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Precise measurement of reactor antineutrino oscillations at Daya Bay Vít Vorobel (on behalf of the Daya Bay Collaboration) Charles University in Prague HEP2007 Conference, Manchester, Jul. 19, 2007 1 The Daya Bay Collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (14)(54) BNL, Caltech, 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 ~ 150 collaborators Asia (18) (88) 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., Hong Kong Univ., Chinese Hong Kong Univ., National Taiwan Univ., National Chiao Tung Univ., National United Univ. 2 13The Last Unknown Neutrino Mixing Angle UMNSP Matrix Maki, Nakagawa, Sakata, Pontecorvo 1 0 0 cos 23 0 sin 23 U e1 U e 2 U U 1 U 2 U 1 U 2 cos13 sin 23 0 i CP cos 23 e sin 13 0 atmospheric, accelerator 23 = ~ 45° U e 3 0.8 U 3 0.4 U 3 0.4 0 ei CP sin 13 cos12 1 0 sin 12 0 cos13 0 reactor, accelerator 13 = ? U e 3 ? 0.6 0.7 0.6 0.7 0.5 sin 12 cos12 0 0 1 0 0 0 e i / 2 1 0 0 SNO, solar SK, KamLAND 12 ~ 32° 0 0 e i / 2i 0 ? • What ise fraction of 3? 23 45 • Ue3 is the gateway to CP violation in neutrino sector: P( e) - P(ˉ ˉe) sin(212)sin(223)cos2(13)sin(213)sin 3 Measuring 13 Using Reactor Anti-neutrinos Electron anti-neutrino disappearance probability 2 2 m L m 2 2 4 2 2 13 21 L cos 13 sin 212 sin Pdis sin 213 sin 4 E 4 E Small oscillation due to 13 < 2 km Large oscillation due to 12 > 50 km Osc. prob. (integrated over E) vs distance e disappearance at short baseline(~2 km): unambiguous measurement of 13 Sin2213 = 0.1 m231 = 2.5 x 10-3 eV2 Sin2212 = 0.825 m221 = 8.2 x 10-5 eV2 4 Objective of Near Term 13 Measurement Previous best experimental limit from Chooz: sin2(213) <0.17 (m231=2.510-3 eV, 90% c.f.) Build an experiment with sensitivity of 0.01 in sin2(213) Increase statistics: Use powerful reactors & large target mass Suppress background: Go deeper underground High performance veto detector to MEASURE the background Reduce systematic uncertainties: Reactor-related: Utilize near and far detectors to minimize reactor-related errors Detector-related: • Use “Identical” pairs of detectors to do relative measurement • Comprehensive program in calibration/monitoring of detectors 5 Daya Bay, China Multiple reactor cores. (at present 4 units with 11.6 GWth; in 2011, 6 units with 17.4 GWth ) Adjacent to mountains. Up to 1000 mwe overburden at the far site. 6 http://dayawane.ihep.ac.cn/ 4 x 20 tons target mass at far site Daya Bay: Powerful reactor close to mountains Far site 1615 m from Ling Ao 1985 m from Daya Overburden: 350 m Ling Ao Near site ~500 m from Ling Ao Overburden: 112 m Mid site 873 m from Ling Ao 1156 m from Daya Overburden: 208 m Ling Ao-ll NPP (under construction) 22.9 GW in 2011 Construction tunnel Filling hall entrance Daya Bay NPP, 22.9 GW Ling Ao NPP, 22.9 GW Daya Bay Near site 363 m from Daya Bay Overburden: 98 m Total length: ~3100 m7 Detection of e Inverse -decay in Gd-doped liquid scintillator: e p e n + p D + (2.2 MeV) (t~180μs) 0.3b + Gd Gd* Gd + ’s(8 MeV) (t~30μs) 50,000b Time, space and energy-tagged signal suppress background events. E Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8 MeV 8 Antineutrino Detector Cylindrical 3-Zone Structure separated by acrylic vessels: I. Target: 0.1% Gd-loaded liquid scintillator, diameter=height= 3.1 m, 20 ton II. -catcher: liquid scintillator, 42.5 cm thick III. Buffer shielding: mineral oil, 48.8 cm thick With 192 PMT’s on circumference and reflective reflectors on top and bottom: E ~ 12.2% 14% , vertex 14cm 13cm E (MeV) 9 Inverse-beta Signals Antineutrino Interaction Rate (events/day per 20 ton module) Daya Bay near site Ling Ao near site Far site Prompt Energy Signal 1 MeV 960 760 90 Ee+(“prompt”) [1,8] MeV En-cap (“delayed”) [6,10] MeV tdelayed-tprompt [0.3,200] s Delayed Energy Signal 8 MeV 6 MeV 10 MeV MC statistics corresponds to a data taking with a single module at far site in 3 years. 10 Muon “Veto” System Resistive plate chamber (RPC) Surround detectors with at least 2.5m of water, which shields the external radioactivity and cosmogenic background Water shield is divided into two optically separated regions (with reflective divider, 8” PMTs mounted at the zone boundaries), which serves as two active and independent muon tagger Augmented with a top muon tracker: RPCs Outer water shield Inner water shield Combined efficiency of tracker > 99.5% with error measured to better than 0.25% 11 Backgrounds Background = “prompt”+”delayed” signals that fake inverse-beta events Three main contributors, all can be measured: Background type Experimental Handle Muon-induced fast neutrons (prompt recoil, delayed capture) from water or rock >99.5% parent “water” muons tagged ~1/3 parent “rock” muons tagged 9Li/8He (T1/2= 178 msec, decay w/neutron emission, delayed capture) Tag parent “showing” muons Accidental prompt and delay coincidences Single rates accurately measured Background/Signal: Fast n / signal 9Li-8He / signal Accidental/signal DYB site LA site Far site 0.1% 0.3% <0.2% 0.1% 0.2% <0.2% 0.1% 0.2% <0.1% 12 Systematic Budget Detector-related Baseline: currently achievable relative uncertainty without R&D Goal: expected relative uncertainty after R&D Swapping: can reduce relative uncertainty further Reactor-related 13 Daya Bay Sensitivity Assume backgrounds are measured to<0.2%. Use rate and spectral shape. Input relative detector systematic error of 0.2%. Milestones Fall 07 Begin civil construction June 09 Start commissioning first two detectors June 10 Begin data taking with near-far 90% confidence level 3 year of data taking 14 Daya Bay: Status and Plan • • • • Passed DOE scientific review Passed US CD-1 review Passed final nuclear safety review in China Began to receive committed project funding for 3 years from Chinese agencies Start civil construction Anticipate US CD-2/3a review Start data taking with 2 detectors at Daya Bay near hall Begin data taking with 8 detectors in final configuration Oct 06 Apr 07 Apr 07 Apr 07 Oct 07 Oct 07 May 09 Apr 10 0.04 Sensitivity C.L.) sin2sin 21322 (90% 13 • • • • 0.03 0.02 0.01 Goal: 0.01 0 1 2 3 4 Run Time Time (Years) Run (Years) 155