Measurements of $\psi (2S)$ and $X(3872)\to J/\psi {\pi }^{+}{\pi }^{-}$ 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 $\psi (2S)$, in the decay mode $J/\psi {\pi }^{+}{\pi }^{-}$, 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 $X(3872)/\psi (2S)$ is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of $X(3872)$ and $\psi (2S)$. Assuming independent single effective lifetimes for non-prompt $X(3872)$ and $\psi (2S)$ production gives $R_B=\frac{\mathcal{B}(B\to X(3872)\text{ + any})\mathcal{B}(X(3872\to J/\psi {\pi }^{+}{\pi }^{-})}{\mathcal{B}(B\to \psi (2S)\text{ + any})\mathcal{B}(\psi (2S)\to J/\psi {\pi }^{+}{\pi }^{-})}=(3.95\pm 0.32(\mathrm{stat})\pm 0.08(\mathrm{sys}))\times 10^{-2}$, while separating short- and long-lived contributions, assuming that the short-lived component is due to $B_c$ decays, gives $R_B=(3.57\pm 0.33(\mathrm{stat})\pm 0.11(\mathrm{sys}))\times 10^{-2}$, with the fraction of non-prompt $X(3872)$ produced via $B_c$ decays for $p_{\mathrm{T}}(X(3872))>10$ GeV being $(25\pm 13(\mathrm{stat})\pm 2(\mathrm{sys})\pm 5(\mathrm{spin}))\%$. The distributions of the dipion invariant mass in the $X(3872)$ and $\psi (2S)$ decays are also measured and compared to theoretical predictions.

42 pages in total, author list starting page 26, 10 figures, 8 tables. Submitted to JHEP. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2015-03/

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