View source for Daya Bay Reactor Neutrino Experiment

{{Short description|Particle physics experiment studying neutrinos}}
{{coord|22.5953|N|114.5431|E|display=title}}
[[File:The Daya Bay Antineutrino Detector (8056998030).jpg|300px|thumb|One of the Daya Bay detectors.]]
The '''Daya Bay Reactor Neutrino Experiment''' is a [[China]]-based multinational [[particle physics]] project studying [[neutrino]]s, in particular [[neutrino oscillations]].  The multinational collaboration includes researchers from China, Chile, the United States, Taiwan (Republic of China), Russia, and the Czech Republic.  The US side of the project is funded by the [[United States Department of Energy|US Department of Energy]]'s Office of High Energy Physics.

It is situated at [[Daya Bay]], approximately 52&nbsp;kilometers northeast of [[Hong Kong]] and 45&nbsp;kilometers east of [[Shenzhen]]. There is an affiliated project in the [[Aberdeen Tunnel Underground Laboratory]] in Hong Kong. The Aberdeen lab measures the [[neutron]]s produced by [[cosmic ray|cosmic]] [[muon]]s which may affect the Daya Bay Reactor Neutrino Experiment.

The experiment consists of eight [[antineutrino]] detectors, clustered in three locations within {{convert|1.9|km|mi|abbr=on}} of six nuclear reactors. Each detector consists of 20&nbsp;tons of liquid scintillator ([[linear alkylbenzene]] doped with [[gadolinium]]) surrounded by [[photomultiplier tube]]s and shielding.<ref>{{Cite journal |title=A side-by-side comparison of Daya Bay antineutrino detectors |url=https://www.researchgate.net/publication/237172571 |arxiv=1202.6181 |author=Daya Bay collaboration |journal=Nuclear Instruments and Methods in Physics Research A |volume=685 |issue=1 |pages=78–97 |date=22 May 2012 |doi=10.1016/j.nima.2012.05.030|bibcode = 2012NIMPA.685...78A |s2cid=7471018 }}</ref>

A much larger follow-up is in development in the form of the [[Jiangmen Underground Neutrino Observatory]] (JUNO) in [[Kaiping]],<ref>{{Cite conference |url=http://vietnam.in2p3.fr/2013/Inauguration/transparencies/XiaoNanLi.pdf |title=Daya Bay II: Jiangmen Underground Neutrino Observatory (JUNO) |first1=Xiaonan |last1=Li |conference=Windows On the Universe |conference-url=http://vietnam.in2p3.fr/2013/Inauguration/ |date=August 2013}}</ref> which will use an acrylic sphere filled with 20,000&nbsp;tons of liquid scintillator to detect reactor antineutrinos. Groundbreaking began 10&nbsp;January 2015, with operation expected in 2020.<ref>{{Cite news |url=http://www.interactions.org/cms/?pid=1034412 |title=Groundbreaking at JUNO |date=10 January 2015 |work=Interactions NewsWire |access-date=2015-01-12}}</ref>

==Neutrino oscillations==
The experiment studies [[neutrino oscillations]] and is designed to measure the mixing angle [[Pontecorvo–Maki–Nakagawa–Sakata matrix|''θ''<sub>13</sub>]] using antineutrinos produced by the reactors of the [[Daya Bay Nuclear Power Plant]] and the [[Ling Ao Nuclear Power Plant]]. Scientists are also interested in whether neutrinos [[CP-violation|violate Charge-Parity conservation]].

On 8&nbsp;March 2012, the Daya Bay collaboration announced<ref>{{cite journal|title=Observation of electron-antineutrino disappearance at Daya Bay |url=http://resolver.caltech.edu/CaltechAUTHORS:20120521-073412262 |author=Daya Bay Collaboration |year=2012 |journal=Physical Review Letters |volume=108 |issue=17 |page=171803 |doi=10.1103/PhysRevLett.108.171803 |arxiv=1203.1669 |bibcode=2012PhRvL.108q1803A |pmid=22680853|s2cid=16580300 }}</ref><ref>{{cite web |author=Adrian Cho |url=https://www.science.org/content/article/physicists-china-nail-key-neutrino-measurement |title=Physicists in China Nail a Key Neutrino Measurement |date=8 March 2012 |publisher=ScienceNow}}</ref><ref>{{cite journal |author=Eugenie Samuel Reich |url=http://www.nature.com/news/neutrino-oscillations-measured-with-record-precision-1.10202 |title=Neutrino oscillations measured with record precision |journal=Nature |date=8 March 2012 |doi=10.1038/nature.2012.10202 |doi-access=}}</ref> a [[Statistical significance#In terms of σ (sigma)|5.2σ]] discovery of ''θ''<sub>13</sub> ≠ 0, with
: <math> \sin^2 (2\ \theta_{13}) = 0.092 \pm 0.016 \, \mathrm{(stat)} \pm 0.005\, \mathrm{(syst)}. </math>

This significant result represents a new type of oscillation and is surprisingly large.<ref>{{cite press release |url=http://neutrino.physics.berkeley.edu/News/Discovery%20of%20a%20New%20Kind%20of%20Neutrino%20Transformation.html |title=Announcing the First Results from Daya Bay: Discovery of a New Kind of Neutrino Transformation |date=8 March 2012 |publisher=[[University of California, Berkeley]]}}</ref> It is consistent with earlier, less significant results by [[T2K]], [[MINOS]] and [[Double Chooz]]. With ''θ''<sub>13</sub> so large, [[NOνA]] has about a 50% probability of being sensitive to the neutrino mass hierarchy. Experiments may also be able to probe CP&nbsp;violation among neutrinos.

The collaboration produced an updated analysis of their results in 2014,<ref>{{cite journal |author=Daya Bay Collaboration |title=Spectral measurement of electron antineutrino oscillation amplitude and frequency at Daya Bay |url=http://resolver.caltech.edu/CaltechAUTHORS:20140327-145449958 |date=10 February 2014 |journal=Physical Review Letters |volume=112 |issue=6 |page=061801 |doi=10.1103/PhysRevLett.112.061801 |arxiv=1310.6732 |bibcode = 2014PhRvL.112f1801A |pmid=24580686|s2cid=7332532 }}</ref> which used the energy spectrum to improve the bounds on the mixing angle:
: <math> \sin^2 (2\ \theta_{13}) = 0.090^{+0.008}_{-0.009} </math>

An independent measurement was also published using events from neutrons captured on hydrogen:<ref>{{Cite journal |url=http://resolver.caltech.edu/CaltechAUTHORS:20141204-112407246 |title=Independent measurement of the neutrino mixing angle ''θ''<sub>13</sub> via neutron capture on hydrogen at Daya Bay |author=Daya Bay Collaboration |date=3 October 2014 |journal=Phys. Rev. D |volume=90 |issue=7 |page=071101 |doi=10.1103/PhysRevD.90.071101 |arxiv=1406.6468 |bibcode = 2014PhRvD..90g1101A |s2cid=14698730 }}</ref>
:<math>\sin^2 (2\ \theta_{13}) = 0.083 \pm 0.018</math>.

Daya Bay has used its data to search for signals of a light sterile neutrino, resulting in exclusions of some previous unexplored mass regions.<ref>{{Cite journal |title=Search for a Light Sterile Neutrino at Daya Bay |url=http://resolver.caltech.edu/CaltechAUTHORS:20141205-151429088 |author=Daya Bay Collaboration |date=1 October 2014 |journal=Phys. Rev. Lett. |volume=113 |issue=14 |page=141802 |doi=10.1103/PhysRevLett.113.141802 |pmid= 25325631|arxiv=1407.7259 |bibcode = 2014PhRvL.113n1802A |s2cid=10500157 }}</ref>

At the Moriond&nbsp;2015 physics conference a new best fit for mixing angle and mass difference was presented:<ref>{{Cite arXiv |eprint=1505.03641 |title=Recent Results from Daya Bay Reactor Neutrino Experiment |date=14 May 2015 |author=Bei-Zhen Hu |display-authors=etal |class=hep-ex}}</ref>
:<math>\sin^2(2\ \theta_{13}) = 0.084 \pm 0.005, \qquad |\Delta m^2_{ee}| = 2.44^{+0.10}_{-0.11} \times 10^{-3} {\rm eV}^2</math>

On 21 April 2023 (published), Daya Bay's reports the following precision measurements: 

<math>\sin^2(2\ \theta_{13}) = 0.0851 \pm 0.0024,\qquad \Delta m^2_{32} = (2.466 \pm 0.060) \times
10^{-3} {\rm eV}^2 </math> for the normal mass ordering or <math> \Delta m^2_{32} = -(2.571\pm 0.060)\times 10^{-3} {\rm eV}^2</math>, for the inverted mass ordering.<ref>{{cite journal | title= Precision Measurement of Reactor Antineutrino Oscillation at Kilometer-Scale Baselines by Daya Bay | author = F. P. An et al. (Daya Bay Collaboration) | journal = Physical Review Letters |volume = 130 |page = 161802 | year = 2023 | issue = 16 | doi= 10.1103/PhysRevLett.130.161802 | arxiv = 2211.14988 }}</ref> The Daya Bay collaboration suggests, "The reported <math>\sin^2(2\ \theta_{13})</math> will likely remain the most precise measurement of <math>\theta_{13}</math> in the foreseeable future and be crucial to the investigation of the mass hierarchy and CP violation in neutrino oscillation."

== Antineutrino spectrum ==
Daya Bay Collaboration measured the anti-neutrino energy spectrum, and found that anti-neutrinos at an energy of around 5&nbsp;MeV are in excess relative to theoretical expectations. This unexpected disagreement between observation and predictions suggested that the [[Standard model]] of particle physics needs improvement.<ref>{{Cite journal |title=Measurement of the reactor antineutrino flux and spectrum at Daya Bay |journal=Physical Review Letters |date=2016-02-12 |page=061801 |volume=116 |issue=6 |doi=10.1103/PhysRevLett.116.061801 |pmid=26918980 |collaboration=Daya Bay Collaboration |first1=F.P. |last1=An |display-authors=etal |bibcode=2016PhRvL.116f1801A |arxiv=1607.05378 |s2cid=8567768 |df=dmy-all}}</ref>

==See also==
* [[Neutrino]]
* [[Sterile neutrino]]
* [[Weak interaction]]

==External links ==
* {{cite web |url=http://dayawane.ihep.ac.cn/ |title=Daya Bay home page}}
* {{cite web |url=http://www.symmetrymagazine.org/cms/?pid=1000393 |title=Catching neutrinos in China |magazine=Symmetry Magazine |access-date=2006-11-15 |archive-url=https://web.archive.org/web/20070927225120/http://www.symmetrymagazine.org/cms/?pid=1000393 |archive-date=2007-09-27 |url-status=dead }}
* {{cite web |url=http://theta13.phy.cuhk.edu.hk/ |title=Daya Bay ''θ''<sub>13</sub> reactor neutrino experiment & Aberdeen cosmic ray muon-induced neutron experiment |department=Department of Physics |publisher=The Chinese University of Hong Kong |access-date=2007-04-27 |archive-url=https://web.archive.org/web/20070510091222/http://theta13.phy.cuhk.edu.hk/ |archive-date=2007-05-10 |url-status=dead }}

== Collaborators ==
{{columns-list|colwidth=22em|
*[[Beijing Normal University]]
*[[Brookhaven National Laboratory]]
*[[Catholic University of Chile]]
*[[California Institute of Technology]]
*[[Charles University]]
*[[Chengdu University of Technology]]
*[[China Guangdong Nuclear Power Group]]
*[[China Institute of Atomic Energy]]
*[[Chinese Academy of Sciences]]
*[[Chinese University of Hong Kong]]
*[[College of William and Mary]]
*[[Dongguan Institute of Technology]]
*[[Illinois Institute of Technology]]
*[[Institute of High Energy Physics]]
*[[Iowa State University]]
*[[Joint Institute for Nuclear Research]]
*[[Kurchatov Institute]]
*[[Lawrence Berkeley National Laboratory]] and [[University of California at Berkeley]]
*[[Nanjing University]]
*[[Nankai University]]
*[[National Chiao-Tung University]]
*[[National Taiwan University]]
*[[National United University]]
*[[Princeton University]]
*[[Rensselaer Polytechnic Institute]]
*[[Shandong University]]
*[[Shanghai Jiao Tong University]]
*[[Shenzhen University]]
*[[Siena College]]
*[[Sun Yat-sen University|Sun Yat-Sen (Zhongshan) University]]
*[[Temple University]]
*[[Tsinghua University]]
*[[University of California at Irvine]]
*[[University of California at Los Angeles]]
*[[University of Hong Kong]]
*[[University of Houston]]
*[[University of Illinois at Urbana–Champaign]]
*[[University of Science and Technology of China]]
*[[University of Wisconsin]]
*[[Yale University]]
*[[Virginia Polytechnic Institute and State University]]
}}

==References==
<references />

{{Neutrino detectors}}

[[Category:Reactor neutrino experiments]]
[[Category:Science and technology in the People's Republic of China]]
[[Category:Nuclear technology in China]]
[[Category:Underground laboratories]]