Study of X(3915) → J/ψω in Two-Photon Collisions

We study the process γγ → J/ψω using a data sample of 519.2  fb⁻¹ recorded by the BABAR detector at SLAC at the PEP-II asymmetric-energy e⁺e⁻ collider at center-of-mass energies near the Υ(nS) (n = 2, 3, 4) resonances. We confirm the existence of the charmoniumlike resonance X(3915) decaying to J/ψω with a significance of 7.6 standard deviations, including systematic uncertainties, and measure its mass (3919.4 ± 2.2 ± 1.6)  MeV/c² and width (13 ± 6 ± 3)  MeV, where the first uncertainty is statistical and the second systematic. A spin-parity analysis supports the assignment J^P = 0⁺ and therefore the identification of the signal as due to the χ_{c0}(2P) resonance. In this hypothesis we determine the product between the two-photon width and the final state branching fraction to be (52 ± 10 ± 3)  eV.