Editing Particle physics (section)

== History ==
{{main|History of subatomic physics}}
[[File:Rutherford_Scattering.svg|alt=see caption|thumb|The [[Geiger–Marsden experiments]] observed that a small fraction of the alpha particles experienced strong deflection when being struck by the gold foil.]]
The idea that all [[matter]] is fundamentally composed of [[elementary particle]]s dates from at least the 6th century BC.<ref>{{cite web |title=Fundamentals of Physics and Nuclear Physics |url=http://novelresearchinstitute.org/library/PhysNuclphys196p.pdf |url-status=usurped |archive-url=https://web.archive.org/web/20121002214053/http://novelresearchinstitute.org/library/PhysNuclphys196p.pdf |archive-date=2 October 2012 |access-date=21 July 2012}}</ref> In the 19th century, [[John Dalton]], through his work on [[stoichiometry]], concluded that each element of nature was composed of a single, unique type of particle.<ref name="MARK I. GROSSMAN">{{cite journal |title=John Dalton and the London Atomists |year=2014 |pmc=4213434 |last1=Grossman |first1=M. I. |journal=Notes and Records of the Royal Society of London |volume=68 |issue=4 |pages=339–356 |doi=10.1098/rsnr.2014.0025 }}</ref> The word ''[[atom]]'', after the Greek word ''[[wikt:ἄτομος|atomos]]'' meaning "indivisible", has since then denoted the smallest particle of a [[chemical element]], but physicists later discovered that atoms are not, in fact, the fundamental particles of nature, but are conglomerates of even smaller particles, such as the [[electron]]. The early 20th century explorations of [[nuclear physics]] and [[quantum physics]] led to proofs of [[nuclear fission]] in 1939 by [[Lise Meitner]] (based on experiments by [[Otto Hahn]]), and [[nuclear fusion]] by [[Hans Bethe]] in that same year; both discoveries also led to the development of [[nuclear weapon]]s. Bethe's 1947 calculation of the [[Lamb shift]] is credited with having "opened the way to the modern era of particle physics".<ref>{{Cite book |last1=Brown |first1=Gerald Edward |url=https://archive.org/details/hansbethehisphys0000unse/page/161 |title=Hans Bethe and His Physics |last2=Lee |first2=Chang-Hwan |date=2006 |publisher=World Scientific Publishing |isbn=978-981-256-609-6 |location=Singapore |pages=161}}</ref>

Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the "[[particle zoo]]". Important discoveries such as the [[CP violation]] by [[James Cronin]] and [[Val Fitch]] brought new questions to [[Baryon asymmetry|matter-antimatter imbalance]].<ref>{{Cite web |date=2021-03-01 |title=Antimatter |url=https://home.cern/science/physics/antimatter |url-status=live |archive-url=https://web.archive.org/web/20180911042958/https://home.cern/topics/antimatter |archive-date=11 September 2018 |access-date=12 March 2021}}</ref> After the formulation of the Standard Model during the 1970s, physicists clarified the origin of the particle zoo. The large number of particles was explained as combinations of a (relatively) small number of more fundamental particles and framed in the context of [[Quantum field theory|quantum field theories]]. This reclassification marked the beginning of modern particle physics.<ref>{{cite book |last1=Weinberg |first1=Steven |title=The quantum theory of fields |date=1995–2000 |publisher=Cambridge University Press |isbn=978-0521670531 |location=Cambridge}}</ref><ref>{{Cite journal |last=Jaeger |first=Gregg |date=2021 |title=The Elementary Particles of Quantum Fields |journal=Entropy |volume=23 |issue=11 |pages=1416 |bibcode=2021Entrp..23.1416J |doi=10.3390/e23111416 |pmc=8623095 |pmid=34828114 |doi-access=free}}</ref>