The Daya Bay Reactor Neutrino Experiment R. D. McKeown Caltech On Behalf of the Daya Bay Collaboration CIPANP 2009

Maki – Nakagawa – Sakata Matrix Gateway to CP Violation! CP violation

3 e Survival Probability “Clean” measurements of ,  m 2 No CP violation Negligible matter effects Dominant  12 Oscillation Subdominant  13 Oscillation

4 reactor cores, 11.6 GW 2 more cores in 2011, 5.8 GW Mountains provide overburden to shield cosmic-ray backgrounds Baseline ~2km Multiple detectors → measure ratio Daya Bay Nuclear Power Plant

Daya Bay NPP Location 55 km

Total Tunnel length ~ 3000 m Experiment Layout Multiple detectors per site cross-check detector efficiency Two near sites sample flux from reactor groups 20T

Antineutrino Detector SS Tank Acrylic Vessels 20 T Gd-doped liquid scintillator 192 8” PMT’s Calibration units Gamma catcher Buffer oil 3 zone design Uniform response No position cut 12%/√ E resolution e +p → e + + n n capture on Gd (30  s delay)

Muon Veto System Water Cerenkov (2 layers) Redundant veto system → 99.5% efficient muon rejection RPC’s

Gd-Liquid Scintillator Test Production Daya Bay: production of 185 ton of 0.1 Gd-LS, 4-ton per batch test batch: production of 3.7 ton 0.1% Gd-LS 500L fluor-LAB Two 1000L 0.5% Gd- LAB 5000L 0.1% Gd-LS Production Steps 1. Produce Gd solid2. Dissolve the Gd solid in LAB and get 0.5% Gd-LAB3. Dissolve fluors in 500L LAB4. Mix 1000L 0.5% Gd-LAB, 500L fluors-LAB, and LAB, to form 0.1% Gd-LS 0.1% Gd-LS in 5000L tank Daya Bay experiment uses 200 ton 0.1% gadolinium-loaded liquid scintillator (Gd-LS). Gd-TMHA + LAB + 3g/L PPO + 15mg/L bis-MSB 4-ton test batch production in April Gd-LS will be produced in multiple batches but mixed in reservoir on-site, to ensure identical detectors. Gd-LS stability in prototype time (days) Absorption

10 Controlling Systematic Uncertainties sin 2 2  13 Measured Ratio of Rates + flow & mass measurement Detector Efficiency Ratio 0.2% Storage Tank Far Near Proton Number Ratio 0.3% Calibration systems

Target Mass Measurement filling platform with clean room ISO Gd-LS weighing tank pump stations detector load cell accuracy < 0.02% Coriolis mass flowmeters < 0.1% 20-ton, teflon-lined ISO tank Gd-LSMO LS

12 Delayed Energy Signal Prompt Energy Signal 1 MeV8 MeV 6 MeV10 MeV Efficiency & Energy Calibrations Stopped positron signal using 68 Ge source (2 x MeV)  e + threshold Neutron (n source, spallation) capture signal 2.2 MeV  e + energy scale 8 MeV  neutron threshold at 6 MeV

13 Calibration Program Routine (weekly) deployment of sources. LED light sources Radioactive sources = fixed energy Tagged cosmogenic background (free) = fixed energy and time (electronics requirement) Automated calibration system e + and neutron sources for energy calibration Monitoring system for optical properties  /E = 0.5% per pixel Requires: 1 day (near) 10 days (far)

(relative)

Rates and Backgrounds 4 near detectors signal 9 Li

Site Preparation 16 Assembly Building Portal of Tunnel Daya Bay Near Hall construction (100m underground) Tunnel lining

Hardware Progress 17 4m Acrylic Vessel Prototype SSV Prototype Calibration Units Transporter

Detector Assembly Delivery of 4m AV SS Tank delivery Clean Room

Sensitivity to Sin 2 2  13 Experiment construction: Start acquiring data: years running 90% CL, 3 years

Project Schedule October 2007: Ground breaking August 2008: CD3 review (DOE start of construction) March 2009: Surface Assembly Building occupancy Summer 2009: Daya Bay Near Hall occupancy Fall 2009: First AD complete Summer 2010: Daya Bay Near Hall ready for data Summer 2011: Far Hall ready for data (3 years of data taking to reach goal sensitivity)

21