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Design Considerations for a  13 Reactor Neutrino Experiment with Multiple Detectors

Design Considerations for a  13 Reactor Neutrino Experiment with Multiple Detectors. Karsten M. Heeger Lawrence Berkeley National Laboratory. Issues of Interest. Baseline Detector Locations Detector Size and Volume Detector Shape Detector Target and Detection Method

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Design Considerations for a  13 Reactor Neutrino Experiment with Multiple Detectors

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  1. Design Considerations for a 13 Reactor Neutrino Experiment with Multiple Detectors Karsten M. Heeger Lawrence Berkeley National Laboratory Beijing, January 18, 2003

  2. Issues of Interest Baseline Detector Locations Detector Size and Volume Detector Shape Detector Target and Detection Method Depth and Overburden Muon Veto and Effficiency Calibrations Beijing, January 18, 2003

  3. M. Appollonio, hep-ex/0301017 Current Knowledge of 13 from Reactors Reactor anti-neutrino measurement at 1 km at Chooz + Palo Verde:e  x Beijing, January 18, 2003

  4. theor. kinetic energy spectrum 2.1% detector response 1.7% total 2.7% neutron capture: lowest efficiency, largest relative error Chooz Systematics Ref: Apollonio et al., hep-ex/0301017 Absolute measurements are difficult! Beijing, January 18, 2003

  5. Future 13 Reactor Experiment detector 1 detector 2 Ratio of Spectra • independent of absolute reactor  flux • largely eliminate cross-section errors • relative detector calibration • rate and shape information Energy (MeV) Reactor Neutrino Measurement of 13 Present Reactor Experiments single detector (a) Flux at detector (b)  cross-section (c)  spectrum in detector Absolute Flux and Spectrum (c) (b) (a) Energy (MeV) Beijing, January 18, 2003

  6. Baseline Beijing, January 18, 2003

  7. 2 underground  detectors 1500 ft nuclear reactor • Powerful (two reactors 3.1+ 3.1 GW Eth) • Overburden (up to 700 mwe) • Infrastructure (roads, controlled access) Diablo Canyon - An Example Beijing, January 18, 2003

  8. Measuring 13 with Reactor Neutrinos atmospheric frequency dominant, sterile contribution possible Diablo Canyon 1500 ft 0.4 km 1-2 km nuclear reactor e + p  e+ + n coincidence signal prompt e+ annihilation delayed n capture (in s)  2-3 underground scintillator  detectors, 50-100 t  study relative rate difference and spectral distortions  projected sensitivity: sin2213  0.01-0.02 Beijing, January 18, 2003

  9. Ref: Huber et al. hep-ph/0303232 Optimum Baseline for a Rate Experiment reactor spectrum Survival Probability E=4 MeV Beijing, January 18, 2003

  10. Detector Baseline • Detector baselines sensitive to matm2. • Tunnel (1-2 km) + fixed detector (0.4 km) preserves option to adjust/optimize baseline • Near detector • Normalizes flux for rate analysis. • Far detectors • Range of distance useful for shape analysis, • more robust to matm2. 0.4 km 1-2 km nuclear reactor < 1 km Adjustable Baseline • to maximize oscillation sensitivity • to demonstrate oscillation effect Beijing, January 18, 2003

  11. Detector Locations Beijing, January 18, 2003

  12. Diablo Canyon, CA Flux Systematics with Multiple Reactor Cores Neutrino flux at detector I from reactors A and B Indivual reactor flux contributions and systematics cancel exactly if Condition I: 1/r2 fall-off of reactor flux the same for all detectors. Condition 2:Survival probabilities are approximately the same • Approximate flux cancellation possible at other locations Relative Error Between Detector 1 and 2 rate shape Relative flux error (1%) < 0.3% < 0.01% Reactor core separation (100 m) < 0.14% < 0.1% Finite detector length (10 m) < 0.2% < 0.1% • Shape analysis largely insensitive to flux systematics. • Distortions are robust signature of oscillations. Systematic effect due to baseline difference baseline  0.2% Beijing, January 18, 2003

  13. Tunnel with Multiple Detector Rooms and Movable Detectors ~12 m detector room 5 m low-background counting room detector room detector rooms at 2 or more distances Movable Detectors • allow relative efficiency calibration • allow background calibration in same environment (overburden) • simplify logistics (construction off-site) Beijing, January 18, 2003

  14. Detector Size and Volume Beijing, January 18, 2003

  15. Detector Size Detector Event Rate/Year Statistical Error ~250,000 ~60,000 stat ~ 0.5%forL= 300t-yr Nominal data taking: 3 years (?) Interaction rate: 300 /yr/ton at 1.8 km Fiducial volume > 30 ton at 1.8 km ~10,000 Muon Flux and Deadtime Muon veto requirements increase with volume. Perhaps we want 2 x 25 t detectors? Beijing, January 18, 2003

  16. Detector Shape and Experimental Layout Beijing, January 18, 2003

  17. Cylindrical vs Spherical? Modular? Access, Infrastructure, and Logistics movable detector in tunnel, or built in place Muon veto efficiency what is most cost effective? Backgrounds spherical symmetry easier to understand Fiducial volume and total volume Beijing, January 18, 2003

  18. Tunnel with Multiple Detector Rooms and Movable Detectors ~12 m detector room 5 m low-background counting room detector room Beijing, January 18, 2003

  19. Tunnel and Detector Halls Beijing, January 18, 2003

  20. 6 m Tunnel Cross-Section Beijing, January 18, 2003

  21. Detector Concept muon veto acrylic vessel 5 m liquid scintillator buffer oil 1.6 m passive shield Movable Detectors • allow relative efficiency calibration • allow background calibration in same environment (overburden) • simplify logistics (construction off-site) Beijing, January 18, 2003

  22. Cylindrical vs Spherical - What is more economical? sphere cylinder total fiducial Beijing, January 18, 2003

  23. Depth and Overburden Beijing, January 18, 2003

  24. Overburden Goal Background/Signal < 1% background = accidental + correlated Chooz candidate events reactor on 2991 reactor off 287 (bkgd) Minimum overburden scaling Chooz background with muon spectrum that generates spallation backgrounds bkgd depth (mwe) 10% 300 < 5% > 400 < 2% > 560 < 1% > 730 Beijing, January 18, 2003

  25. Muon-Induced Production of Radioactive Isotopes in LS correlated: -n cascade, ~few 100ms. Only 8He, 9Li, 11Li (instable isotopes). uncorrelated: single ratedominated by 11C rejection through muon tracking and depth Beijing, January 18, 2003

  26. Neutron Production in Rock A. da Silva PhD thesis, UCB 1996 Beijing, January 18, 2003

  27. 300 mwe 700 mwe Overburden FAR I @ 1.8 km/ ~700 mwe FAR I @ 1 km/ ~300 mwe NEAR @ 400 m/ < 100 mwe Overburden and Muon Flux Beijing, January 18, 2003

  28. Muon Veto and Efficiency Beijing, January 18, 2003

  29. Detector and Shielding Concept Active muon tracker + passive shielding + inner liquid scintillator detector Beijing, January 18, 2003

  30. Detector and Shielding Concept  allows you to measure fast n backgrounds   rock 3-layer muon tracker and active veto n passive shielding Beijing, January 18, 2003

  31. Muon Veto and Efficiency Chooz have 98% (?) > 99.5% possible (?) Chooz has 9.5% irreducible background, presumably due to spallation backgrounds. Improvement in muon veto can reduce backgrounds. event candidates reactor on 2991 reactor off 287 bkgd muon veto efficiency 10% 98% 2% 99.5% < 0.5% 99.9% Beijing, January 18, 2003

  32. Calibrations Beijing, January 18, 2003

  33. Relative Detector Calibration Neutrino detection efficiency in same location (under same overburden) to have same backgrounds Energy response and reconstruction of detectors can be done with movable calibration system Beijing, January 18, 2003

  34. Calibration Systems (I): Inner Liquid Scintillator Inner Deployment System Kevlar • Modeled after SNO: - Kevlar ropes and gravity used to position source • Calibrates most of inner volume • Can deploy passive and active calibration sources:  neutron laser e- (e+ ?) • Minimum amount of material introduced into the detector Beijing, January 18, 2003

  35. Calibration Systems (II): Buffer Oil Region Calibration Track Passive calibration source mounted on track. Allows calibration at fixed distance from PMT. Automatic calibration, ‘parked’ outside tank. Fixed LED’s Beijing, January 18, 2003

  36. Fiducial Volume Weight sensor Inner Detector Kevlar • Precise determination of mass of inner liquid scintillator; - fill volume (< 0.5%) - weight • Outstanding R&D Issues 1. Gd-doping? 2. Position reconstruction? 3. Scintillating buffer volume? (scintillating buffer around target to see from e+ capture and Gd decays) Beijing, January 18, 2003

  37. Need to overconstrain experiment Nothing can replace good data …. overburden critical Beijing, January 18, 2003

  38. Positron Energy (MeV) Statistics and Systematics Detector Event Rate/Year ~250,000 ~60,000 Nobs/Nno-osc ~10,000 Positron Energy (MeV) Statistical error: stat ~ 0.5%forL= 300t-yr Reactor Flux• near/far ratio, choice of detector location flux < 0.2% Detector Efficiency• near and far detector of same design • calibrate relative detector efficiency rel eff ≤ 1% target ~ 0.3% Target Volume &• no fiducial volume cut Backgrounds• external active and passive shielding acc < 0.5% nbkgd< 1% Total Systematics syst ~ 1-1.5% Beijing, January 18, 2003

  39. Beijing, January 18, 2003

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