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SUMMARY:Understanding Uncertainties: an extensive survey of theoretical un
 certainty estimates for perturbative observables - Alberto Guffanti (Bohr 
 Institute\, Copenaghen)
DTSTART:20140613T150000Z
DTEND:20140613T160000Z
UID:TALK52017@talks.cam.ac.uk
CONTACT:Marco Nardecchia
DESCRIPTION:We consider two approaches to estimate and characterize the th
 eoretical uncertainties stemming from the missing higer orders in perturba
 tive calculations in Quantum Chromodynamics: the traditional one based on 
 renormalisation and factorisation scales variations\, and the Bayesian fra
 mework proposed recently by Cacciari and Houdeau. We estimate uncertaintie
 s with these two method for about thirty different observables in perturba
 tive 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 fact
 or of two of a central scale gives uncertainty intervals that tend to be s
 omewhat too small to be interpretable as "68%-confidence-level-heuristic" 
 ones.\nA slightly modified version of the Bayesian approach of Cacciari an
 d Houdeau tends to perform well for non-hadronic observables and\, after a
 n empirical tuning of the relevant expansion parameter for the perturbativ
 e series\, for hadronic ones too.
LOCATION:Seminar Room B\, Rutherford Building\, Cavendish Laboratory
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