Study of the lineshape of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>χ</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>3872</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> state

A study of the lineshape of the c1 3872 state is made using a data sample corresponding to an integrated luminosity of 3 fb -1 collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate c1 3872 and 2S mesons from b-hadron decays are selected in the J= -decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the c1 3872 and 2S states, m, and the width of the c1 3872 state, BW , are determined to be m185.598AE0.067AE0.068 MeV; BW 1.39AE0.24AE0.10 MeV; where the first uncertainty is statistical and the second systematic. Using a Flattinspired model, the mode and full width at half maximum of the lineshape are determined to be mode3871.69 0.000.05 -0.04-0.13 MeV; FWHM0.22 0.070.11 -0.06-0.13 MeV: An investigation of the analytic structure of the Flatt amplitude reveals a pole structure, which is compatible with a quasibound D 0 D0 state but a quasivirtual state is still allowed at the level of 2 standard deviations.