Editing Neutron (section)

=== Antineutron ===
{{Main|Antineutron}}

The antineutron is the [[antiparticle]] of the neutron. It was discovered by [[Bruce Cork]] in 1956, a year after the [[antiproton]] was discovered. [[CPT-symmetry]] puts strong constraints on the relative properties of particles and antiparticles, so studying antineutrons provides stringent tests on CPT-symmetry. The fractional difference in the masses of the neutron and antineutron is {{val|9|6|e=-5}}. Since the difference is only about two [[standard deviation]]s away from zero, this does not give any convincing evidence of CPT-violation.<ref name="RPP">{{cite journal|doi=10.1088/0954-3899/37/7A/075021|title=Review of Particle Physics|year=2010|last1=Nakamura|first1=K|journal=[[Journal of Physics G]]|volume=37|issue=7A|pages=1–708|pmid=10020536|bibcode= 2010JPhG...37g5021N|doi-access=free|hdl=10481/34593|hdl-access=free}} [http://pdg.lbl.gov/2011/listings/rpp2011-list-n.pdf PDF with 2011 partial update for the 2012 edition] {{Webarchive|url=https://web.archive.org/web/20120920183244/http://pdg.lbl.gov/2011/listings/rpp2011-list-n.pdf |date=2012-09-20 }}.
The exact value of the mean lifetime is still uncertain, due to conflicting results from experiments.
The Particle Data Group reports values up to six seconds apart (more than four standard deviations), commenting that "our 2006, 2008, and 2010 Reviews stayed with 885.7±0.8 s; but we noted that in light of SEREBROV 05 our value should be regarded as suspect until further experiments clarified matters. Since our 2010 Review, PICHLMAIER 10 has obtained a mean life of 880.7±1.8 s, closer to the value of SEREBROV 05 than to our average. And SEREBROV 10B[...] claims their values should be lowered by about 6 s, which would bring them into line with the two lower values. But those re-evaluations have not received an enthusiastic response from the experimenters in question; and in any case the Particle Data Group would have to await published changes (by those experimenters) of published values.

At this point, we can think of nothing better to do than to average the seven best but discordant measurements, getting {{val|881.5|1.5|u=s}}. Note that the error includes a scale factor of 2.7. This is a jump of 4.2 old (and 2.8 new) standard deviations. This state of affairs is a particularly unhappy one, because the value is so important. We again call upon the experimenters to clear this up."</ref>