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Measuring sin 2 2 q 13 with the Daya Bay nuclear power reactors

Measuring sin 2 2 q 13 with the Daya Bay nuclear power reactors. Yifang Wang Institute of High Energy Physics. Neutrinos. Basic building blocks of matter ： Tiny mass, neutral, almost no interaction with matter, very difficult to detect.

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Measuring sin 2 2 q 13 with the Daya Bay nuclear power reactors

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  1. Measuring sin22q13 with the Daya Bay nuclear power reactors Yifang Wang Institute of High Energy Physics

  2. Neutrinos • Basic building blocks of matter： • Tiny mass, neutral, almost no interaction with matter, very difficult to detect. • Enormous amount in the universe, ~ 100/cm3 , about 0.3% -1% of the total mass of the universe • Most of particle and nuclear reactions produce neutrinos: particle and nuclear decays, fission reactors, fusion sun, supernova,g-burst，cosmic-rays …… • Important in the weak interactions：P violation from left-handed neutrinos • Important to the formation of the large structure of the universe, may explain why there is no anti-matter in the universe

  3. Brief history of neutrinos 1930 Pauli postulated neutrinos 1956 Neutrinos discovered（1995 Nobel prize） 1962 μ-neutrino discovered（1988 Nobel prize ） 1957 Pontecorvo proposed neutrino oscillation 1968 solar neutrino deficit, oscillation ? （2002 Nobel prize ） 1998 atmospheric neutrino anomaly => oscillation (2002 Nobel prize） 2001 SNO:solar ne conversion => oscillation 2002 KamLAND:reactor ne deficit => oscillation Neutrino oscillation: a way to detect neutrino mass A new window for particle physics, astrophysics, and cosmology

  4. Neutrino oscillation: PMNS matrix IfMass eigenstates  Weak eigenstates Neutrino oscillation Oscillation probability： P(n1->n2)  sin2(1.27Dm2L/E) Atmospheric crossing：CP 与q13 solar bb decays EXO Genius CUORE NEMO Homestake Gallex SNO KamLAND Super-K K2K Minos T2K Daya Bay Double Chooz NOVA A total of 6 parameters: 2 Dm2, 3 angles, 1 phases + 2 Majorana phases

  5. Evidence of Neutrino Oscillations Unconfirmed: LSND: Dm2 ~ 0.1-10 eV2 Confirmed: Atmospheric: Dm2 ~ 210-3 eV2 Solar: Dm2 ~ 8 10-5 eV2 2 flavor oscillation in vacuum: P(n1->n2) = sin22qsin2(1.27Dm2L/E)

  6. A total of six n mixing parameters： Known： |D m232|, sin22q32 --Super-K D m221, sin22q21 --SNO,KamLAND Unknown：sin22q13，d, sign of Dm232 at reactors: Pee  1 sin22q13sin2 (1.27Dm213L/E)  cos4q13sin22q12sin2 (1.27Dm212L/E) at LBL accelerators: Pme ≈ sin2q23sin22q13sin2(1.27Dm223L/E) + cos2q23sin22q12sin2(1.27Dm212L/E)  A(r)cos2q13sinq13sin(d)

  7. Why at reactors • Clean signal, no cross talk with d and matter effects • Relatively cheap compare to accelerator based experiments • Can be very quick • Provides the direction to the future of neutrino physics Small-amplitude oscillation due to 13 Large-amplitude oscillation due to 12

  8. Current Knowledge of 13 Global fit fogli etal., hep-ph/0506083 Direct search PRD 62, 072002 Sin2(213) < 0.18 Sin2(213) < 0.09 Allowed region

  9. No good reason(symmetry) for sin22q13 =0 • Even if sin22q13 =0 at tree level, sin22q13 will not vanish at low energies with radiative corrections • Theoretical models predict sin22q13 ~ 0.1-10 % model prediction of sin22q13 Experimentally allowed at 3s level An experiment with a precision for sin22q13 less than 1% is desired

  10. Importance to know q13 1）A fundamental parameter 2）important to understand the relation between leptons and quarks, in order to have a grand unified theory beyond the Standard Model 3）important to understand matter-antimatter asymmetry • If sin22q13>0.01，next generation LBL experiment for CP • If sin22q13<0.01, next generation LBL experiment for CP ??? 4）provide direction to the future of the neutrino physics: super-neutrino beams or neutrino factory ?

  11. Recommendation of APS study report: 2004.11.4 APS

  12. How to do this experiment

  13. How Neutrinos are produced in reactors ? The most likely fission products have a total of 98 protons and 136 neutrons, hence on average there are 6 n which will decay to 6p, producing 6 neutrinos Neutrino flux of a commercial reactor with 3 GWthermal : 6 1020 /s

  14. Fission rate evolution with time in the Reactor Neutrino rate and spectrum depend on the fission isotopes and their fission rate

  15. Neutrino energy spectrum K. Schreckenbach et al., PLB160,325 A.A. Hahn, et al., PLB218,365 F  exp(a+bEn+cEn2) P. Vogel et al., PRD39,3378

  16. Reactor thermal power Fission rate depend on the thermal power Typically Known to ~ 1%

  17. Prediction of reactor neutrino spectrum • Three ways to obtain reactor neutrino spectrum: • Direct measurement • First principle calculation • Sum up neutrino spectra from 235U, 239Pu, 241Pu and 238U 235U, 239Pu, 241Pu from their measured b spectra 238U(10%) from calculation (10%) • They all agree well within 3%

  18. neutrino detection: Inverse-β reaction in liquid scintillator t  180 or 28 ms(0.1% Gd) n + p  d + g (2.2 MeV) n + Gd  Gd* + g (8 MeV) Neutrino Event: coincidence intime, space and energy Neutrino energy: 10-40 keV 1.8 MeV: Threshold

  19. Reactor Experiment: comparing observed/expected neutrinos: • Palo Verde • CHOOZ • KamLAND Typical precision: 3-6%

  20. How to reach 1% precision ? • Three main types of errors: reactor related(~2-3%), background related (~1-2%) and detector related(~1-2%) • Use far/near detector to cancel reactor errors • Movable detectors, near far, to cancel part of detector systematic errors • Optimize baseline to have best sensitivity and reduce reactor related errors • Sufficient shielding to reduce backgrounds • Comprehensive calibration to reduce detector systematic errors • Careful design of the detector to reduce detector systematic errors • Large detector to reduce statistical errors

  21. Systematic error comparison

  22. xperi Proposed Reactor Neutrino Experiments Krasnoyasrk, Russia Chooz, France Braidwood, USA Kashiwazaki,Japan Young Gwang, South Korea Diablo Canyon, USA Daya Bay, China Angra, Brazil

  23. Currently Proposed experiments

  24. Daya Bay nuclear power plant • 4 reactor cores, 11.6 GW • 2 more cores in 2011, 5.8 GW • Mountains near by, easy to construct a lab with enough overburden to shield cosmic-ray backgrounds

  25. DYB NPP region - Location and surrounding Convenient Transportation,Living conditions, communications 60 km

  26. Cosmic-muons at sea level: modified Gaisser formula

  27. Cosmic-muons at the laboratory

  28. Baseline optimization and site selection • Neutrino spectrum and their error • Neutrino statistical error • Reactor residual error • Estimated detector systematical error: total, bin-to-bin • Cosmic-rays induced background (rate and shape) taking into mountain shape: fast neutrons, 9Li, … • Backgrounds from rocks and PMT glass

  29. Best location for far detectors Rate only Rate + shape

  30. The Layout Far: 80 ton 1600m to LA, 1900m to DYB Overburden: 350m Muon rate: 0.04Hz/m2 • Total Tunnel length • 3200 m • Detector swapping • in a horizontal tunnel cancels most detector systematic error. Residual error ~0.2% • Backgrounds • B/S of DYB,LA ~0.5% • B/S of Far ~0.2% • Fast Measurement • DYB+Mid, 2008-2009 • Sensitivity (1 year) ~0.03 • Full Measurement • DYB+LA+Far, from 2010 • Sensitivity (3 year) <0.01 LA: 40 ton Baseline: 500m Overburden: 98m Muon rate: 0.9Hz/m2 0% slope 0% slope Mid: Baseline: ~1000m Overburden: 208m Waste transport portal 0% slope DYB: 40 ton Baseline: 360m Overburden: 97m Muon rate: 1.2Hz/m2 Access portal 8% slope

  31. Geologic survey completed, including boreholes far Faults(small) near mid Weathering bursa (风化囊） near

  32. Site investigation completed

  33. Engineering Geological Map

  34. Engineering geological sections Line A

  35. Tunnel construction • The tunnel length is about 3000m • Local railway construction company has a lot of experience (similar cross section) • Cost estimate by professionals, ~ 3K $/m • Construction time is ~ 15-24 months • A similar tunnel on site as a reference

  36. How large the detectorshould be ?

  37. Detector: Multiple modules • Multiple modules for cross check, reduce uncorrelated errors • Small modules for easy construction, moving, handing, … • Small modules for less sensitive to scintillator aging • Scalable Two modules at near sites Four modules at far site: Side-by-side cross checks

  38. Central Detector modules • Three zones modular structure: I. target: Gd-loaded scintillator II. g-ray catcher: normal scintillator III. Buffer shielding: oil • Reflection at two ends • 20t target mass, ~200 8”PMT/module sE = 5%@8MeV, ss ~ 14 cm I III II Oil buffer thickness g Catcher thickness

  39. Water Buffer & VETO • 2m water buffer to shield backgrounds from neutrons and g’s from lab walls • Cosmic-muon VETO Requirement: • Inefficiency < 0.5% • known to <0.25% • Solution: Two active vetos • active water buffer, Eff.>95% • Muon tracker, Eff. > 90% • RPC • scintillator strips • total ineff. = 10%*5% = 0.5% Neutron background vs water shielding thickness 2m water

  40. Two tracker options : • RPC outside the steel cylinder • Scintillator Strips sink into the water RPC from IHEP Scintillator Strips from Ukraine Contribution of JINR,Dubna

  41. Background related error • Need enough shielding and an active veto • How much is enough ?  error < 0.2% • Uncorrelated backgrounds: U/Th/K/Rn/neutron single gamma rate @ 0.9MeV < 50Hz single neutron rate < 1000/day 2m water + 50 cm oil shielding • Correlated backgrounds: n  Em0.75 Neutrons:>100 MWE + 2m water Y.F. Wang et al., PRD64(2001)0013012 8He/9Li: > 250 MWE(near) & >1000 MWE(far) T. Hagner et al., Astroparticle. Phys. 14(2000) 33

  42. Precision to determine the 9Li background in situ Spectrum of accidental background Fast neutron spectrum

  43. Background estimated by GEANT MC simulation

  44. Sensitivity to Sin22q13 • Reactor-related correlated error: sc ~ 2% • Reactor-related uncorrelated error: sr ~ 1-2% • Calculated neutrino spectrum shape error: sshape ~ 2% • Detector-related correlated error: sD ~ 1-2% • Detector-related uncorrelated error: sd ~ 0.5% • Background-related error: • fast neutrons: sf ~ 100%, • accidentals: sn ~ 100%, • isotopes(8Li, 9He, …) : ss ~ 50-60% • Bin-to-bin error: sb2b ~ 0.5% Many are cancelled by the near-far scheme and detector swapping

  45. Sensitivity to Sin22q13 Other physics capabilities: Supernova watch, Sterile neutrinos, …

  46. Prototype: 45 PMT for 0.6 t LS

  47. Backgrounds 60Co spectrum s=5.6% @ 2.5MeV In agreement with or better than expectation linearity Uniformity before correction

  48. Development of Gd-loaded LS LS (Gd0.1% Mesitylene 40%60% bicron mineral oil) IHEP and BNL both developed Gd-loaded LS using LAB: high light yield, high flash point, low toxicity, cheap, long attenuation length

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