Lund and Cambridge multiplicities for precision physics

Abstract

Abstract We revisit the calculation of the average jet multiplicity in high-energy collisions. First, we introduce a new definition of (sub)jet multiplicity based on Lund declusterings obtained using the Cambridge jet algorithm. We develop a new systematic resummation approach. This allows us to compute both the Lund and the Cambridge average multiplicities to next-to-next-to-double (NNDL) logarithmic accuracy in electron-positron annihilation, an order higher in accuracy than previous works in the literature. We match our resummed calculation to the exact NLO ($$ \mathcal{O} $$ O ($$ {\alpha}_s^2 $$ α s 2 )) result, showing predictions for the Lund multiplicity at LEP energies with theoretical uncertainties up to 50% smaller than the previous state-of-the-art. Adding hadronisation corrections obtained by Monte Carlo simulations, we also show a good agreement with existing Cambridge multiplicity data. Finally, to highlight the flexibility of our method, we extend the Lund multiplicity calculation to hadronic collisions where we reach next-to-double logarithmic accuracy for colour singlet production.