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Observation of J/$\psi$ pair production in pp collisions at $\sqrt{s}$=7 TeV

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Abstract

The production of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ pairs in proton-proton collisions at a centre-of-mass energy of $7 \mathrm{TeV}$ has been observed using an integrated luminosity of $37.5 \mathrm{pb}^{-1}$ collected with the LHCb detector. The production cross-section for pairs with both $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in the rapidity range $2<y^{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} }<4.5$ and transverse momentum $p_{\mathrm{T}}^{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} }<10 \mathrm{GeV}/c$ is \begin{equation*} \sigma^{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}{ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} } = 5.1\pm1.0\pm1.1 \mathrm{nb}, \end{equation*} where the first uncertainty is statistical and the second systematic.

Figures and captions

The fitted yields of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \rightarrow \left(\mu ^+\mu ^- \right)_1$ in bins of $(\mu ^+\mu ^- )_2$ invariant mass: (a) the raw signal yield observed in the data; (b) the efficiency corrected yield (Sect. 6). The result of a fit with a double-sided Crystal Ball function for the signal and an exponential background is superimposed.

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Differential production cross-section for $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ pairs as a function of the invariant mass of the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}{ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ system. The points correspond to the data. Only statistical uncertainties are included in the error bars. The shaded area corresponds to prediction by the model described in Ref. [20].

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Tables and captions

Relative systematic uncertainties on the cross-section measurement. The total uncertainty is calculated as the quadratic sum of the individual components.

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Created on 21 October 2019.