The Daya Bay Reactor Neutrino Experiment Lisa Whitehead Brookhaven National Laboratory for the Daya Bay Collaboration APS Meeting, Washington, D.C.
Measuring 13 at a Reactor S jk =sin jk C jk =cos jk Neutrino mixing: 1 0 0 U MNSP = 0 C 3 S 3 0 S 3 C 3 i C13 0 S 13 e 0 1 0 i S 13 e 0 C 13 C 1 S 1 0 S 1 C 1 0 0 0 1 Look for disappearance of reactor e over a baseline of ~ km where the probability is dominated by sin 13 3 1 P dis sin 13 sin 1.7 m L/ E 4 C 13 sin 1 sin 1.7 m L / E Disappearance Probability known: 3 & 1, mass differences m3 & m1; unknown: 13 and (CP-violating) log10(l/km)
Keys to a Precise Measurement high statistics identical near and far detectors (systematic uncertainties from flux and cross sections cancel) control of detector-related systematic uncertainties background suppression 3
The Daya Bay Site 17.4 GW reactor power nuclear power complex located in China ~55 km from Hong Kong Ling Ao - x.9 GW cores - more.9 GW cores by 011 Daya Bay x.9 GW cores ~e0 e /s per GW 4
The Daya Bay Site Far Site 4 x 0 ton detectors near detector sites Far site: 1985 m from Daya Bay cores 1615 m from Ling Ao cores Ling Ao Near Site x 0 ton detectors movable detectors entrance LS Hall more than one detector at each site allows side-by-side comparison shielding provided by mountain Daya Bay Near Site x 0 ton detectors Far Ling Ao Daya Bay 5
Antineutrino Detectors -catcher: 0 tons LABbased liquid scintillator Target region: 0 tons Gdloaded (0.1%) LAB-based liquid scintillator Inverse Beta Decay + e p e n PMTs: 19 8-inch PMTs around the tank, reflectors on top and bottom 5m signal is coincidence between prompt positron energy and delayed neutron capture Steel tank Acrylic vessels 5m oil buffer: 40 tons mineral oil 6
Muon Veto System a.5 m active water shield around the antineutrino detectors instrumented with 8-inch PMTs water shield divided into inner region and outer region separated by Tyvek partitions RPCs on top of the water pool combined system has muon tagging efficiency of >99.5% 7
Sensitivity sin 13 sensitivity Daya Bay's sensitivity: sin 13 < 0.01 in 3 years of running (90% C.L.) { 0.05 0.04 0.03 0.0 0.01 Region of interest for m from atmospheric experiments 0 1 3 4 5 years Source Detector Reactor Signal Statistics 0. Uncertainty 0.38% (baseline) 0.18% (goal) 0.13% 0.% 8
Status surface assembly building tunnel entrance control room 9
Status Tunneling progress as of midjanuary Inside the tunnel Daya Bay Near Hall 10
Status Test assembly Test batch of 0.1% Gd-LS in 5000 L tank Test batch of Gd-LS has been studied for almost one year now! Vehicle to transport the detectors Assembled PMT ladder 4m acrylic vessel 11
Project Schedule October 007: Ground breaking August 008: CD 3 reviews completed 010: Daya Bay Near Hall ready for data 011: Far Hall ready for data 1
The Daya Bay Collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (15)(~83) Asia (18) (~16) BNL, Caltech, Cincinnati, George Mason Univ., LBNL, Iowa State Univ., Illinois Inst. Tech., Princeton, RPI, UC-Berkeley, UCLA, Univ. of Houston, Univ. of Wisconsin, Virginia Tech., Univ. of Illinois-Urbana-Champaign IHEP, Beijing Normal Univ., Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ., Nankai Univ., Shandong Univ., Shenzhen Univ., Tsinghua Univ., USTC, Zhongshan Univ., Univ. of Hong Kong, Chinese Univ. of Hong Kong, National Taiwan Univ., National Chiao Tung Univ., National United Univ. > 00 collaborators 13
Backup Slides 14
Backgrounds 840 740 1) 9Li/8He isotopes have significant beta-neutron decay branching fractions ) Fast neutrons recoil proton gives prompt signal followed by neutron capture 3) Accidentals coincidence of neutron capture with natural radioactivity in the detector 15
Systematic Uncertainties Detectorrelated uncertainty assumptions for systematics in sensitivity calculation uncertainty reactor-related correlated % reactor-related per core % spectrum shape % detector-related correlated % detector-related per module 0.38% accidental background 100% fast neutron background 100% He/Li background 0.3% bin to bin 0.3% 16
Global Sensitivity Comparison arxiv:0907.1896 17