Loterre: Astronomie: baryon number

physical parameter > quantum number > baryon number

baryon number

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. (An Etymological Dictionary of Astronomy and Astrophysics, by M. Heydari-Malayeri, https://dictionary.obspm.fr/index.php?formSearchTextfield=baryon+number&formSubmit=Search&showAll=1)

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