lambda baryon

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,{{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}} i.e. different in kind from the K meson discovered in 1947 by Rochester and Butler;{{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 }} they were produced by cosmic rays and detected in photographic emulsions flown in a balloon at {{convert|70000|ft}}.{{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 }} Though the particle was expected to live for {{val|p=~|e=-23|u=seconds}},[http://hyperphysics.phy-astr.gsu.edu/Hbase/Particles/quark.html#c4 The Strange Quark] it actually survived for {{val|p=~|e=-10|u=seconds}}. The property that caused it to live so long was dubbed strangeness and led to the discovery of the strange quark. 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). The {{Subatomic particle|Lambda0}} with its uds quark decays via weak force to a nucleon and a pion − either {{nowrap|1=Λ → p + π⁻}} or {{nowrap|1=Λ → n + π⁰}}.

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 10⁻¹⁴ 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 10⁻¹³ s. A follow-up experiment WA17 with the SPS confirmed the existence of the {{SubatomicParticle|Charmed Lambda+}} (charmed lambda baryon), with a lifetime of {{val|7.3|0.1|e=-13|u=s}}.{{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 |pages=131–152 |jstor=769868 |doi=10.1098/rsbm.1981.0006|s2cid=123018692 }}{{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 }}

In 2011, the international team at JLab used high-resolution spectrometer measurements of the reaction H(e, e′K⁺)X at small Q² (E-05-009) to extract the pole position in the complex-energy plane (primary signature of a resonance) for the Λ(1520) with mass = 1518.8 MeV and width = 17.2 MeV which seem to be smaller than their Breit–Wigner values.{{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 }} 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.{{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}} 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.{{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}}

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 (⁰) or carries a positive charge (⁺). 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}} seconds;

{{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

}} 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), {{mvar|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 {{mvar|Q, B, S, C, B′, T,}} would be of opposite signs. {{mvar|I, 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.{{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}}{{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 }} 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.{{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 $t\; \backslash bar\{t\}$ states and no top-flavored mesons or baryons ... .}}

‡ {{note|Undiscovered}} Particle unobserved, because the top-quark decays before it has sufficient time to bind into a hadron ("hadronizes").

The following table compares the nearly-identical Lambda and neutral Sigma baryons:

{{Portal|Physics}}

• List of baryons

{{reflist|25em}}

• {{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}}

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{{DEFAULTSORT:Lambda baryon}}

Category:Baryons

Category:Strange quark