Editing Hypernucleus

{{Short description|Nucleus which contains at least one hyperon}}
A '''hypernucleus''' is similar to a conventional [[atomic nucleus]], but contains at least one [[hyperon]] in addition to the normal [[proton]]s and [[neutron]]s. Hyperons are a category of [[baryon]] particles that carry non-zero [[strangeness]] quantum number, which is conserved by the [[strong interaction|strong]] and [[electromagnetic interaction]]s.

A variety of reactions give access to depositing one or more units of strangeness in a nucleus. Hypernuclei containing the lightest hyperon, the [[lambda baryon|lambda]] (Λ), tend to be more tightly bound than normal nuclei, though they can decay via the weak force with a mean lifetime of around {{val|200|ul=ps}}. [[Sigma baryon|Sigma]] (Σ) hypernuclei have been sought, as have doubly-strange nuclei containing [[xi baryon]]s (Ξ) or two Λ's.

== Nomenclature ==
Hypernuclei are named in terms of their [[atomic number]] and [[baryon number]], as in normal nuclei, plus the hyperon(s) which are listed in a left subscript of the symbol, with the caveat that atomic number is interpreted as the total charge of the hypernucleus, including charged hyperons such as the xi minus (Ξ<sup>−</sup>) as well as protons. For example, the hypernucleus {{PhysicsParticle|[[Oxygen|O]]|TL=16|BL=Λ}} contains 8 protons, 7 neutrons, and one Λ (which carries no charge).{{sfn|Gal|Hungerford|Millener|2016|p=2}}

== History ==
The first was discovered by [[Marian Danysz]] and [[Jerzy Pniewski]] in 1952 using a [[nuclear emulsion]] plate exposed to [[cosmic ray]]s, based on their energetic but delayed decay. This event was inferred to be due to a nuclear fragment containing a Λ baryon.<ref>{{cite journal |last1=Danysz |first1=M. |last2=Pniewski |first2=J. |title=Delayed disintegration of a heavy nuclear fragment: I |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |date=March 1953 |volume=44 |issue=350 |pages=348–350 |doi=10.1080/14786440308520318}}</ref> Experiments until the 1970s would continue to study hypernuclei produced in emulsions using cosmic rays, and later using [[pion]] (π) and [[kaon]] (K) beams from [[particle accelerator]]s.{{sfn|Gal|Hungerford|Millener|2016|p=2}}

Since the 1980s, more efficient production methods using pion and kaon beams have allowed further investigation at various accelerator facilities, including [[CERN]], [[Brookhaven National Laboratory]], [[KEK]], [[DAφNE]], and [[JPARC]].{{sfn|Gal|Hungerford|Millener|2016|p=4}}{{sfn|Tolos|Fabbietti|2020|p=29}} In the 2010s, [[heavy ion]] experiments such as [[ALICE experiment|ALICE]] and [[STAR experiment|STAR]] first allowed the production and measurement of light hypernuclei formed through [[hadronization]] from [[quark–gluon plasma]].{{sfn|Tolos|Fabbietti|2020|pp=53–54}}

== Properties ==
Hypernuclear physics differs from that of normal nuclei because a hyperon is distinguishable from the four nucleon [[Spin (physics)|spin]] and [[isospin]]. That is, a single hyperon is not restricted by the [[Pauli exclusion principle]], and can sink to the lowest energy level.<ref name="Feliciello"/> As such, hypernuclei are often smaller and more tightly bound than normal nuclei;<ref name=jpg08>
{{cite journal
 |author=C. Samanta, P. Roy Chowdhury and D.N.Basu
 |date=2008
 |title=Lambda hyperonic effect on the normal driplines
 |journal=[[Journal of Physics G]]
 |volume=35 |pages=065101–065110
 |doi=10.1088/0954-3899/35/6/065101
 |bibcode = 2008JPhG...35f5101S
 |issue=6 |arxiv = 0802.3172 |s2cid=118482655
 }}</ref> for example, the [[lithium]] hypernucleus {{PhysicsParticle|Li|TL=7|BL=Λ}} is 19% smaller than the normal nucleus <sup>6</sup>Li.<ref>{{cite magazine |last=Brumfiel |first=Geoff |title=The Incredible Shrinking Nucleus |magazine=[[Physical Review Focus]] |volume=7 |issue=11 |date=1 March 2001 |url=http://physics.aps.org/story/v7/st11}}</ref><ref>{{cite journal |last1=Tanida |first1=K. |last2=Tamura |first2=H. |last3=Abe |first3=D. |last4=Akikawa |first4=H. |last5=Araki |first5=K. |last6=Bhang |first6=H. |last7=Endo |first7=T. |last8=Fujii |first8=Y. |last9=Fukuda |first9=T. |last10=Hashimoto |first10=O. |last11=Imai |first11=K. |last12=Hotchi |first12=H. |last13=Kakiguchi |first13=Y. |last14=Kim |first14=J. H. |last15=Kim |first15=Y. D. |last16=Miyoshi |first16=T. |last17=Murakami |first17=T. |last18=Nagae |first18=T. |last19=Noumi |first19=H. |last20=Outa |first20=H. |last21=Ozawa |first21=K. |last22=Saito |first22=T. |last23=Sasao |first23=J. |last24=Sato |first24=Y. |last25=Satoh |first25=S. |last26=Sawafta |first26=R. I. |last27=Sekimoto |first27=M. |last28=Takahashi |first28=T. |last29=Tang |first29=L. |last30=Xia |first30=H. H. |last31=Zhou |first31=S. H. |last32=Zhu |first32=L. H. |title=Measurement of the B(E2) of <math>^{7}_\Lambda\mathrm{Li}</math> and Shrinkage of the Hypernuclear Size |journal=Physical Review Letters |date=5 March 2001 |volume=86 |issue=10 |pages=1982–1985 |doi=10.1103/PhysRevLett.86.1982|pmid=11289835 }}</ref> However, the hyperons can decay via the [[weak force]]; the mean lifetime of a free Λ is {{val|263|2|ul=ps}}, and that of a Λ hypernucleus is usually slightly shorter.{{sfn|Gal|Hungerford|Millener|2016|p=18}}

A generalized mass formula developed for both the non-strange normal nuclei and strange hypernuclei can estimate masses of hypernuclei containing Λ, ΛΛ, Σ, and Ξ hyperon(s).<ref name=WS06>{{cite book
 |author=C. Samanta
 |date=2006
 |chapter=Mass formula from normal to hypernuclei
 |editor1=S. Stoica |editor2=L. Trache |editor3=R.E. Tribble |chapter-url=http://www.worldscibooks.com/physics/6222.html
 |title=Proceedings of the Carpathian Summer School of Physics 2005
 |pages=29
 |publisher=[[World Scientific]]
 |isbn=978-981-270-007-0
}}</ref><ref name=jpg06>
{{cite journal
 |author=C. Samanta, P. Roy Chowdhury, D.N.Basu
 |date=2006
 |journal=[[Journal of Physics G]]
 |volume=32 |pages=363–373
 |title=Generalized mass formula for non-strange and hyper nuclei with SU(6) symmetry breaking
 |doi=10.1088/0954-3899/32/3/010
|arxiv = nucl-th/0504085 |bibcode = 2006JPhG...32..363S
 |issue=3 |s2cid=118870657
 }}</ref> The neutron and proton [[Nuclear drip line|driplines]] for hypernuclei are predicted and existence of some exotic hypernuclei beyond the normal neutron and proton driplines are suggested.<ref name=jpg08/> This generalized mass formula was named the "Samanta formula" by Botvina and Pochodzalla and used to predict relative yields of hypernuclei in heavy-ion collisions.<ref name=bop07>
{{cite journal
 |author1=A.S. Botvina |author2=J. Pochodzalla |date=2007
 |title= Production of hypernuclei in multifragmentation of nuclear spectator matter
 |journal=[[Physical Review C]]
 |volume=76 |pages=024909–024912
 |doi=10.1103/PhysRevC.76.024909
|bibcode = 2007PhRvC..76b4909B
 |issue=2 |arxiv = 0705.2968 |s2cid=119652113 }}</ref>

== Types ==
=== Λ hypernuclei ===
The simplest, and most well understood, type of hypernucleus includes only the lightest hyperon, the Λ.<ref name="Feliciello">{{cite journal |last1=Feliciello |first1=A |last2=Nagae |first2=T |title=Experimental review of hypernuclear physics: recent achievements and future perspectives |journal=Reports on Progress in Physics |date=1 September 2015 |volume=78 |issue=9 |pages=096301 |doi=10.1088/0034-4885/78/9/096301|pmid=26317857 |bibcode=2015RPPh...78i6301F |s2cid=25818699 |url=https://www.openaccessrepository.it/record/75858 |archive-url=https://web.archive.org/web/20220530112234/https://www.openaccessrepository.it/record/75858 |url-status=dead |archive-date=May 30, 2022 }}</ref>

<!-- Wanted: Feynman diagrams (at the hadronic level) illustrating the dominant terms of the Λ–nucleon interaction -->
While two nucleons can interact through the [[nuclear force]] mediated by a [[virtual particle|virtual]] pion, the Λ becomes a Σ baryon upon emitting a pion,{{efn|name=isospin|[[Isospin]] ({{math|''I''}}), a number describing the up and down quark content of the system, is preserved in the strong interaction. Since the isospin of a pion is 1, the Λ baryon ({{math|1=''I'' = 0}}) must become a Σ ({{math|1=''I'' = 1}}) upon emitting a pion.{{sfn|Gal|Hungerford|Millener|2016|p=20}}}} so the Λ–nucleon interaction is mediated solely by more massive mesons such as the [[eta meson|η]] and [[omega meson|ω]] mesons, or through the simultaneous exchange of two or more mesons.{{sfn|Gal|Hungerford|Millener|2016|pp=2,20–21}} This means that the Λ–nucleon interaction is weaker and has a shorter range than the standard nuclear force, and the [[potential well]] of a Λ in the nucleus is shallower than that of a nucleon;{{sfn|Gal|Hungerford|Millener|2016|p=6}} in hypernuclei, the depth of the Λ potential is approximately 30&nbsp;[[MeV]].{{sfn|Tolos|Fabbietti|2020|p=50}} However, one-pion exchange in the Λ–nucleon interaction does cause quantum-mechanical mixing of the Λ and Σ baryons in hypernuclei (which does not happen in free space), especially in neutron-rich hypernuclei.{{sfn|Gal|Hungerford|Millener|2016|pp=20–21}}{{sfn|Tolos|Fabbietti|2020|p=52}}<ref>{{cite journal |last1=Umeya |first1=A. |last2=Harada |first2=T. |title=Λ–Σ coupling effect in the neutron-rich Λ hypernucleus <math>^{10}_{\Lambda}\mathrm{Li}</math> in a microscopic shell-model calculation |journal=Physical Review C |date=20 February 2009 |volume=79 |issue=2 |pages=024315 |doi=10.1103/PhysRevC.79.024315|arxiv=0810.4591|s2cid=117921775 }}</ref> Additionally, the [[three-body force]] between a Λ and two nucleons is expected to be more important than the three-body interaction in nuclei, since the Λ can exchange two pions with a virtual Σ intermediate, while the equivalent process in nucleons requires a relatively heavy [[delta baryon]] (Δ) intermediate.{{sfn|Gal|Hungerford|Millener|2016|pp=2,20–21}}

Like all hyperons, Λ hypernuclei can decay through the [[weak interaction]], which changes it to a lighter baryon and emits a meson or a [[lepton]]–antilepton pair. In free space, the Λ usually decays via the weak force to a proton and a π<sup>–</sup> meson, or a neutron and a π<sup>0</sup>, with a total half-life of {{val|263|2|ul=ps}}.<ref name="PDG">{{cite web|first1=C.|last1=Amsler|collaboration=Particle Data Group|display-authors=etal|year=2008|series=Particle listings|title={{Subatomic particle|Lambda}}|publisher=Lawrence Berkeley Laboratory|url=http://pdg.lbl.gov/2008/listings/s018.pdf}}</ref> A nucleon in the hypernucleus can cause the Λ to decay via the weak force without emitting a pion; this process becomes dominant in heavy hypernuclei, due to suppression of the pion-emitting decay mode.{{sfn|Tolos|Fabbietti|2020|p=50–51}} The half-life of the Λ in a hypernucleus is considerably shorter, plateauing to about {{val|215|14|u=ps}} near {{physics particle|[[Iron|Fe]]|TL=56|BL=Λ}},<ref>{{cite journal |last1=Sato |first1=Y. |last2=Ajimura |first2=S. |last3=Aoki |first3=K. |last4=Bhang |first4=H. |last5=Hasegawa |first5=T. |last6=Hashimoto |first6=O. |last7=Hotchi |first7=H. |last8=Kim |first8=Y. D. |last9=Kishimoto |first9=T. |last10=Maeda |first10=K. |last11=Noumi |first11=H. |last12=Ohta |first12=Y. |last13=Omata |first13=K. |last14=Outa |first14=H. |last15=Park |first15=H. |last16=Sekimoto |first16=M. |last17=Shibata |first17=T. |last18=Takahashi |first18=T. |last19=Youn |first19=M. |title=Mesonic and nonmesonic weak decay widths of medium-heavy Λ hypernuclei |journal=Physical Review C |date=9 February 2005 |volume=71 |issue=2 |pages=025203 |doi=10.1103/PhysRevC.71.025203|arxiv=nucl-ex/0409007v2|bibcode=2005PhRvC..71b5203S |s2cid=119428665 }}</ref> but some empirical measurements substantially disagree with each other or with theoretical predictions.{{sfn|Gal|Hungerford|Millener|2016|pp=17–18}}

===Hypertriton===
The simplest hypernucleus is the [[hypertriton]] ({{PhysicsParticle|[[Hydrogen|H]]|TL=3|BL=Λ}}), which consists of one proton, one neutron, and one Λ hyperon. The Λ in this system is very loosely bound, having a [[separation energy]] of 130&nbsp;keV and a large radius of 10.6&nbsp;[[Femtometer|fm]],{{sfn|Tolos|Fabbietti|2020|p=53}} compared to about {{val|2.13|u=fm}} for the [[deuteron]].<ref>{{cite journal |last1=Tiesinga |first1=Eite |last2=Mohr |first2=Peter J. |last3=Newell |first3=David B. |last4=Taylor |first4=Barry N. |title=CODATA Recommended Values of the Fundamental Physical Constants: 2018 |journal=Journal of Physical and Chemical Reference Data |date=1 September 2021 |volume=50 |issue=3 |pages=033105 |doi=10.1063/5.0064853 |pmid=36733295 |pmc=9890581 |bibcode=2021JPCRD..50c3105T |language=en |issn=0047-2689}}</ref>

This loose binding would imply a lifetime similar to a free Λ. However, the measured hypertriton lifetime averaged across all experiments (about {{val|206|15|13|u=ps}}) is substantially shorter than predicted by theory, as the non-mesonic decay mode is expected to be relatively minor; some experimental results are substantially shorter or longer than this average.{{sfn|Tolos|Fabbietti|2020|pp=52–53}}<ref>{{cite journal |author=ALICE Collaboration |title=<math>^{3}_{\Lambda}\mathrm{H}</math> and <math>\overline{^{3}_{\Lambda}\mathrm{H}}</math> lifetime measurement in Pb–Pb collisions at s NN = 5.02 TeV via two-body decay |journal=Physics Letters B |date=October 2019 |volume=797 |pages=134905 |doi=10.1016/j.physletb.2019.134905| s2cid=204776807 |doi-access=free |arxiv=1907.06906 }}</ref>

=== Σ hypernuclei ===
The existence of hypernuclei containing a Σ baryon is less clear. Several experiments in the early 1980s reported bound hypernuclear states above the Λ [[separation energy]] and presumed to contain one of the slightly heavier Σ baryons, but experiments later in the decade ruled out the existence of such states.<ref name="Feliciello"/> Results from [[exotic atoms]] containing a Σ<sup>−</sup> bound to a nucleus by the [[electromagnetic force]] have found a net repulsive Σ–nucleon interaction in medium-sized and large hypernuclei, which means that no Σ hypernuclei exist in such mass range.<ref name="Feliciello"/> However, an experiment in 1998 definitively observed the light Σ hypernucleus {{PhysicsParticle|[[Helium|He]]|TL=4|BL=Σ}}.<ref name="Feliciello"/>

=== ΛΛ and Ξ hypernuclei ===
Hypernuclei containing two Λ baryons have been made. However, such hypernuclei are much harder to produce due to containing two strange quarks and, as of 2016, only seven candidate ΛΛ hypernuclei have been observed.{{sfn|Gal|Hungerford|Millener|2016|p=41}} Like the Λ–nucleon interaction, empirical and theoretical models predict that the Λ–Λ interaction is mildly attractive.{{sfn|Tolos|Fabbietti|2020|pp=43–45,59}}<ref>{{cite journal |author=ALICE Collaboration|title=Study of the Λ–Λ interaction with femtoscopy correlations in pp and p–Pb collisions at the LHC |journal=Physics Letters B |date=10 October 2019 |volume=797 |pages=134822 |doi=10.1016/j.physletb.2019.134822 |arxiv=1905.07209 |bibcode=2019PhLB..79734822A |s2cid=161048820 |url=https://www.sciencedirect.com/science/article/pii/S0370269319305362 |language=en |issn=0370-2693}}</ref>

Hypernuclei containing a Ξ baryon are known.{{citation needed|date=January 2024}} Empirical studies and theoretical models indicate that the Ξ<sup>–</sup>–proton interaction is attractive, but weaker than the Λ–nucleon interaction.{{sfn|Tolos|Fabbietti|2020|pp=43–45,59}} Like the Σ<sup>–</sup> and other negatively charged particles, the Ξ<sup>–</sup> can also form an exotic atom. When a Ξ<sup>–</sup> is bound in an exotic atom or a hypernucleus, it quickly decays to a ΛΛ hypernucleus or to two Λ hypernuclei by exchanging a strange quark with a proton, which releases about 29&nbsp;MeV of energy in free space:{{efn|name=qvalue|The initial proton and Ξ<sup>–</sup> have respective masses of approximately 938.3 and 1321.7&nbsp;MeV, while the outgoing Λ's are each about 1115.7&nbsp;MeV;<ref>{{cite journal |last1=Workman |first1=R L |last2=Burkert |first2=V D |last3=Crede |first3=V |last4=Klempt |first4=E |last5=Thoma |first5=U |last6=Tiator |first6=L |display-authors=1|collaboration=Particle Data Group|title=Review of Particle Physics |journal=Progress of Theoretical and Experimental Physics |date=8 August 2022 |volume=2022 |issue=8 |page=083C01 |doi=10.1093/ptep/ptac097|doi-access=free |hdl=11585/900713 |hdl-access=free }}</ref> the energy that is released is equal to the amount of mass that is lost (times ''c''<sup>2</sup>).}}
:Ξ<sup>−</sup> + p → Λ + Λ<ref name="JPARC E07"/>{{sfn|Gal|Hungerford|Millener|2016|pp=16,43}}{{sfn|Tolos|Fabbietti|2020|p=53}}

=== Ω hypernuclei ===
Hypernuclei containing the [[omega baryon]] (Ω) were predicted using [[lattice QCD]] in 2018; in particular, the proton–Ω and Ω–Ω [[dibaryon]]s (bound systems containing two baryons) are expected to be stable.<ref>{{cite journal |last1=Iritani |first1=Takumi |collaboration=HALQCD Collaboration |title=NΩ dibaryon from lattice QCD near the physical point |journal=Physics Letters B |date=May 2019 |volume=792 |pages=284–289 |doi=10.1016/j.physletb.2019.03.050|arxiv=1810.03416
|bibcode=2019PhLB..792..284I |s2cid=102481007 }}</ref><ref>{{cite journal |last1=Gongyo |first1=Shinya |collaboration=HALQCD Collaboration |title=Most Strange Dibaryon from Lattice QCD |journal=Physical Review Letters |date=23 May 2018 |volume=120 |issue=21 |pages=212001 |doi=10.1103/PhysRevLett.120.212001|pmid=29883161 |arxiv=1709.00654 |bibcode=2018PhRvL.120u2001G |s2cid=43958833 }}</ref> {{As of|2022}}, no such hypernuclei have been observed under any conditions, but the lightest such species could be produced in heavy-ion collisions,<ref>{{cite journal |last1=Zhang |first1=Liang |last2=Zhang |first2=Song |last3=Ma |first3=Yu-Gang |title=Production of ΩNN and ΩΩN in ultra-relativistic heavy-ion collisions |journal=The European Physical Journal C |date=May 2022 |volume=82 |issue=5 |pages=416 |doi=10.1140/epjc/s10052-022-10336-7|arxiv=2112.02766 |bibcode=2022EPJC...82..416Z |s2cid=244908731 |doi-access=free }}</ref> and measurements by the STAR experiment are consistent with the existence of the proton–Ω dibaryon.<ref>{{cite journal |author=STAR Collaboration |title=The proton–Ω correlation function in Au + Au collisions at s NN = 200 GeV |journal=Physics Letters B |date=March 2019 |volume=790 |pages=490–497 |doi=10.1016/j.physletb.2019.01.055| s2cid=127339678 |doi-access=free |hdl=11368/2940231 |hdl-access=free }}</ref>

=== Hypernuclei with higher strangeness ===
Since the Λ is electrically neutral and its nuclear force interactions are attractive, there are predicted to be arbitrarily large hypernuclei with high strangeness and small net charge, including species with no nucleons. [[nuclear binding energy|Binding energy]] per baryon in multi-strange hypernuclei can reach up to 21&nbsp;MeV/''A'' under certain conditions,<ref name=jpg08/> compared to 8.80&nbsp;MeV/''A'' for the ordinary nucleus [[Nickel-62|<sup>62</sup>Ni]].<ref>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin2.html |website=hyperphysics.phy-astr.gsu.edu |title=The Most Tightly Bound Nuclei |accessdate=October 23, 2019 }}</ref> Additionally, formation of Ξ baryons should quickly become energetically favorable, unlike when there are no Λ's, because the exchange of strangeness with a nucleon would be impossible due to the Pauli exclusion principle.{{sfn|Gal|Hungerford|Millener|2016|p=43}}

== Production ==
Several modes of production have been devised to make hypernuclei through bombardment of normal nuclei.

===Strangeness exchange and production===
One method of producing a K<sup>−</sup> meson exchanges a strange quark with a nucleon and changes it to a Λ:{{sfn|Gal|Hungerford|Millener|2016|pp=6–10}}
:p + K<sup>−</sup> → Λ + π<sup>0</sup>
:n + K<sup>−</sup> → Λ + π<sup>−</sup>
The [[cross section (physics)|cross section]] for the formation of a hypernucleus is maximized when the momentum of the kaon beam is approximately 500&nbsp;MeV/''c''.{{sfn|Tolos|Fabbietti|2020|p=49}} Several variants of this setup exist, including ones where the incident kaons are either brought to rest before colliding with a nucleus.{{sfn|Gal|Hungerford|Millener|2016|pp=6–10}}

In rare cases, the incoming K<sup>−</sup> can instead produce a Ξ hypernucleus via the reaction:
:p + K<sup>−</sup> → Ξ<sup>−</sup> + K<sup>+</sup>{{sfn|Gal|Hungerford|Millener|2016|p=16}}

The equivalent [[strangeness production]] reaction involves a π<sup>+</sup> meson reacts with a neutron to change it to a Λ:{{sfn|Gal|Hungerford|Millener|2016|pp=10–12}}
:n + π<sup>+</sup> → Λ + K<sup>+</sup>
This reaction has a maximum cross section at a beam momentum of 1.05&nbsp;GeV/''c'', and is the most efficient production route for Λ hypernuclei, but requires larger targets than strangeness exchange methods.{{sfn|Gal|Hungerford|Millener|2016|pp=10–12}}

===Elastic scattering===
[[Electron scattering]] off of a proton can change it to a Λ and produce a K<sup>+</sup>:{{sfn|Gal|Hungerford|Millener|2016|p=12}}
:p + e<sup>−</sup> → Λ + e<sup>−</sup>{{prime}} + K<sup>+</sup>
where the prime symbol denotes a scattered electron. The energy of an electron beam can be more easily tuned than pion or kaon beams, making it easier to measure and calibrate hypernuclear energy levels.{{sfn|Gal|Hungerford|Millener|2016|p=12}} Initially theoretically predicted in the 1980s, this method was first used experimentally in the early 2000s.<ref>{{cite journal |last1=Nakamura |first1=Satoshi N. |last2=Fujii |first2=Yuu |last3=Tsukada |first3=Kyo |title=Precision spectroscopy of lambda hypernuclei using electron beams |journal=Nippon Butsuri Gakkai-Shi |date=2013 |volume=68 |issue=9 |pages=584–592 |url=https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecord&RN=45008322 |issn=0029-0181}}</ref>

===Hyperon capture===
The capture of a Ξ<sup>−</sup> baryon by a nucleus can make a Ξ<sup>−</sup> exotic atom or hypernucleus.<ref name="JPARC E07"/> Upon capture, it changes to a ΛΛ hypernucleus or two Λ hypernuclei.{{sfn|Gal|Hungerford|Millener|2016|p=16,43}} The disadvantage is that the Ξ<sup>−</sup> baryon is harder to make into a beam than singly strange hadrons.{{sfn|Tolos|Fabbietti|2020|p=43}} However, an experiment at [[J-PARC]] begun in 2020 will compile data on Ξ and ΛΛ hypernuclei using a similar, non-beam setup where scattered Ξ<sup>−</sup> baryons rain onto an emulsion target.<ref name="JPARC E07">{{cite journal |last1=Yoshida |first1=J. |collaboration=The J-PARC 07 Collaboration|title=J-PARC E07: Systematic Study of Double Strangeness System with Hybrid Emulsion Method |journal=Proceedings of the 3rd J-PARC Symposium (J-PARC2019) |date=25 March 2021 |volume=33 |page=011112 |doi=10.7566/jpscp.33.011112 |bibcode=2021jprc.confa1112Y |isbn=978-4-89027-146-7 |s2cid=233692057 |doi-access=free }}</ref>

===Heavy-ion collisions===
{{empty section|date=December 2022}}

== Similar species ==
===Kaonic nuclei===
The K<sup>–</sup> meson can orbit a nucleus in an exotic atom, such as in [[kaonic hydrogen]].<ref>{{cite journal |last1=Iwasaki |first1=M. |last2=Hayano |first2=R. S. |last3=Ito |first3=T. M. |last4=Nakamura |first4=S. N. |last5=Terada |first5=T. P. |last6=Gill |first6=D. R. |last7=Lee |first7=L. |last8=Olin |first8=A. |last9=Salomon |first9=M. |last10=Yen |first10=S. |last11=Bartlett |first11=K. |last12=Beer |first12=G. A. |last13=Mason |first13=G. |last14=Trayling |first14=G. |last15=Outa |first15=H. |last16=Taniguchi |first16=T. |last17=Yamashita |first17=Y. |last18=Seki |first18=R. |title=Observation of Kaonic Hydrogen K α X Rays |journal=Physical Review Letters |date=21 April 1997 |volume=78 |issue=16 |pages=3067–3069 |doi=10.1103/PhysRevLett.78.3067|bibcode=1997PhRvL..78.3067I }}</ref> Although the K<sup>–</sup>-proton strong interaction in kaonic hydrogen is repulsive,<ref>{{cite journal |last1=Bazzi |first1=M. |last2=Beer |first2=G. |last3=Bombelli |first3=L. |last4=Bragadireanu |first4=A.M. |last5=Cargnelli |first5=M. |last6=Corradi |first6=G. |last7=Curceanu (Petrascu) |first7=C. |last8=dʼUffizi |first8=A. |last9=Fiorini |first9=C. |last10=Frizzi |first10=T. |last11=Ghio |first11=F. |last12=Girolami |first12=B. |last13=Guaraldo |first13=C. |last14=Hayano |first14=R.S. |last15=Iliescu |first15=M. |last16=Ishiwatari |first16=T. |last17=Iwasaki |first17=M. |last18=Kienle |first18=P. |last19=Levi Sandri |first19=P. |last20=Longoni |first20=A. |last21=Lucherini |first21=V. |last22=Marton |first22=J. |last23=Okada |first23=S. |last24=Pietreanu |first24=D. |last25=Ponta |first25=T. |last26=Rizzo |first26=A. |last27=Romero Vidal |first27=A. |last28=Scordo |first28=A. |last29=Shi |first29=H. |last30=Sirghi |first30=D.L. |last31=Sirghi |first31=F. |last32=Tatsuno |first32=H. |last33=Tudorache |first33=A. |last34=Tudorache |first34=V. |last35=Vazquez Doce |first35=O. |last36=Widmann |first36=E. |last37=Zmeskal |first37=J. |title=A new measurement of kaonic hydrogen X-rays |journal=Physics Letters B |date=October 2011 |volume=704 |issue=3 |pages=113–117 |doi=10.1016/j.physletb.2011.09.011|arxiv=1105.3090|bibcode=2011PhLB..704..113S |s2cid=118473154 }}</ref> the K<sup>–</sup>–nucleus interaction is attractive for larger systems, so this meson can enter a strongly bound state closely related to a hypernucleus;<ref name="Feliciello"/> in particular, the K<sup>–</sup>–proton–proton system is experimentally known and more tightly bound than a normal nucleus.<ref>{{cite journal |last1=Sakuma |first1=F. |last2=Ajimura |first2=S. |last3=Akaishi |first3=T. |last4=Asano |first4=H. |last5=Bazzi |first5=M. |last6=Beer |first6=G. |last7=Bhang |first7=H. |last8=Bragadireanu |first8=M. |last9=Buehler |first9=P. |last10=Busso |first10=L. |last11=Cargnelli |first11=M. |last12=Choi |first12=S. |last13=Clozza |first13=A. |last14=Curceanu |first14=C. |last15=Enomoto |first15=S. |last16=Fujioka |first16=H. |last17=Fujiwara |first17=Y. |last18=Fukuda |first18=T. |last19=Guaraldo |first19=C. |last20=Hashimoto |first20=T. |last21=Hayano |first21=R. S. |last22=Hiraiwa |first22=T. |last23=Iio |first23=M. |last24=Iliescu |first24=M. |last25=Inoue |first25=K. |last26=Ishiguro |first26=Y. |last27=Ishikawa |first27=T. |last28=Ishimoto |first28=S. |last29=Itahashi |first29=K. |last30=Iwasaki |first30=M. |last31=Iwai |first31=M. |last32=Kanno |first32=K. |last33=Kato |first33=K. |last34=Kato |first34=Y. |last35=Kawasaki |first35=S. |last36=Kienle |first36=P. |last37=Kou |first37=H. |last38=Ma |first38=Y. |last39=Marton |first39=J. |last40=Matsuda |first40=Y. |last41=Miliucci |first41=M. |last42=Mizoi |first42=Y. |last43=Morra |first43=O. |last44=Murayama |first44=R. |last45=Nagae |first45=T. |last46=Noumi |first46=H. |last47=Ohnishi |first47=H. |last48=Okada |first48=S. |last49=Outa |first49=H. |last50=Ozawa |first50=K. |last51=Piscicchia |first51=K. |last52=Sada |first52=Y. |last53=Sakaguchi |first53=A. |last54=Sato |first54=M. |last55=Scordo |first55=A. |last56=Sekimoto |first56=M. |last57=Shi |first57=H. |last58=Shirotori |first58=K. |last59=Simon |first59=M. |last60=Sirghi |first60=D. |last61=Sirghi |first61=F. |last62=Suzuki |first62=S. |last63=Suzuki |first63=T. |last64=Tanida |first64=K. |last65=Tatsuno |first65=H. |last66=Tokuda |first66=M. |last67=Tomono |first67=D. |last68=Toyoda |first68=A. |last69=Tsukada |first69=K. |last70=Doce |first70=O. Vázquez |last71=Widmann |first71=E. |last72=Yamaga |first72=T. |last73=Yamazaki |first73=T. |last74=Yoshida |first74=C. |last75=Zhang |first75=Q. |last76=Zmeskal |first76=J.|display-authors= 1 |title=Recent Results and Future Prospects of Kaonic Nuclei at J-PARC |journal=Few-Body Systems |date=December 2021 |volume=62 |issue=4 |pages=103 |doi=10.1007/s00601-021-01692-3|arxiv=2110.03150 |bibcode=2021FBS....62..103S |s2cid=238419423 }}</ref>

===Charmed hypernuclei===
Nuclei containing a [[charm quark]] have been predicted theoretically since 1977,<ref>{{cite journal |last1=Dover |first1=C. B. |last2=Kahana |first2=S. H. |title=Possibility of Charmed Hypernuclei |journal=Physical Review Letters |date=12 December 1977 |volume=39 |issue=24 |pages=1506–1509 |doi=10.1103/PhysRevLett.39.1506|bibcode=1977PhRvL..39.1506D }}</ref> and are described as '''charmed hypernuclei''' despite the possible absence of strange quarks.<ref name="Gastão">{{cite book |last1=Krein |first1=Gastão |title=Central European Symposium on Thermophysics 2019 (Cest) |chapter=Charmed hypernuclei and nuclear-bound charmonia |date=2019 |volume=2133 |pages=020022 |doi=10.1063/1.5118390|s2cid=201510645 }}</ref> In particular, the lightest charmed baryons, the Λ<sub>c</sub> and Σ<sub>c</sub> baryons,{{efn|name=csub|The subscript ''c'' in the symbols for charmed baryons indicate that a strange quark in a hyperon is replaced with a charm quark; the superscript, if present, still represents the total charge of the baryon.}} are predicted to exist in bound states in charmed hypernuclei, and could be created in processes analogous to those used to make hypernuclei.<ref name="Gastão"/> The depth of the Λ<sub>c</sub> potential in nuclear matter is predicted to be 58&nbsp;MeV,<ref name="Gastão"/> but unlike Λ hypernuclei, larger hypernuclei containing the positively charged Λ<sub>c</sub> would be less stable than the corresponding Λ hypernuclei due to [[Coulomb repulsion]].<ref>{{cite journal |last1=Güven |first1=H. |last2=Bozkurt |first2=K. |last3=Khan |first3=E. |last4=Margueron |first4=J. |title=Ground state properties of charmed hypernuclei within a mean field approach |journal=Physical Review C |date=10 December 2021 |volume=104 |issue=6 |pages=064306 |doi=10.1103/PhysRevC.104.064306|arxiv=2106.04491 |bibcode=2021PhRvC.104f4306G |s2cid=235368356 }}</ref> The mass difference between the Λ<sub>c</sub> and the {{physics particle|Σ|TR=+|BR=c}} is too large for appreciable mixing of these baryons to occur in hypernuclei.<ref>{{cite journal |last1=Vidaña |first1=I. |last2=Ramos |first2=A. |last3=Jiménez-Tejero |first3=C. E. |title=Charmed nuclei within a microscopic many-body approach |journal=Physical Review C |date=23 April 2019 |volume=99 |issue=4 |pages=045208 |doi=10.1103/PhysRevC.99.045208|arxiv=1901.09644 |bibcode=2019PhRvC..99d5208V |s2cid=119100085 }}</ref> Weak decays of charmed hypernuclei have strong [[special relativity|relativistic]] corrections compared to those in ordinary hypernuclei, as the energy released in the decay process is comparable to the mass of the Λ baryon.<ref>{{cite journal |last1=Fontoura |first1=C E |last2=Krmpotić |first2=F |last3=Galeão |first3=A P |last4=Conti |first4=C De |last5=Krein |first5=G |title=Nonmesonic weak decay of charmed hypernuclei |journal=Journal of Physics G: Nuclear and Particle Physics |date=1 January 2018 |volume=45 |issue=1 |pages=015101 |doi=10.1088/1361-6471/aa982a|arxiv=1711.04579 |bibcode=2018JPhG...45a5101F |s2cid=119184293 }}</ref>

=== Antihypernuclei ===
In August 2024 the [[STAR collaboration|STAR Collaboration]] reported the observation of the heaviest [[antimatter]] nucleus known, antihyperhydrogen-4 <math>{}_{\bar{{\boldsymbol{\Lambda }}}}{}^{{\bf{4}}}\bar{{\bf{H}}}</math> consisting of one [[antiproton]], two [[Antineutron|antineutrons]] and an [[antihyperon]].<ref>{{Cite journal |last1=Abdulhamid |first1=M. I. |last2=Aboona |first2=B. E. |last3=Adam |first3=J. |last4=Adamczyk |first4=L. |last5=Adams |first5=J. R. |last6=Aggarwal |first6=I. |last7=Aggarwal |first7=M. M. |last8=Ahammed |first8=Z. |last9=Aschenauer |first9=E. C. |last10=Aslam |first10=S. |last11=Atchison |first11=J. |last12=Bairathi |first12=V. |last13=Cap |first13=J. G. Ball |last14=Barish |first14=K. |last15=Bellwied |first15=R. |date=2024-08-21 |title=Observation of the antimatter hypernucleus $${}_{\bar{{\boldsymbol{\Lambda }}<nowiki>}}{}^</nowiki>{{\bf{4}}}\bar{{\bf{H}}}$$ |url=https://www.nature.com/articles/s41586-024-07823-0 |journal=Nature |volume=632 |issue=8027 |language=en |pages=1026–1031 |doi=10.1038/s41586-024-07823-0 |pmid=39169195 |issn=1476-4687}}</ref><ref>{{Cite web |author1=Ben Turner |date=2024-08-21 |title=Heaviest antimatter particle ever discovered could hold secrets to our universe's origins |url=https://www.livescience.com/physics-mathematics/particle-physics/scientists-discover-the-heaviest-antimatter-particle-ever-and-it-could-hold-secrets-to-our-universes-origins |access-date=2024-08-26 |website=livescience.com |language=en}}</ref><ref>{{Cite web |last=Egede |first=Ulrik |date=2024-08-21 |title=Heaviest antimatter observation yet will fine-tune numbers for dark matter search |url=https://theconversation.com/heaviest-antimatter-observation-yet-will-fine-tune-numbers-for-dark-matter-search-237127 |access-date=2024-08-26 |website=The Conversation |language=en-US}}</ref> 

The anti-lambda hyperon <math>\bar{\Lambda }</math><ref>{{Cite journal |last1=Prowse |first1=D. J. |last2=Baldo-Ceolin |first2=M. |date=1958-09-01 |title=Anti-Lambda Hyperon |url=https://link.aps.org/doi/10.1103/PhysRevLett.1.179 |journal=Physical Review Letters |language=en |volume=1 |issue=5 |pages=179–180 |doi=10.1103/PhysRevLett.1.179 |bibcode=1958PhRvL...1..179P |issn=0031-9007|url-access=subscription }}</ref> and the antihypertriton <math>{}_{\bar{\Lambda }}{}^{3}\bar{{\rm{H}}}</math><ref>{{Cite journal |last1=The STAR Collaboration |last2=Abelev |first2=B. I. |last3=Aggarwal |first3=M. M. |last4=Ahammed |first4=Z. |last5=Alakhverdyants |first5=A. V. |last6=Alekseev |first6=I. |last7=Anderson |first7=B. D. |last8=Arkhipkin |first8=D. |last9=Averichev |first9=G. S. |last10=Balewski |first10=J. |last11=Barnby |first11=L. S. |last12=Baumgart |first12=S. |last13=Beavis |first13=D. R. |last14=Bellwied |first14=R. |last15=Betancourt |first15=M. J. |date=2010-04-02 |title=Observation of an Antimatter Hypernucleus |url=https://www.science.org/doi/10.1126/science.1183980 |journal=Science |language=en |volume=328 |issue=5974 |pages=58–62 |doi=10.1126/science.1183980 |pmid=20203011 |issn=0036-8075|arxiv=1003.2030 |bibcode=2010Sci...328...58. }}</ref> have also been previously observed.

==See also==
*[[Strangelet]], a hypothetical form of matter that also contains strange quarks

==Notes==
{{reflist|group=lower-alpha}}

==References==
{{Reflist|30em}}
*{{cite journal |last1=Gal |first1=A. |last2=Hungerford |first2=E.V. |last3=Millener |first3=D.J. |title=Strangeness in nuclear physics |journal=Reviews of Modern Physics |date=26 August 2016 |volume=88 |issue=3 |page=035004 |doi=10.1103/RevModPhys.88.035004|arxiv=1605.00557|bibcode=2016RvMP...88c5004G |s2cid=118395559}}
*{{cite journal |last1=Tolos |first1=L. |last2=Fabbietti |first2=L. |title=Strangeness in nuclei and neutron stars |journal=Progress in Particle and Nuclear Physics |date=May 2020 |volume=112 |pages=103770 |doi=10.1016/j.ppnp.2020.103770|arxiv=2002.09223|bibcode=2020PrPNP.11203770T |s2cid=211252559 }}

{{Authority control}}

[[Category:Exotic matter]]
[[Category:Nuclear physics]]
[[Category:Strange quark]]