= J/psi meson
{c}
{title2=$J/\psi$}
{wiki}
The <J psi meson> is the ground spin-triplet S-wave vector state of <charmonium>, with leading valence content $c\bar c$ and quantum numbers $J^{PC}=1^{--}$. It has zero net charm and can decay into <hadrons> or charged-lepton pairs.<Review of Particle Physics by Particle Data Group (2022)>[J/psi(1S) listing, pp. 1–2: quantum numbers, width and decay modes]{ref}
Its comparatively narrow <decay width> makes it a conspicuous resonance in reconstructed mass distributions. An <electron>–<Positron> mass peak in a fixed-target experiment and an enhanced event rate during an <energy> scan in an <electron-positron collider> were complementary observations in the <Richter-Ting independent J psi discovery experiments> of 1974.<Experimental Observation of a Heavy Particle J by J. J. Aubert>[Abstract: proton–beryllium experiment and electron–positron invariant-mass spectrum]{ref}<Discovery of a Narrow Resonance in e+e- Annihilation by J.-E. Augustin>[Abstract: enhanced collision cross section during the center-of-mass energy scan]{ref} A peak's measured width also includes detector resolution or beam-energy spread, so it must not automatically be identified with the intrinsic lifetime width.
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