University of Cambridge > Talks.cam > HEP phenomenology joint Cavendish-DAMTP seminar > Understanding Uncertainties: an extensive survey of theoretical uncertainty estimates for perturbative observables

Understanding Uncertainties: an extensive survey of theoretical uncertainty estimates for perturbative observables

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We consider two approaches to estimate and characterize the theoretical uncertainties stemming from the missing higer orders in perturbative calculations in Quantum Chromodynamics: the traditional one based on renormalisation and factorisation scales variations, and the Bayesian framework proposed recently by Cacciari and Houdeau. We estimate uncertainties with these two method for about thirty different observables in perturbative QCD and, when higher orders are known, we discuss their performance in estimating correctly the size of the missing terms. We find that scale vari- ations with the conventional choice of varying scales within a factor of two of a central scale gives uncertainty intervals that tend to be somewhat too small to be interpretable as “68%-confidence-level-heuristic” ones. A slightly modified version of the Bayesian approach of Cacciari and Houdeau tends to perform well for non-hadronic observables and, after an empirical tuning of the relevant expansion parameter for the perturbative series, for hadronic ones too.

This talk is part of the HEP phenomenology joint Cavendish-DAMTP seminar series.

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