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{{other uses|Nova}}
{{Infobox observatory
|name=NOvA Neutrino Experiment
|background=
|image=[[File:NOvA Far Detector.jpg|300px]]
|caption=Photo of the NOvA Far Detector
|organization=NOvA collaboration
|location=Ash River, Minnesota, United States
|coords={{coord|48|22|45|N|92|50|1|W|region:AQ|display=inline,title}}
|website={{URL|http://novaexperiment.fnal.gov/}}
}}

[[File:NormanAirbusComparison.pdf|thumb|A comparison of the NOvA far and near detectors with the size of an Airbus A380.]]
The '''NOνA''' ([[NuMI]] Off-Axis ν<sub>e</sub> Appearance) experiment is a [[particle physics]] experiment designed to detect [[neutrinos]] in [[Fermilab]]'s [[NuMI]] (Neutrinos at the Main Injector) [[Accelerator neutrino|beam]].  Intended to be the successor to [[MINOS]], NOνA consists of two detectors, one at Fermilab (the ''near detector''), and one in northern Minnesota (the ''far detector'').  Neutrinos from [[NuMI]] pass through 810&nbsp;km of Earth to reach the far detector.  NOνA's main goal is to observe the [[neutrino oscillation|oscillation]] of muon neutrinos to electron neutrinos.  The primary physics goals of NOvA are:<ref name="RadovicWC">{{cite web|last1=Radovic|first1=Alexander|title=Latest Oscillation Results from NOvA from NOvA|url=http://nova-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=25938&filename=radovicJETPFinalPublic.pdf&version=3|website=NOvA Document Database|publisher=Femilab|access-date=30 March 2018|format=Joint Experimental-Theoretical Physics|date=12 January 2018}}</ref> 
* Precise measurement, for neutrinos and antineutrinos, of the [[PMNS matrix|mixing angle]] θ<sub>23</sub>, especially whether it is larger than, smaller than, or equal to 45°
* Precise measurement, for neutrinos and antineutrinos, of the associated mass splitting Δm<sup>2</sup><sub>32</sub>
* Strong constraints on the [[CP symmetry|CP-violating]] phase δ
* Strong constraints on the neutrino mass hierarchy

== Physics goals ==

=== Primary goals ===
Neutrino oscillation is parameterized by the [[PMNS matrix]] and the mass squared differences between the neutrino mass [[eigenstate]]s. Assuming that three [[flavor (physics)|flavors]] of neutrinos participate in neutrino mixing, there are six variables that affect neutrino oscillation: the three angles ''θ''<sub>12</sub>, ''θ''<sub>23</sub>, and ''θ''<sub>13</sub>, a CP-violating phase ''δ'', and any two of the three mass squared differences. There is currently no compelling theoretical reason to expect any particular value of, or relationship between, these parameters.

''θ''<sub>23</sub> and ''θ''<sub>12</sub> have been measured to be non-zero by several experiments but the most sensitive search for non-zero ''θ''<sub>13</sub> by the [[Chooz (experiment)|Chooz collaboration]] yielded only an upper limit. In 2012, ''θ''<sub>13</sub> was measured at [[Daya Bay]] to be non-zero to a [[statistical significance]] of [[Statistical significance#In terms of σ (sigma)|5.2&nbsp;''σ'']].<ref>{{cite journal |collaboration=Daya Bay Collaboration |arxiv=1203.1669 |title=Observation of electron-antineutrino disappearance at Daya Bay |date=8 March 2012 |doi=10.1103/PhysRevLett.108.171803 |volume=108 |journal=Physical Review Letters |bibcode=2012PhRvL.108q1803A |pmid=22680853 |page=171803 |last1=An |first1=F. P. |last2=Bai |first2=J. Z. |last3=Balantekin |first3=A. B. |last4=Band |first4=H. R. |last5=Beavis |first5=D. |last6=Beriguete |first6=W. |last7=Bishai |first7=M. |last8=Blyth |first8=S. |last9=Boddy |first9=K. |last10=Brown |first10=R. L. |last11=Cai |first11=B. |last12=Cao |first12=G. F. |last13=Cao |first13=J. |last14=Carr |first14=R. |last15=Chan |first15=W. T. |last16=Chang |first16=J. F. |last17=Chang |first17=Y. |last18=Chasman |first18=C. |last19=Chen |first19=H. S. |last20=Chen |first20=H. Y. |last21=Chen |first21=S. J. |last22=Chen |first22=S. M. |last23=Chen |first23=X. C. |last24=Chen |first24=X. H. |last25=Chen |first25=X. S. |last26=Chen |first26=Y. |last27=Chen |first27=Y. X. |last28=Cherwinka |first28=J. J. |last29=Chu |first29=M. C. |last30=Cummings |first30=J. P. |issue=17 |s2cid=16580300 |display-authors=1 }}</ref> The following year, [[T2K]] discovered the transition <math>\nu_{\mu}\rightarrow\nu_{e}</math> excluding the non-appearance hypothesis with a significance of 7.3&nbsp;''σ''.<ref>{{cite journal |author1=Abe, K. |display-authors=etal |collaboration=T2K Collaboration |arxiv=1311.4750 |title=Observation of electron neutrino appearance in a muon neutrino beam <!-- |edition=2nd vers. --> |journal=Physical Review Letters |date=16 Apr 2014 <!-- |orig-year=2013 -->|volume=112 |issue=6 |page=061802 |doi=10.1103/PhysRevLett.112.061802 |pmid=24580687 |bibcode=2014PhRvL.112f1802A |s2cid=2586182 }}</ref> No measurement of ''δ'' has been made. The absolute values of two mass squared differences are known, but because one is very small compared to the other, the ordering of the masses has not been determined.

[[Image:Nu e appearance for various delta.png|thumb|Oscillation probabilities, ignoring matter effects and assuming ''θ''<sub>13</sub> is near the current limit. NOνA will observe the first peak.]]

NOνA is an order of magnitude more sensitive to ''θ''<sub>13</sub> than the previous generation of experiments, such as [[MINOS]]. It will measure it by searching for the transition <math>\nu_{\mu}\rightarrow\nu_{e}</math> in the Fermilab [[NuMI]] beam. If a non-zero value of ''θ''<sub>13</sub> is resolvable by NOνA, it will be possible to obtain measurements of ''δ'' and the mass ordering by also observing <math>\bar{\nu}_{\mu}\rightarrow\bar{\nu}_{e}.</math> The parameter ''δ'' can be measured because it modifies the probabilities of oscillation differently for neutrinos and anti-neutrinos. The mass ordering, similarly, can be determined because the neutrinos pass through the Earth, which, through the [[MSW effect]], modifies the probabilities of oscillation differently for neutrinos and anti-neutrinos.<ref name="proposal">{{cite arXiv |title=NOνA proposal to build a 30&nbsp;kiloton off-axis detector to study neutrino oscillations in the Fermilab [[NuMI]] beamline |author1=Ayres, D.S. |year=2005 |display-authors=etal |collaboration=NOνA Collaboration |eprint=hep-ex/0503053}}</ref>

=== Importance ===
The neutrino masses and mixing angles are, to the best of our knowledge, fundamental constants of the universe. Measuring them is a basic requirement for our understanding of physics. Knowing the value of the [[CP-violation|CP violating]] parameter ''δ'' will help us understand why the universe has a [[Baryogenesis|matter-antimatter asymmetry]]. Also, according to the [[Seesaw mechanism]] theory, the very small masses of neutrinos may be related to very large masses of particles that we do not yet have the technology to study directly.  Neutrino measurements are then an indirect way of studying physics at extremely high energies.<ref name="proposal" />

In our current theory of physics, there is no reason why the neutrino mixing angles should have any particular values. And yet, of the three neutrino mixing angles, only ''θ''<sub>12</sub> has been resolved as being neither maximal or minimal. If the measurements of NOνA and other future experiments continue to show ''θ''<sub>23</sub> as maximal and ''θ''<sub>13</sub> as minimal, it may suggest some as yet unknown symmetry of nature.<ref name="proposal" />

=== Relationship to other experiments ===
NOνA can potentially resolve the mass hierarchy because it operates at a relatively high energy. Of the experiments currently running it has the broadest scope for making this measurement unambiguously with least dependence on the value of ''δ''. Many future experiments that seek to make precision measurements of neutrino properties will rely on NOνA's measurement to know how to configure their apparatus for greatest accuracy, and how to interpret their results.

An experiment similar to NOνA is [[T2K]], a neutrino beam experiment in Japan similar to NOνA. Like NOνA, it is intended to measure ''θ''<sub>13</sub> and ''δ''. It will have a 295&nbsp;km baseline and will use lower energy neutrinos than NOνA, about 0.6&nbsp;GeV. Since [[MSW effect|matter effects]] are less pronounced both at lower energies and shorter baselines, it is unable to resolve the mass ordering for the majority of possible values of ''δ''.<ref>{{cite web |url=http://neutrino.kek.jp/jhfnu/loi/loi.v2.030528.pdf |type=Letter of Intent |title=Neutrino Oscillation Experiment at JHF |publisher=JHF |department=The T2K Collaboration |date=21 Jan 2003}}</ref>

The interpretation of [[Neutrinoless double beta decay]] experiments will also benefit from knowing the mass ordering, since the mass hierarchy affects the theoretical lifetimes of this process.<ref name="proposal" />

[[Nuclear reactor|Reactor]] experiments also have the ability to measure ''θ''<sub>13</sub>. While they cannot measure ''δ'' or the mass ordering, their measurement of the mixing angle is not dependent on knowledge of these parameters. The three experiments that have measured a value for ''θ''<sub>13</sub>, in deceasing order of sensitivity are [[Daya Bay Reactor Neutrino Experiment|Daya Bay]] in China, [[Reactor Experiment for Neutrino Oscillation|RENO]] in South Korea and [[Double Chooz]] in France, which use 1-2&nbsp;km baselines, optimized for observation of the first ''θ''<sub>13</sub>-controlled oscillation maximum.<ref>{{cite journal |title=Daya Bay Neutrino Experiment |author=Cao, J. |journal=Nuclear Physics B - Proceedings Supplements |arxiv=hep-ex/0509041 |date=27 Sep 2005|volume=155 |pages=229–230 |doi=10.1016/j.nuclphysbps.2006.02.057 |s2cid=242130 }}</ref>

=== Secondary goals ===
In addition to its primary physics goals, NOνA will be able to improve upon the measurements of the already measured oscillation parameters. NOνA, like [[MINOS]], is well suited to detecting muon neutrinos and so will be able to refine our knowledge of ''θ''<sub>23</sub>.

The NOνA near detector will be used to conduct measurements of neutrino interaction [[cross section (physics)|cross sections]] which are currently not known to a high degree of precision. Its measurements in this area will complement other similar upcoming experiments, such as [[MINERνA]], which also uses the [[NuMI]] beam.<ref>{{cite journal |title=MINERνA: A dedicated neutrino scattering experiment at NuMI |author1=McFarland, K. |journal=Nuclear Physics B - Proceedings Supplements |year=2006 |volume=159 |pages=107–112 |doi=10.1016/j.nuclphysbps.2006.08.073 |display-authors=etal |collaboration=MINERνA collaboration |arxiv=physics/0605088|bibcode=2006NuPhS.159..107M |s2cid=14356072 }}</ref>

Since it is capable of detecting [[Supernova neutrinos|neutrinos]] from [[Milky Way|galactic]] [[supernova]]s, NOνA will form part of the [[Supernova Early Warning System]]. Supernova data from NOνA can be correlated with that from Super-Kamiokande to study the matter effects on the oscillation of these neutrinos.<ref name="proposal" />

== Design ==
To accomplish its physics goals, NOνA needs to be efficient at detecting electron neutrinos, which are expected to appear in the [[NuMI]] [[Accelerator neutrino|beam]] (originally made only of muon neutrinos) as the result of neutrino oscillation.

[[Image:Cross section of earth showing numi beam, minos and nova.png|thumb|Cross section of the earth showing Fermilab, [[MINOS]] and NOνA, to scale. The red line is the central axis of the [[NuMI]] beam.]]
Previous neutrino experiments, such as [[MINOS]], have reduced backgrounds from [[cosmic rays]] by being underground. However, NOνA is on the surface and relies on precise timing information and a well-defined beam energy to reduce spurious background counts. It is situated 810&nbsp;km from the origin of the [[NuMI]] beam and 14&nbsp;[[milliradian]]s (12&nbsp;km) west of the beam's central axis. In this position, it samples a beam that has a much narrower energy distribution than if it were centrally located, further reducing the effect of backgrounds.<ref name="proposal" />

The detector is designed as a pair of finely grained liquid scintillator detectors. The near detector is at Fermilab and samples the unoscillated{{typo help inline|date=May 2021}} beam.  The far detector is in northern Minnesota, and consists of about 500,000&nbsp;cells, each 4&nbsp;cm × 6&nbsp;cm × 16&nbsp;m, filled with liquid [[scintillator]]. Each cell contains a loop of bare [[fiber optic]] cable to collect the scintillation light, both ends of which lead to an [[avalanche photodiode]] for readout.

[[File:NOvA Near Detector.jpg|thumb|The NOνA near detector. (More figures at Fermilab<ref>{{cite web |url=http://www-nova.fnal.gov/plots_and_figures/plots_and_figures.html#1000_Detector_Overview |title=Detector overview |series=NOνA |publisher=Fermilab |website=fnal.gov}}</ref>)]]
The near detector has the same general design, but is only about {{frac|1|200}} as massive. This 222&nbsp;ton detector is constructed of 186&nbsp;planes of scintillator-filled cells (6&nbsp;blocks of 31&nbsp;planes) followed by a [[muon]] catcher. Although all the planes are identical, the first&nbsp;6 are used as a veto region; particle showers which begin in them are assumed to not be neutrinos and ignored. The next 108&nbsp;planes serve as the fiducial region; particle showers beginning in them are neutrino interactions of interest. The final 72&nbsp;planes are a "shower containment region" which observe the trailing portion of particle showers which began in the fiducial region. Finally, a 1.7&nbsp;meter long "muon catcher" region is constructed of steel plates interleaved with 10&nbsp;active planes of liquid scintillator.


== Collaboration ==

The NOνA experiment includes scientists from a large number of institutions.  Different institutions take on different tasks.  The collaboration, and subgroups thereof, meets regularly via phone for weekly meetings, and in person several times a year.  Participating institutions as of May 2024 are:<ref>[http://novaexperiment.fnal.gov/collaboration/ NOνA webpage: The NOvA Collaboration], retrieved 2024 May 31</ref>

{{columns-list|colwidth=22em|
*[[Argonne National Laboratory]]
*[[Universidad del Atlantico]]
*[[Banaras Hindu University]]
*[[California Institute of Technology]]
*[[Cochin University of Science and Technology]]
*Institute of Computer Science of the [[Academy of Sciences of the Czech Republic]]
*Institute of Physics of the [[Academy of Sciences of the Czech Republic]]
*[[Charles University in Prague]], Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics
*[[University of Cincinnati]]
*[[Colorado State University]]
*[[Czech Technical University]]
*[[University of Delhi]]
*[[Joint Institute For Nuclear Research]], Dubna
*[[Erciyes University]]
*[[Fermi National Accelerator Laboratory]]
*[[Universidade Federal de Goias]]
*[[Florida State University]]
*[[Indian Institute of Technology Guwahati]]
*[[Harvard University]]
*[[University of Houston]]
*[[Indian Institute of Technology Hyderabad]]
*[[University of Hyderabad]]
*[[Illinois Institute of Technology]]
*[[Indiana University]]
*[[University of Iowa]]
*[[Iowa State University]]
*[[University of California, Irvine]]
*[[University College London]]
*[[Universidad del Magdalena]]
*[[Michigan State University]]
*[[University of Minnesota, Duluth]]
*[[University of Minnesota, Minneapolis]]
*[[University of Mississippi]]
*[[National Institute of Science Education and Research]], Bhubaneswar, India
*[[Institute for Nuclear Research]], Moscow
*[[Panjab University]]
*[[University of Pittsburgh]]
*[[Queen Mary University of London]]
*[[University of South Alabama]]
*[[University of South Carolina, Columbia]]
*[[Southern Methodist University]]
*[[Stanford University]]
*[[University of Sussex]]
*[[Syracuse University]]
*[[University of Texas, Austin]]
*[[Tufts University]]
*[[University of Virginia|University of Virginia, Charlottesville]]
*[[Wichita State University]]
*[[The College of William and Mary]]
*[[University of Wisconsin–Madison]]}}

== Funding history ==
In late 2007, NOνA passed a [[United States Department of Energy|Department of Energy]] "Critical Decision&nbsp;2" review, meaning roughly that its design, cost, schedule, and scientific goals had been approved. This also allowed the project to be included in the Department of Energy congressional budget request. (NOνA still required a "Critical Decision&nbsp;3" review to begin construction.)

On 21&nbsp;December 2007, President Bush signed an [[omnibus spending bill]], H.R.&nbsp;2764, which cut the funding for high energy physics by 88 million dollars from the expected value of 782&nbsp;million dollars.<ref>{{cite news |url=http://www.aip.org/fyi/2007/121.html |publisher=American Institute of Physics |series=FYI Number 121 |date=December 18, 2007 |title=Budget cycle closing with disappointing DOE science outcome |access-date=21 Dec 2007 |df=dmy-all}}</ref> The budget of [[Fermilab]] was cut by 52&nbsp;million dollars.<ref>{{cite news |url=http://www.chicagotribune.com/business/chi-fermilab_21_webdec21,0,6083502.story?coll=chi_tab01_layout |newspaper=Chicago Tribune |date=20 Dec 2007 |title=Fermilab budget slashed by $52&nbsp;million, layoffs likely |first=Russell |last=Working |access-date=21 Dec 2007 |archive-url=https://web.archive.org/web/20071224003349/http://www.chicagotribune.com/business/chi-fermilab_21_webdec21,0,6083502.story?coll=chi_tab01_layout |archive-date=2007-12-24 |df=dmy-all |url-status=dead}}</ref> This bill explicitly stated that "Within funding for Proton Accelerator-Based Physics, no funds are provided for the NOνA activity in Tevatron Complex Improvements."<ref>{{cite web |url=http://www.rules.house.gov/110/text/omni/jes/jesdivc.pdf |title=House Amendments to Senate Amendment to H.R.&nbsp;2764 – State, Foreign Operations, and Related Programs Appropriations Act, 2008 |series=Consolidated Appropriations Act, 2008 |department=Division C – Energy and Water |archive-url=https://web.archive.org/web/20071226202416/http://www.rules.house.gov/110/text/omni/jes/jesdivc.pdf |archive-date=2007-12-26 |df=dmy-all |page=39 (PDF page 79 |access-date=21 Dec 2007}}</ref><ref>{{cite web |url=http://www.rules.house.gov/110_fy08_omni.htm |title=Index page for the whole Amendment |series=H.R.&nbsp;2764 |archive-url=https://web.archive.org/web/20071226202601/http://www.rules.house.gov/110_fy08_omni.htm |archive-date=2007-12-26 |df=dmy-all}}</ref> So although the NOνA project retained its approval from both the Department of Energy and Fermilab, [[United States Congress|Congress]] left NOνA with no funds for the 2008 fiscal year to build its detector, pay its staff, or to continue in the pursuit of scientific results. However, in July&nbsp;2008, Congress passed, and the President signed, a supplemental budget bill,<ref>{{cite news |url=https://www.scientificamerican.com/article/fermilab-saved-from-chopp/ |title=Fermilab saved from chopping block — for now |first=J.R. |last=Minkel |date=7 July 2008 |magazine=[[Scientific American]] |df=dmy-all}}</ref> which included funding for NOνA, allowing the collaboration to resume its work.

The NOνA prototype near detector (Near Detector on Surface, or NDOS) began running at Fermilab in November and registered its first neutrinos from the [[NuMI]] beam on 15&nbsp;December 2010.<ref>{{cite news |url=http://www.fnal.gov/pub/today/archive_2010/today10-12-21.html |title=First neutrinos for NOvA prototype detector |newspaper=Fermilab Today |date=21 Dec 2010 |page=1 |access-date=22 Dec 2010 |df=dmy-all}}</ref> As a prototype, NDOS served the collaboration well in establishing a use case and suggesting improvements in the design of detector components that were later installed as a near detector at Fermilab, and a far detector at Ash River, MN ({{Coord|48.37912|N|92.83164|W|type:landmark_region:US-MN|name=NOνA far detector}}).

Once construction of the NOvA building was complete, construction of the detector modules began. On 26&nbsp;July 2012 the first module was laid in place. Placement and gluing of the modules continued over a year until the detector hall was filled.

The first detection occurred on 11&nbsp;February 2014 and construction completed in September that year. Full operation began in October&nbsp;2014.<ref>{{cite news |url=http://www.interactions.org/cms/?pid=1034170 |title=Fermilab's 500&nbsp;mile neutrino experiment up and running |date=6 October 2014 |agency=Interactions NewsWire |df=dmy-all}}</ref>

== References ==
{{reflist|25em}}

== External links ==
* {{Official website|http://novaexperiment.fnal.gov/|NOνA's official website}}
*[https://web.archive.org/web/20120603082826/http://www.symmetrymagazine.org/cms/?pid=1000240 "NOνA: a neutrino appearance experiment" article in ''Symmetry'' magazine]
*[http://www.symmetrymagazine.org/breaking/2009/09/14/nova-neutrino-detector-construction-photos/ Photos of the construction of the NOνA detector]
{{Neutrino detectors}}

{{DEFAULTSORT:Nova}}
[[Category:Accelerator neutrino experiments]]
[[Category:Fermilab]]
[[Category:Fermilab experiments]]