 | |
| Composition | Elementary particle |
|---|---|
| Statistics | Fermionic |
| Family | Quark |
| Generation | Second |
| Interactions | strong,weak,electromagnetic force,gravity |
| Symbol | s |
| Antiparticle | Strange antiquark (s) |
| Theorized | Murray Gell-Mann (1964) George Zweig (1964) |
| Discovered | 1947Department of Physics and Astronomy, University of Manchester, 1968SLAC |
| Mass | 95+9 −3 MeV/c2[1] |
| Decays into | Up quark |
| Electric charge | −1/3 e |
| Color charge | Yes |
| Spin | 1/2 ħ |
| Weak isospin | LH: −1/2,RH: 0 |
| Weak hypercharge | LH:1/3,RH: −2/3 |
Thestrange quark ors quark (from its symbol, s) is the third lightest of allquarks, a type ofelementary particle. Strange quarks are found insubatomic particles calledhadrons. Examples of hadrons containing strange quarks includekaons (K),strange D mesons (D
s),sigma baryons (Σ), and otherstrange particles.
According to theIUPAP, the symbols is the official name, while "strange" is to be considered only as a mnemonic.[2] The namesideways has also been used because the s quark (but also the other three remaining quarks) has anI3 value of 0 while the u ("up") and d ("down") quarks have values of +1/2 and −1/2 respectively.[3]
Along with thecharm quark, it is part of thesecond generation of matter. It has anelectric charge of−+1/3 e and abare mass of95+9
−3 MeV/c2.[1] Like allquarks, the strange quark is anelementaryfermion withspin1/2, and experiences all fourfundamental interactions:gravitation,electromagnetism,weak interactions, andstrong interactions. Theantiparticle of the strange quark is thestrange antiquark (sometimes calledantistrange quark or simplyantistrange), which differs from it only in that some of its properties haveequal magnitude but opposite sign.
The firststrange particle (a particle containing a strange quark) was discovered byGeorge Rochester andClifford Butler inDepartment of Physics and Astronomy, University of Manchester in 1947 (kaons), with the existence of the strange quark itself (and that of theup anddown quarks) postulated in 1964 byMurray Gell-Mann andGeorge Zweig to explain theeightfold way classification scheme ofhadrons. The first evidence for the existence of quarks came in 1968, indeep inelastic scattering experiments at theStanford Linear Accelerator Center. These experiments confirmed the existence of up and down quarks, and by extension, strange quarks, as they were required to explain theeightfold way.
In the beginnings of particle physics (first half of the 20th century),hadrons such asprotons,neutrons andpions were thought to beelementary particles. However, new hadrons were discovered and the "particle zoo" grew from a few particles in the early 1930s and 1940s to several dozens of them in the 1950s. Some particles were much longer lived than others; most particles decayed through thestrong interaction and hadlifetimes of around 10−23 seconds. When they decayed through theweak interactions, they had lifetimes of around 10−10 seconds. While studying these decays,Murray Gell-Mann (in 1953)[4][5] andKazuhiko Nishijima (in 1955)[6] developed the concept ofstrangeness (which Nishijima calledeta-charge, after theeta meson (η)) to explain the "strangeness" of the longer-lived particles. TheGell-Mann–Nishijima formula is the result of these efforts to understand strange decays.
Despite their work, the relationships between each particle and the physical basis behind the strangeness property remained unclear. In 1961, Gell-Mann[7] andYuval Ne'eman[8] independently proposed a hadron classification scheme called theeightfold way, also known asSU(3)flavor symmetry. This ordered hadrons intoisospin multiplets. The physical basis behind both isospin and strangeness was only explained in 1964, when Gell-Mann[9] andGeorge Zweig[10][11] independently proposed thequark model, which at that time consisted only of the up, down, and strange quarks.[12] Up and down quarks were the carriers of isospin, while the strange quark carried strangeness. While the quark model explained theeightfold way, no direct evidence of the existence of quarks was found until 1968 at theStanford Linear Accelerator Center.[13][14]Deep inelastic scattering experiments indicated thatprotons had substructure, and that protons made of three more-fundamental particles explained the data (thus confirming thequark model).[15]
At first people were reluctant to identify the three-bodies as quarks, instead preferringRichard Feynman'sparton description,[16][17][18] but over time the quark theory became accepted (seeNovember Revolution).[19]
By the end of the summer ... [Gell-Mann] completed his first paper, 'Isotopic Spin and Curious Particles' and send it of toPhysical Review. The editors hated the title, so he amended it to 'Strange Particles'. They wouldn't go for that either—never mind that almost everybody used the term—suggesting insteand [sic] 'Isotopic Spin and New Unstable Particles'.
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