Lund multiplicity in QCD jets

We compute the average Lund multiplicity of high-energy QCD jets. This extends an earlier calculation, done for event-wide in $e^+e^-$ collisions [arxiv:2205.02861], to large energy range available at LHC. Our calculation achieves next-to-next-to-double logarithmic (NNDL) accuracy. results are split into a universal collinear piece, common and non-universal large-angle contribution. The latter amounts 10-15% total multiplicity. provide accurate LHC predictions by matching our resummed fixed-order NLO incorporating non-perturbative corrections via Monte Carlo simulations. Including NNDL terms leads 50% reduction theoretical uncertainty, with remaining below 5% down transverse momentum scales few GeV. proves suitability multiplicities robust theory-to-data comparisons