Study of the lineshape of the 𝜒𝑐⁢1⁡(3872) state

A study of the lineshape of the 𝜒𝑐⁢1⁡(3872) state is made using a data sample corresponding to an integrated luminosity of 3  fb−1 collected in 𝑝⁢𝑝 collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate 𝜒𝑐⁢1⁡(3872) and 𝜓⁡(2⁢𝑆) mesons from 𝑏-hadron decays are selected in the 𝐽/𝜓⁢𝜋+⁢𝜋− decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the 𝜒𝑐⁢1⁡(3872) and 𝜓⁡(2⁢𝑆) states, Δ⁢𝑚, and the width of the 𝜒𝑐⁢1⁡(3872) state, ΓBW, are determined to be Δ⁢𝑚=185.598±0.067±0.068  MeV,
ΓBW=1.39±0.24±0.10  MeV, where the first uncertainty is statistical and the second systematic. Using a Flatté-inspired model, the mode and full width at half maximum of the lineshape are determined to be ode=3871.6⁢9+0.00+0.05
−0.04−0.13  MeV, FWHM=0.2⁢2+0.07+0.11−0.06−0.13  MeV. An investigation of the analytic structure of the Flatté amplitude reveals a pole structure, which is compatible with a quasibound 𝐷0⁢¯𝐷*0 state but a quasivirtual state is still allowed at the level of 2 standard deviations.