baryon number عدد ِ باریونی adad-e bâriyoni (#) Fr.: nombre baryonique The difference between the total number of → baryons and
the total number of → antibaryons in a system of
→ subatomic particles.
It is a measure of → baryon asymmetry and is
defined by the quantity
η = (nb - nb-)/nγ,
called the → baryon-photon ratio,
where nb is the → comoving number
density of baryons, nb- is the number of
antibaryons, and nγ is that of photons. The value of η for
the → cosmic microwave background radiation (CMBR)
has been very well determined by the → WMAP satellite to be
η = (6.14 ± 0.25) x 10-10. The baryon number is assumed to be
constant. The photons created in
stars amount to only a small fraction, less than 1%, of those in the CMBR.
A property of an → elementary particle represented by a
→ quantum number. It is
equal to +1 for a baryon and -1 for an antibaryon.
→ Bosons, → leptons, and
→ mesons have a baryon number B = 0.
→ Quarks and → antiquarks
have baryon numbers of B = +1/3 and -1/3, respectively.
The baryon number is → conserved in all observed types of
particle-particle interaction.
See also: → baryon; → number. |
