Sigma baryon

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 higher flavour generations, in a combination where the wavefunction does not swap sign 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
Σ+
,
Σ0
,
Σ
), a charm (symbols
Σ++
c
,
Σ+
c
,
Σ0
c
), a bottom (symbols
Σ+
b
,
Σ0
b
,
Σ
b
) or a top (symbols
Σ++
t
,
Σ+
t
,
Σ0
t
) quark. However, the top Sigmas are not expected to be observed as the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s.[1] This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.

List

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.[2][3]

JP = 1/2+ Sigma baryons

JP = 1/2+ Sigma baryons
Particle name Symbol Quark
content
Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to
Sigma[4]
Σ+

u

u

s
1,189.37 ± 0.07 1 1/2+ +1 −1 0 0 0 8.018 ± 0.026 × 10−11
p+
+
π0
or


n0
+
π+

Sigma[5]
Σ0

u

d

s
1,192.642 ± 0.024 1 1/2+ 0 −1 0 0 0 7.4 ± 0.7 × 10−20
Λ0
+
γ
Sigma[6]
Σ

d

d

s
1,197.449 ± 0.030 1 1/2+ −1 −1 0 0 0 1.479 ± 0.011 × 10−10
n0
+
π
charmed Sigma[7]
Σ++
c
(2455)

u

u

c
2,454.02 ± 0.18 1 1/2 + +2 0 +1 0 0 3.0 ± 0.4 × 10−22[a]
Λ+
c
+
π+
charmed Sigma[7]
Σ+
c
(2455)

u

d

c
2,452.9 ± 0.4 1 1/2 + +1 0 +1 0 0 >1.4 × 10−22[a]
Λ+
c
+
π0
charmed Sigma[7]
Σ0
c
(2455)

d

d

c
2,453.76 ± 0.18 1 1/2 + 0 0 +1 0 0 3.0 ± 0.5 × 10−22[a]
Λ+
c
+
π
bottom Sigma[8]
Σ+
b

u

u

b
5,807.7 ± 3.8 1 1/2 + +1 0 0 −1 0 Unknown
Λ0
b
+
π+
(seen)
bottom Sigma
Σ0
b

u

d

b
Unknown 1 1/2 + 0 0 0 −1 0 Unknown Unknown
bottom Sigma[8]
Σ
b

d

d

b
5,815.2 ± 2.7 1 1/2 + −1 0 0 −1 0 Unknown
Λ0
b
+
π
(seen)
Top Sigma
Σ++
t

u

u

t
1 1/2 + +2 0 0 0 +1
Top Sigma
Σ+
t

u

d

t
1 1/2 + +1 0 0 0 +1
Top Sigma
Σ0
t

d

d

t
1 1/2 + 0 0 0 0 +1

^ 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
Σ
b
(5810).

JP = 3/2+ Sigma baryons

JP = 3/2+ Sigma baryons
Particle name Symbol Quark
content
Rest mass (MeV/c2) I JP Q (e) S C B' T Mean lifetime (s) Commonly decays to
Sigma[9]
Σ∗+
(1385)

u

u

s
1,382.8 ± 0.4 1 3/2+ +1 −1 0 0 0 1.84 ± 0.04 × 10−23[c]
Λ0
+
π+
or


Σ+
+
π0
or


Σ0
+
π+

Sigma[9]
Σ∗0
(1385)

u

d

s
1,383.7 ± 1.0 1 3/2+ 0 −1 0 0 0 1.8 ± 0.3 × 10−23[c]
Λ0
+
π0
or


Σ+
+
π
or


Σ0
+
π0

Sigma[9]
Σ∗−
(1385)

d

d

s
1,387.2 ± 0.5 1 3/2+ −1 −1 0 0 0 1.67 ± 0.09 × 10−23[c]
Λ0
+
π
or


Σ0
+
π
or


Σ
+
π0
or

charmed Sigma[10]
Σ∗++
c
(2520)

u

u

c
2,518.4 ± 0.6 1 3/2 + +2 0 +1 0 0 4.4 ± 0.6 × 10−23[c]
Λ+
c
+
π+
charmed Sigma[10]
Σ∗+
c
(2520)

u

d

c
2,517.5 ± 2.3 1 3/2 + +1 0 +1 0 0 >3.9 × 10−23[c]
Λ+
c
+
π0
charmed Sigma[10]
Σ∗0
c
(2520)

d

d

c
2,518.0 ± 0.5 1 3/2 + 0 0 +1 0 0 4.1 ± 0.5 × 10−23[c]
Λ+
c
+
π
bottom Sigma
Σ∗+
b

u

u

b
Unknown 1 3/2 + +1 0 0 −1 0 Unknown Unknown
bottom Sigma
Σ∗0
b

u

d

b
Unknown 1 3/2 + 0 0 0 −1 0 Unknown Unknown
bottom Sigma
Σ∗−
b

d

d

b
Unknown 1 3/2 + −1 0 0 −1 0 Unknown Unknown
Top Sigma
Σ∗++
t

u

u

t
1 3/2 + +2 0 0 0 +1
Top Sigma
Σ∗+
t

u

d

t
1 3/2 + +1 0 0 0 +1
Top Sigma
Σ∗0
t

d

d

t
1 3/2 + 0 0 0 0 +1

^ The standard model predicts that this particle cannot exist due to the short lifetime of the top quark.
[c] ^ PDG reports the resonance width (Γ). Here the conversion τ = ħ/Γ is given instead.

See also

References

  1. ^ A. Quadt (2006). "Top quark physics at hadron colliders" (PDF). European Physical Journal C. 48 (3): 835–1000. Bibcode:2006EPJC...48..835Q. doi:10.1140/epjc/s2006-02631-6.
  2. ^ C. Amsler et al. (2008): Particle summary tables – Baryons
  3. ^ J. G. Körner et al. (1994)
  4. ^ Amsler, C.; et al. (2008). "
    Σ+
    "
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.
  5. ^ Amsler, C.; et al. (2008). "
    Σ0
    "
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.
  6. ^ Amsler, C.; et al. (2008). "
    Σ
    "
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.
  7. ^ a b c Amsler, C.; et al. (2008). "
    Σ
    c
    (2455)"
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.
  8. ^ a b T. Aaltonen et al. (2007a)
  9. ^ a b c Amsler, C.; et al. (2008). "
    Σ
    (1385)"
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.
  10. ^ a b c Amsler, C.; et al. (2008). "
    Σ
    c
    (2520)"
    (PDF). Particle Data Group. Particle listings. Lawrence Berkeley Laboratory.

Bibliography

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Gauge bosons are different from the other kinds of bosons: first, fundamental scalar bosons (the Higgs boson); second, mesons, which are composite bosons, made of quarks; third, larger composite, non-force-carrying bosons, such as certain atoms.

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Lambda baryon

The Lambda baryons 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 differing from a Sigma baryon). They are thus baryons, with total isospin of 0, and have either neutral electric charge or the elementary charge +1.

Lambda baryons are usually represented by the symbols Λ0, Λ+c, Λ0b, and Λ+t. 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 (Λ0) (no subscript), a charm quark (Λ+c), a bottom quark (Λ0b), or a top quark (Λ+t). Physicists do not expect to 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 5×10−25 seconds; that is about 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.

Mainz Microtron

The Mainz Microtron (German name: Mainzer Mikrotron), abbreviated MAMI,

is a microtron (particle accelerator) which provides a continuous wave, high intensity, polarized electron beam with an energy up to 1.6 GeV. MAMI is the core of an experimental facility for particle, nuclear and X-ray radiation physics at the Johannes Gutenberg University in Mainz (Germany). It is one of the largest campus-based accelerator facilities for basic research in Europe. The experiments at MAMI are performed by about 200 physicists of many countries organized in international collaborations.

Omega baryon

The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol Ω and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons containing top quarks are not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale for strong interactions, and therefore that they do not form hadrons.

The first omega baryon discovered was the Ω−, made of three strange quarks, in 1964. The discovery was a great triumph in the study of quark processes, since it was found only after its existence, mass, and decay products had been predicted in 1961 by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist Yuval Ne'eman. Besides the Ω−, a charmed omega particle (Ω0c) was discovered, in which a strange quark is replaced by a charm quark. The Ω− decays only via the weak interaction and has therefore a relatively long lifetime. Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.Since omega baryons do not have any up or down quarks, they all have isospin 0.

V particle

In particle physics, V was a generic name for heavy, unstable subatomic particles that decay into a pair of particles, thereby producing a characteristic letter V in a bubble chamber or other particle detector. Such particles were first detected in cosmic ray interactions in the atmosphere in the late 1940s and were first produced using the Cosmotron particle accelerator at Brookhaven National Laboratory in the 1950s. Since all such particles have now been identified and given specific names, such as K meson or Sigma baryon, this term has fallen into disuse.

V0 is still used on occasion to refer generally to neutral particles that may confuse the B-tagging algorithms in a modern particle detector, as is used in Section 7 of

this ATLAS conference note.

Xi baryon

The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge (Q) of +2 e, +1 e, 0, or −1 e, where e is the elementary charge. Like all conventional baryons, they contain three quarks. Xi baryons, in particular, contain one up or down quark plus two more massive quarks: either strange, charm or bottom. They are historically called the cascade particles because of their unstable state; they decay rapidly into lighter particles through a chain of decays. The first discovery of a charged Xi baryon was in cosmic ray experiments by the Manchester group in 1952. The first discovery of the neutral Xi particle was at Lawrence Berkeley Laboratory in 1959. It was also observed as a daughter product from the decay of the omega baryon (Ω−) observed at Brookhaven National Laboratory in 1964. The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as Lattice QCD.

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