عدد ِ باریونی adad-e bâriyoni (#)
*Fr.: nombre baryonique*
1) The difference between the total number of → *baryon*s and
the total number of → *antibaryon*s in a system of
→ *subatomic particle*s.
It is a measure of → *baryon asymmetry* and is
defined by the quantity
η = (*n*_{b} - *n*_{b-})/*n*_{γ},
called the → *baryon-photon ratio*,
where *n*_{b} is the → *comoving* number
density of baryons, *n*_{b-} is the number of
antibaryons, and *n*_{γ} 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.
2) A property of an → *elementary particle* represented by a
→ *quantum number*. It is
equal to +1 for a baryon and -1 for an antibaryon.
→ *Boson*s, → *lepton*s, and
→ *meson*s have a baryon number B = 0.
→ *Quark*s and → *antiquark*s
have baryon numbers of B = +1/3 and -1/3, respectively.
The baryon number is → *conserve*d in all observed types of
particle-particle interaction. → *baryon*; → *number*. |