Editing Baryon number (section)

{{Short description|Quantum number relating the quantity of quarks and antiquarks in a system}}
{{more citations needed|date=July 2013}}
{{Flavour_quantum_numbers}}

In [[particle physics]], the '''baryon number (B)''' is an <!--Baryon number violation has never been observed. Despite there being much theoretical support--> additive [[quantum number]] of a [[Quantum mechanics|system]]. It is defined as
<math display="block">B = \frac{1}{3}(n_\text{q} - n_{\rm \overline q}), </math>
where {{tmath|n_{\rm q} }} is the number of [[quark]]s, and {{tmath|n_{\rm \overline q} }} is the number of [[antiquark]]s. [[Baryon]]s (three quarks) have '''B''' = +1, [[meson]]s (one quark, one antiquark) have '''B''' = 0, and antibaryons (three antiquarks) have '''B''' = &minus;1. [[Exotic hadron]]s like [[pentaquark]]s (four quarks, one antiquark) and [[tetraquark]]s (two quarks, two antiquarks) are also classified as baryons and mesons depending on their baryon number. In the [[Standard Model|standard model]] '''B''' conservation is an accidental symmetry<ref>{{Citation |last1=Altmannshofer |first1=Wolfgang |title=Gauging the accidental symmetries of the standard model, and implications for the flavor anomalies |date=2019-09-18 |url=https://arxiv.org/abs/1909.02021 |access-date=2025-03-18 |arxiv=1909.02021 |last2=Davighi |first2=Joe |last3=Nardecchia |first3=Marco|journal=Physical Review D |volume=101 |page=015004 |doi=10.1103/PhysRevD.101.015004 }}</ref> which means that it appears in the [[Standard Model|standard model]] but is often violated when going beyond it. [[Physics beyond the Standard Model]] theories that contain baryon number violation are, for example, Standard Model with extra dimensions,<ref name=":0">{{Cite journal |last1=Addazi |first1=A |last2=Anderson |first2=K |last3=Ansell |first3=S |last4=Babu |first4=K S |last5=Barrow |first5=J L |last6=Baxter |first6=D V |last7=Bentley |first7=P M |last8=Berezhiani |first8=Z |last9=Bevilacqua |first9=R |last10=Biondi |first10=R |last11=Bohm |first11=C |last12=Brooijmans |first12=G |last13=Broussard |first13=L J |last14=Cedercäll |first14=J |last15=Crawford |first15=C |date=2021-07-01 |title=New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the HIBEAM/NNBAR experiment at the European Spallation Source |url=https://iopscience.iop.org/article/10.1088/1361-6471/abf429 |journal=Journal of Physics G: Nuclear and Particle Physics |volume=48 |issue=7 |pages=070501 |doi=10.1088/1361-6471/abf429 |arxiv=2006.04907 |bibcode=2021JPhG...48g0501A |issn=0954-3899}}</ref> [[Supersymmetry]], [[Grand Unified Theory]] and [[String theory]].