J/psi particle

• J/ψ meson
• J/psi meson
• J/ψ particle
• J particle
• psion (obsolete)

A compound of J, ψ (psi), and particle. The particle was discovered independently in 1974 by two research groups, leading to the "November Revolution" in particle physics.

• The group led by Samuel Ting at Brookhaven National Laboratory proposed the name J, reputedly because the shape of the Chinese character for Ting (丁) resembles a J, though Ting also cited the symbol for electromagnetic current, ${\displaystyle j_{\mu }(x)}$, as a reason.^[1]
• The group led by Burton Richter at SLAC proposed the name ψ (psi). Richter initially preferred "SP" (for the SPEAR accelerator), but chose "psi" as it contained "SP" in reverse order and was the only remaining Greek letter deemed suitable; coincidently, the particle's decay pattern in spark chambers resembled the letter ψ.

The compromise name J/ψ was adopted to acknowledge both discoveries.

• (UK) IPA^(key): /ˌdʒeɪ ˈsaɪ ˈpɑːtɪkl̩/
• (US) IPA^(key): /ˌdʒeɪ ˈsaɪ ˈpɑɹtɪkəl/, /ˌdʒeɪ ˈpsaɪ ˈpɑɹtɪkəl/
• Hyphenation: J‧ψ‧par‧ti‧cle
• Rhymes: -ɑː(ɹ)tɪkəl

J/ψ particle (plural J/psi particles)

1. (particle physics) A subatomic particle with an unusually long lifetime (7.2 × 10⁻²¹ s) and a large mass (approx. 3.097 GeV/c²); a bound state of a charm quark and an anti-charm quark (the most common form of charmonium).

   Synonyms: J/psi meson, psion

   • 1974, J. J. Aubert et al., “Experimental Observation of a Heavy Particle J”, in Physical Review Letters, volume 33, number 23, →DOI, pages 1404–1406:

     We report the observation of a heavy particle J, with mass m = 3.1 GeV and width approximately zero.

   • 1974, J. E. Augustin et al., “Discovery of a Narrow Resonance in e⁺e^- Annihilation”, in Physical Review Letters, volume 33, number 23, →DOI, pages 1406–1408:

     We denote this resonance as ψ(3105).

• “J/psi particle”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.