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.

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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

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The Daya Bay Collaboration

4

~230 collaborators

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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

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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

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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

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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

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∣ 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

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IBD Prompt Spectra

• Clear observation of spectral distortion

• Agree with 3-neutrino oscillation hypothesis

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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)

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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…

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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

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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”

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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

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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

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