signal: β’ Total 8 MeV πΏ $ π‘ from n-Gd (well above natural radioactivity) β’ 2 MeV πΏ from n-H capture β’ Background is strongly suppressed by requiring time/space correlation Prompt signal Delayed signal Ξ³ π ' Ξ³ π # Gd ΞT p Reactor 2 n Ξ³βs from n-capture Detector
Μ 3 Precision measurement of π ;< with reactor ! π # β’ Simple two flavor oscillation formula is valid at ~1km distance FG H I π # β 1 β sin D 2π ;< sin D β’ π π # β Μ JK L β’ Direct measurement of ΞΈ 13 from energy dependent deficit (no parameter degeneracy and matter effects) ππ£π¨ π ππΎ ππ sin D 2π ;< = 0.1 D = 2.5Γ10 R< eV D βπ <;
4 CHOOZ experiment β’ CHOOZ experiment measured βReactor-ONβ β βReactor-OFFβ (= BG) spectrum at π~1km β’ Rate compared with an integrated flux measured at 15m (Bugey4: Phys. Lett. B338, 383 (1994) β’ No significant deficit observed: π = 1.01 Β± 2.8%(stat) Β± 2.7%(syst) Phys. Lett. B466, 415 (1999) Current reactor combined
Double Chooz experiment 5 Ξ½ e Near Detector Far Detector L = 400m L = 1050m 10m 3 target 10m 3 target Chooz Reactors 120m.w.e. 300m.w.e. 4.27GW th x 2 cores Since 2015 Since 2011
6 Improvements from CHOOZ β’ Stable Gd loaded liquid scintillator β Improve statistics with stable operation β’ 4 layers detector structure with buffer region to suppress background from PMT and surrounding rock β Improve background reduction β’ Experimental setup with multi-detectors β Improve systematics 4MeV 2MeV 3MeV Far Detector Near Detector
7 Double Chooz collaboration France Germany Japan Russia Spain USA Brazil CBPF APC (IN2P3) EKU Tübingen Tohoku U. INR RAS CIEMAT-Madrid Alabama U. UNICAMP CEA/IRFU: MPIK Heidelberg Tokyo Inst. Tech. RRC Kurchatov ANL SPP RWTH Aachen Tokyo Metro. U. Chicago U. SPhN TU München Tokyo U. Science Drexel U. SEDI Kitasato U. Hawaii U. SIS Kobe U. Notre Dame U. SENAC Virginia Tech. CENBG (IN2P3) LNCA (IN2P3/CEA) Subatech (IN2P3) Spokesperson: ⨠A. Cabrera (IN2P3/CNRS) Project Manager: Ch. Veyssière (CEA) 97 scientists 25 institutions (Americas, Asia, Europe) web: doublechooz.in2p3.fr
8 Double Chooz Detector From the innermost volume: β’ π -target (NT): Gd loaded liquid scintillator ( 10 m < ) β’ πΏ -catcher (GC): Liquid scintillator ( 22 m < ) β π target volume with n-H capture β’ Buffer: Mineral oil ( 110 m < ) monitored with inward facing 390 10-inch PMT β’ Inner Veto (IV): Liquid scintillator ( 90 m < ) monitored with 78 8-inch PMT + Outer Veto (OV): Plastic scintillator strips on top of the detector
Μ 9 Signal & Background IBD signal Ξ³ π # e + n-Gd capture Gd p π ~30πs n 8MeV n-H capture H π ~200πs 2.2MeV
Μ 10 Signal & Background π Accidental BG IBD signal Random coincidence of two signals Ξ³ πΏ + πΏ π # e + πΏ + n-capture n-Gd capture Gd p π ~30πs n n 8MeV 9 Li Cosmogenic BG p n-H capture Fast neutron: H π ~200πs p-recoil + n-capture πΎ + π emitter 2.2MeV ( 9 Li, π = 257ms ) : electron + n-capture
Background reduction 11 Powerful background reduction by β’ Requirement of time and spatial correlations + ANN β’ Various active vetoes FD ND Events/day 110 820 Signal to BG 11 20 β’ Cosmogenic (muon-induced) BG are dominant in final sample β’ Validity of BG reduction confirmed with reactor off data β Detection of total neutron capture
Reactor power vs. rate 12 β’ Simple setup with two reactors β’ Reactor rate modulation analysis β’ Direct measurement of background with reactor-OFF data β’ Precise measurement of ! π # yield j = (5.71 Β± 0.06)Γ10 RJ< cm D /nission π Phys.Lett. B735 (2014) 51-56
Total neutron capture detection 13 β’ Initial analyses used n-Gd capture and n-H capture separately β’ New approach to collect all neutron captures (n-Gd, n-C and n-H) β’ To improve statistics with extend effective target mass (GdT + GC) β’ To suppress systematics associated with detection (e.g. Gd-fraction)
14 Three reactor experiments in the world Double Chooz Daya Bay RENO ND: 120 m.w.e FD: 923 m.w.e ND: 1,600m 750m 400m 4.27GW th 230 m.w.e ND:291 m.w.e B2 290m B1 1,380m 1,985m 481m 750m FD: 1,146m 1,050m 300m.w.e 2.3GW th FD: ND: 255 m.w.e 360m 675m.w.e Nearly iso-flux condition: π p;Rqr β π pDRqr Reactor 2.9GW th π p;Rsr π pDRsr Detector β’ π ;< is measured by reactor experiments with <1% systematic uncertainties β’ Reactor π ;< is used as input to current and future neutrino experiments aiming for precise measurement of neutrino mixing including π uv and MH β’ Validation by multi-experiments with different systematics are important
15 Three reactor experiments in the world sin D 2π ;< = 0.1 D = 2.5Γ10 R< eV D βπ <; 4MeV 3MeV 2MeV Double Chooz Daya Bay RENO
16 Double Chooz detector layout ND DC: nearly iso-flux setup B2 β reactor flux error highly Reactor B1 suppressed with multi-detectors FD-I (single-detector phase) 481days + FD-II (multi-detectors phase) 384 days Google Earth
17 Measured spectrum arXiv:1901.09445 Near detector Far detector β’ Energy dependent deficit consistent with neutrino oscillation with π ;< β’ Clear spectral distortion especially around 5MeV β’ Impact to π ;< was evaluated β negligible impact to multi-detector analysis
18 Measured spectrum arXiv:1901.09445 ND FD β’ Energy dependent deficit consistent with neutrino oscillation with π ;< β’ Clear spectral distortion especially around 5MeV β’ Impact to π ;< was evaluated β negligible impact to multi-detector analysis
19 π ;< measurement sin D 2π ;< = 0.105 Β± 0.014(π‘π’ππ’. +π‘π§π‘π’. ) Breakdown of the uncertainties Uncertainty Single syst. Total - x Rector flux 0.0081 (7.6%) 0.0112 Detection 0.0073 (6.8%) 0.0113 Energy 0.0018 (1.7%) 0.0121 Background 0.0018 (1.7%) 0.0134 D βπ ## 0.0018 (1.7%) 0.0140 Statistics 0.0054 (5.0%) Total 0.0141 (13.3%) Reference sin D 2π ;< = 0.0856 Β± 0.0029 β’ Daya Bay PRL121, 241805 (2018) sin D 2π ;< = 0.0896 Β± 0.0067 β’ RENO PRL121, 201801(2018)
20 π ;< measurement sin D 2π ;< = 0.105 Β± 0.014(π‘π’ππ’. +π‘π§π‘π’. ) β’ Cross-check analyses including rate only and shape only fits were carried out β consistent results show robustness of π ;< measurement
21 Spectral distortion β’ Significant distortion was observed in reactor neutrino spectrum β’ Three experiments with different background compositions reported similar distortion β unlikely due to background β’ The cause is not yet understood DC, arXiv:1901.09445
22 Summary β’ Double Chooz reported π ;< measurement with multi-detectors β’ Double Chooz employed total neutron detection method to improve statistics and suppress systematic uncertainties associated with the detection including Gd-fraction β’ Uncertainties of flux prediction are largely cancelled in nearly iso-flux condition in Double Chooz β’ Significant spectral distortion was observed but we demonstrated the impact to π ;< measurement is negligible in multi-detectors analysis β’ Prospects β’ Double Chooz detectors already finished their operation but the analyses are still ongoing for the final results
23 backup
24 Reactor model: rate β’ Several past experiments reported rate observation lower than prediction (Huber-Mueller model) by ~6% β reactor anomaly Light Sterile Neutrinos: A White Paper, arXiv:1204.5379 With a new neutrino mass state
25 Reactor model: rate β’ Several past experiments reported rate observation lower than prediction (Huber-Mueller model) by ~6% β reactor anomaly β’ Data taken with different fuel-compositions indicate the deficit is in neutrinos from 235 U Daya Bay RENO PRL118, 251801 (2017) arXiv:1806.00574 (2018)
Recommend
More recommend
