Search for at the Daya Bay Neutrino Experiment, Aug 14, 2009
Outline Neutrino oscillation and the search for θ 13 The Daya Bay neutrino experiment - Design of the Daya Bay detector - Systematic uncertainty control - Simulated performance - Systematic budget, sensitivity and discovery potential Summary, timeline and current status 2
E. Kearns, NuFact09 Plenary
E. Kearns, NuFact09 Plenary
E. Kearns, NuFact09 Plenary
Continue the Neutrino Exploration U P MNS = 1 0 0 0 cos θ 23 sin θ 23 0 sin θ 23 cos θ 23 atmospheric & long-baseline accelerator experiments cos θ 13 0 e iδ CP sin θ 13 0 1 0 e iδ CP sin θ 13? 0 cos θ 13 cos θ 12 sin θ 12 0 sin θ 12 cos θ 12 0 0 0 1 solar & long-baseline reactor experiments θ13 is the gateway to lepton CP-V. Its value is crucial for the planning of the next generation appearance experiments for CP Two ways to measure θ13 - Short-baseline reactor experiments: P νe ν e - Long-baseline appearance experiments: ( ) P νµ ν e = sin θ 31 23 sin 2θ 13 31 al ( ) m =1 sin 2 2θ 13 sin 2 2 31 L 4E sin( 31 al)e i( 32+δ CP ) + cos θ 23 sin 2θ 12 ( 21 al ) sin(al) 2 6
Direct Search Limits on θ 13 Boehm et al PRD62 072002 Direct Search: sin 2 2θ 13 <0.17 @ 90% C.L. 7
The Daya Bay Neutrino Experiment 2 near-sites + 1 far-site 8 identical 20 t detectors To reach ~0.01 in sin22θ13 Far Ling Ao near Water hall The Daya Bay Site, Southern China Depth DYB Site 98 m LA Site 112 m Far Site 350 m Construction tunnel Ling Ao II cores Ling Ao cores LS hall Entrance Daya Bay near Daya Bay cores 8
The Daya Bay Collaboration Asia America Europe Total 17 institutions 14 institutions 3 institutions ~200 collaborators 9
How to Achieve High Sensitivity? Increase statistics - powerful sources, large detectors, high detection efficiency Strengthen the signal - optimize the baselines Reduce systematic uncertainties - reactor related: using near-far detector arrangement - detector related: using identical detectors Suppress backgrounds - go deeper underground - both passive and active veto systems 10
The Detection Technique 0.1% Gd doped liquid scintillator as target ν e + p e + + n 50,000b 0.3b n + p D + γ(2.2 MeV) E νe E e + + m n m p n + Gd Gd Gd + γ( 8 MeV) Delayed 8 MeV signal background suppression well-defined target zone 11
Baselines of the Daya Bay Experiment P νe ν x = sin 2 2θ 13 sin 2 ( m 2 31 L 4E Assume sin 2 2θ 13 =0.1 ) ( ) m + cos 4 θ 13 sin 2 2θ 12 sin 2 2 21 L 4E DYB Site (m) Baselines LA Site (m) Far Site (m) DYB 363 1347 1985 LA 857 481 1618 LA II 1307 526 1613 near sites far site Expected number of IBD events IBD Evts (/day/det) DYB Site LA Site Far Site 840 760 90 12
The Design of the Detectors Calibration Boxes Overflow Reflector PMT Radial Shield Stainless Tank Mineral Oil Outer AV & LS Inner AV & Gd doped LS 3-zone design: Gd-LS, LS & mineral oil 20 t target mass: 0.1% Gd doped LS 192 PMTs+ top/bottom reflectors submerged in water Cherenkov/RPC veto 13
Detector Systematic Uncertainty Control Some examples: Acrylic vessels and liquid scintillator - manufactured and filled in pairs from a common storage tank Target mass - load cells to measure the target mass to 0.1% - flow meter during filling 0.1% - overflow tank liquid level monitoring with ultrasonic devices Energy calibration to reach uncertainty 1%~2% - automated calibration: 68 Ge(positron), 60 Co + 241 Am- 13 C(neutron) & LED - being practiced on the prototype: 133 Ba(0.356 MeV), 137 Cs(0.662 MeV), 60 Co(1.17+1.33 MeV), 22 Na(1.022+1.275 MeV), Pu-C(6.13 MeV), 252 Cf(neutron) 14
Precision Target Mass Control and Monitoring Gd-LS and LS filling are measured with loadcells and Coriolis flowmeter: precision <0.02%; During running: 3 independent systems to monitor overflow levels <0.05% Center GdLS/LS overflow to control target mass uncertainty LS calibration port Ultrasonic liquid surface sensor (uncertainty < 0.01%) Capacitance liquid level sensor Off-center GdLS/LS calibration port CCD cameras to monitor the liquid level. Cross check the central overflow monitoring system 15
Production and Evaluation of Liquid Scintillator Daya Bay uses LAB, which is compatible with acrylic. Two main challenges: - dissolve inorganic Gd into organic LS. - keep it stable (lessons from Chooz and Palo Verde). 16
The Detector Simulation Baseline GEANT4 model of the antineutrino detector: - Geometry: an idealized 3-zone detector plus top and bottom reflectors. - Material properties: based on past knowledge, current R&D programs and the IHEP prototype. - For details, hep-ex/0701029. Effects of the realistic designs such as ribs, overflow/calibration tubes, etc are simulated separately. 17
Detector Performance from Simulation Detection efficiencies: - 1 MeV cut for prompt positrons: >99%, uncertainty negligible. - 6 MeV cut for delayed neutrons: 91.5%, uncertainty 0.22% assuming 1% energy uncertainty. Energy resolution: ~12%/ E e + vertex resolution: ~13 cm Events 350 300 250 200 150 vertex res: ~13 cm Entries Mean RMS 4833 12.89 7.000 Resolution (%) 12 10 8 6 Energy res: ~12%/ E 16.69 / 7 P1 11.62 Arbitrary Units 400 350 300 250 200 150 100 50 4000 3500 3000 2500 2000 1500 1000 500 0 0 1 2 3 4 5 6 7 8 9 10 True Energy Geant Energy Reconstructed Energy 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Positron Energy Spectrum (MeV) 100 4 50 0 0 20 40 60!r (cm) 2 0 2 4 6 8 Energy (MeV) 18
The Systematic Summary Detector Uncertainty Sources Baseline Goal Number of protons 0.3% 0.1% Energy cut 0.2% 0.1% H/Gd ratio 0.1% 0.1% Detector Efficiency Time cut 0.1% 0.03% Neutron Multiplicity 0.05% 0.05% Trigger 0.01% 0.01% Live time <0.01% <0.01% Total uncertainty 0.38% 0.18% 19
Modeling the Experiment in Computer χ 2 = min γ + α2 c σ 2 c 8 A=1 + r N bins i=1 α 2 r σ 2 r [ M A i + N bins i=1 T A i β 2 i σ 2 shp ( 1+αc + r ωa r α r + β i + ε D + ε A d + ε2 D σ 2 D + A=1 ) η A f F A i η A n N A i η A s S A i Ti A +(σ b2b Ti A)2 8 ) ( ε A 2 ( ) d η A 2 ( ) f η A 2 ( + + n η A + s σ d σ A f σ A n σ A s ) 2 ] 2 Mi A,Ti A : measured and expected numbers of events ωr A : reactor weight factors due to different baselines α, β, ε, η: nuisance parameters Fi A, Ni A, Si A : accidental, fast neutron and 8 He/ 9 Li backgrounds Minimizing the chi-square with respect to the nuisance parameters, we are able to predict the Daya Bay sensitivity. 20
Sensitivity Calculation Inputs (Baseline) Uncertainty Description Value σc The correlated reactor uncertainty 2.0% Reactor Related σr The uncorrelated reactor uncertainty 2.0% σshp The shape uncertainty of the neutrino spectra 2.0% σd Correlated detector uncertainty 2.0% Detector Related σd Uncorrelated detector uncertainty 0.38% σb2b Bin-to-bin uncertainty 0.3% Site Related σf, σn, σs Background uncertainty 0.3% 21
The Daya Bay Sensitivity "m 2 ( 10-3 ev 2 ) 5 4.5 4 3.5 Chooz Daya Bay 3 y Sensitivity at 90% C.L. Δm 312 =2.5 10-3 ev 2 3 2.5 2 1.5 1 0.5 10-2 10-1 sin 2 2! 13 22
Daya Bay Discovery Potential Another Global Analysis Fogli et al, arxiv: 0806.2649 "m 2 ( 10-3 ev 2 ) 5 4.5 4 3.5 Daya Bay 3# Atm & LBL & CHOOZ Solar & KamLAND 3 2.5 ALL! oscillation data 2 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 sin 2 " 13 1.5 1 0.5 10-2 10-1 sin 2 2! 13 23
Summary and Schedule The Daya Bay neutrino experiment deploys 8 identical antineutrino detectors to cancel out the correlated systematic uncertainties With the current technique and ongoing R&D, the Daya Bay neutrino experiment will reach a sensitivity of ~0.01 to sin 2 2θ 13 with 3 years of data taking Daya Bay is currently assembling the first detector A dry run of the first detector is scheduled for December 2009; The first pair detectors will be installed at the Daya Bay near site in Spring 2010; Data taking with the first pair will begin in Summer 2010 In the Summer of 2011 all 8 detectors will begin data taking 24
θ 13 in Coming Years P. Huber et al, arxiv:0907.1896