charmquark

Charm quark (symbol c) is a fundamental particle of the Standard Model. It is an up-type quark of the second generation, with electric charge +2/3e and spin 1/2. Like other quarks, it carries color charge and participates in the strong, weak, and electromagnetic interactions. Its mass is commonly quoted around 1.27 GeV/c^2 in the current-quark framework, placing it heavier than up and down quarks but lighter than bottom and top quarks.

In hadrons, charm quarks combine with lighter quarks to form mesons and baryons. Notable examples are D mesons (such as D0 = c ū and D+ = c d̄) and the charmonium bound states (cc̄) like the J/ψ, which have played a crucial role in testing quantum chromodynamics. Charm-containing baryons include Λc+ and various Σc states. The charm sector thus provides important laboratories for studying strong interactions in the heavy-quark regime.

Historically, the charm quark was postulated to explain the suppression of flavor-changing neutral currents via the GIM mechanism, and it was experimentally established in 1974 with the discovery of the J/ψ particle by experiments at SLAC and CERN. In weak decays, charm quarks typically transition to strange or down quarks through emission of a W boson, with rates governed by the CKM matrix elements V_cs and V_cd. Production and decay of charm hadrons in high-energy experiments continue to be a key area for tests of QCD and for searches for new physics in the flavor sector.