antineutron
{{Short description|Subatomic particle}}
{{Distinguish||text=Antineutrinos}}
{{Infobox particle
| bgcolour =
| name = Antineutron| image = 200px
| caption = The quark structure of the antineutron.
| num_types =
| classification = antibaryon
| composition = 1 up antiquark, 2 down antiquarks
| statistics = fermionic
| group = hadron
| generation =
| interaction = strong, weak, electromagnetic, gravity
| particle =
| antiparticle = neutron
| status =
| theorized =
| discovered = Bruce Cork (1956)
| symbol = {{SubatomicParticle|Antineutron}}
| mass = {{physconst|mnc2_MeV|unit={{val|ul=MeV/c2}}}}
| mean_lifetime =
| decay_particle =
| electric_charge = 0
| charge_radius =
| electric_dipole_moment =
| electric_polarizability =
| magnetic_moment = {{val|+1.91|u=μN}}
| 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 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 antiquarks, while neutrons are composed of quarks. The antineutron consists of one up antiquark and two down antiquarks.
Background
The antineutron was discovered in proton–antiproton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by the team of Bruce Cork, Glen Lambertson, Oreste Piccioni, and William Wenzel in 1956,{{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 }} 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 decay into an antiproton, a positron, and a neutrino in a process analogous to the beta decay of free neutrons. There are theoretical proposals of neutron–antineutron oscillations, a process that implies the violation of the baryon number conservation.{{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}}{{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 }}{{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}} There is a project to search for neutron-antineutron oscillations using ultracold neutrons.{{cite journal | last1=Serebrov | first1=A. | last2=Fomin | first2=A. | last3=Kamyshkov | first3=Y. | title=Sensitivity of Experiment on Search for Neutron–Antineutron Oscillations on the Projected Ultracold Neutron Source at the WWR-M Reactor | journal=Technical Physics Letters | volume=42 | issue=1 | year=2016 | doi=10.1134/S1063785016010314 | pages=99–101| bibcode=2016TePhL..42...99S }}{{cite journal | last=A.K. Fomin | display-authors=et al.| title=Experiment on search for neutron–antineutron oscillations using a projected UCN source at the WWR-M reactor | journal=Journal of Physics: Conference Series | volume=798 | year=2017 | issue=1| doi=10.1088/1742-6596/798/1/012115 | pages=012115| bibcode=2017JPhCS.798a2115F| doi-access=free }}{{cite journal | last=A.K. Fomin | title=Experiment On Search For n-nbar Oscillations Using A Projected UCN Source At The WWR-M Reactor | journal=Proceedings of Science | volume=281 | year=2017 | doi=10.22323/1.281.0189 | pages=189| doi-access=free }}{{cite journal | last=A.K. Fomin | display-authors=et al.| title=Project on searching for neutron-antineutron oscillation at the WWR-M reactor | journal=Journal of Physics: Conference Series | volume=1390 | year=2019 | issue=1| doi=10.1088/1742-6596/1390/1/012133 | pages=012133| bibcode=2019JPhCS1390a2133F| doi-access=free }}
Magnetic moment
The magnetic moment of the antineutron is the opposite of that of the neutron.{{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}} It is {{val|+1.91|u=μN}} for the antineutron but {{val|-1.91|u=μN}} for the neutron (relative to the direction of the spin). Here μN is the nuclear magneton.
See also
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}}