Charm (symbol ''C'') is a
flavour quantum number representing the difference between the number of
charm quark
The charm quark, charmed quark, or c quark is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including th ...
s () and
charm antiquarks () that are present in a particle:
:
By convention, the sign of flavour quantum numbers agree with the sign of the
electric charge
Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...
carried by the
quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...
s of corresponding flavour. The charm quark, which carries an electric charge (''Q'') of +, therefore carries a charm of +1. The charm antiquarks have the opposite
charge (), and flavour quantum numbers ().
As with any flavour-related quantum numbers, charm is preserved under
strong
Strong may refer to:
Education
* The Strong, an educational institution in Rochester, New York, United States
* Strong Hall (Lawrence, Kansas), an administrative hall of the University of Kansas
* Strong School, New Haven, Connecticut, United ...
and
electromagnetic interaction, but not under
weak interaction
In nuclear physics and particle physics, the weak interaction, weak force or the weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, and gravitation. It is th ...
(see
CKM matrix). For first-order weak decays, that is processes involving only one quark decay, charm can only vary by 1 (). Since first-order processes are more common than second-order processes (involving two quark decays), this can be used as an approximate "
selection rule
In physics and chemistry, a selection rule, or transition rule, formally constrains the possible transitions of a system from one quantum state to another. Selection rules have been derived for electromagnetic transitions in molecules, in atoms, in ...
" for weak decays.
[Alexander Belyae]
Chapter 17 Weak Interactions
''PHYS3002: Nuclei and Particles'', p. 129
See also
*
Quantum number
In quantum physics and chemistry, quantum numbers are quantities that characterize the possible states of the system.
To fully specify the state of the electron in a hydrogen atom, four quantum numbers are needed. The traditional set of quantu ...
References
Quarks
Flavour (particle physics)
he:קסם (פיזיקה)
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