The Daya Bay Experiment and the Quest for θ13
David E. Jaffe for the Daya Bay Collaboration
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 1 / 22
Why θ13?
|νf 〉 =∑
i U∗fi |νi〉 Interaction eigenstates 6=Mass eigenstates
cij ≡ cos θij , sij ≡ sin θij
Uif =
1 0 00 c23 s23
0 −s23 c23
× c13 0 s13e
iδ
0 1 0−s13e
−iδ 0 c13
× c12 s12 0−s12 c12 0
0 0 1
θ23 ≈ 45◦ θ13 < 10◦ θ12 ≈ 35◦Atmospheric ν Short-baseline Reactor ν Solar ν
Accelerator ν Future accelerator ν Long-baseline Reactor ν
Daya Bay design sensitivity: sin2 2θ13 < 0.01 (90%CL)
Short-baseline Reactor νe is a disappearance experiment:P(νe → νe) ≈ 1− sin2 2θ13 sin2(1.27∆m2
31L/E )
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 2 / 22
Chooz: Best experimental limit on θ13
all data
0
50
100
150
200
250
300
0 2 4 6 8 10
e+ energy
MeV
Eve
nts
Reactor ON
Reactor OFF
5 ton target exposed to 2reactors, total thermal power8.5 GW, 1 km baselinePhys.Lett.B466 (1999) 415
10-2
10-1
sin2θ13
10-3
10-2
∆m2 31
[eV
2 ]
SK+K2K+MINOS
SOL+KAML+CHOOZ
CHOOZ
GLOBAL
90% CL (2 dof)2007
Recent global ν analysisarXiv:0710.5027
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 3 / 22
Getting to sin2 2θ13 < 0.01
Increase statistics: 4× 20 tontarget at far site, 11.6 GWth
(17.4 GWth in 2011).1 GWth = 2× 1020νe/s
Suppress cosmogenicbackground: Go deeper.
Reduce systematicuncertainties: Deploy“identical” near/far detectorpairs.
Optimize baseline
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 4 / 22
νe detection method
Inverse-beta decay: νep → e+n
Target: 0.1% Gd-loaded LiquidScintillatornGd → Gd∗ → Gd + γs(8 MeV)
∼30µs mean neutron capture time
Delayed coincidence providespowerful background rejection
Reactor anti-neutrinospectrum
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 5 / 22
Anti-neutrino Detectors (ADs)
8 identical detectors: Reducesystematic uncertainties
Each detector 3 nested cylinders:
1 Inner: 20t GdLS a (r=3m)2 Mid: 20t LS b (r=4m)3 Outer: 40t mineral oil (r=5m)
192 8-inch PMTs/detector
Top/bottom reflectors
Provides 12%/√
E (MeV) energyresolution
aGdLS=Gd-loaded Liquid ScintillatorbLS=Liquid Scintillator
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 6 / 22
Cosmic veto and shielding
Multiple muon veto detectors
Water Cerenkov
ADs submerged in water(≥ 2.5m shielding)Inner/Outer regionsoptically separated byTyvek sheets8-inch PMTs on frames(289/near, 384/far site)
RPC: Provides independentveto above water pool
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 7 / 22
Reducing systematic uncertainties
Reducing systematic uncertainties
Detector ChoozUncertainty Source Baseline Goal Experience
Number of protons 0.3% 0.1% 0.8%Energy cuts 0.2% 0.1% 0.8%H/Gd ratio 0.1% 0.1% 1.0%
Detection Time cut 0.1% 0.03% 0.4%Efficiency Neutron mult. 0.05% 0.05% 0.5%
Trigger 0.01% 0.01% 0.01%Live time < 0.01% < 0.01% < 0.01%
Total Uncertainty 0.38% 0.18% 1.7%Two detector One detector
relative absoluteuncertainty uncertainty
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 8 / 22
Reducing systematic uncertainties
Requirements on systematic uncertainties
Nf
Nn=
(Np,f
Np,n
) (Lf
Ln
)2 (εf
εn
)P(Lf , E ; sin2 2θ13)
P(Ln, E ; sin2 2θ13)Measured
Number of Efficiency ratioratio ofprotonsrates
Attain ≤ 0.3% on proton ratio by monitoringfilling mass with load cells(accuracy < 0.02%) andCoriolis mass flowmeters(accuracy < 0.1%).Fill ADs in pairs.
Attain ≤ 0.2% on efficiency ratio with calibration
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 9 / 22
Reducing systematic uncertainties
Detector efficiency
Simulation: Achieving 0.2% eff’ysystematic, implies knowing e+ thresholdto 2% (easy) and relative neutronthreshold to 1% (more difficult)
Positron energy cuts at 1 & 8 MeV.Calibrate e+ threshold with 68Gesource.
Neutron capture energy cut at 6MeV. Calibrate with spallation nGdcapture over full fiducial volume +weekly deployment of AmC sourceon 3 vertical axes.
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 10 / 22
Background
Background processes and rates
Background due to natural radioactivity & cosmic ray interactions
1 Muon interactions in the LS produce 9Li/8He.A β−, n emitter with Q=13 MeV, τ=0.178s.Expect bkgd/signal ∼0.003. Can be measuredwith data (NIMA564(2005)081801).
2 Muon interactions outside AD in water androck produce “fast” neutrons that interact inGdLS, LS. Expect bkgd/signal ∼0.001. Canestimate rate from data and simulation.
3 Accidental coincidences of radioactivebackground with cosmogenic background.Expect bkgd/signal ∼0.003. Calculable fromobserved singles rates.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 1 2 3 4 5 6 7 8 9 10Evis (MeV)
Arbitary Units
(b)
(b) 9Li (0.2%)
(c)
(c) Fast Neutrons (0.1%)
(d)
(d) Accidentals (0.1%)
(a)
(a) Oscillation Signal
Oscillation signal for
sin2 2θ13 = 0.01
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 11 / 22
Optimize baseline
Optimize baseline
1−P(νe → νe) = sin2 2θ13 sin2 1.27∆m231L
E−cos4 θ13 sin2 2θ12 sin2 1.27∆m2
21L
E
Expt’l siteReactors DyB LA Far
DayaBay 363 1348 1986LingAo I 857 481 1618LingAo II 1307 526 1613
Overburden 98 112 355
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 12 / 22
Expected sensitivity
Expected sensitivity
90% CL limit on sin2 2θ13 assuming baseline systematics
3 years of data
∆m2 = 0.0025 eV2
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 13 / 22
Expected sensitivity
The Daya Bay Collaboration
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 14 / 22
Schedule
Status
Nov07 Began civil constructionAug08 CD-3b ApprovalMar09 Occupancy of onsite assembly building
Winter09 Install AD pair in Daya Bay near siteWinter10 Begin data taking with near and far
sites
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 15 / 22
Other physics with Daya Bay
Possible non-θ13 topics
1 ν decay (appearance measurement)
2 CPT violation via sidereal variations in IBD rate
3 atmospheric ν and upward-going muons
4 supernova detection
5 precise determination of reactor spectrum
6 neutron (and alpha) emission after µ− capture: multiplicityand/or energy spectra
7 measurement of muon spallation products at three depths
8 cosmic ray air showers
9 cosmic muon charge ratio
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 16 / 22
The last slide
The Daya Bay Reactor Neutrino Experiment will be able toprovide the most accurate measurement of sin2 2θ13 in the nextfew years.The experiment is being funded. Civil construction and detectorfabrication is progressing.
See hep-ex/0701029 for more details.Many thanks to my Daya Bay collaborators for their help in preparing this
presentation.David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 17 / 22
Extra
Intentionally blank
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 18 / 22
Prototype Antineutrino Detector Performance
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 19 / 22
Prototype filled with 0.1% GdLS
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 20 / 22
Cancellation of Flux Uncertainty with Multiple Reactors
Q: Cancellation νe flux uncertainty with multiple reactor sites?
A: Deweight the oversampled cores by a factor α:Ratio = αNear1
Far+ Near2
Far
α =(L2
22L21F )−1 − (L2
21L22F )−1
(L211L
22F )−1 − (L2
12L21F )−1
For 4(6) cores, α = 0.34(0.39) and 2%reactor flux uncertainty is reduced to0.035% (0.1%). Slightly morecomplicated expression if flux/reactordiffers.
David E. Jaffe for the Daya Bay Collaboration (BNL) Quest for θ13 17 Dec 08 21 / 22