Measurements of ψ(2S) and X(3872) → J/ψπ ⁺ π ⁻ production in pp collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

Abstract

Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and ψ(2S), in the decay mode J/ψπ ⁺ π ⁻, measured using 11.4 fb⁻¹ of pp collisions at $\sqrt{s}=8$ TeV by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/ψ(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and ψ(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and ψ(2S) production gives ${R}_B=\frac{\mathrm{\mathcal{B}}\left(B\to X(3872)+\mathrm{any}\right)\mathrm{\mathcal{B}}\left(X(3872)\to J/\psi {\pi}^{+}{\pi}^{-}\right)}{\mathrm{\mathcal{B}}\left(B\to \psi (2S)+\mathrm{any}\right)\mathrm{\mathcal{B}}\left(\psi (2S)\to J/\psi {\pi}^{+}{\pi}^{-}\right)}=\left(3.95\pm 0.32\left(\mathrm{s}\mathrm{tat}\right)\pm 0.08\left(\mathrm{s}\mathrm{y}\mathrm{s}\right)\right)\times {10}^{-2}$ separating short- and long-lived contributions, assuming that the short-lived component is due to B _c decays, gives R _B = (3.57 ± 0.33(stat) ± 0.11(sys)) × 10⁻², with the fraction of non-prompt X(3872) produced via B _c decays for p _T(X(3872)) > 10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and ψ(2S) decays are also measured and compared to theoretical predictions.