Parton Distribution Functions, $α_s$ and Heavy-Quark Masses for LHC Run II

Abstract: We determine a new set of parton distribution functions (ABMP16), the strong coupling constant $\alpha_s$ and the quark masses $m_c$, $m_b$ and $m_t$ in a global fit to next-to-next-to-leading order (NNLO) in QCD. The analysis uses the $\overline{\mathrm{MS}}$ scheme for $\alpha_s$ and all quark masses and is performed in the fixed-flavor number scheme for $n_f=3, 4, 5$. Essential new elements of the fit are the combined data from HERA for inclusive deep-inelastic scattering (DIS), data from the fixed-target experiments NOMAD and CHORUS for neutrino-induced DIS, and data from Tevatron and the LHC for the Drell-Yan process and the hadro-production of single-top and top-quark pairs. The theory predictions include new improved approximations at NNLO for the production of heavy quarks in DIS and for the hadro-production of single-top quarks. The description of higher twist effects relevant beyond the leading twist collinear factorization approximation is refined. At NNLO we obtain the value $\alpha_s^{(n_f=5)}(M_Z) = 0.1147 \pm 0.0008$.

• The paper refines the ABMP16 Parton Distribution Functions by integrating NNLO QCD fits with the latest HERA Run I+II data and precise heavy-quark mass determinations.
• It implements advanced NNLO heavy-quark coefficient schemes that significantly reduce extrapolation errors in gluon and sea-quark distributions at small x.
• The study establishes key correlations among αₛ, top-quark mass, and gluon distributions to improve predictions for Higgs production and top-quark pair processes.

An Evaluation of ABMP16 Parton Distribution Functions for LHC Run II

The development of accurate Parton Distribution Functions (PDFs) is fundamental for making precise predictions of cross sections at hadron colliders, helping unravel the intricate inner structure of the proton essential for testing the boundaries of the Standard Model and investigating phenomena beyond it. The paper discusses the ABMP16 PDFs, which are derived from a comprehensive global fit to data, integrating latest findings from HERA run I+II, CHORUS, NOMAD, and various others, with the inclusion of updated theoretical frameworks for heavy flavor production.

This work showcases a meticulous approach to updating previous fits such as ABM12 and ABMP15. Notably, it highlights quintessential enhancements by accommodating new HERA data, which provide improved constraints on small-x gluon and quark sea distributions, pivotal for precision physics at the LHC. Moreover, by integrating refined theoretical predictions for heavy-quark production at NNLO — utilizing fixed flavor-number schemes — the authors present a marked advancement in reducing the inherent model uncertainties associated with heavy flavor mass determinations.

The ABMP16 analysis, conducted at NNLO QCD, identifies the strong coupling constant $\alpha_s$ and heavy-quark masses in the $\overline{\text{MS}}$ scheme as critical parameters, incorporating their simultaneous determination to retain correlations with PDFs. The findings suggest $\alpha_s(M_Z)=0.1147 \pm 0.0008$, a mildly increased central value compared to prior iterations, reflecting significant inclusion of new datasets and modeling of higher twist contributions which are indispensable for consistency across overlapping kinematic regimes, particularly at small $Q^2$.

By creating tailored heavy-quark coefficients for NNLO approximations and deploying advanced methodologies to address higher twist contributions, the study achieves notable precision with minimized extrapolation error — a prevalent issue in large-scale QCD analyses. In addition, the analysis identifies key correlations between the strong coupling, top-quark mass, and gluon distributions, which are essential for examining key physics processes, including Higgs production via gluon fusion and top-quark pair production at high-energy colliders.

In terms of practical and theoretical implications, the refined ABMP16 PDFs bridge existing gaps in precision and reliability by accommodating a broader data spectrum and offering a robust framework that aligns well with recent lattice QCD computations for moments of PDFs. Furthermore, the authors discuss extrapolated implications for the stability of the electroweak vacuum — pointing towards a self-consistent framework within the Standard Model up to the Planck scale.

Moving forward, the ABMP16 PDFs present a promising prospect for further refinements, particularly in light of potential new data from Run III of the LHC and pertinent theoretical advancements. Integration of emerging results from high-energy experiments alongside continual improvements in theoretical modeling offers a continuous opportunity to refine these PDFs, enhancing their accuracy and applicability for exploring higher order QCD corrections, electroweak processes, and physics beyond the Standard Model.

In conclusion, ABMP16 presents an NNdLO analysis with comprehensive improvements in theoretical predictions, data accommodation, and parameter sensitivity analysis, positioning it as a cornerstone for interpreting ongoing and future high-energy physics experiments. Through precise methodology and comprehensive data utilization, this set provides a refined baseline, keen for further exploration and cross-examination with global analysis efforts, continually shaping our understanding of QCD and particle physics at large.