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Results and Prospectives of Reactor Neutrino Experiments
Liangjian Wen
The 12th particle physics phenomenology workshop (PPP12) 16-19 May, NCTU, Hsinchu, Taiwan
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Outline• Reactor Neutrinos• Oscillation measurement: θ13 and Δm2
ee– Daya Bay, Double Chooz, RENO
• Sterile Neutrino Search• Rate and spectrum anomaly• Future: determining Neutrino Mass Ordering
– JUNO, RENO-50
• Summary
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What we have learned?
3
𝑉𝑉 =1 0 00 𝑐𝑐23 𝑠𝑠230 −𝑠𝑠23 𝑐𝑐23
𝑐𝑐13 0 𝑠𝑠13𝑒𝑒−𝑖𝑖𝛿𝛿0 1 0
−𝑠𝑠13𝑒𝑒𝑖𝑖𝛿𝛿 0 𝑐𝑐13
𝑐𝑐12 𝑠𝑠12 0−𝑠𝑠12 𝑐𝑐12 0
0 0 1
𝑒𝑒𝑖𝑖𝜌𝜌 0 00 𝑒𝑒𝑖𝑖𝜎𝜎 00 0 1
Standard Parametrization of the PMNS Matrix
𝜽𝜽𝟐𝟐𝟐𝟐 ~ 𝟒𝟒𝟒𝟒∘
Atmospheric,LBL accelerator
𝜽𝜽𝟏𝟏𝟐𝟐 ~ 𝟗𝟗∘
Reactor,LBL accelerator
𝜽𝜽𝟏𝟏𝟐𝟐 ~ 𝟐𝟐𝟒𝟒∘
Solar,KamLAND
0ν2β, LNV?
Quarks vs. Leptons: A big puzzle of fermion flavor mixings
|𝑈𝑈| = |𝑉𝑉| =
CKM PMNS
Hierarchy! Approximate μ-τ symmetry?
|𝚫𝚫𝒎𝒎𝟐𝟐𝟐𝟐𝟐𝟐 | ~ 𝟐𝟐.𝟒𝟒 × 𝟏𝟏𝟏𝟏−𝟐𝟐 eV𝟐𝟐 𝜹𝜹 ~ ? 𝚫𝚫𝒎𝒎𝟐𝟐𝟏𝟏
𝟐𝟐 ~ 𝟖𝟖× 𝟏𝟏𝟏𝟏−𝟒𝟒 eV𝟐𝟐
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• Discovery of neutrino in 1956• Early search for oscillation 70’s-80’s• Small θ13 in 1990s• limit on neutrino magnetic moment (00’s)• Observation of reactor 𝝂𝝂𝒆𝒆 disappearance in 2003• Discovery of non-zero θ13 in 2012• Mass hierarchy and precision measurements• Sterile neutrinos, Magnetic moment, …
Reactor Neutrinos
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Neutrino spectra of fission isotopes, ILL
Isotope evolution
fissio
n fra
ctio
n (%
)
X
• Neutrino flux of a commercial reactor with 3 GWth : ~6×1020 ν/s
• Distinguishing correlated and un-correlated errors is important
Reactor ν Flux
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Capture on H
Capture on Gd
0.1% Gd
nepe +→+ +ν
10-40 keV
++ +−++≅ epnne mMMTTE )(ν
1.8 MeV: Threshold
• ν-e scattering• Inverse-β reaction (IBD)
Reactor ν Detection
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A little history of νe disappearance …
7
PRD 62 (2000) 072002
PRL 90, 021802 (2003)
Precision of early Reactor experiments (3-6%):• Reactor power:~1%• ν spectrum:~0.3%• Fission rate: ~ 2%• Target mass:~1-2%• Backgrounds:~1-3%• Efficiency:~2-3%
Near-far relative measurement was proposed (Mikaelyan and Sinev, hep-ex/9908047) to reduce the uncertainties from reactor and detector
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Daya Bay, Double Chooz, RENO
8
Daya Bay Double Chooz
RENO
Daya BayRENO
Double Chooz
40t
40t80t
365 m
490 m17.4 GWth
8.5 GWth
8t
8t290 m
1380 m
16t 16t
16.8 GWth
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Daya Bay: Best Site for θ13
• Powerful reactor complex (Top 5)• Close to mountains enough shielding • Luminosity 5-20 times of DC and RENO• Featured design side-by-side
calibration (2-4 ADs at each site) actual relative det. error 0.13% /√N,
• Discovered an unexpectedly large θ13 in Mar. 2012. precision measurement afterwards Huber et al. JHEP 0911:044, 2009
9
Daya Bay
RENO
DC
Designs Luminosity(ton⋅GW)
Detector Systematics
Overburden (near/far, mwe)
Sensitivity(3y, 90%CL)
Daya Bay 1400 0.38%/√N 250 / 860 ~ 0.008Double Chooz 70 0.6% 120 / 300 ~ 0.03
RENO 260 0.5% 120 / 450 ~ 0.02
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Daya Bay Experiment
10
Aug. 2011
Nov. 2011
Dec, 2012
Full detectors:Aug, 2012
Water pool
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The Daya Bay Detectors
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• Multiple AD modules at each site to check Uncorr. Syst. Err. – Far: 4 modules,near: 2 modules
• Multiple muon detectors to reduce veto eff. uncertainties– Water Cherenkov: 2 layers – RPC: 4 layers at the top + telescopes Redundancy !!!
40 t MO
20 t LS20 t Target
reflector
reflector
Automated Calibration Units (ACU)
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Data Periods
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EH1 EH2 EH3
2017/02, EH1-AD1 offline
θ13, ∆𝑚𝑚𝑒𝑒𝑒𝑒2 [PRD]θ13, ∆𝑚𝑚𝑒𝑒𝑒𝑒
2 [PRL]nH θ13 [PRD]sterile ν [PRL, PRL]reactor [CPC]wave packet [EPJC*]
θ13, ∆𝑚𝑚𝑒𝑒𝑒𝑒2 [PRL]
nH θ13 [PRD(R)]sterile ν [PRL]reactor [PRL]
θ13 [PRL]
θ13 [CPC]
*submitted
55 d
ays
139
days
217
days
621
days
1230
day
s
8-AD Data Taking6-AD 2012 Summer
reactor evolution [PRL*]
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40 t MO
20 t LS20 t Target
reflector
reflector
Automated Calibration Units (ACU)
Energy Calibration
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The relative energy scale uncertainty <0.2%
PMT gain calibration
(dark noise, LED)
Energy Rec.
• calibration Sources• spallation neutrons
Relative Energy Scale
• 68Ge, 60Co, 241Am-13C• Neutrons (IBD, spallation)• Special sources• Natural radioactivity
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Detector energy response model
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• Energy model: fit to various gamma lines and 12B beta-decay spectrum
• Validated with– 208Th, 212Bi, 214Bi beta-decay spectrum; Michel electron
– Bench tests of Compton scattering electrons in LS
• Non-linear energy response in Liquid scintillator– Quenching (known as Birks’ law) and Cerenkov (particle-, E- dep.)
– Electronics (E- dep, modeled based on MC and single channel FADC measurement)
gamma electron positron
Uncertainty <1%
Experience on DYB energy model is valuable to JUNO (similar LS).
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Signal & Backgrounds
15nGd Background (Far hall)n-H Background (Far hall)
• Accidental background• 9Li/8He• Fast neutrons• Am-C neutron calib. sources• 13C(α,n)16O
AD
IWS
RPC Array
Telescope RPC
RPC-only taggedOWS tagged
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Side-By-Side Comparison• Cross check with multiple detectors at the same site• The relative detection efficiency uncertainty down to 0.13%,
verified by comparing the rates of detectors
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χ2/NDF = 232.6/263
Precision Oscillation Measurement
17
1230 days
Sin22θ13 = [8.41 ± 0.33] × 10-2
NH: Δm232 = [2.45 ± 0.08] × 10-3 eV2
IH: Δm232 = [-2.55 ± 0.08] × 10-3 eV2
1230 days• Independent sin22θ13 meas. from nH• run until 2020, achieve uncertainty ≤3%
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Global Comparison
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NH
Most precise measurement• Sin22θ13 uncertainty: 3.9%• |Δm2
32| uncertainty: 3.4%
Consistent results with reactor and accelerator experiments.
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Independent n-H analysis
19
The n-H analysis, where the neutron captures on hydrogen, is statistically and (largely) systematically independent from the nGd one.One of the challenges: large accidental background
Phys. Rev. D 93, 072011 (2016)Rate analysis: sin22θ13 = 0.071±0.11, χ2/ndf = 6.3/6
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Future Sensitivity• Daya Bay:
– Δ(sin22θ13) ~ 0.003 ~3%– Δ(Δm2
ee) ~ 0.07 ~ 3%
• RENO: ~5%. • Double Chooz: ~10%
20
Daya Bay: operation till 2020RENO: “operation funding secured until Feb. 2019”Double Chooz: “secured to Jan. 2018 (may change)”
by J. Zhao
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Reactor Anomaly• ILL spectra agree with data• Mueller/Huber spectra higher than data• Sterile neutrino?
21
G. Mention et al. Phys.Rev. D83 (2011) 073006
fit with sterile 𝜈𝜈Δ𝑚𝑚2 ≈ 1 𝑒𝑒𝑉𝑉2
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Absolute Reactor νe flux
22
Discrepancies to the Huber+Mueller model indicate: Over estimated flux and/or underestimated flux uncertainty Or the existence of a sterile neutrino
Consistent flux measurement with previous short baseline reactor experiments
PRL 116, 061801 (2016)
• Daya Bay measurement of absolute Flux– Data/(Huber+Mueller):0.946±0.020– Data/(ILL+Vogel):0.992 ± 0.021
621 days data
CPC Vol. 41, No. 1 (2017) 013002
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Future Reactor Exp. for Sterile Neutrino
23
• Different technologies: (Gd, Li, B) (seg.)(movable)(2 det.)• Most have sensitivity 0.02~0.03 @∆m~1eV2 @90%CL
Talk by Nathaniel Bowden @NEUTRINO2016
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Search for light sterile neutrinos
24
• An unique opportunity for sterile neutrino searches– Sterile neutrino would introduce additional oscillation mode– Relative meas. at multiple baselines: EH1 (~350m), EH2 (~500m), EH3 (~1600m)
• Oscillation analysis– No significant signal observed, consistent with 3-flavor neutrino oscillation. – Set most stringent limit at 10-3 eV2 < Δm2
41 < 0.1 eV2
PRL 113, 141802 (2014)
Excluded
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MINOS, Daya Bay and Bugey-3
25
Parameter space allowed by LSND and MiniBooNE is excludedPRL. 117, 151801 (2016)
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5 MeV Bump on Reactor Spectrum
26
• Events are reactor power related & time independent
• Events are IBD-like:– Disfavors unexpected backgrounds
• No effect to θ13 if near-far meas.• Possibly due to forbidden decays
(PRL112: 2021501; PRL114:012502)
RENO, Neutrino 2014
DC, Neutrino 2014
Jetter, Tau2014
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Reactor Antineutrino Spectrum• Bump local significance ~ 4.4 σ• Unfolding the reactor neutrino spectrum
27Chin. Phys. C, 41(1) 13002-013002 (2017) PRL 116, 061801 (2016)
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Evolution of reactor neutrino flux and spectrum
28
Probe the reactor anomaly
1230 days
Rescaled model (equal deficit in the IBD yields from four fission isotopes)
arXiv:1704.01082
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Evolution of reactor neutrino flux and spectrum
29
• Combined fit for major fission isotopes 235U and 239Pu
• σ235 is 7.8% lower than Huber-Mueller model (2.7% meas. uncertainty)
• σ239 is consistent with the prediction (6% meas. uncertainty)
• 2.8σ disfavor equal deficit (H-M model & sterile hypothesis)
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Exploring ν mass ordering with Reactors
30
Phys.Rev.D78:111103,2008
• Large θ13 open doors to MH– Exploit L/E spectrum with reactorsPrecision energy spectrum measurementLook for interference between solar- and atmospheric- oscillations relative measurement
S.T. Petcov et al., PLB533(2002)94S.Choubey et al., PRD68(2003)113006J. Learned et al., PRD78, 071302 (2008)L. Zhan, Y. Wang, J. Cao, L. Wen, PRD78:111103, 2008, PRD79:073007, 2009J. Learned et al., arXiv:0810.2580…
Independent on CP phase and θ23 (Acc. & Atm. do)Energy Resolution is the key
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JUNO and RENO-50
31
Hong KongJUNO
Daya Bay
RENO-50
RENO
18 kton LS Detector ~47 km from YG reactors
Mt. Guemseong (450 m) ~900 m.w.e. overburden
20 kton LS Detector
~53 km from Taishan & Yangjiang reactors ~750 m rock overburden
J. Phys. G43:030401 (2016)(arXiv: 1507.05613)
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∆M223
6 years,3σ
Determine NMO at JUNO
32
L. Zhan, Y. Wang, J. Cao, L. Wen, PRD78:111103, 2008, PRD79:073007, 2009
Detector size: 20kt Energy resolution: 3%/√EThermal power: 36 GWBaseline 58 km
3%/ 𝐸𝐸
17.4 GW18.4 GW
17.4 GW
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Cosmic muons~ 250k/day
Atmospheric νseveral/day
Geo-neutrinos1-2/day
Solar ν(10s-1000s)/day
reactor ν, ~ 60/day
700 m
Supernova ν~ 5k in 10s for 10kpc
36 GW, 53 km
0.003 Hz/m2
215 GeV10% multiple-muon
Neutrino Rates
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Δχ2 Relative Meas.
(a)Use absolute ∆mμμ
2
Ideal case 4 5(b)Realistic case 3 4
Sensitivity on NMO
Y.F Li et alPRD 88, 013008 (2013)
JUNO MH sensitivity with 6 years' data:
(a) If accelerator experiments, e.g NOvA, T2K, can measure ∆M2
µµ to ~1% level(b) Take into account multiple reactor cores, uncertainties from energy non-linearity, etc
Ideal Core distr. DYB & HZ Shape B/S (stat.) B/S (shape) |∆m2µµ|
Size 52.5 km Real Real 1% 6.3% 0.4% 1%
∆χ2ΜΗ +16 - 3 -1 - 1 - 0.6 - 0.1 + (4-12)
34
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Precision Measurement
0.16%0.24% 0.39%0.54%0.16%0.27%E resolution
Correlation among parameters
Statistics+BG, +1% b2b+1% EScale , +1% EnonL
sin2 θ12 0.54% 0.67%
Δm221 0.24% 0.59%
Δm2ee 0.27% 0.44%
Probing the unitarity of UPMNS to ~1%, more precise than CKM matrix elements!
35
Current precision
J. Phys. G43:030401 (2016)
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Matter Effects
36
• With six years of running, the Δχ2 of mass ordering measurements will reduce from 10.28 (vacuum) to 9.64 (matter).
• The reduction of Δχ2 is comparable with other systematic error.
Chinese Physics C 40(9) (2016) 091001
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Supernova neutrinos at JUNO
37
no osc.complete
Measure energy spectra & fluxes of almost all types of neutrinos
Correlated events. Better detection in LSthan in Water
Typical galactic SN assumptions: 10 kpc galactic distance, 3×1053 erg, Lν the same for all types
SN researches at JUNO• NMO sensitivity• Absolute v mass• SN direction• flux/spectra meas. & recon.• time evolution• test various SN models• …
J. Phys. G43:030401 (2016)
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Supernova neutrinos
38
• Test average-energy hierarchy of SN ν, and how total energy is partitioned among ν flavors
• ν mass: < 0.83±0.24 eV at 95% CL (JCAP 05 (2015) 044)• Locating the SN: ~9°
PRD 94, 023006 (2016)
Spectra
Precision of 1%
Precision of 10%
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Supernova neutrinos• Reconstruct the flux & spectra of all flavor neutrinos from the
observed ν-e, ν-p and IBD interactions, by using the SVD-unfolding technique
• Toy MC including E-resolution, quenching, E-threshold, etc• Verify the method with different SN models model
independent
39H. Li et al, paper to appear soon
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Supernova neutrinos
40
K-C. Lai et al, JCAP 1607 (2016) no.07, 039
Probing neutrino mass ordering with SN νs
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Diffuse Supernova Neutrino Background
• DSNB: Past core-collapse events– Cosmic star-formation rate– Core-collapse neutrino spectrum– Rate of failed SNe
10 Years’ sensitivity
34J. Phys. G43:030401 (2016)
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Other Physics Topics
42
• JUNO will have 1-2 σ NMO sensitivity with atmospheric neutrinos– Measure both lepton and hadron energy– Good tracking and energy resolution
• Geo-v measurement at JUNO– Huge reactor neutrino backgrounds– Need accurate reactor spectra
– 20 x statistics than previous meas.KamLAND: 30±7 TNU (PRD 88 (2013) 033001)
Borexino: 38.8±12.2 TNU (PLB 722 (2013) 295)
Best fit 3 y 5 y 10 y
U+Thfix ratio
0.96 10% 8% 6%
U (free) 1.03 19% 15% 11%
Th (free) 0.80 37% 30% 21%
Combined shape fit of geo-ν and reactor-ν
Others (sterile neutrinos, proton decay, neutrinos from dark matter… etc)
J. Phys. G43:030401 (2016)
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Central detector
Water Cherenkov
Top Tracker
Calibration
Pool
Dep
th: 4
4m
Pool ID:43.5m
AS: ID35.4m
SSLS: ID40.1m
AS: Acrylic sphere; SSLS: stainless steel latticed shell
Filling +Overflow
Acrylic sphere(20Kt LS in it)
~18000 20” PMT+~25000 3’’ PMT
~2000 20’’ PMT
SS latticed shell
Electronics
Acrylic Sphere: ID: 35.4mThickness:120mm
SSLS:ID: 40.1mOD: 41.1m
Water poolID: 43.5mHeight: 44mWater Depth: 43.5m
JUNO Detectors
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R&D of 20” MCP-PMT
44
MCP Principle
Project Team
• Advantages:– Higher QE: transmissive
photocathode at top + reflective photocathode at bottom
– High CE: less shadowing effect– Easy for production: less manual
operation and steps
5”(8”) Prototype
20” Prototype
Design Production
2009 2010~2013 2013~2015 2016~2019
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MCP-PMT Performance
45Min:24.5%; Max:29%
Average:26.5%
QE & uniformity Dark rate
After pulse
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PMT Purchasing of JUNO
46
15k MCP-PMT (75%) from NNVT5k Dynode(25%) from Hamamatzu
Dec.16, 2015Characteristics unit MCP-PMT
(NNVC)R12860
(Hamamatsu)Detection Efficiency
(QE*CE*area) % 27%, > 24% 27%, > 24%
P/V of SPE 3.5, > 2.8 3, > 2.5TTS on the top point ns ~12, < 15 2.7, < 3.5Rise time/ Fall time ns R~2, F~12 R~5,F~9 Anode Dark Count Hz 20K, < 30K 10K, < 50K
After Pulse Rate % 1, <2 10, < 15
Radioactivity of glass ppb238U:50232Th:5040K: 20
238U:400232Th:40040K: 40
By Scaling PMT Spec for LS quantity to reach 3σ@ 6year
Decision based on risk, price, performance merit for physics
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47
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Acrylic Sphere R&D
48
Acrylic divided into 200+ panels Acrylic nodes test:
Upto ~700 kN pulling forces when it breaks
Part of sphere are manufactured to test the techniques
Sphere sheet manufacturing: 3m X 8m X 0.12 mThe problems of shrinkage and shape variation were
resolved.
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Progress of LS R&D
49
Al2O3column
LAB and Al2O3mixing tank
Pure LAB
• Test the overall design of purification system at Daya Bay. Replaced the target LS in one detector
• Quantify the effectivities of subsystems– Optical : > 20m A.L @430nm– Radio-purity: < 10-15 g/g (U, Th)
• Determine the choice of sub-systems– Al2O3 column, distillation, gas striping, water extraction
Distillation system
Steam stripping system
Distillation and steam stripping system.
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JUNO-LS Pilot plant
50
Full system tested in Daya Bay LS hall.A new batch of purified LS was produced and filled into DYB-AD1.LS radioactivity being evaluated with data. Further tests to optimize the LS recipe
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CLS GT
Calibration System
51
Guide Tube
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JUNO Schedule
52
Schedule:• Civil preparation:2013-2014• Civil construction:2014-2018• Detector component production:2016-2017• Detector assembly & installation:2018-2019 • Filling & data taking:2020-2021
Future Plan• Run for 20-30 years• Likely, double beta decay experiment in 2030
vertical shaft sloped tunnel
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Exploring nature of v’s mass• 0νββ is currently the viable and
sensitive probe to the Majorananature of ν
53
Z.Z. Xing, Y.L. Zhou, CPC39 (2015) 011001
Current Limit
Next generation𝑻𝑻𝟏𝟏/𝟐𝟐𝟏𝟏𝝊𝝊𝝊𝝊𝝊𝝊~1028 yr
ν is MajoranaYes
NO
Inverted NMO? Yes(by other exp.)
Observed 0νββ?
ν is Dirac(if NOT intro. new physics)
NO
Little hope for next generation 0νββexperiment to determine ν’s Majorana
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The JUNO LS detector has good potential for DBD search• 3%/ 𝐸𝐸 energy resolution• 35.4 m diameter of LS• Clean balloon hold enrXe gas (>80% 136Xe) dissolved LS• LS purity: 10-15 g/g (U/Th) 10-17 g/g (U/Th)• Excellent muon track rec. reject cosmogenic
isotopes
54
Ultimate 0νββ search at JUNO
Chin.Phys.C 2017, 41(5): 53001-053001
Expected Background: 1.34/FWHM/ (ton 136Xe)/yr
Possibly in 2030
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Summary• Significant improvement on Sin22θ13 precision from the Daya
Bay, Double Chooz and RENO experiments. Ultimate precision of Sin22θ13 will reach ~ 3%
• Precision measurement of the absolute neutrino flux and spectrum.
• Reactor anomaly may have a definite answer before 2020.• Future reactor neutrino experiments:
– Mass hierarchy (3-4 σ in 2026)– Precision measurement of 3/6 mixing parameters up to <
~1% level unitarity test of the mixing matrix– Sterile neutrinos– Rich physics topics with a detector like JUNO
55
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Thanks!
56
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Spectra of Isotopes
57
• Ab initio: Nuclear database, Σ fragments, Σ chains, Σ branches 10%uncertainty (e.g. Vogel et al., PRC24, 1543 (1981)).
• ILL measured the β-spectra convert to neutrino spectra– ILL spectra: Use spectra of 30 virtual branches, fit amplitude and
endpoints – Mueller spectra: 90% Ab initio, 10% fit rate anomaly– Huber spectra: fit w/ improved nuclear effects
K. Schreckenbach et al. PLB118, 162 (1985)A.A. Hahn et al. PLB160, 325 (1985) Shape verified by Bugey-3 data
Normalization by Bugey-4, 1.6%
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Combination Prospectives• The 3 experiments started to discuss combination• To the end of 2016 (by J. Zhao)
– Daya Bay: 0.00307– Daya Bay + RENO: 0.00287 improve by 6.5%– Daya Bay + RENO + DC: 0.00282 improve by 8.2%
• Assumed uncorrelated– Reactor, detector, background– Cosmogenic bkg correlation worse– Cosmogenic bkg (50% systematic uncer.) reduction better
58
Zoom
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Beyond Photo-statistics
• Generic form of E resolution– a: stochastic term– b: constant term– c: noise term
Impact to MH sensitivity
41
• Data validated Full MC (DYB&DC)• Noise term dominated by PMT dark noise• Constant term
– Residual non-uniformity– Flaws in readout electronics– Artifacts from resolution plotting
• No JUNO show stopper found in DYB model
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NH IH
Dighe & Smirnov, hep-ph/9907423
L – Resonance Res. for neutrinos Always adiabatic
( )12221 θ ,Δm H – Resonance
Res. for neutrinos (NH) Res. for antineutrinos (IH)
( )13231 θ ,Δm
Adiabatic for a ‘large’ θ13
Supernova Neutrinos: Elementary Particle Physics
Flavor Conversion: MSW effects in the SN envelope
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for
for
for
0eF0
eF0
xF
eν
eν
ττµµ νννν ,,,
00 )1( xee FpFpF −+=00 )1( xee FpFpF −+=
000
41
41
42
41
eexx FpFpFppF −+
−+
++=∑
Normal
Inverted
sin2(2θ13)
≳ 10−3
Mass ordering
sin2(θ12)
0 cos2(θ12)
0
Case
A
B
Survival probabilities
)for(p eν )for(p eν
Dighe & Smirnov, hep-ph/9907423 Dighe, Kachelriess, Raffelt & Tomàs, hep-ph/0311172
Primary fluxes (+ collective) Leaving the SN (+ Collective & MSW effects)
Supernova Neutrinos: Elementary Particle Physics
Flavor Conversion: MSW effects in the SN envelope
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Short Baseline Exp. with Gas TPC• Gas TPC detector at ~20 m from a reactor
– ν-e scattering– High energy precision ( <3%/sqrt(E) )
• Major motivation: high precision reactor spectrum to 1%– Input for JUNO. Daya Bay energy resolution 8%, JUNO 3%
• Other motivations:– The weak mixing angle θw– Abnormal magnetic moment– Sterile neutrino
• Prototyping at IHEP. Prepare LOI in 2017MUNU exp:µν < 0.9 × 10−10 µBCF4 , T > 700 keVPLB 615(2005)153
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Instrumental background: PMT Flasher
63
Flashers
Signal Flasher
Common phenomena in the past large neutrino experiments (KamLAND, Super-K, Borexino, SNO), caused by discharge on dynodes or bases. Not easy to efficiently reject at that time Turn off the problematic PMTA highly-efficient flasher cut developed for DYB: ~100% eff., 0.01% error
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8He/9Li
8He/9Li background
64
Old approachNew approach
Classical method: time-since-last-muon fitDifficulty: large error when muon rate is high, impossible to estimate the Li9 production yield for muons that havelow energy deposition
Guess: 8He/9Li production accompanied with neutron reduce the rate of muon sampleResult: successful data-driven test and significantly reduced the error
L. J. Wen et al., NIMA 564 (2006) 471-474
β-n emitter: muon spallation on Carbon nuclei
13C μn?
8He/9Li dominates the background uncertainty
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Optical Model for large LS detectors
65
L.J Wen, Ph.D thesisX.F. Ding, L.J. Wen,et al, CPC 39 (12) (2015) 126001.X.Y. Li, L.J. Wen, et al, paper in preparation
Developed a new optical model to address those issues. Key optical parameters:• Molar attn. coefficient of
each composition• Quantum yield of each fluor
LAB PPO
bis-SMB
• What’s the best LS recipe?– Detector size dependent, cannot rely on lab
experiment
• Predict the detector non-uniformity• Understand non-linearity from Cerenkov
PreliminaryTab-top meas.
By Wavelength shifter (WLS)?
By Primary fluor (PF)?
By Solvent ?Photon
Absorbed?
TransportationReemission?
Dead
Reemission?
Re-emission (by PF or WLS)
Dead
Yes
NO