Measurement of χ _c1(3872) production in proton-proton collisions at √s = 8 and 13 TeV

The production cross-section of the χ _c1(3872) state relative to the ψ(2S) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of s = 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb ⁻¹, respectively. The two mesons are reconstructed in the J/ψπ ⁺π ⁻ final state. The ratios of the prompt and nonprompt χ _c1(3872) to ψ(2S) production cross-sections are measured as a function of transverse momentum, p _T, and rapidity, y, of the χ _c1(3872) and ψ(2S) states, in the kinematic range 4 < p _T< 20 GeV/c and 2.0 < y < 4.5. The prompt ratio is found to increase with p _T, independently of y. For the prompt component, the double ratio of the χ _c1(3872) and ψ(2S) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of p _T and centre-of-mass energy. [Figure not available: see fulltext.].