An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) 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 = (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. → 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.

→ baryon; → number.