| Composition |
|
|---|---|
| Statistics | Bosonic |
| Family | Mesons |
| Interactions | Strong,Weak,Gravitational,Electromagnetic |
| Symbol | B+ , B− , B0 , B0 , B0 s, B0 s, B+ c, B− c |
| Antiparticle |
|
| Mass |
|
| Mean lifetime |
|
| Electric charge | |
| Spin | 0 |
| Strangeness | B0 s: −1 |
| Charm | B+ c: +1 |
| Bottomness | +1 |
| Isospin |
|
| Parity | −1 |
Inparticle physics,B mesons aremesons composed of abottomantiquark and either anup (
B+
),down (
B0
),strange (
B0
s) orcharmquark (
B+
c). The combination of a bottom antiquark and atop quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but ratherbottomonium, which is something else entirely.
Each B meson has anantiparticle that is composed of a bottom quark and anup (
B−
),down (
B0
),strange (
B0
s) orcharm (
B−
c) antiquark respectively.
| Particle | Symbol | Anti- particle | Quark content | Charge | Isospin (I) | Spin andparity, (JP) | Rest mass (MeV/c2) | S | C | B' | Mean lifetime (s) | Commonly decays to |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Charged B meson | B+ | B− | u b | +1 | 1/2 | 0− | 5279.34±0.12 | 0 | 0 | +1 | (1.638±0.004)×10−12 | See B± decay modes |
| Neutral B meson | B0 | B0 | d b | 0 | 1/2 | 0− | 5279.65±0.12 | 0 | 0 | +1 | (1.519±0.004)×10−12 | See B0 decay modes |
| Strange B meson | B0 s | B0 s | s b | 0 | 0 | 0− | 5366.88±0.14 | −1 | 0 | +1 | (1.515±0.004)×10−12 | See B0 s decay modes |
| Charmed B meson | B+ c | B− c | c b | +1 | 0 | 0− | 6274.9±0.8 | 0 | +1 | +1 | (0.510±0.009)×10−12 | See B± c decay modes |
The neutral B mesons,
B0
and
B0
s, spontaneously transform into their own antiparticles and back. This phenomenon is calledflavor oscillation. The existence of neutral B meson oscillations is a fundamental prediction of theStandard Model ofparticle physics. It has been measured in the
B0
–
B0
system to be about0.496 /picoseconds,[1] and in the
B0
s–
B0
s system to beΔms = 17.77 ± 0.10 (stat) ± 0.07 (syst) /picosecond measured byCDF experiment atFermilab.[2] A first estimation of the lower and upper limit of the
B0
s–
B0
s system value have been made by theDØ experiment also atFermilab.[3]
On 25 September 2006,Fermilab announced that they had claimed discovery of previously-only-theorized
B0
s meson oscillation.[4] According to Fermilab's press release:
This first major discovery of Run 2 continues the tradition of particle physics discoveries at Fermilab, where the bottom (1977) and top (1995) quarks were discovered. Surprisingly, the bizarre behavior of the
B0
s (pronounced "B sub s") mesons is actually predicted by the Standard Model of fundamental particles and forces. The discovery of this oscillatory behavior is thus another reinforcement of the Standard Model's durability ...
CDF physicists have previously measured the rate of the matter-antimatter transitions for the
B0
s meson, which consists of the heavy bottom quark bound by the strong nuclear interaction to a strange antiquark. Now they have achieved the standard for a discovery in the field of particle physics, where the probability for a false observation must be proven to be less than about 5 in 10 million(5/10000000=1/2000000). For CDF's result the probability is even smaller, at 8 in 100 million(8/100000000=1/12500000).
Ronald Kotulak, writing for theChicago Tribune, called the particle "bizarre" and stated that the meson "may open the door to a new era of physics" with its proven interactions with the "spooky realm of antimatter".[5]
On 14 May 2010, physicists at the Fermi National Accelerator Laboratory reported that the oscillations decayed into matter 1% more often than into antimatter, which may help explain the abundance of matter over antimatter in the observed Universe.[6] However, more recent results atLHCb with larger data samples have suggested no significant deviation from the Standard Model.[7]
B mesons are an important probe for exploringquantum chromodynamics.[8] Various uncommon decay paths of the B mesons are sensitive to physics processesoutside the standard model. Measuring these rare branching fractions sets limits on new particles. The LHCb experiment has observed and searched for several of these decays such asBs → μ+ μ−.[9]
On 21 February 2017, the LHCb collaboration announced that the rare decay of a neutral B meson into two oppositely chargedkaons had been observed to a statistical significance of 5σ.[10]
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