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Xin Qian, BNL 1
Results from Daya Bay
Xin QianOn behalf of Daya Bay Collaboration
Xin Qian, BNL 2
Design goal for systematic 0.2~0.4% (relative)
The largest, deepest reactor Θ13 experiment in Town, aimed for
sin22θ13 <0.01 @ 90% C. L.
Xin Qian, BNL 3
Key to reach 0.01• (Stat) Powerful reactors (17.6 GW) +Large Mass (80 ton)
• (Sys) Reactor related: using near/far to form ratio + baseline (near ~0.4 km, far ~1.7 km)
• (Sys) Detector related: “identical detectors” + “precise detector calibration”
• (Sys) Background related: deep underground to reduce cosmic + active/passive shielding
Far/Near νe Ratio
Detector Target Mass
Distances from reactor
Detector efficiency
Oscillation deficit
Xin Qian, BNL 4
The Daya Bay Collaboration
4
~230 collaborators
Xin Qian, BNL 5
Daya Bay Anti-νe Detector
192 Photomultipliers on the surrounding wall
Outer acrylic tank22 ton liquid scintillator (gamma catching)
Automated calibration system
Inner acrylic tank20 ton Gd-loaded liquid scintillator (Target)
Steel tank40 ton mineral oil (Shielding)
Reflectors at top/bottom of cylinderEffective photo-cathode coverage ~12%
7.5( 0.9)%
( )
E
E E MeV
5 m diameter
Xin Qian, BNL 6
Muon Veto SystemDual tagging systems: 2.5 meter thick two-section
water shield and Resistance Plate Chambers (RPC)
Two Zone ultrapure water Cherenkov detector
AD: Anti-neutrino Detector
Xin Qian, BNL 7
Uncertainty BudgetsBackgrounds Near Far + systematic uncertainties
Accidental ~1.7% ~4.6% + negligible sys.
ACU-N ~0.04% ~0.36% + 50% relative sys
Li9/He8 ~0.35% ~0.3% + 24% relative sys
Fast-N ~0.14% ~0.05% + 50% relative
Alpha-N ~0.01% ~0.05% + 50% relative sys
Really small background contamination!Detector related:
0.12% (energy calibration) + ~0.1% (Gd capture ratio) + …
Reactor related: 0.8% ~0.04% in ratio
Xin Qian, BNL 8
The Hunting Race for θ13 Since 20112011
2013
March 2012, Daya Bay reported the discovery of non-zero value of θ13 with a statistical significance > 5σ
Xin Qian, BNL 9
∣ Δ𝑚𝑒𝑒2 ∣≈ ∣Δ𝑚32
2 ∣±5.21×10− 5𝑒𝑉 2
Due to the short baseline, Daya Bay can observe one effective |Δm2
ee|, which is is a constant shift of |Δm2
32| for two mass hierarchies
Monte Carlo
UnoscillatedOscillated
Spectral Oscillation
𝑃 ( ν̄𝑒→ν̄ 𝑒)≈1−sin22θ13sin2(1.27 Δ𝑚𝑒𝑒2 𝐿𝐸 )
|Δm2ee|
+(-) for Normal (Inverted) Mass Hierarchy
Normal Inverted
|Δm2ee|
m12
m22
m32
m12
m22
m32
5.21×10− 5𝑒𝑉 2
We can also measure |Δm2ee| thanks to the “large” θ13
Xin Qian, BNL 10
IBD Prompt Spectra
• Clear observation of spectral distortion
• Agree with 3-neutrino oscillation hypothesis
Xin Qian, BNL 11
Rate and Spectral Analysis 𝐬𝐢𝐧𝟐𝟐𝛉𝟏𝟑=𝟎 .𝟎𝟗𝟎−𝟎.𝟎𝟎𝟗+𝟎 .𝟎𝟎𝟖
∣𝚫𝐦𝑒𝑒𝟐 ∣=𝟐 .𝟓𝟗−𝟎 .𝟐𝟎
+𝟎.𝟏𝟗×𝟏𝟎−𝟑 (𝑒𝑉 𝟐 )
𝚫𝐦𝟑𝟐𝟐 =𝟐 .𝟓𝟒−𝟎 .𝟐𝟎
+𝟎 .𝟏𝟗 ×𝟏𝟎−𝟑 (𝑒𝑉 𝟐 )
𝚫𝐦𝟑𝟐𝟐 =−𝟐 .𝟔𝟒−𝟎.𝟐𝟎
+𝟎 .𝟏𝟗×𝟏𝟎−𝟑 (𝑒𝑉 𝟐 )
χ 2/𝑁𝐷𝐹=162.7/153
𝚫𝐦𝟑𝟐𝟐 =𝟐 .𝟑𝟕−𝟎 .𝟎𝟗
+𝟎 .𝟎𝟗 ×𝟏𝟎−𝟑 (𝑒𝑉 𝟐)
𝚫𝐦𝟑𝟐𝟐 =−𝟐 .𝟒𝟏−𝟎.𝟎𝟗
+𝟎 .𝟏𝟏×𝟏𝟎−𝟑 (𝑒𝑉 𝟐 )
Normal
Inverted
A.Radovic, DPF2013
Consistent with the MINOS result
Daya Bay (νe disappearance) MINOS (νμ disappearance)
Xin Qian, BNL 12
Current Status and Upcoming Results n-H rate-only results
8% improvement with nGd
Compiled with latest results2
13sin 2 0.083 0.018n H
Results to be reported at Neutrino 14 and ICHEP:1. Oscillation results with ~ 4 x data 2. Light sterile neutrino search with spectral distortion3. Absolute reactor flux…
Xin Qian, BNL 13
Search for Light Sterile Neutrino
2 24 2 2 2 2 41
14 13 14( ) 1 cos sin 2 sin sin 2 sin4 4ee
e em L m L
PE E
• Effects of sterile neutrino would appear as additional spectral distortion and overall rate deficit
• Unique feature of Daya Bay with multiple baseline
• Can probe largely unexplored region at 2 241 0.1 m eV
Claims from cosmologye.g. arXiv:1403.7028
Xin Qian, BNL 14
Absolute Normalization Projection
Reactor Anomaly
• Reactor, LSND, Gallium anomalies ~ eV sterile neutrino ???
• Daya Bay can provide new information at ~ 360 m
• Currently ~ 2.2% • Goal to reach < 1% in
the future
• U235, Pu239, Pu241 from Huber PRC84,024617
• U238 from Mueller et al. PRC83,054615
• Also A. C. Hayes et al. arXiv:1309.4146“… forbidden transitions can lead to antineutrino spectra that differ both in shape and magnitude at ~ 4% level”
Xin Qian, BNL 15
Precision Measurement Phase
Combination of n-Gd and n-H with anticipated systematics improvements(sin22θ13 =0.09, Δm2
ee =2.41e-3 eV2)
The most precise measurement of sin22θ13 for the foreseeable future
sin22θ13 Δm2ee
Xin Qian, BNL 16
Summary
• We now determined θ13
• Large value of θ13 opens doors to study mass hierarchy, leptonic CP phase …– JUNO , LBNE, Hyper-K, LBNO …
• We enter the precision era of neutrino physics– Exciting decades to come!
2 0.00813 0.009
2 0.20 3 20.19
Daya Bay: sin 2 0.090
| | 2.59 10 eVeem
Xin Qian, BNL 17
Xin Qian, BNL 18