The Daya Bay Reactor Neutrino Experiment Jonathan Link

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The Daya Bay Reactor Neutrino Experiment Jonathan Link Virginia Tech On behalf of the

The Daya Bay Reactor Neutrino Experiment Jonathan Link Virginia Tech On behalf of the Daya Bay Collaboration October 20, 2011

Nuclear Reactors as a Neutrino Source Nuclear reactors are a very intense sources of

Nuclear Reactors as a Neutrino Source Nuclear reactors are a very intense sources of νe coming from the b-decay of the neutron-rich fission fragments. A typical commercial reactor, with 3 GW thermal power, produces 6× 1020 νe/s Arbitrary From Bemporad, Gratta and Vogel Observable ν Spectrum n Flu x The observable ne spectrum is the product of the flux and the cross section. s s S o r C Jonathan Link, Virginia Tech e o i t c

Reactor Neutrino Event Signature The reaction process is inverse β-decay (Used by Reines and

Reactor Neutrino Event Signature The reaction process is inverse β-decay (Used by Reines and Cowan in the neutrino discovery experiment) ne p→ e+n n capture Two part coincidence signal is crucial for background reduction Minimum energy for the primary signal is 1. 022 Me. V from e+e− annihilation at threshold Positron energy implies the anti-neutrino energy Eν = Ee + 0. 8 Me. V ( =mn-mp+me-1. 022) Neutron capture on Gd provides a secondary burst of light approximately 30 μs later Jonathan Link, Virginia Tech

Reactor Oscillation Experiment Basics νe νe νe Unoscillated flux νe observed here Well understood,

Reactor Oscillation Experiment Basics νe νe νe Unoscillated flux νe observed here Well understood, isotropic source of electron anti-neutrinos Oscillations observed as a deficit of νe Detectors are located underground to shield against cosmic rays. Probability νe 1. 0 sin 22θ 13 πEν /2Δm 213 Distance (L/E) Jonathan Link ~1800 meters (at 3 Me. V) 10/21/11

The Daya Bay Nuclear Power Plant Located in Guangdong Province, China, about one hour

The Daya Bay Nuclear Power Plant Located in Guangdong Province, China, about one hour from Hong Kong. 6 reactors on site for a total of 17. 4 GW of thermal power. It is among the most powerful nuclear power plants in the world The mountainous terrain is well suited for shielding underground detectors The utility company (China Guangdong Nuclear Power Group) has joined the collaboration Jonathan Link 10/21/11

Daya Bay Design Principles Identical near and far detectors cancel many systematic error. Multiple

Daya Bay Design Principles Identical near and far detectors cancel many systematic error. Multiple modules boost statistics while reducing systematic errors with multiple independent measurements and direct comparisons of detector counting rates in a common ν flux. Three zone detector design eliminates the need for spatial cuts which can introduce systematic uncertainties. Shielding from cosmic rays and natural radioactivity reduces background rates and provides measurable handles on remaining background. Movable detectors allows for concurrent civil and detector construction, early detector commissioning at the near site, and possible cross calibration between near and far detectors to further reduce systematic errors. Jonathan Link 10/21/11

Experimental Setup Total tunnel length ~ 3000 m Far site Overburden: 355 m 900

Experimental Setup Total tunnel length ~ 3000 m Far site Overburden: 355 m 900 m Ling Ao Near Overburden: 112 m Filled detectors are transported between halls via horizontal tunnels. 465 m 810 m Water hall Construction tunnel Liquid Scintillator hall Entrance 295 m Daya Bay Near Overburden: 98 m Daya Bay Reactors Ling Ao II Reactors (Starting 2011)

Experimental Setup Far site Overburden: 355 m • 8 identical anti-neutrino detectors (two at

Experimental Setup Far site Overburden: 355 m • 8 identical anti-neutrino detectors (two at each near site and four at the far site) to cross-check detector efficiency • Two near sites sample flux from reactor groups 9 different baselines Ling Ao Near Overburden: 112 m Ling Ao II Reactors (Starting 2011) Ling Ao Reactors Halls Reactors Daya Bay Near Overburden: 98 m Daya Bay Reactors Daya Bay Ling Ao Near (m) Far (m) Daya Bay 363 1347 1985 Ling Ao I 857 481 1618 Ling Ao II 1307 526 1613

5 meters The Daya Bay Detector Design Mineral Oil LS Gd-Loaded LS (20 tons)

5 meters The Daya Bay Detector Design Mineral Oil LS Gd-Loaded LS (20 tons) 1. 55 m 1. 99 m 2. 49 m Three zone, cylindrical design − 0. 1% wt Gd-Loaded LS target − LS gamma catcher − Mineral oil buffer Reflectors at top and bottom 196 PMT’s arrayed around the barrel of the cylinder 5 meter total diameter Designed to sit in a pool of ultrapure water Jonathan Link 10/21/11

The Daya Bay Detector Design Jonathan Link 10/21/11

The Daya Bay Detector Design Jonathan Link 10/21/11

Water Shield and Muon Tagging System The water pool shields the detectors from energetic

Water Shield and Muon Tagging System The water pool shields the detectors from energetic γ-rays from the decay chains of 238 U, 232 Th and 40 K in surrounding the rock It also detects the Čerenkov light produced by cosmic ray muons which pass near the detectors The pool is lined with white Tyvek and sparsely populated with PMTs RPCs The pool is optically separated into two zones (inner and outer) The two zones allow a better measurement of efficiency Water Pool The top is covered with 4 layers of RPC Minimum 2. 5 m water shielding in all directions. Jonathan Link 10/21/11

Water Shield and Muon Tagging System Jonathan Link 10/21/11

Water Shield and Muon Tagging System Jonathan Link 10/21/11

Water Controls Radioactive Backgrounds in air in water Singles events verses height in the

Water Controls Radioactive Backgrounds in air in water Singles events verses height in the partially filled pool show the suppression of radioactive backgrounds by water. Jonathan Link 10/21/11

Filled Water Pool in First Near Hall Jonathan Link 10/21/11

Filled Water Pool in First Near Hall Jonathan Link 10/21/11

Completed Near Hall Ready for Data Taking Jonathan Link 10/21/11

Completed Near Hall Ready for Data Taking Jonathan Link 10/21/11

Muon Induced Correlated Backgrounds p n n m m Tag muons that pass near

Muon Induced Correlated Backgrounds p n n m m Tag muons that pass near the detectors. Range out fast neutrons from muons that are further away. Jonathan Link 10/21/11

Muon Spallation Backgrounds Isotopes like 9 Li and 8 He are produced in the

Muon Spallation Backgrounds Isotopes like 9 Li and 8 He are produced in the detectors in the spallation of 12 C nuclei by muons. 9 Li and 8 He decay with Antineutrino Rate half-lives of tenths of seconds to β+n. Can be identified by their time correlation with muons in the detector. Jonathan Link 10/21/11

Signal to Background (a) (d) (c) (b) (1%) After all filters the background rates

Signal to Background (a) (d) (c) (b) (1%) After all filters the background rates are small compared to a disappearance due to oscillations with sin 22θ 13 of 1%. In addition, each background has a characteristic and distinct energy spectrum. Jonathan Link 10/21/11

Measuring sin 22θ 13 The measurement is a ultimately a ratio of observed inverse

Measuring sin 22θ 13 The measurement is a ultimately a ratio of observed inverse β-decay events in near and far detectors in initially one, but ultimately many energy bins (sampling a broad range of oscillation phases). Proton Number Ratio of Detector Efficiencies ± 0. 3% Calibration Jonathan Link sin 22θ 13 ± 0. 2% 10/21/11

Systematic and Statistical Errors Source of Uncertainty Number of Protons Detector Energy Cuts Efficiency

Systematic and Statistical Errors Source of Uncertainty Number of Protons Detector Energy Cuts Efficiency Position Cuts Time Cuts H/Gd Ratio N Multiplicity Trigger Live Time Total Detector Related Uncertainty Background (per detector) Neutrino Flux Signal Statistics Sensitivity to sin 22θ 13 (at 90% CL) Chooz (absolute) 0. 8% 0. 32% 0. 4% 1. 0% 0. 5% 0% 0% 1. 7% 0. 85% 2. 7% 1. 8% ~13% Jonathan Link Daya Bay (relative) Baseline Goal w/Swapping 0. 3% 0. 1% 0. 006% 0. 2% 0. 1% 0. 0% 0. 1% 0. 03% 0. 1% 0. 05% 0. 01% <0. 01% 0. 38% 0. 12% <0. 4% 0. 13% 0. 2% 0. 8% 0. 7% 0. 6% 10/21/11

Sensitivity Jonathan Link 10/21/11

Sensitivity Jonathan Link 10/21/11

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 Jonathan Link 10/21/11

Installation in Second Near Hall Jonathan Link 10/21/11

Installation in Second Near Hall Jonathan Link 10/21/11

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 • Muon system installation underway in hall 3. Jonathan Link 10/21/11

Muon Installation in the Far Hall Jonathan Link 10/21/11

Muon Installation in the Far Hall Jonathan Link 10/21/11

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of

Project Schedule and Status • October 2007: Official Ground Breaking • 4 out of 8 detectors completed • August 2011: Hall 1 data taking begins • Detector installation underway in hall 2 • Muon system installation underway in hall 3. • Summer 2012: Start of data with full installation Three years of data taking to reach sensitivity goal. Jonathan Link 10/21/11

The Daya Bay Collaboration Europe. : Charles U. , JINR, Kurchatov Institute Asia: U.

The Daya Bay Collaboration Europe. : Charles U. , JINR, Kurchatov Institute Asia: U. S. : BNL, Caltech, Cincinnati, George Mason, Houston, IIT, Iowa State, LBNL, Princeton, RPI, UC Berkeley UCLA, UIUC, Virginia Tech, William and Nary, Wisconsin Beijing Normal, Chengdu U. of Tech. , CGNPE, CIAE, CUHK, Dongguan Polytech, IHEP Beijing, Nankai, Nanjing, National Chiao-Tung U. , National Taiwan U. , National United U. , Shangdong U. , SJTU, Shenzhen U. , Tsinghua U. , HKU, USTC, Zhongshan U.