Measurement of inclusive $J/\psi$ pair production cross section in $pp$ collisions at $\sqrt{s}=13$ TeV

The production cross section of inclusive $J/\psi$ pairs in $pp$ collisions at a center-of-mass energy $\sqrt{s}=13$ TeV is measured with ALICE. The measurement is performed for $J/\psi$ in the rapidity interval $2.5<y<4.0$ and for transverse momentum $p_T>0$. The production cross section of inclusive $J/\psi$ pairs is reported to be $10.3\pm 2.3(\mathrm{stat}.)\pm 1.3(\mathrm{syst}.)$ nb in this kinematic interval. The contribution from nonprompt $J/\psi$ (i.e., originated from beauty-hadron decays) to the inclusive sample is evaluated. The effective double-parton scattering cross section is computed, neglecting the single-parton scattering contribution.

Figure 1

Projections of a fit to the two-dimensional invariant mass distribution for inclusive $J/\psi$ pair candidates for (a) $m_1\left({\mu }_1^{+}{\mu }_1^{-}\right)$ and (b) $m_2\left({\mu }_2^{+}{\mu }_2^{-}\right)$. The (black) markers show data. The (black) solid line represents the total fit function. The (blue and green) dashed-dotted lines indicate the background contribution from a combination of a real $J/\psi$ signal with a combinatorial candidate. The (yellow) dotted line represents muon pairs from combinatorial background.