CMS-PAS-HIN-19-005

CMS-PAS-HIN-19-005
Evidence for $\chi_{c1}\text{(3872)}$ in PbPb collisions and studies of its prompt production at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV
CMS Collaboration
November 2019

Abstract: The first evidence for $\chi_{c1}\text{(3872)}$ in relativistic heavy ion collisions is reported. Prompt $\chi_{c1}\text{(3872)}$ production is studied in PbPb collisions at a center-of-mass energy of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV per nucleon pair, using the decay chain $\chi_{c1}\text{(3872)} \rightarrow {\rm J}/\psi\pi^+\pi^-\rightarrow \mu^+\mu^-\pi^+\pi^-$ . The data were recorded by the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 $\pm$ 0.1 nb $^{-1}$ . The measurement is performed in a kinematic range in which the $\chi_{c1}\text{(3872)}$ candidates have a transverse momentum 15 $< p_{\mathrm{T}} <$ 50 GeV/ $c$ and rapidity $\|y\| <$ 1.6. The statistical significance of the $\chi_{c1}\text{(3872)}$ signal is in excess of 3 standard deviations. The production and survival of the prompt $\chi_{c1}\text{(3872)}$ in the quark-gluon plasma is expected to depend upon its internal structure. The ratio of the $\chi_{c1}\text{(3872)}$ and $\psi\text{(2S)}$ yields is found to be $R =$ 1.10 $\pm$ 0.51(stat) $\pm$ 0.53 (syst). This results is compared to the similar ratio measured in pp collisions at $\sqrt{s} =$ 7 and 8 TeV. An indication of larger $R$ in PbPb collisions with respect to the pp reference is reported.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here.

CMS Publications