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 $2.50$. The production cross section of inclusive $J/\psi $ pairs is reported to be $10.3±2.3\phantom{\rule{0.16em}{0ex}}\left(\mathrm{stat}.\right)±1.3\phantom{\rule{0.16em}{0ex}}\left(\mathrm{syst}.\right)$ 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.