R Aaij, C Abellán Beteta,
T Ackernley, B Adeva… - Physical Review Letters, 2021 - APS
The first observation of exotic states with a new quark content cc¯ us¯ decaying to the J/ψ
K+ final state is reported with high significance from an amplitude analysis of the B+→ J/ψ ϕ …