{{Short description|Baryon made of specific quark combinations}} {{Infobox Particle | name = Lambda baryon | num_types = 3 | composition = {{plainlist| * {{SubatomicParticle|Lambda0}}: {{SubatomicParticle|Up quark}}{{SubatomicParticle|Down quark}}{{SubatomicParticle|Strange quark}} * {{SubatomicParticle|Charmed Lambda+}}: {{SubatomicParticle|Up quark}}{{SubatomicParticle|Down quark}}{{SubatomicParticle|Charm quark}} * {{SubatomicParticle|Bottom Lambda0}}: {{SubatomicParticle|Up quark}}{{SubatomicParticle|Down quark}}{{SubatomicParticle|Bottom quark}}}} | statistics = Fermionic | group = Baryons | interaction = Strong, weak, electromagnetic, and gravity | antiparticle = |image=Quark structure lambda baryon.svg | status = | theorized = | discovered = | symbol = | mass = {{plainlist| * {{nowrap|{{SubatomicParticle|Lambda0}}: {{val|1115.683|0.006|ul=MeV/c2}}<ref name="pdg">{{cite journal| title=Review of Particle Physics | last1=Zyla | first1=P. A. | last2=Barnett | first2=R. M. | display-authors=1 | collaboration = Particle Data Group | journal=Progress of Theoretical and Experimental Physics | volume = 2020 | page = 083C01 | year = 2020 | issue=8 | doi=10.1093/ptep/ptaa104| bibcode=2020PTEP.2020h3C01P | doi-access=free | hdl=11585/772320 | hdl-access=free }}</ref>}} * {{nowrap|{{SubatomicParticle|Charmed Lambda+}}: {{val|2286.46|0.14|u=MeV/c2}}}} * {{nowrap|{{SubatomicParticle|Bottom Lambda0}}: {{val|5619.60|0.17|u=MeV/c2}}}}}} | mean_lifetime = | width = | decay_particle = | electric_charge = | charge_radius = | electric_dipole_moment = | electric_polarizability = | magnetic_moment = | magnetic_polarizability = | color_charge = | spin = {{sfrac|1|2}}&nbsp;''ħ'' | num_spin_states = | baryon_number = | strangeness = | charm = | bottomness = | topness = | isospin = 0 | weak_isospin = | weak_isospin_3 = | hypercharge = | weak_hypercharge = | chirality = | B-L = | X_charge = | parity = | g_parity = | c_parity = | r_parity = | condensed_symmetries = |caption=Quark structure of the lambda baryon.}}

The '''lambda baryons''' (Λ) are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of any two quarks being swapped (thus slightly different from a neutral sigma baryon, {{SubatomicParticle|Sigma0}}). They are thus baryons, with total isospin of 0, and have either neutral electric charge or the elementary charge +1.

== Overview ==

The lambda baryon {{Subatomic particle|Lambda0}} was first discovered in October 1950, by V. D. Hopper and S. Biswas of the University of Melbourne, as a neutral V particle with a proton as a decay product, thus correctly distinguishing it as a baryon, rather than a meson,<ref>{{Cite journal | last1=Hopper | first1=V.D. | last2=Biswas | first2=S. | title=Evidence Concerning the Existence of the New Unstable Elementary Neutral Particle | journal=Phys. Rev. | volume=80 | issue=6 | page=1099 | year=1950 | doi=10.1103/physrev.80.1099 | bibcode=1950PhRv...80.1099H}}</ref> i.e. different in kind from the K meson discovered in 1947 by George Rochester and Clifford Charles Butler;<ref>{{Cite journal | last1=Rochester | first1=G. D. | last2=Butler| first2=C. C. | title=Evidence for the Existence of New Unstable Elementary Particles | journal=Nature | volume=160 | issue=4077 | year=1947 | pages=855–7 | doi=10.1038/160855a0 | pmid=18917296 | bibcode=1947Natur.160..855R | s2cid=33881752 }}</ref> they were produced by cosmic rays and detected in photographic emulsions flown in a balloon at {{convert|70000|ft}}.<ref>{{Cite book | last=Pais | first=Abraham | title=Inward Bound | url=https://archive.org/details/inwardboundofmat00pais_0 | url-access=registration | publisher=Oxford University Press| pages= [https://archive.org/details/inwardboundofmat00pais_0/page/21 21], 511–517 | year=1986| isbn=978-0-19-851971-3 }}</ref> Though the particle was expected to live for {{val|p=~|e=-23|u=seconds}},<ref name="LambdaFound">[http://hyperphysics.phy-astr.gsu.edu/Hbase/Particles/quark.html#c4 The Strange Quark]</ref> it actually survived for {{val|p=~|e=-10|u=seconds}}.<ref name="Lambda0"/> The property that caused it to live so long was dubbed ''strangeness'' and led to the discovery of the strange quark.<ref name="LambdaFound"/> Furthermore, these discoveries led to a principle known as the ''conservation of strangeness'', wherein lightweight particles do not decay as quickly if they exhibit strangeness (because non-weak methods of particle decay must preserve the strangeness of the decaying baryon).<ref name="LambdaFound"/> The {{Subatomic particle|Lambda0}} with its uds quark decays via weak force to a nucleon and a pion − either {{nowrap|1=Λ → p + π<sup>−</sup>}} or {{nowrap|1=Λ → n + π<sup>0</sup>}}.

In 1974 and 1975, an international team at the Fermilab that included scientists from Fermilab and seven European laboratories under the leadership of Eric Burhop carried out a search for a new particle, the existence of which Burhop had predicted in 1963. He had suggested that neutrino interactions could create short-lived (perhaps as low as 10<sup>−14</sup>&nbsp;s) particles that could be detected with the use of nuclear emulsion. Experiment E247 at Fermilab successfully detected particles with a lifetime of the order of 10<sup>−13</sup>&nbsp;s. A follow-up experiment, WA17, which made use of the SPS accelerator at CERN confirmed the existence of the {{SubatomicParticle|Charmed Lambda+}} (charmed lambda baryon), with a lifetime of {{val|7.3|0.1|e=-13|u=s}}.<ref>{{cite journal |title=Eric Henry Stoneley Burhop 31 January 1911 – 22 January 1980 |first1=Harrie |last1=Massey |author-link=Harrie Massey |first2=D. H. |last2=Davis |journal=Biographical Memoirs of Fellows of the Royal Society |volume=27 |date=November 1981 |issue=27 |pages=131–152 |jstor=769868 |doi=10.1098/rsbm.1981.0006 |doi-access=free|s2cid=123018692 }}</ref><ref>{{cite thesis |type=MSc |first=Eric |last=Burhop |url=http://trove.nla.gov.au/work/21419586?versionId=256398321933 |title=The Band Spectra of Diatomic Molecules |publisher=University of Melbourne |year=1933 }}</ref>

In 2011, the international team at JLab used high-resolution spectrometer measurements of the reaction H(e, e′K<sup>+</sup>)X at small Q<sup>2</sup> (E-05-009) to extract the pole position in the complex-energy plane (primary signature of a resonance) for the Λ(1520) with mass {{val|1518.8|u=MeV/c2}} and width {{val|17.2|u=MeV/c2}}, which seem to be smaller than their Breit–Wigner values.<ref>{{cite journal |first=Y. |last=Qiang |display-authors=etal |title=Properties of the Lambda(1520) resonance from high-precision electroproduction data |journal=Physics Letters B |date=2010 |volume=694 |issue=2 |pages=123–128 |doi=10.1016/j.physletb.2010.09.052 |arxiv=1003.5612 |bibcode=2010PhLB..694..123Q |s2cid=119290870 }}</ref> This was the first determination of the pole position for a hyperon.

The lambda baryon has also been observed in atomic nuclei called hypernuclei. These nuclei contain the same number of protons and neutrons as a known nucleus, but also contains one or in rare cases two lambda particles.<ref>{{cite web|title=Media Advisory: The Heaviest Known Antimatter|url=http://www.bnl.gov/rhic/news2/news.asp?a=1236&t=pr|publisher=bnl.gov|access-date=2013-03-10|archive-date=2017-02-11|archive-url=https://web.archive.org/web/20170211164015/https://www.bnl.gov/rhic/news2/news.asp?a=1236&t=pr|url-status=dead}}</ref> In such a scenario, the lambda slides into the center of the nucleus (it is not a proton or a neutron, and thus is not affected by the Pauli exclusion principle), and it binds the nucleus more tightly together due to its interaction via the strong force. In a lithium isotope ({{PhysicsParticle|Li|TL=7|BL=Λ}}), it made the nucleus 19% smaller.<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>

== Types ==

Lambda baryons are usually represented by the symbols {{math| {{Subatomic particle|Lambda0}},}} {{math| {{Subatomic particle|Charmed Lambda+}},}} {{math| {{Subatomic particle|Bottom Lambda0}},}} and {{math| {{Subatomic particle|Top Lambda+}}.}} In this notation, the superscript character indicates whether the particle is electrically neutral (<sup>0</sup>) or carries a positive charge (<sup>+</sup>). The subscript character, or its absence, indicates whether the third quark is a strange quark {{nobr|{{math| ({{Subatomic particle|Lambda0}})}} }} (no subscript), a charm quark {{nobr|{{math| ({{Subatomic particle|Charmed Lambda+}})}},}} a bottom quark {{nobr|{{math| ({{Subatomic particle|Bottom Lambda0}})}},}} or a top quark {{nobr|{{math| ({{Subatomic particle|Top Lambda+}})}}.}} Physicists expect to not observe a lambda baryon with a top quark, because the Standard Model of particle physics predicts that the mean lifetime of top quarks is roughly {{val|5|e=-25}}&nbsp;seconds;<ref name=Quadt> {{cite journal | first=A. | last=Quadt | year=2006 | title=Top quark physics at hadron colliders | journal=European Physical Journal C | volume=48 | issue=3 |pages=835–1000 | doi=10.1140/epjc/s2006-02631-6 | bibcode = 2006EPJC...48..835Q | s2cid=121887478 | url=https://cds.cern.ch/record/1339554/files/978-3-540-71060-8_BookTOC.pdf }}</ref> that is about {{sfrac|1|20}} of the mean timescale for strong interactions, which indicates that the top quark would decay before a lambda baryon could form a hadron.

The symbols encountered in this list are: {{mvar|I}} (''isospin''), {{mvar|J}} (''total angular momentum quantum number''), {{mvar|P}} (''parity''), {{mvar|Q}} (''charge''), {{mvar|S}} (''strangeness''), {{mvar|C}} (''charmness''), {{math|''B''′}} (''bottomness''), {{mvar|T}} (''topness''), u (''up quark''), d (''down quark''), s (''strange quark''), c (''charm quark''), b (''bottom quark''), t (''top quark''), as well as other subatomic particles.

Antiparticles are not listed in the table; however, they simply would have all quarks changed to antiquarks, and {{math|''Q''}}, {{math|''B''}}, {{math|''S''}}, {{math|''C''}}, {{math|''B''′}}, {{math|''T''}}, would be of opposite signs. {{mvar|I}}, {{math|''J''}}, and {{mvar|P}} values in red have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements.<ref>{{cite web |first1=C. |last1=Amsler |collaboration=Particle Data Group |display-authors=etal |year=2008 |title=Baryons |series=Particle summary tables |publisher=Lawrence Berkeley Laboratory |url=http://pdg.lbl.gov/2008/tables/rpp2008-sum-baryons.pdf}}</ref><ref>{{cite journal |author1=Körner, J.G. |author2=Krämer, M. |author3=Pirjol, D. |year=1994 |title=Heavy Baryons |journal=Progress in Particle and Nuclear Physics |volume=33 |pages=787–868 |doi=10.1016/0146-6410(94)90053-1 |arxiv=hep-ph/9406359 |bibcode=1994PrPNP..33..787K|s2cid=118931787 }}</ref> The top lambda {{math|({{Subatomic particle|Top Lambda+}})}} is listed for comparison, but is expected to never be observed, because top quarks decay before they have time to form hadrons.<ref name="HoKim">{{cite book |last1=Ho-Kim |first1=Quang |first2=Xuan Yem |last2=Pham |year=1998 |title=Elementary Particles and their Interactions: Concepts and phenomena |publisher=Springer-Verlag |location=Berlin |isbn=978-3-540-63667-0 |oclc=38965994 |page=262 |chapter=Quarks and SU(3) Symmetry |quote=Because the top quark decays before it can be hadronized, there are no bound <math alt="t anti-t">t \bar{t}</math> states and no top-flavored mesons or baryons&nbsp;...&nbsp;.}}</ref>

{| class="wikitable sortable" style="text-align: center;" |+ Lambda baryons |- ! class=unsortable|Particle name ! Symbol ! class=unsortable|Quark<br/>content ! Rest mass {{bracket|MeV/{{mvar|c}}<sup>2</sup>}} ! width="50"|{{mvar|I}} ! width="50"|{{mvar|J}}<sup>P</sup> ! width="50"|{{mvar|Q}} {{bracket|{{mvar|e}}}} ! width="50"|S ! width="50"|{{mvar|C}} ! width="50"|{{math|''B''′}} ! width="50"|{{mvar|T}} ! Mean lifetime {{bracket|{{mvar|s}}}} ! class=unsortable|Commonly decays to |- style="height:40px" |align="left"| Lambda<ref name="Lambda0"> {{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> | {{math| {{Subatomic particle|Lambda0}} }} | {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Strange quark}} | {{val|1115.683|0.006}} | 0 | {{nowrap|{{sfrac|1|2}}<sup>+</sup>}} | 0 | −1 | 0 | 0 | 0 | {{val|2.631|0.020|e=-10}} | {{nobr|{{math| {{Subatomic particle|link=yes|Proton+}} + {{Subatomic particle|link=yes|Pion-}} }}or}}<br/>{{nobr|{{math|{{Subatomic particle|link=yes|Neutron0}} + {{Subatomic particle|link=yes|Pion0}} }} }} |- style="height:40px" |align="left"| charmed lambda<ref name=PDGCharmedLamdba> {{cite web |first1=C. |last1=Amsler |collaboration=Particle Data Group |display-authors=etal |year=2008 |title={{Subatomic particle|Charmed Lambda}} |series=Particle listings |publisher=Lawrence Berkeley Laboratory |url=http://pdg.lbl.gov/2008/listings/s033.pdf }} </ref> | {{math| {{Subatomic particle|Charmed Lambda+}} }} | {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Charm quark}} | {{val|2286.46|0.14}} | 0 | <span style="color:red">{{nowrap|{{sfrac|1|2}}<sup>+</sup>}}</span> | +1 | 0 | +1 | 0 | 0 | {{val|2.00|0.06|e=-13}} | decay modes<ref> {{cite web |first1=C. |last1=Amsler |collaboration=Particle Data Group |display-authors=etal |year=2008 |title={{Subatomic particle|Charmed lambda+}} |series=Decay modes |publisher=Lawrence Berkeley Laboratory |url=http://pdg.lbl.gov/2008/listings/s033.pdf }} </ref> |- style="height:40px" |align="left"| bottom lambda<ref name=PDGBottomLambda0> {{cite web |first1=C. |last1=Amsler |collaboration=Particle Data Group |display-authors=etal |year=2008 |title={{Subatomic particle|Bottom Lambda}} |series=Particle listings |publisher=Lawrence Berkeley Laboratory |url=http://pdg.lbl.gov/2008/listings/s040.pdf }} </ref> | {{math| {{Subatomic particle|Bottom Lambda0}} }} | {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Bottom quark}} | {{val|5620.2|1.6}} | <span style="color:red">0</span> | <span style="color:red">{{nowrap|{{sfrac|1|2}}<sup>+</sup>}}</span> | 0 | 0 | 0 | −1 | 0 | {{val|1.409|0.055|-0.054|e=-12}} | Decay modes<ref> {{cite web |first1=C. |last1=Amsler |collaboration=Particle Data Group |display-authors=etal |year=2008 |title={{Subatomic particle|Bottom Lambda0}} |series=Decay modes |publisher=Lawrence Berkeley Laboratory |url=http://pdg.lbl.gov/2008/listings/s040.pdf }} </ref> |- style="height:40px" |align="left"| top lambda<sup>{{ref|Undiscovered|‡}}</sup> | {{math| {{Subatomic particle|Top Lambda+}} }} | {{Subatomic particle|link=yes|Up quark}}{{Subatomic particle|link=yes|Down quark}}{{Subatomic particle|link=yes|Top quark}} | — | <span style="color:red">0</span> | <span style="color:red">{{nowrap|{{sfrac|1|2}}<sup>+</sup>}}</span> | +1 | 0 | 0 | 0 | +1 | — | {{ref|Undiscovered|‡}} |} ‡ {{note|Undiscovered}} Particle unobserved, because the top-quark decays before it has sufficient time to bind into a hadron ("hadronizes").

== See also == {{Portal|Physics}} * List of baryons

== References == {{reflist|25em}}

== Further reading == * {{cite journal |author1=Amsler, C. |display-authors=etal |year=2008 |title=Review of Particle Physics |journal=Physics Letters B |volume=667 |issue=1–5 |pages=1–6 |doi=10.1016/j.physletb.2008.07.018 |bibcode=2008PhLB..667....1A |url=https://www.zora.uzh.ch/id/eprint/11249/2/scalarsV.pdf|hdl=1854/LU-685594 |s2cid=227119789 |hdl-access=free }} * {{cite journal |author1=Caso, C. |display-authors=etal |year=1998 |title=Review of Particle Physics |journal=European Physical Journal C |volume=3 |issue=1–4 |pages=1–783 |doi=10.1007/s10052-998-0104-x |bibcode=1998EPJC....3....1P|s2cid=195314526 }} * {{cite web |author=Nave, R. |date=12 April 2005 |title=The Lambda baryon |url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/lambda.html |work=HyperPhysics |access-date=2010-07-14 |df=dmy-all}}

{{Particles}} {{Authority control}}

{{DEFAULTSORT:Lambda baryon}} Category:Baryons Category:Strange quark