Impact of the heavy-quark matching scales in PDF fits

V. Bertone; D. Britzger; S. Camarda; A. Cooper-Sarkar; A. Geiser; F. Giuli; A. Glazov; E. Godat; A. Kusina; A. Luszczak; F. Lyonnet; F. Olness; R. Plačakytė; V. Radescu; I. Schienbein; O. Zenaiev; The xFitter Developers’ Team

doi:10.1140/epjc/s10052-017-5407-3

Impact of the heavy-quark matching scales in PDF fits

V. Bertone, D. Britzger, S. Camarda, A. Cooper-Sarkar, A. Geiser, F. Giuli, A. Glazov, E. Godat, A. Kusina, A. Luszczak, F. Lyonnet, F. Olness^*, R. Plačakytė, V. Radescu, I. Schienbein, O. Zenaiev, The xFitter Developers’ Team

^*Corresponding author for this work

(Astro)-Particles Physics

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μ_m determines at which energy scale μ the QCD theory transitions from N_F to N_F+ 1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling α_S(μ). 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 μ_m 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 N_F= 3 to 4), we find a large μ_m= μ_c dependence of the global fit χ² at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from N_F= 4 to 5), we have a reduced μ_m= μ_b dependence of the χ² 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.

Original language	English
Article number	837
Journal	European Physical Journal C
Volume	77
Issue number	12
DOIs	https://doi.org/10.1140/epjc/s10052-017-5407-3
Publication status	Published - 1 Dec 2017

Funding

Acknowledgements The authors would like to thank M. Botje, J. C. Collins, and J. Rojo for valuable discussions. V. B and A. G. are particularly grateful to A. Mitov, A. Papanastasiou, and M. Ubiali for many stimulating discussions on the role of the bottom-quark threshold for bottom-initiated processes at the LHC. We acknowledge the hospitality of CERN, DESY, and Fermilab where a portion of this work was performed. We are grateful to the DESY IT department for their support of the xFitter developers. This work was also partially supported by the U.S. Department of Energy under Grant no. DE-SC0010129. V. B. is supported by an European Research Council Starting Grant “PDF4BSM”. A. L. is supported by the Polish Ministry under program Mobility Plus, Grant no. 1320/MOB/IV/2015/0.

Funders	Funder number
Polish Ministry	1320/MOB/IV/2015/0
U.S. Department of Energy	DE-SC0010129
Seventh Framework Programme	335260
Science and Technology Facilities Council	ST/N000447/1
European Research Council	PDF4BSM

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Bertone, V., Britzger, D., Camarda, S., Cooper-Sarkar, A., Geiser, A., Giuli, F., Glazov, A., Godat, E., Kusina, A., Luszczak, A., Lyonnet, F., Olness, F., Plačakytė, R., Radescu, V., Schienbein, I., Zenaiev, O., & The xFitter Developers’ Team (2017). Impact of the heavy-quark matching scales in PDF fits. European Physical Journal C, 77(12), Article 837. https://doi.org/10.1140/epjc/s10052-017-5407-3

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title = "Impact of the heavy-quark matching scales in PDF fits",

abstract = "We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μm determines at which energy scale μ the QCD theory transitions from NF to NF+ 1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling αS(μ). 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 μm 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 NF= 3 to 4), we find a large μm= μc dependence of the global fit χ2 at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from NF= 4 to 5), we have a reduced μm= μb dependence of the χ2 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.",

author = "V. Bertone and D. Britzger and S. Camarda and A. Cooper-Sarkar and A. Geiser and F. Giuli and A. Glazov and E. Godat and A. Kusina and A. Luszczak and F. Lyonnet and F. Olness and R. Pla{\v c}akytė and V. Radescu and I. Schienbein and O. Zenaiev and {The xFitter Developers{\textquoteright} Team}",

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Bertone, V, Britzger, D, Camarda, S, Cooper-Sarkar, A, Geiser, A, Giuli, F, Glazov, A, Godat, E, Kusina, A, Luszczak, A, Lyonnet, F, Olness, F, Plačakytė, R, Radescu, V, Schienbein, I, Zenaiev, O & The xFitter Developers’ Team 2017, 'Impact of the heavy-quark matching scales in PDF fits', European Physical Journal C, vol. 77, no. 12, 837. https://doi.org/10.1140/epjc/s10052-017-5407-3

TY - JOUR

T1 - Impact of the heavy-quark matching scales in PDF fits

AU - Bertone, V.

AU - Britzger, D.

AU - Camarda, S.

AU - Cooper-Sarkar, A.

AU - Geiser, A.

AU - Giuli, F.

AU - Glazov, A.

AU - Godat, E.

AU - Kusina, A.

AU - Luszczak, A.

AU - Lyonnet, F.

AU - Olness, F.

AU - Plačakytė, R.

AU - Radescu, V.

AU - Schienbein, I.

AU - Zenaiev, O.

AU - The xFitter Developers’ Team

PY - 2017/12/1

Y1 - 2017/12/1

N2 - We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μm determines at which energy scale μ the QCD theory transitions from NF to NF+ 1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling αS(μ). 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 μm 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 NF= 3 to 4), we find a large μm= μc dependence of the global fit χ2 at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from NF= 4 to 5), we have a reduced μm= μb dependence of the χ2 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.

AB - We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μm determines at which energy scale μ the QCD theory transitions from NF to NF+ 1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling αS(μ). 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 μm 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 NF= 3 to 4), we find a large μm= μc dependence of the global fit χ2 at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from NF= 4 to 5), we have a reduced μm= μb dependence of the χ2 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.

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DO - 10.1140/epjc/s10052-017-5407-3

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SN - 1434-6044

VL - 77

JO - European Physical Journal C

JF - European Physical Journal C

IS - 12

M1 - 837

ER -

Impact of the heavy-quark matching scales in PDF fits

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