View source for MINOS

{{Short description|Particle physics experiment}}
{{other uses|Minos (disambiguation)}}

[[File:MINOS Project in Soudan Mine.jpg|thumb|Front face of the MINOS far detector. On the left is the control room and on the right is a mural by [[Joseph Giannetti]].]]
'''Main injector neutrino oscillation search''' ('''MINOS''') was a [[particle physics]] experiment designed to study the phenomena of [[neutrino oscillation]]s, first discovered by a [[Super-Kamiokande]] (Super-K) experiment in 1998. [[Neutrino]]s produced by the [[NuMI]] ("Neutrinos at Main Injector") [[Accelerator neutrino|beamline]] at [[Fermilab]] near [[Chicago]] are observed at two detectors, one very close to where the beam is produced (the ''near detector''), and another much larger detector 735&nbsp;km away in northern [[Minnesota]] (the ''far detector'').

The MINOS experiment started detecting neutrinos from the NuMI beam in February 2005. On 30 March 2006, the MINOS collaboration announced that the analysis of the initial data, collected in 2005, is consistent with neutrino oscillations, with the oscillation parameters which are consistent with Super-K measurements.<ref>
{{cite press release
 |date=30 March 2006 
 |url=http://www.fnal.gov/pub/presspass/press_releases/minos_3-30-06.html 
 |title=MINOS experiment sheds light on mystery of neutrino disappearance 
 |access-date=2009-08-03 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20070919005158/http://www.fnal.gov/pub/presspass/press_releases/minos_3-30-06.html 
 |archive-date=19 September 2007 
}}</ref>
MINOS received the last neutrinos from the NUMI beam line at midnight on 30 April 2012.<ref>{{cite web|title=MINOS Run Period Run Subrun Ranges (MRPRSR)|url=http://homepages.spa.umn.edu/~strait/minos/MINOS_runs|access-date=4 November 2012}}</ref><ref>{{cite web|last=de Jong|first=Jeffrey|title='Final' MINOS Results|url=http://www.ba.infn.it/~now/now2012/web-content/TALKS/Wedsnday12/parallel1/NOW2012_jdejong.pdf|date=12 September 2012|access-date=13 December 2012}}</ref> It was upgraded to [[MINOS+]] which started taking data in 2013.<ref>{{cite journal|last=Tzanankos|first=G|display-authors=etal|title=MINOS+: a Proposal to FNAL to run MINOS with the medium energy NuMI beam|journal=Fermilab-Proposal-1016|date=2011|url=http://lss.fnal.gov/archive/test-proposal/1000/fermilab-proposal-1016.pdf}}</ref> The experiment was shut down on June 29, 2016, and the far detector has been dismantled and removed. It was moved to Puerto Vallarta, Jalisco in Mexico.<ref>{{cite news|last1=Olmstead|first1=Molly|title=Fermilab bids a fond farewell to MINOS|url=http://news.fnal.gov/2016/08/fermilab-bids-fond-farewell-minos/|access-date=16 May 2017|agency=Fermi National Accelerator Lab|date=2016-08-01}}</ref>

==Detectors==
[[File:MINOS service building at Fermilab.jpg|thumb|MINOS service building at Fermilab, the entrance to the underground MINOS hall that hosts the near detector.<ref>{{cite news|last1=Basu|first1=Paroma|title=Physicists Say Multi-million Dollar Experiment Advancing Smoothly|url=https://www.wisconline.com/feature/neutrinos_images.html|access-date=14 August 2015|work=Wisconsin Online|date=30 March 2006}}</ref>]]

There are two detectors in the experiment.
*The near detector is similar to the far detector in design, but smaller in size with a mass of {{val|980|u=[[tonne|ton]]s}} (t). It is located at Fermilab, a few hundred meters away from the [[graphite]] target which the [[protons]] interact with, and approximately 100&nbsp;meters underground.  The commissioning of the near detector was completed in December 2004, and it is now fully operational.
*The far detector has a mass of {{val|5.4|u=[[tonne|kt]]}}. It is located in the [[Soudan mine]] in Northern Minnesota at a depth of 716&nbsp;meters. The far detector has been fully operational since summer 2003, and has been taking [[cosmic ray]] and atmospheric [[neutrino]] data since early in its construction.

Both MINOS detectors are [[steel]]-[[scintillator]] sampling [[calorimeter]]s made out of alternating planes of magnetized steel and [[plastic]] scintillators. The [[magnetic field]] causes the path of a [[muon]] produced in a [[muon neutrino]] [[weak interaction|interaction]] to bend, making it possible to distinguish interactions with neutrinos from those with antineutrinos. This feature of the MINOS detectors allows MINOS to search for [[CPT-symmetry|CPT-violation]] with atmospheric neutrinos and anti-neutrinos.

==Neutrino beam==
[[File:NuMI Target Hall at Femilab.jpg|thumb|NuMI Target Hall (left), the starting point of the NuMI tunnel with the Main Injector in the background.<ref>{{cite web|title=Site map of NuMI/MINOS|url=http://www-numi.fnal.gov/MinosAreas/SiteMap.jpg|website=Fermilab|access-date=14 August 2015}}</ref>]]

To produce the [[NuMI]] [[Accelerator neutrino|beamline]], 120&nbsp;GeV [[Fermilab#Accelerators|Main Injector]] proton pulses hit a water-cooled [[graphite]] target. The resulting interactions of protons with the target material produce [[pion]]s and [[kaon]]s, which are focused by a system of [[magnetic horn]]s. The neutrinos from subsequent decays of pions and kaons form the [[neutrino#Artificially produced neutrinos|neutrino beam]].  Most of these are muon neutrinos, with a small [[electron neutrino]] contamination.  Neutrino interactions in the near detector are used to measure the initial neutrino [[flux]] and energy spectrum.  Because they are weakly interacting and therefore usually pass through matter, the vast majority of the neutrinos travel through the near detector and the 734&nbsp;km of rock, then through the far detector and off into space. On the way toward Soudan, about 20% of the muon neutrinos oscillate into other [[flavor (physics)|flavor]]s.

==Physics goals and results==

MINOS measures the difference in neutrino beam composition and energy distribution in the near and far detectors with the aim of producing precision measurements of the neutrino squared mass difference and [[PMNS matrix|mixing angle]].  In addition, MINOS looks for the appearance of electron neutrinos in the far detector, and will either measure or set a limit on the oscillation probability of muon neutrinos into electron neutrinos.

On 29 July 2006, the MINOS collaboration published a paper giving their initial measurements of oscillation parameters as judged from muon neutrino disappearance.  These are: {{nowrap|Δ''m''{{su|p=2|b=23}} {{=}} {{val|2.74|0.44|-0.26}}}} × 10<sup>−3</sup> eV<sup>2</sup>/c<sup>4</sup> and {{nowrap|sin<sup>2</sup>(2''θ''<sub>23</sub>) > 0.87}} ([[standard deviation|68% confidence limit]]).<ref>
{{cite journal
 |author=D.G. Michael
 |display-authors=etal
 |date=2006
 |title=Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam
 |journal=[[Physical Review Letters]]
 |volume=97 |pages=191801
 |doi=10.1103/PhysRevLett.97.191801
 |arxiv=hep-ex/0607088
|pmid=17155614
|bibcode = 2006PhRvL..97s1801M
 |issue=19 |s2cid=119458915
 }}</ref><ref>
{{cite journal
 |author=P. Adamson
 |display-authors=etal
 |date=2008
 |journal=[[Physical Review D]]
 |volume=77 |pages=072002
 |title=Study of muon neutrino disappearance using the Fermilab Main Injector neutrino beam
 |doi=10.1103/PhysRevD.77.072002
 |arxiv=0711.0769
|bibcode = 2008PhRvD..77g2002A
 |issue=7 |s2cid=5626908
 }}</ref>

In 2008, MINOS released a further result using over twice the previous data (3.36×10<sup>20</sup> protons-on-target; this includes the first data set).  This is the most precise measurement of Δ''m''<sup>2</sup>. The results are: {{nowrap|Δ''m''{{su|p=2|b=23}} {{=}} {{val|2.43|0.13|-0.13}}}} × 10<sup>−3</sup> eV<sup>2</sup>/c<sup>4</sup> and {{nowrap|sin<sup>2</sup>(2''θ''<sub>23</sub>) > 0.90}} ([[standard deviation|90% confidence limit]]).<ref>
{{cite journal
 |author=P. Adamson
 |display-authors=etal
 |date=2008
 |title=Measurement of neutrino oscillations with the MINOS detectors in the NuMI beam
 |journal=[[Physical Review Letters]]
 |volume=101 |pages=131802
 |doi=10.1103/PhysRevLett.101.131802
|pmid=18851439
|bibcode = 2008PhRvL.101m1802A
 |issue=13 |arxiv = 0806.2237 |s2cid=1036381
 }}</ref>

In 2011, the above results were updated again, using a more than double data sample (exposure of 7.25×10<sup>20</sup> protons on target) and improved analysis methodology. The results are: {{nowrap|Δ''m''{{su|p=2|b=23}} {{=}} {{val|2.32|0.12|-0.08}}}} × 10<sup>−3</sup> eV<sup>2</sup>/c<sup>4</sup> and {{nowrap|sin<sup>2</sup>(2''θ''<sub>23</sub>) > 0.90}} (90% confidence limit).<ref>
{{cite journal
 |author=P. Adamson
 |display-authors=etal
 |date=2011
 |title=Measurement of the neutrino mass splitting and flavor mixing by MINOS
 |journal=[[Physical Review Letters]]
 |volume=106 |pages=181801
 |doi=10.1103/PhysRevLett.106.181801
|pmid=21635083
|bibcode = 2011PhRvL.106r1801A
 |issue=18 |arxiv = 1103.0340 |s2cid=2264842
 }}</ref>

In 2010 and 2011, MINOS reported results according to which there is a difference in the disappearance and consequently the masses between antineutrinos and neutrinos, which would violate [[CPT symmetry]].
<ref>{{cite web|title=New measurements from Fermilab's MINOS experiment suggest a difference in a key property of neutrinos and antineutrinos|url =http://www.fnal.gov/pub/presspass/press_releases/minos-antineutrinos-20100614.html|publisher=Fermilab press release |access-date=14 December 2011 |date=June 14, 2010}}</ref><ref>{{cite journal |author=MINOS Collaboration |title=First Direct Observation of Muon Antineutrino Disappearance |date=2011 |journal=Physical Review Letters |volume=107 |issue=2 |pages=021801 |arxiv=1104.0344 |doi=10.1103/PhysRevLett.107.021801|bibcode =2011PhRvL.107b1801A |pmid=21797594|s2cid=14782259 }}</ref><ref>{{cite journal |author=MINOS Collaboration |title=Search for the disappearance of muon antineutrinos in the NuMI neutrino beam |date=2011 |journal=Physical Review D |volume=84 |issue=7 |pages=071103 |arxiv=1108.1509 |doi=10.1103/PhysRevD.84.071103|bibcode =2011PhRvD..84g1103A|s2cid=6250231 }}</ref>
However, after additional data were evaluated in 2012, MINOS reported that this gap has closed and no excess is there any more.<ref>{{cite web|title=Fermilab experiment announces world's best measurement of key property of neutrinos|url =http://www.fnal.gov/pub/presspass/press_releases/2012/minos-antineutrinos-20120605.html|publisher=Fermilab press release |access-date=June 20, 2012 |date=June 5, 2012}}</ref><ref>{{cite journal |author=MINOS Collaboration |title=An improved measurement of muon antineutrino disappearance in MINOS |journal=Physical Review Letters|volume=108|issue=19|pages=191801|date=2012 |arxiv=1202.2772|doi=10.1103/PhysRevLett.108.191801|bibcode = 2012PhRvL.108s1801A |pmid=23003026|s2cid=7735148 }}</ref>

[[Cosmic ray]] results from the MINOS far detector have shown that there is a strong correlation between high energy cosmic rays measured and the temperature of the [[stratosphere]]. This is the first time, daily variations in secondary cosmic rays from an underground muon detector are shown to be associated with planetary–scale meteorological phenomena in the stratosphere such as the [[sudden stratospheric warming]]<ref>{{cite journal|last=Osprey|first=S.|author2=Barnett, J. |author3=Smith, J. |author4= the MINOS Collaboration |title=Sudden stratospheric warmings seen in MINOS deep underground muon data|journal=Geophysical Research Letters|date=7 March 2009|volume=36|issue=5|pages=L05809|doi=10.1029/2008GL036359|bibcode = 2009GeoRL..36.5809O |s2cid=13986839 |url=http://discovery.ucl.ac.uk/148293/1/2008GL036359.pdf}}</ref> as well as the change in seasons.<ref>{{cite journal|last=Adamson|first=P. |display-authors=etal |title=Observation of muon intensity variations by season with the MINOS far detector|journal=Physical Review D|date=1 January 2010|volume=81|issue=1|pages=012001 |doi=10.1103/PhysRevD.81.012001|arxiv = 0909.4012 |bibcode = 2010PhRvD..81a2001A |s2cid=119126084 }}</ref>  The MINOS far detector is also able to observe a reduction in cosmic rays caused by the [[Sun]] and the [[Moon]].<ref>{{cite journal|last=Adamson|first=P.|display-authors=etal|title=Observation in the MINOS far detector of the shadowing of cosmic rays by the sun and moon|journal=Astroparticle Physics|volume=34|issue=6|pages=457–466|doi=10.1016/j.astropartphys.2010.10.010|arxiv = 1008.1719 |bibcode = 2011APh....34..457A |year=2011|s2cid=119225041 }}</ref>

===Time of flight of neutrinos===
{{Main|Measurements of neutrino speed}}
In 2007, an experiment with the MINOS detectors found the speed of {{val|3|ul=GeV}} neutrinos to be {{val|1.000051|(29)|ul=c}} at 68% confidence level, and at 99% confidence level a range between {{val|0.999976|u=c}} to {{val|1.000126|u=c}}. The central value was higher than the speed of light; however, the uncertainty was great enough that the result also did not rule out speeds less than or equal to light at this high confidence level.<ref>
{{cite journal
 |author=P. Adamson et al. (MINOS Collaboration)
 |date=2007
 |issue=7
 |pages=072005
 |title=Measurement of neutrino velocity with the MINOS detectors and NuMI neutrino beam
 |volume=76 |journal=[[Physical Review D]]
 |arxiv=0706.0437
 |bibcode=2007PhRvD..76g2005A
 |doi=10.1103/PhysRevD.76.072005
|s2cid=14358300
 }}</ref><ref>
{{cite news
 |author=D. Overbye
 |date= 22 September 2011
 |title=Tiny neutrinos may have broken cosmic speed limit
 |url=https://www.nytimes.com/2011/09/23/science/23speed.html
 |newspaper=[[New York Times]]
 |quote= That group found, although with less precision, that the neutrino speeds were consistent with the speed of light.
}}</ref>

After the detectors for the project were upgraded in 2012, MINOS corrected their initial result and found agreement with the speed of light, with the difference in the arrival times of −0.0006% (±0.0012%) between neutrinos and light. Further measurements are going to be conducted.<ref>{{cite web|title=MINOS reports new measurement of neutrino velocity |publisher=Fermilab today|url=http://www.fnal.gov/pub/today/archive_2012/today12-06-08.html|date=June 8, 2012|access-date= June 8, 2012}}</ref>

==References==

<references />

{{coord|47|49|12|N|92|14|30|W|region:US_type:mountain|display=title}}

==External links==
* [http://www-numi.fnal.gov/ NuMI and MINOS]
* [https://inspirehep.net/experiments/1671995 MINOS experiment] record on [[INSPIRE-HEP]]

{{Neutrino detectors}}

[[Category:Accelerator neutrino experiments]]
[[Category:Fermilab]]
[[Category:Fermilab experiments]]
[[Category:Particle experiments]]