Design Considerations for a 13 Reactor Neutrino Experiment

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

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 Karsten Heeger Beijing, January 18, 2003

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

Chooz Systematics theor. Ref: Apollonio et al. , hep-ex/0301017 neutron capture: lowest efficiency, largest relative error Absolute measurements are difficult! Karsten Heeger Beijing, January 18, 2003 kinetic energy spectrum 2. 1% detector response 1. 7% total 2. 7%

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

Baseline Karsten Heeger Beijing, January 18, 2003

Diablo Canyon - An Example 1500 ft 2 underground detectors nuclear reactor • Powerful (two reactors 3. 1+ 3. 1 GW Eth) • Overburden (up to 700 mwe) • Infrastructure (roads, controlled access) Karsten Heeger Beijing, January 18, 2003

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 2 -3 underground scintillator detectors, 50 -100 t study relative rate difference and spectral distortions 2 0. 01 -0. 02 Karstencted Heegersensitivity: sin 2 13 Beijing, January 18, 2003 proje coincidence signal prompt e+ annihilation delayed n capture (in s)

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

Detector Baseline • Detector baselines sensitive to matm 2. • Tunnel (1 -2 km) + fixed detector (0. 4 km) preserves option to adjust/optimize baseline Near detector Normalizes flux for rate analysis. 0. 4 km 1 -2 km nuclear reactor Far detectors < 1 km Range of distance useful for shape analysis, more robust to matm 2. Adjustable Baseline • to maximize oscillation sensitivity • to demonstrate oscillation effect Karsten Heeger Beijing, January 18, 2003

Detector Locations Karsten Heeger Beijing, January 18, 2003

Flux Systematics with Multiple Reactor Cores flux at detector from reactors A and B Indivual reactor flux contributions. Neutrino and systematics cancel Iexactly if Condition I: 1/r 2 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 flux error (1%) Reactor core separation (100 m) Finite detector length (10 m) Relative Error Between Detector 1 and 2 rate shape < 0. 3% < 0. 01% < 0. 14% < 0. 1% < 0. 2% < 0. 1% Shape analysis largely insensitive to flux systematics. Distortions are robust signature of oscillations. Karsten Heeger Beijing, January 18, 2003

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

Detector Size and Volume Karsten Heeger Beijing, January 18, 2003

Detector Size Detector Event Rate/Year Statistical Error ~250, 000 ~60, 000 stat ~ 0. 5% for L = 300 t-yr ~10, 000 Nominal data taking: 3 years (? ) Interaction rate: 300 /yr/ton at 1. 8 km Fiducial volume > 30 ton at 1. 8 km Muon Flux and Deadtime Muon veto requirements increase with volume. Perhaps we want 2 x 25 t detectors? Karsten Heeger Beijing, January 18, 2003

Detector Shape and Experimental Layout Karsten Heeger Beijing, January 18, 2003

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 Karsten Heeger Beijing, January 18, 2003

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

Tunnel and Detector Halls Karsten Heeger Beijing, January 18, 2003

Tunnel Cross-Section 6 m Karsten Heeger Beijing, January 18, 2003

Detector Concept muo acry lic v n ve 5 m ess el liqui d sc buff er o il to intill ator 1. 6 m Movable Detectors • allow relative efficiency calibration • allow background calibration in same environment (overburden) • simplify logistics (construction off-site) Karsten Heeger Beijing, January 18, 2003 passive shield

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

Depth and Overburden Karsten Heeger Beijing, January 18, 2003

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 Karsten Heeger Beijing, January 18, 2003 bkgd depth (mwe) 10% < 5% < 2% < 1% 300 > 400 > 560 > 730

Muon-Induced Production of Radioactive Isotopes in LS - +, EC Karsten Heeger Isotope T 1/2 Emax (Me. V) Type 12 B 0. 02 s 13. 4 Uncorrelated 11 Be 13. 80 s 11. 5 Uncorrelated 11 Li 0. 09 s 20. 8 Correlated 9 Li 0. 18 s 13. 6 8 Li 0. 84 s 16. 0 8 He 0. 12 s 10. 6 6 He 0. 81 s 3. 5 Uncorrelated 11 C 20. 38 m 0. 96 uncorrelated: Uncorrelated 10 C 19. 30 s 1. 9 Uncorrelated 9 C 0. 13 s 16. 0 Uncorrelated 8 B 0. 77 s 13. 7 Uncorrelated 7 Be 53. 3 d 0. 48 Uncorrelated: Correlated -n cascade, ~few 100 ms. Only 8 He, 9 Li, 11 Li (instable Uncorrelated isotopes). Correlated single rate dominated by 11 C rejection through muon tracking and depth Beijing, January 18, 2003

Neutron Production in Rock A. da Silva Ph. D thesis, UCB 1996 Karsten Heeger Beijing, January 18, 2003

Overburden and Muon Flux 300 mwe 700 mwe Overburden FAR I @ 1. 8 km/ ~700 mwe FAR I @ 1 km/ ~300 mwe NEAR @ 400 m/ < 100 mwe Karsten Heeger Beijing, January 18, 2003

Muon Veto and Efficiency Karsten Heeger Beijing, January 18, 2003

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

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

Muon Veto and Efficiency Chooz have 98% (? ) > 99. 5% possible (? ) event candidates reactor on 2991 reactor off 287 Chooz has 9. 5% irreducible background, presumably due to spallation backgrounds. Improvement in muon veto can reduce backgrounds. Karsten Heeger Beijing, January 18, 2003 bkgd muon veto efficiency 10% 2% < 0. 5% 98% 99. 5% 99. 9%

Calibrations Karsten Heeger Beijing, January 18, 2003

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 Karsten Heeger Beijing, January 18, 2003

Calibration Systems (I): Inner Liquid Scintillator Inner Deployment System • 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 Karsten Heeger Beijing, January 18, 2003 Kevlar

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 Karsten Heeger Beijing, January 18, 2003

Fiducial Volume Weight sensor Inner Detector • 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) Karsten Heeger Beijing, January 18, 2003 Kevlar

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

Statistics and Systematics ~250, 000 ~60, 000 ~10, 000 Nobs/Nno-osc Detector Event Rate/Year Positron Energy (Me. V) Statistical error: stat ~ 0. 5% for L = 300 t-yr Reactor Flux • near/far ratio, choice of detector location Detector Efficiency • near and far detector of same design • calibrate relative detector efficiency Target Volume & • no fiducial volume cut Backgrounds Karsten Heeger • external active and passive shielding Beijing, January 18, 2003 Total Systematics flux < 0. 2% rel eff ≤ 1% target ~ 0. 3% acc < 0. 5% n bkgd < 1% syst ~ 1 -1. 5%

Karsten Heeger Beijing, January 18, 2003