Lund and Cambridge multiplicities for precision physics

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-nextto-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 (O α 2 s ) 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.

Jet substructure at the Large Hadron Collider: A review of recent advances in theory and machine learning

“…Many more details and calculations are presented in the literature, e.g., Refs. [447,312,448,449], but here we will just discuss one effect, the running, or scale-dependence, of the coupling α s . QCD exhibits asymptotic freedom in which its coupling α s decreases in value as the relevant energy scale increases.…”

“…where at right we have replaced the explicit scale dependence with the value of the running coupling, α s (µ). More details about this calculation and how higher-order effects can be included can be found in the original literature [464,465,466,467,468,469,448].…”

PanScales showers for hadron collisions: all-order validation

“…Recently, the subjet multiplicity in colour singlet production has been computed up to NDL accuracy [69] (earlier calculations gave similar structures [70][71][72]). In a shower context, up to NDL, it applies equally well to the number of particles in the event (N shower ) when one sets the strong coupling to zero below a given value of k t,cut .…”