Lund and Cambridge multiplicities for precision physics
Rok Medves, Alba Soto-Ontoso, Grégory Soyez
Abstract
A bstract 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 ( $$ \mathcal{O} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>O</mml:mi> </mml:math> ( $$ {\alpha}_s^2 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>α</mml:mi> <mml:mi>s</mml:mi> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> )) 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.