B meson

In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (
B+
), down (
B0
), strange (
B0
s) or charm quark (
B+
c). The combination of a bottom antiquark and a top 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 rather bottomonium.

Each B meson has an antiparticle that is composed of a bottom quark and an up (
B−
), down (
B0
), strange (
B0
s) or charm antiquark (
B−
c) respectively.

List of B mesons

B mesons
Particle Symbol Anti-particle Quark
content		 Charge Isospin
(I)		 Spin and parity
(JP)		 Rest mass
(MeV/c2)		 S C B' Mean lifetime
(s)		 Commonly decays to
B meson
B+
B−
u

b
 +1 1/2 0− 5279.29±0.15 0 0 +1 (1.638±0.004)×10−12 See decay modes
B meson
B0
B0
d

b
 0 1/2 0− 5279.61±0.16 0 0 +1 (1.520±0.004)×10−12 See
B0
 decay modes
Strange B meson
B0
s
B0
s
s

b
 0 0 0− 5366.79±0.23 −1 0 +1 (1.510±0.005)×10−12 See
B0
s decay modes
Charmed B meson
B+
c
B−
c
c

b
 +1 0 0− 6275.1±1.0 0 +1 +1 (0.507±0.009)×10−12 See
B±
c decay modes


B
–
B
 oscillations

Main article:
B
–
B
 oscillation

The neutral B mesons,
B0
 and
B0
s, spontaneously transform into their own antiparticles and back. This phenomenon is called flavor oscillation. The existence of neutral B meson oscillations is a fundamental prediction of the Standard Model of particle physics. It has been measured in the
B0
–
B0
 system to be about 0.496 ps−1,[1] and in the
B0
s–
B0
s system to be Δms = 17.77 ± 0.10 (stat) ± 0.07 (syst) ps−1 measured by CDF experiment at Fermilab.[2] A first estimation of the lower and upper limit of the
B0
s–
B0
s system value have been made by the DØ experiment also at Fermilab.[3]

On 25 September 2006, Fermilab announced that they had claimed discovery of previously-only-theorized Bs 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 B_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 B_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 (5/10,000,000). For CDF's result the probability is even smaller, at 8 in 100 million (8/100,000,000).

Ronald Kotulak, writing for the Chicago 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 at LHCb with larger data samples have suggested no significant deviation from the Standard Model.[7]

Rare Decays

B-mesons are an important probe for exploring quantum chromodynamics.[8] Various uncommon decay paths of the B mesons are sensitive to physics processes outside 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 as Bs → µ+µ−.[9]

See also

References

  1. ↑ http://repository.ubn.ru.nl/bitstream/2066/26242/
  2. ↑ A. Abulencia et al. (CDF Collaboration) (2006). "Observation of
    B0
    s    –
    B0
    s     Oscillations". Physical Review Letters. 97 (24): 242003. arXiv:hep-ex/0609040Freely accessible. Bibcode:2006PhRvL..97x2003A. doi:10.1103/PhysRevLett.97.242003.
  3. ↑ V.M. Abazov et al. (D0 Collaboration) (2006). "Direct Limits on the Bs0 Oscillation Frequency" (PDF). Physical Review Letters. 97 (2): 021802. arXiv:hep-ex/0603029Freely accessible. Bibcode:2006PhRvL..97b1802A. doi:10.1103/PhysRevLett.97.021802.
  4. ↑ "It might be…It could be…It is!!!" (Press release). Fermilab. 25 September 2006. Retrieved 2007-12-08.
  5. ↑ R. Kotulak (26 September 2006). "Antimatter discovery could alter physics: Particle tracked between real world, spooky realm". Deseret News. Archived from the original on 29 November 2007. Retrieved 2007-12-08.
  6. ↑ A New Clue to Explain Existence
  7. ↑ Article on LHCb results
  8. ↑ CMS Collaboration; LHCb Collaboration (2015-06-04). "Observation of the rare B0
    s    →µ+µ− decay from the combined analysis of CMS and LHCb data"    . Nature. 522 (7554): 68–72. arXiv:1411.4413Freely accessible. Bibcode:2015Natur.522...68C. doi:10.1038/nature14474. PMID 26047778.
  9. ↑ Aaij, R.; Beteta first3=B., C. Abellán; Adeva; Adinolfi, M.; Affolder, A.; Ajaltouni, Z.; Akar, S.; Albrecht, J. (2015-10-16). "Search for the rare decays B0→J/ψγ and B0
    s    →J/ψγ". Physical Review D. 92 (11). arXiv:1510.04866Freely accessible. Bibcode:2015PhRvD..92k2002A. doi:10.1103/PhysRevD.92.112002.

External links

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