https://doi.org/10.1140/epjc/s10052-017-5407-3
Regular Article - Theoretical Physics
Impact of the heavy-quark matching scales in PDF fits
1
Department of Physics and Astronomy, VU University, 1081 HV, Amsterdam, The Netherlands
2
Nikhef Theory Group Science Park 105, 1098 XG, Amsterdam, The Netherlands
3
DESY Hamburg, Notkestraße 85, 22609, Hamburg, Germany
4
CERN, 1211, Geneva 23, Switzerland
5
University of Oxford, 1 Keble Road, Oxford, OX1 3NP, UK
6
SMU Physics, Box 0175, Dallas, TX, 75275-0175, USA
7
Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, 38026, Grenoble, France
8
Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342, Kraków, Poland
9
T.Kosciuszko Cracow University of Technology, 30-084, Kraków, Poland
10
Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany
* e-mail: olness@smu.edu
Received:
28
July
2017
Accepted:
22
November
2017
Published online:
7
December
2017
We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale 
determines at which energy scale 
the QCD theory transitions from 
to 
in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling 
. We study the variation of the matching scales, and their impact on a global PDF fit of the combined HERA data. As the choice of the matching scale effectively is a choice of scheme, this represents a theoretical uncertainty; ideally, we would like to see minimal dependence on this parameter. For the transition across the charm quark (from 
to 4), we find a large 
dependence of the global fit 
at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from 
to 5), we have a reduced 
dependence of the at both NLO and NNLO as compared to the charm. This feature is now implemented in xFitter 2.0.0, an open source QCD fit framework.
© The Author(s), 2017
