What is the meaning of the word "j particle"?

Definitions:

  1. A neutral meson with a large mass. copy to clipboard NOUN
  2. A subatomic particle that is electrically neutral and unstable. copy to clipboard NOUN
  3. A type of elementary particle (meson) thought to be formed from charmed quarks. copy to clipboard NOUN
  4. An early name for the J/psi particle. copy to clipboard NOUN

Synonyms: