Lund and Cambridge multiplicities for precision physics

TL;DR

This paper introduces a new resummation approach for jet multiplicity calculations in high-energy physics, achieving higher accuracy and better agreement with experimental data, and extends the method to hadronic collisions.

Contribution

We develop a systematic resummation method for jet multiplicities at NNDL accuracy, introducing a new definition based on Lund declusterings and extending to hadronic collisions.

Findings

Achieved NNDL accuracy for Lund and Cambridge multiplicities in electron-positron collisions.

Predictions show up to 50% reduction in theoretical uncertainties compared to previous results.

Good agreement with existing data when including hadronisation corrections.

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 ($\mathcal{O}(\alpha_s^2)$) 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.