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 1985, 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.
Particle | Symbol | Quark content |
Rest mass ( MeV/ c2) |
J P |
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 | (268±24)×10−15 | 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.
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
DØ 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.
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 1985, 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.
Particle | Symbol | Quark content |
Rest mass ( MeV/ c2) |
J P |
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 | (268±24)×10−15 | 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.
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
DØ 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.