Determination of $$\alpha _{S}$$ beyond NNLO using event shape averages

Abstract

We consider a method for determining the QCD strong coupling constant using fits of perturbative predictions for event shape averages to data collected at the LEP, PETRA, PEP and TRISTAN colliders. To obtain highest accuracy predictions we use a combination of perturbative $${{{\mathcal {O}}}}(\alpha _{S}^{3})$$ O ( α S 3 ) calculations and estimations of the $${{{\mathcal {O}}}}(\alpha _{S}^{4})$$ O ( α S 4 ) perturbative coefficients from data. We account for non-perturbative effects using modern Monte Carlo event generators and analytic hadronization models. The obtained results show that the total precision of the $$\alpha _{S}$$ α S determination cannot be improved significantly with the higher-order perturbative QCD corrections alone, but primarily requires a deeper understanding of the non-perturbative effects.

Determination of $α_{S}$ beyond $NNLO$ using the event shape averages

“…In the fit procedure it is also essential to take into account the hadronization effects and we consider two types of models to handle this problem. Namely, we consider the Monte Carlo event generator (MCEG) models generating predictions at NLO accuracy in pQCD and in addition to that we consider analytic hadronization models [4] extended to O(α 4 S ) for the first time. The hadron level predictions by the MCEGs for the averages of event shape observables [4] reasonably well describe the data for a wide range of center-of-mass energies.…”

QCD at the FCC-ee

“…The sensitivity of final-state observables on α s makes them suitable for precise extractions of the strong coupling. Currently, different α s determinations from these observables [39][40][41][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] can differ from each other by a few standard deviations. Besides the high-precision perturbative ingredients described above, such fits require input on hadronisation effects.…”

Eikonal Dressed Gluon Exponentiation to study power corrections to Thrust, C-parameter, and Angularity

“…Due to the infrared safety of the event shape variables, they can be calculated in the perturbation theory. The state of the art is NNLO calculations at fixed orders [7][8][9][10][11], while NLL [12][13][14][15], and NNLL resummation [16][17][18][19][20][21][22][23][24][25][26][27] frameworks have been developed over several years. If one denotes the event shape variable by e, then its corresponding distribution dσ/d e peaks in the two jet limit (e → 0).…”