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Concept
Baryon Sigma
Résumé
The sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation (up and / or down quarks), and a third quark from a higher flavour generation, in a combination where the wavefunction sign remains constant when any two quark flavours are swapped. They are thus baryons, with total isospin of 1, and can either be neutral or have an elementary charge of +2, +1, 0, or −1. They are closely related to the Lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.
The third quark can hence be either a strange (symbols _Sigma+, _Sigma0, _Sigma-), a charm (symbols _Charmed Sigma++, _Charmed Sigma+, _Charmed Sigma0), a bottom (symbols _Bottom Sigma+, _Bottom Sigma0, _Bottom Sigma-) or a top (symbols _Top Sigma++, _Top Sigma+, _Top Sigma0) quark. However, the top sigmas are expected to never be observed, since the Standard Model predicts the mean lifetime of top quarks to be roughly 5e-25s. This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.
The symbols encountered in these lists are: I (isospin), J (total angular momentum), P (parity), u (up quark), d (down quark), s (strange quark), c (charm quark), t (top quark), b (bottom quark), Q (electric charge), S (strangeness), C (charmness), B′ (bottomness), T (topness), as well as other subatomic particles (hover for name).
Antiparticles are not listed in the table; however, they simply would have all quarks changed to antiquarks (and vice versa), and Q, B, S, C, B′, T, would be of opposite signs. I, J, and P values in red have not been firmly established by experiments, but are predicted by the quark model and are consistent with the measurements.
† The standard model predicts that this particle cannot exist due to the short lifetime of the top quark.
[a] PDG reports the resonance width (Γ). Here the conversion τ = ħ/Γ is given instead.
[b] The specific values of the name has not been decided yet, but will likely be close to _Bottom Sigma(5810).
Source officielle
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