View source for Antineutron

{{Short description|Subatomic particle}}
{{Distinguish||text=[[Neutrino#Antineutrinos|Antineutrinos]]}}
{{Infobox particle
| bgcolour =
| name = Antineutron| image = [[Image:Quark structure antineutron.svg|200px]]
| caption = The quark structure of the antineutron.
| num_types = 
| classification = [[antibaryon]]
| composition = 1 [[up quark|up antiquark]], 2 [[down quark|down antiquarks]]
| statistics = [[fermionic]]
| group = hadron
| generation = 
| interaction = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]], [[gravity]]
| particle = 
| antiparticle = [[neutron]]
| status =
| theorized = 
| discovered =  [[Bruce Cork]] (1956)
| symbol = {{SubatomicParticle|Antineutron}}
| mass = {{physconst|mnc2_MeV|unit=no|after=&nbsp;{{val|ul=MeV/c2}}}}
| mean_lifetime = 
| decay_particle = 
| electric_charge = 0
| charge_radius = 
| electric_dipole_moment = 
| electric_polarizability = 
| magnetic_moment = {{val|+1.91|u=[[Nuclear magneton|''μ''<sub>N</sub>]]}}
| magnetic_polarizability = 
| color_charge = 
| spin = {{sfrac|1|2}}
| num_spin_states = 
| lepton_number = 
| baryon_number = 
| strangeness = 
| charm = 
| bottomness = 
| topness = 
| isospin = {{sfrac|1|2}}
| weak_isospin = 
| hypercharge = 
| weak_hypercharge = 
| parity = 
| g_parity = 
| c_parity = 
| r_parity = 
| condensed_symmetries =
}}
{{antimatter}}The '''antineutron''' is the [[antiparticle]] of the [[neutron]] with symbol {{SubatomicParticle|Antineutron}}. It differs from the neutron only in that some of its properties have [[additive inverse|equal magnitude but opposite sign]]. It has the same [[mass]] as the neutron, and no net [[electric charge]], but has opposite [[baryon number]] (+1 for neutron, −1 for the antineutron). This is because the antineutron is composed of [[antiquark]]s, while neutrons are composed of [[quark]]s. The antineutron consists of one [[up antiquark]] and two [[down antiquark]]s.

==Background ==

The antineutron was discovered in [[proton–antiproton collision]]s at the [[Bevatron]] ([[Lawrence Berkeley National Laboratory]]) by the team of [[Bruce Cork]], Glen Lambertson, [[Oreste Piccioni]], and William Wenzel in 1956,<ref>{{cite journal |last1=Cork |first1=Bruce |last2=Lambertson |first2=Glen R. |last3=Piccioni |first3=Oreste |last4=Wenzel |first4=William A. |title=Antineutrons Produced from Antiprotons in Charge-Exchange Collisions |journal=Physical Review |date=15 November 1956 |volume=104 |issue=4  |pages=1193–1197 |doi=10.1103/PhysRev.104.1193 |bibcode=1956PhRv..104.1193C |s2cid=123156830 |url=http://www.escholarship.org/uc/item/0cn7n2mz }}</ref> one year after the [[antiproton]] was discovered.

Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its [[annihilation]] with ordinary matter are observed. In theory, a free antineutron should [[particle decay|decay]] into an [[antiproton]], a [[positron]] and a [[neutrino]] in a process analogous to the [[beta decay]] of [[free neutron]]s. There are theoretical proposals of [[Neutron–antineutron oscillation|neutron–antineutron oscillations]], a process that implies the violation of the [[baryon number]] conservation.<ref>{{cite journal|author=R. N. Mohapatra|date=2009|title=Neutron-Anti-Neutron Oscillation: Theory and Phenomenology|journal=[[Journal of Physics G]]|volume=36|issue=10|pages=104006|doi=10.1088/0954-3899/36/10/104006|arxiv=0902.0834|bibcode = 2009JPhG...36j4006M |s2cid=15126201}}</ref><ref>{{cite web|author=C. Giunti |author2=M. Laveder |date=19 August 2010 |title=Neutron Oscillations |url=http://www.nu.to.infn.it/Neutron_Oscillations/ |work=Neutrino Unbound |publisher=[[Istituto Nazionale di Fisica Nucleare]] |access-date=19 August 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110927180013/http://www.nu.to.infn.it/Neutron_Oscillations/ |archive-date=27 September 2011 }}</ref><ref>{{cite web|author=Y. A. Kamyshkov|date=16 January 2002|title=Neutron → Antineutron Oscillations|url=http://muonstoragerings.web.cern.ch/muonstoragerings/NuWorkshop02/presentations/kamyshkov1.pdf|work=NNN 2002 Workshop on "Large Detectors for Proton Decay, Supernovae and Atmospheric Neutrinos and Low Energy Neutrinos from High Intensity Beams" at CERN|access-date=19 August 2010}}</ref>

==Magnetic moment==
The [[magnetic moment]] of the antineutron is the opposite of [[Nucleon magnetic moment|that of the neutron]].<ref>{{cite web|author=Lorenzon, Wolfgang|date=6 April 2007|url=http://www-personal.umich.edu/~lorenzon/classes/2007/solutions/mPhys390-hw7-sol.pdf|title=Physics 390: Homework set #7 Solutions|work=Modern Physics, Physics 390, Winter 2007|access-date=22 December 2009}}</ref> It is {{val|+1.91|u=[[Nuclear magneton|''μ''<sub>N</sub>]]}} for the antineutron but {{val|-1.91|u=[[Nuclear magneton|''μ''<sub>N</sub>]]}} for the neutron (relative to the direction of the [[Spin (physics)|spin]]). Here ''μ''<sub>N</sub> is the [[nuclear magneton]].

==See also==
*[[Antimatter]]
*[[Neutron magnetic moment]]
*[[List of particles]]

==References==
{{Reflist}}

==External links==
* [http://pdg.lbl.gov/2005/tables/contents_tables.html LBL Particle Data Group: summary tables]
* [https://arxiv.org/abs/hep-ph/9503300 suppression of neutron-antineutron oscillation]
* [https://web.archive.org/web/20040928080137/http://www.science.uwaterloo.ca/~cchieh/cact/nuclear/particles.html Elementary particles]: includes information about antineutron discovery (archived link)
* "[http://www.fnal.gov/pub/inquiring/questions/antineutron.html Is Antineutron the Same as Neutron?]" explains how the antineutron differs from the regular neutron despite having the same, that is zero, charge.

{{Particles}}

[[Category:Antimatter]]
[[Category:Baryons]]
[[Category:Neutron]]
[[Category:Nucleons]]