The Effect of Variable Flavour Number Scheme Variations on PDFs and Cross Sections

Abstract

I consider variations in the definition of a General-Mass Variable Flavour Number Scheme (GM-VFNS) for heavy flavour structure functions, both at next-to-leading order (NLO) and at next-to-next-to leading order (NNLO). I also define a new "optimal" scheme choice improving the smoothness of the transition from one flavour number to the next. At both NLO and NNLO I investigate the variation of the structure function for a fixed set of parton distribution functions (PDFs) and also the change in the distributions when a new MSTW-type global fit to data is performed for each GM-VFNS. At NLO the parton distributions, and predictions using them at hadron colliders, can vary by ~2% from the mean value. Use of the the Zero-Mass Variable Flavour Number Scheme, which is simpler but only an approximation, leads to results a further couple of percent or more outside this range. At NNLO there is far more stability with varying GM-VFNS definition. Typical changes in PDFs and predictions are less than 1%, with most variation at very small x values. This demonstrates that mass-scheme variation is an additional and significant source of uncertainty when considering parton distributions, but like other theoretical uncertainties, it diminishes quickly as higher orders are included.

5 pages, 2 figures; to appear in the proceedings of DIS2010

References in corpus (10)

• Parton distributions for the LHC
• Leptoproduction of Heavy Quarks II -- A Unified QCD Formulation of Charged and Neutral Current Processes from Fixed-target to Collider Energies
• Heavy quarks in deep-inelastic scattering
• Charm electroproduction viewed in the variable-flavour number scheme versus fixed-order perturbation theory
• An Ordered Analysis of Heavy Flavour Production in Deep Inelastic Scattering
• A Variable-Flavour Number Scheme for NNLO
• Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues
• Comparison between variable flavor number schemes for charm quark electroproduction
• Soft Gluon Resummation for Heavy Quark Electroproduction
• Improved formulation of global QCD analysis with zero-mass hard cross sections

Cited by in corpus (4)

• Parton Distributions for LHC
• Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions
• Effect of changes of variable flavor number scheme on parton distribution functions and predicted cross sections
• Generalisation of DGLAP equations to massive partons