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.[1] 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,[2] 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.[3] 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 (
Ω0
c
) 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.[4] Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.[5]

Since omega baryons do not have any up or down quarks, they all have isospin 0.

Omega Baryon
Bubble chamber trace of the first observed Ω baryon event at Brookhaven National Laboratory

Omega baryons

Omega
Particle Symbol Quark
content
Rest mass
(MeV/c2)
JP Q
(e)
S C B′ Mean lifetime
(s)
Decays to
Omega[6]
Ω

s

s

s
1672.45±0.29 3/2+ −1 −3 0 0 (8.21±0.11)×10−11
Λ0
+
K
or

Ξ0
+
π
or

Ξ
+
π0

Charmed omega[7]
Ω0
c

s

s

c
2697.5±2.6 1/2+ 0 −2 +1 0 (6.9±1.2)×10−14 See
Ω0
c
Decay Modes
Bottom omega[8]
Ω
b

s

s

b
6054.4±6.8 1/2+ −1 −2 0 −1 (1.13±0.53)×10−12
Ω
+
J/ψ
(seen)
Double charmed omega†
Ω+
cc

s

c

c
1/2+ +1 −1 +2 0
Charmed bottom omega†
Ω0
cb

s

c

b
1/2+ 0 −1 +1 −1
Double bottom omega†
Ω
bb

s

b

b
1/2+ −1 −1 0 −2
Triple charmed omega†
Ω++
ccc

c

c

c
3/2+ +2 0 +3 0
Double charmed bottom omega†
Ω+
ccb

c

c

b
1/2+ +1 0 +2 −1
Charmed double bottom omega†
Ω0
cbb

c

b

b
1/2+ 0 0 +1 −2
Triple bottom omega†
Ω
bbb

b

b

b
3/2+ −1 0 0 −3

† Particle (or quantity, i.e. spin) has neither been observed nor indicated.

Recent discoveries

The
Ω
b
particle is a "doubly strange" baryon containing two strange quarks and a bottom quark. A discovery of this particle was first claimed in September 2008 by physicists working on the experiment at the Tevatron facility of the Fermi National Accelerator Laboratory.[9][10] However, the reported mass of 6165±16 MeV/c2 was significantly higher than expected in the quark model. The apparent discrepancy from the Standard Model has since been dubbed the "
Ω
b
puzzle". In May 2009, the CDF collaboration made public their results on the search for the
Ω
b
based on analysis of a data sample roughly four times the size of the one used by the DØ experiment.[8] CDF measured the mass to be 6054.4±6.8 MeV/c2, which was in excellent agreement with the Standard Model prediction. No signal has been observed at the DØ reported value. The two results differ by 111±18 MeV/c2, which is equivalent to 6.2 standard deviations and are therefore inconsistent. Excellent agreement between the CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the
Ω
b
. In February 2013 the LHCb collaboration published a measurement of the
Ω
b
mass that is consistent with, but more precise than, the CDF result.[11]

In March 2017, the LHCb collaboration announced the observation of five new narrow
Ω0
c
states decaying to
Ξ+
c

K
, where the
Ξ+
c
was reconstructed in the decay mode
p

K

π+
.[12][13] The states are named
Ω
c
(3000)0,
Ω
c
(3050)0,
Ω
c
(3066)0,
Ω
c
(3090)0 and
Ω
c
(3119)0. Their masses and widths were reported, but their quantum numbers could not be determined due to the large background present in the sample.

See also

References

  1. ^ Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons" (PDF). Retrieved 26 December 2011.
  2. ^ A. Quadt (2006). "Top quark physics at hadron colliders". European Physical Journal C. 48 (3): 835–1000. Bibcode:2006EPJC...48..835Q. doi:10.1140/epjc/s2006-02631-6.
  3. ^ V. E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Minus Three" (PDF). Physical Review Letters. 12 (8): 204. Bibcode:1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204.
  4. ^ R. Nave. "The Omega baryon". HyperPhysics. Retrieved 26 November 2009.
  5. ^ Körner, J.G; Krämer, M; Pirjol, D (1 January 1994). "Heavy baryons". Progress in Particle and Nuclear Physics. 33: 787–868. doi:10.1016/0146-6410(94)90053-1.
  6. ^ Particle Data Group. "2006 Review of Particle Physics –
    Ω
    "
    (PDF). Retrieved 20 April 2008.
  7. ^ Particle Data Group. "
    Ω0
    c
    listing –
    Ω0
    c
    "
    (PDF). Retrieved 13 August 2018.
  8. ^ a b T. Aaltonen et al. (CDF Collaboration) (2009). "Observation of the
    Ω
    b
    and Measurement of the Properties of the
    Ξ
    b
    and
    Ω
    b
    ". Physical Review D. 80 (7): 072003. arXiv:0905.3123. Bibcode:2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003. hdl:1721.1/52706.
  9. ^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 4 September 2008.
  10. ^ V. Abazov et al. (DØ Collaboration) (2008). "Observation of the doubly strange b baryon
    Ω
    b
    ". Physical Review Letters. 101 (23): 232002. arXiv:0808.4142. Bibcode:2008PhRvL.101w2002A. doi:10.1103/PhysRevLett.101.232002. PMID 19113541.
  11. ^ R. Aaij et al. (LHCb collaboration) (2013). "Measurement of the
    Λ0
    b
    ,
    Ξ
    b
    and
    Ω
    b
    baryon masses". Physical Review Letters. 110 (18): 182001. arXiv:1302.1072. Bibcode:2013PhRvL.110r2001A. doi:10.1103/PhysRevLett.110.182001. PMID 23683191.
  12. ^ "LHCb observes an exceptionally large group of particles". CERN.
  13. ^ R. Aaij et al. (LHCb collaboration) (2017). "Observation of five new narrow
    Ω0
    c
    states decaying to
    Ξ+
    c

    K
    ". Physical Review Letters. 11801 (2017): 182001. arXiv:1703.04639. Bibcode:2017PhRvL.118r2001A. doi:10.1103/PhysRevLett.118.182001. PMID 28524669.

External links

Eightfold way (physics)

In physics, the eightfold way is an organizational scheme for a class of subatomic particles known as hadrons that led to the development of the quark model. American physicist Murray Gell-Mann and Israeli physicist Yuval Ne'eman both proposed the idea in 1961. The name comes from Gell-Mann's 1961 paper and is an allusion to the Noble Eightfold Path of Buddhism.

Fermilab

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance, a joint venture of the University of Chicago, and the Universities Research Association (URA). Fermilab is a part of the Illinois Technology and Research Corridor.

Fermilab's Tevatron was a landmark particle accelerator; until the startup in 2008 of the Large Hadron Collider (LHC) near Geneva, Switzerland, it was the most powerful particle accelerator in the world, accelerating antiprotons to energies of 500 GeV, and producing proton-proton collisions with energies of up to 1.6 TeV, the first accelerator to reach one "tera-electron-volt" energy. At 3.9 miles (6.3 km), it was the world's fourth-largest particle accelerator in circumference. One of its most important achievements was the 1995 discovery of the top quark, announced by research teams using the Tevatron's CDF and DØ detectors. It was shut down in 2011.

In addition to high-energy collider physics, Fermilab hosts fixed-target and neutrino experiments, such as MicroBooNE (Micro Booster Neutrino Experiment), NOνA (NuMI Off-Axis νe Appearance) and SeaQuest. Completed neutrino experiments include MINOS (Main Injector Neutrino Oscillation Search), MINOS+, MiniBooNE and SciBooNE (SciBar Booster Neutrino Experiment). The MiniBooNE detector was a 40-foot (12 m) diameter sphere containing 800 tons of mineral oil lined with 1,520 phototube detectors. An estimated 1 million neutrino events were recorded each year. SciBooNE sat in the same neutrino beam as MiniBooNE but had fine-grained tracking capabilities. The NOνA experiment uses, and the MINOS experiment used, Fermilab's NuMI (Neutrinos at the Main Injector) beam, which is an intense beam of neutrinos that travels 455 miles (732 km) through the Earth to the Soudan Mine in Minnesota and the Ash River, Minnesota, site of the NOνA far detector.

In the public realm, Fermilab is home to a native prairie ecosystem restoration project and hosts many cultural events: public science lectures and symposia, classical and contemporary music concerts, folk dancing and arts galleries. The site is open from dawn to dusk to visitors who present valid photo identification.

Asteroid 11998 Fermilab is named in honor of the laboratory.

Gauge boson

In particle physics, a gauge boson is a force carrier, a bosonic particle that carries any of the fundamental interactions of nature, commonly called forces. Elementary particles, whose interactions are described by a gauge theory, interact with each other by the exchange of gauge bosons—usually as virtual particles.

All known gauge bosons have a spin of 1. Therefore, all known gauge bosons are vector bosons.

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.

Gell-Mann–Okubo mass formula

In physics, the Gell-Mann–Okubo mass formula provides a sum rule for the masses of hadrons within a specific multiplet, determined by their isospin (I) and strangeness (or alternatively, hypercharge)

where a0, a1, and a2 are free parameters.

The rule was first formulated by Murray Gell-Mann in 1961 and independently proposed by Susumu Okubo in 1962. Isospin and hypercharge are generated by SU(3), which can be represented by eight hermitian and traceless matrices corresponding to the "components" of isospin and hypercharge. Six of the matrices correspond to flavor change, and the final two correspond to the third-component of isospin projection, and hypercharge.

Glossary of string theory

This page is a glossary of terms in string theory, including related areas such as supergravity, supersymmetry, and high energy physics.

Greek letters used in mathematics, science, and engineering

Greek letters are used in mathematics, science, engineering, and other areas where mathematical notation is used as symbols for constants, special functions, and also conventionally for variables representing certain quantities. In these contexts, the capital letters and the small letters represent distinct and unrelated entities. Those Greek letters which have the same form as Latin letters are rarely used: capital A, B, E, Z, H, I, K, M, N, O, P, T, Y, X. Small ι, ο and υ are also rarely used, since they closely resemble the Latin letters i, o and u. Sometimes font variants of Greek letters are used as distinct symbols in mathematics, in particular for ε/ϵ and π/ϖ. The archaic letter digamma (Ϝ/ϝ/ϛ) is sometimes used.

The Bayer designation naming scheme for stars typically uses the first Greek letter, α, for the brightest star in each constellation, and runs through the alphabet before switching to Latin letters.

In mathematical finance, the Greeks are the variables denoted by Greek letters used to describe the risk of certain investments.

Index of physics articles (O)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

List of Horizon episodes

Horizon is a current and long-running BBC popular science and philosophy documentary

programme. Series one was broadcast in 1964 and as of August 2018 is in its 54th series. Over 1200 episodes have been broadcast (including specials) with an average of 24 episodes per series during the 54-year run.

1964–1969 – 135 episodes

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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, Σ0c), a bottom (symbols Σ+b, Σ0b, Σ−b) or a top (symbols Σ++t, Σ+t, Σ0t) 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. This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.

Strangeness production

Strangeness production is a signature and a diagnostic tool of quark–gluon plasma (or QGP) formation and properties. Unlike up and down quarks, from which everyday matter is made, strange quarks are formed in pair-production processes in collisions between constituents of the plasma. The dominant mechanism of production involves gluons only present when matter has become a quark–gluon plasma. When quark–gluon plasma disassembles into hadrons in a breakup process, the high availability of strange antiquarks helps to produce antimatter containing multiple strange quarks, which is otherwise rarely made. Similar considerations are at present made for the heavier charm flavor, which is made at the beginning of the collision process in the first interactions and is only abundant in the high-energy environments of CERN's Large Hadron Collider.

Tevatron

The Tevatron was a circular particle accelerator (inactive since 2011) in the United States, at the Fermi National Accelerator Laboratory (also known as Fermilab), east of Batavia, Illinois, and holds the title of the second highest energy particle collider in the world, after the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. The Tevatron was a synchrotron that accelerated protons and antiprotons in a 6.28 km (3.90 mi) ring to energies of up to 1 TeV, hence its name. The Tevatron was completed in 1983 at a cost of $120 million and significant upgrade investments were made in 1983–2011.

The main achievement of the Tevatron was the discovery in 1995 of the top quark—the last fundamental fermion predicted by the standard model of particle physics. On July 2, 2012, scientists of the CDF and DØ collider experiment teams at Fermilab announced the findings from the analysis of around 500 trillion collisions produced from the Tevatron collider since 2001, and found that the existence of the suspected Higgs boson was highly likely with only a 1-in-550 chance that the signs were due to a statistical fluctuation. The findings were confirmed two days later as being correct with a likelihood of error less than 1 in a million by data from the LHC experiments.The Tevatron ceased operations on 30 September 2011, due to budget cuts and because of the completion of the LHC, which began operations in early 2010 and is far more powerful (planned energies were two 7 TeV beams at the LHC compared to 1 TeV at the Tevatron). The main ring of the Tevatron will probably be reused in future experiments, and its components may be transferred to other particle accelerators.

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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