Evidence for X(3872) in PbPb collisions and studies of its prompt production at $\sqrt{{s_{_{\mathrm{NN}}}}}=5.02$ TeV

The first evidence for X(3872) in heavy ion collisions is reported. Prompt X(3872) production is studied with the CMS detector in PbPb collisions at a center-of-mass energy of $\sqrt{{s_{_{\mathrm{NN}}}}} = 5.02$ TeV per nucleon pair, using the decay chain X(3872)$\rightarrow {\rm J}/\psi\pi^+\pi^-\rightarrow \mu^+\mu^-\pi^+\pi^-$. The measurement is performed in a kinematic range in which the X(3872) candidates have a transverse momentum $15 < p_{\mathrm{T}} < 50 $ GeV and rapidity $\lvert y\rvert <1.6$. The statistical significance of the X(3872) signal is in excess of 3 standard deviations. The production and survival of the prompt X(3872) in the quark-gluon plasma is expected to depend upon its internal structure. The ratio of the X(3872) and $\psi$(2S) yields is found to be $R = 1.10 \pm 0.51\;\mathrm{(stat.)}\: \pm 0.53\;\mathrm{(syst.)}$ and is compared to the ratio measured in pp collisions at $\sqrt{s} = 7$ and 8 TeV.