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David E. Jaffe

The last unknown neutrino mixing angle  13 and the Daya Bay Experiment. David E. Jaffe. Motivation Antineutrino source Detector Systematics Sensitivity Status & summary. Neutrino Mixing. Inverted hierarchy. Normal hierarchy. m 3 2. m 2 2.  m 2 32. m 1 2. m 2 2.  m 2 21.

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David E. Jaffe

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  1. The last unknown neutrino mixing angle 13 and the Daya Bay Experiment David E. Jaffe Motivation Antineutrino source Detector Systematics Sensitivity Status & summary David E. Jaffe

  2. Neutrino Mixing Inverted hierarchy Normal hierarchy m32 m22 m232 m12 m22 m221 m32 m12 • For three generations of massive neutrinos, the weak eigenstates are • not the same as the mass eigenstates: Pontecorvo-Maki- Nakagawa-Sakata Matrix • Parametrize the PMNS matrix as: Majorana phases solarnreactornatmosphericnneutrinoless reactornaccelerator LBL n accelerator LBL n double- decay Six parameters: 2 m2, 3 angles, 1 phase+ 2 Majorana phases David E. Jaffe

  3. Evidence for neutrino oscillations Unconfirmed: LSND: Dm2 ~ 0.1-10 eV2 Dm2(eV2) |m232|=(2.4+0.4-0.3)  10-3 eV2 23 =(45-11) m221 =(7.8+0.6-0.5)  10-5 eV2 12 =(32+4-3) Dm231Dm232 >> Dm221 q12andq23are large q13 is small, d and sign of Dm232 unknown sin22q 2 flavor oscillation in vacuum: P(n1->n2) = sin22qsin2(1.27Dm2L/E) Units: Dm2(eV2) L(m) E(MeV) David E. Jaffe

  4. Current Knowledge of 13 At m231 = 2.5  103 eV2, sin22 < 0.17 sin2213 < 0.11 (90% CL) sin2213 = 0.04 Best fit value of m232 = 2.4  103 eV2 Global fit Direct search allowed region Fogli etal., hep-ph/0506083 David E. Jaffe

  5. Determining13 absorber decay pipe detector p target horn + + + Method 1: Accelerator Experiments •   eappearance experiment • need other mixing parameters to extract 13 • baseline O(100-1000 km), matter effects present • expensive Disagreement between appearance and disappearance experiments would be more evidence of new physics Method 2: Reactor Experiments • e  X disappearance experiment • baseline O(1 km), no matter effect, no ambiguity • • relatively cheap David E. Jaffe

  6. Reactore • Fission processes in nuclear reactors produce huge number of low-energy : 1 GWthermal generates 2 × 1020 per sec Change of fuel composition leads to time-dependent energy spectrum of e/MeV/fisson Resultant spectrum known to ~1% David E. Jaffe

  7. Detecting  in liquid scintillator:Inverse  Decay From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator: 0.3b  + p  D + (2.2 MeV) (t~180μs) • + Gd  Gd*  Gd + ’s(8 MeV) (t~30μs) 50,000b • Time- and energy-tagged signal is a good • tool to suppress background events. • Energy of eis given by: E Te+ + Tn + (mn - mp) + m e+  Te+ + 1.8 MeV 10-40 keV David E. Jaffe

  8. Summary of Chooz P = 8.4 GWth L = 1.05 km ~3000 ecandidates (included 10% bkg) in 335 days D = 300 mwe 5-ton 0.1% Gd-loaded liquid scintillator to detect At m231 = 2.5  103 eV2, sin22 < 0.17 @ 90%CL Systematic uncertainties Rate: ~5 evts/day/ton (full power) including 0.2-0.4 bkg/day/ton David E. Jaffe

  9. How To Reach A Precision of 0.01 in sin22q13? • Increase statistics: • Use more powerful nuclear reactors • Utilize larger target mass • Suppress background: • Go deeper underground to gain overburden for reducing cosmogenic background • Reduce systematic uncertainties: • Reactor-related: • Optimize baseline for best sensitivity and smaller residual reactor-related errors • Use near and far detectors to minimize reactor-related errors • Detector-related: • Use “Identical” pairs of detectors to do relative measurement • Comprehensive program in calibration/monitoring of detectors • Interchange near and far detectors (optional) David E. Jaffe

  10. The Daya Bay Nuclear Power Facilities 45 km 55 km Ling Ao II NPP: 2  2.9 GWth Ready by 2010-2011 Ling Ao NPP: 22.9 GWth 1 GWth generates 2 × 1020eper sec • 12th most powerful in the world (11.6 GW) • Top five most powerful by 2011 (17.4 GW) • Adjacent to mountain, easy to construct • tunnels to reach underground labs with • sufficient overburden to suppress cosmic rays Daya Bay NPP: 22.9 GWth David E. Jaffe

  11. Where To Place The Detectors ? Rate and spectral distortion for sin22q13=0.01 Prompt energy – 2me (MeV) • Since reactor eare low-energy, it is a disappearance experiment: Small-amplitude oscillation due to 13integrated over E Large-amplitude oscillation due to 12 • Place near detector(s) close to • reactor(s) to measure raw flux • and spectrum of e, reducing • reactor-related systematic • Position a far detector near • the first oscillation maximum • to get the highest sensitivity, • and also be less affected by 12 Sin22q13 = 0.1 Dm231 = 2.5 x 10-3 eV2 Sin22q12 = 0.825 Dm221 = 8.2 x 10-5 eV2 far detector near detector David E. Jaffe

  12. Empty detectors: moved to underground halls through access tunnel. Filled detectors: transported between underground halls via horizontal tunnels. Mid site 873 m from Ling Ao 1156 m from Daya Overburden: 208 m Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m Daya Bay Near site 363 m from Daya Bay Overburden: 98 m 4 x 20 tons target mass at far site 900 m Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m Ling Ao-ll NPP (under construction) 465 m Construction tunnel 810 m Ling Ao NPP Filling hall entrance 295 m • Antineutrino • detector deployment Daya Bay NPP Total length: ~3100 m David E. Jaffe

  13. Antineutrino Detector Design 20 t Gd-LS 12.2% 13cm LS oil Oil buffer thickness Isotopes (Rate from PMT glass) Purity (ppb) 20cm (Hz) 25cm (Hz) 30cm (Hz) 40cm (Hz) 92% 238U(>1MeV) 40 2.2 1.6 1.1 0.6 g Catcher thickness 232Th(>1MeV) 40 1.0 0.7 0.6 0.3 40K(>1MeV) 25 4.5 3.3 2.3 1.2 Total 7.7 5.6 4.0 2.1 A 45cm buffer provides ~20cm of shielding against PMT glass g-catcher thickness (cm) Cylindrical(5m diam., 5m height) three-ZoneStructure: I. Target: 0.1% Gd-loaded liquid scint., 1.6m II. g-catcher: liquid scintillator(LS), 45cm III.Buffer: mineral oil, ~45cm 1cm thick transparent acrylic vessels With 224 PMT’s on circumference and diffuse reflector on top and bottom: David E. Jaffe

  14. Baselines (meters) David E. Jaffe Hydrogen capture Gd capture

  15. Shield and veto system • Surround detectors with at • least 2.5m of active water shield • Water shield also serves as a • Cherenkov counter for tagging • muons • Water Cherenkov modules • along the walls and floor • Augmented with a muon • tracker: RPCs • Combined efficiency of Cherenkov • and tracker > 99.5% with error • measured to better than 0.25% David E. Jaffe

  16. Fast neutrons (prompt recoil, delayed capture) 9Li/8He (T1/2= 178 msec, b decay w/neutron emission, delayed capture) Accidental coincidences Backgrounds Assuming 99.5% muon veto, even with delayed coincidence event signature, the following backgrounds remain: (Other smaller contributions can be neglected) All three are small (Bkgd/signal <1%) and can be measured and/or constrained using data. David E. Jaffe

  17. Cosmic Muons Fast neutrons and 9Li/8He are produced by cosmic muons, so we need to simulate muons David E. Jaffe

  18. Cosmic Muons Detailed topo map, modified Gaisser formula, and MUSIC David E. Jaffe

  19. Fast Neutrons I II n n m m David E. Jaffe

  20. Fast Neutron Simulations David E. Jaffe

  21. Fast Neutron Simulations Rates per day per 20T module David E. Jaffe

  22. Cosmogenically produced 9Li/8He 9Li → e- + ne + 9Be* → 8Be +n Q=13 MeV T1/2= 178 msec (Long T1/2 & poor spatial correlation with m track make rejection problematic.) Rates computed from CERN measurements (Hagner et al.,) Note: Background/Signal ~ 0.3% for all sites Strategy: measure rate and statistically subtract from event sample. David E. Jaffe

  23. Measuring 9Li/8He < 0.3% background 4 near detectors n signal 9Li Can measure time of e+ candidate since time of muon passage through antineutrino detector for candidate events: Projected results: s(B/S) = 0.3% (near), 0.1%(far) David E. Jaffe

  24. Photon energy spectrum of radioactive background Mainly 238U, 232Th, & 40K Energy (kev) 2678 keV Measured energy spectrum in Aberdeen tunnel (Hong Kong). Site has similar rock composition as Daya Bay. David E. Jaffe

  25. Background Summary sin22q13=0.01 • B/S ~ same for near and far sites • constrained by measurements to required precision • input to sensitivity calculations • (assume 100% uncertainty) David E. Jaffe

  26. Systematic Uncertainties Two types: • Reactor-related • Detector-related David E. Jaffe

  27. Reactor Uncertainties • Power levels of each reactor core - thermal power measurements: 2% correlated, 2% uncorrelated errors • Non-trivial arrangement of reactor cores • Relative location of each reactor core and each detector (i.e. baseline) David E. Jaffe

  28. Reactor Power Measurements Coolant flow rate, steam enthalpy, temperatures Z. Djurcic, U. Alabama, KamLAND (Note CHOOZ and Palo Verde quote 0.6% and 0.7% absolute power uncertainty.) There is great (financial) interest in reactor power measurements for the power company Future studies with DB NPP collaborators will determine the level of precision we can achieve for the DB reactors. David E. Jaffe

  29. Cancellation of Fluctuations in Reactor Power FAR 1600m 1600m NEAR1 NEAR2 350 m 350 m NEAR1 + NEAR2 FAR FAR Hypothetical Example #1 Note that FAR and NEAR1+NEAR2 sample all 4 reactors with equal weight →“Perfect” cancellation in ratio combination : David E. Jaffe

  30. Cancellation of Fluctuation in Reactor Power Hypothetical Example #2 FAR Near2 cores oversampled, define a ~ (1600/2000)2 1600m 2000m NEAR1 NEAR2 350 m 350 m “Perfect” cancellation in ratio combination: NEAR1 + NEAR2 a FAR FAR David E. Jaffe

  31. More Generally: L1f L2f Exactly cancels relative power deviations L21 L12 L22 L11 For Daya Bay, 4 cores a = 0.34 David E. Jaffe

  32. Cancellation of Fluctuation in Reactor Power FAR Daya-Bay Design Ling-Ao cores oversampled, aprovides partial cancellation 1613m 1618m LA DB 1985m 526 m 481 m 363 m Factor 20 cancellation in ratio combination: DB + LA a FAR FAR David E. Jaffe

  33. Cancellation of Fluctuation in Reactor Power • Symmetric case  perfect cancellation • Realistic case  adjust weight of near sites • 4 cores: Factor 50 cancellation: 2%  0.035% • 6 cores: Factor 20 cancellation: 2%  0.1% • Can preserve cancellation under swapping David E. Jaffe

  34. Reactor Uncertainties We estimate that relative locations of detectors and cores can be determined to 30 cm. David E. Jaffe

  35. Controlling Detector Systematics • Careful fabrication, measurements of vessels • Fill modules in pairs from common scintillator tank with common precision instrumentation, then split the pairs and deploy 1 module at a near site and 1 module at far site to provide cancellation of LS differences. • Calibrate and monitor status of each module. • Swap detectors between near and far site (option) David E. Jaffe

  36. Measuring Acrylic Vessels • Survey walls using many “targets” before filling • <0.1mm → 0.01% volume measurement • Goal is 0.1% volume uncertainty when vessel is full David E. Jaffe

  37. Filling Procedure • Fill pair of detectors from a single tank of Gd-LS ( deploy one detector at near site and one detector at far site, thus no chemical differences between near and far sites) • Use high precision flow devices flowmeters (0.02% repeatable) mass flow meters (0.1% repeatable) • Load cell measurements of filling tank David E. Jaffe

  38. Calibration/Monitoring Scheme • Initial commissioning of detector module: • complete characterization of detector properties • After moving/swapping module or if a significant change occurs: - simplified procedure to assess condition and decide whether commissioning procedure is necessary • Routine monitoring of detector modules: - weekly or daily procedure - automated system David E. Jaffe

  39. Routine Monitoring Goals • Establish 8 MeV energy scale → neutron efficiency (~0.1%) • Determine 1 MeV threshold energy → positron efficiency (~0.02%) • Monitor different scintillator regions • Overall detector health and status - optical attenuation - scintillation yield - reflectivity, transmission of surfaces - dead PMT’s • Provide input to corrections → All detectors should have “identical”, “constant” response David E. Jaffe

  40. Basic Requirements • Identicalradioactive sources → energy stability = “perfect” • >10,000 counts per measurement → energy precision of ~0.1% • Automatic insertion and removal of several sources, 1 MeV < E < 10 MeV. • Source deployment • Outer radius of target region • Central axis • Gamma catcher region Fixed point source measurements combined with uniform cosmogenic data to realize high precision over complete central region of detector module. David E. Jaffe

  41. Source selection • 68Ge (T1/2=271 days) EC → 68Ga (T1/2=68 min), b+, Q=2.921 MeV → 2 x 0.511 MeV g‘s, Etotal=1.022 MeV (e+ threshold!) • 60Co (T1/2=5.3 yrs) →2 g’s, Etotal = 2.505 MeV • 252Cf (T1/2=2.6 yrs) Fission → ~4 x 2 MeV neutrons (neutron efficiency) David E. Jaffe

  42. Comparison of estimated cosmogenic data and signal rates Notes: - ~1000 events needed to monitor 8 MeV energy to 0.1% - Uniform distribution in detector David E. Jaffe

  43. Summary and comparison of detector-related systematic uncertainties →    → → David E. Jaffe

  44. H/C ratio options • Combustion analysis (<0.3%?) • Neutron capture/scattering (needs R&D) • Filling detector pairs from common batch 40 Ton Mixing tank No difference in H/C between Far and Near sites Far Near David E. Jaffe

  45. Neutron Efficiency I.) Tagged n source at center (252Cf or AmBe) → direct measurement(>106 events) II.) Measure components of neutron detection efficiency en Time cuts H/Gd Energy cut David E. Jaffe

  46. Gd fraction Thermal neutron capture rate: • N(t) = N0 exp(- Gt); t > 10 msec • → Measure G to <1% for each module during • commissioning (need ~105 captures) • G(meas.) –GH → GGd → dPGd < 0.1% David E. Jaffe

  47. Neutron time cuts N(t) t 0.3ms 200ms These cut times must be the same to ~10ns for all modules → use common clock → 0.05% contribution to neutron efficiency David E. Jaffe

  48. Energy cut and 2- or 3-zone detector 3-ZONE 2-ZONE cut cut • 2-zones implies simpler design/construction, some cost reduction but with increased risk to systematic effects (neutron e and E spectrum) • 3-zones provides increased confidence in systematic uncert. associated with detection efficiency and fiducial volume, but smaller volume n capture on Gd yields 8 MeV with 3-4 g’s(2.2MeV g from n capture on H not shown) Uncertainty ~ 0.2% Uncertainty ~ 0.4% 40 ton 20 ton • 4 MeV cut can reduce the error by x2, but residual radioactivity in LS volume does not allow us to do so David E. Jaffe

  49. Uniform response of 3zone detector Outer(1.6m) Inner(1.6m) Outer-15cm Simulated response as a function of radial location of a 1 MeV e- energy deposit. The mineral oil volume is removed and the PMTs are directly outside the g-catcher. David E. Jaffe

  50. Systematics Summary • Reactor-related systematics ~0.1% • Detector-related systematics ~0.38%/module - could be reduced to 0.18% or lower (R&D) - requires care in construction, assembly, calibration, and monitoring David E. Jaffe

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