The ABM parton distributions tuned to LHC data

Abstract: We present a global fit of parton distributions at next-to-next-to-leading order (NNLO) in QCD. The fit is based on the world data for deep-inelastic scattering, fixed-target data for the Drell-Yan process and includes, for the first time, data from the Large Hadron Collider (LHC) for the Drell-Yan process and the hadro-production of top-quark pairs. The analysis applies the fixed-flavor number scheme for n_f=3,4,5, uses the MS-bar scheme for the strong coupling \alpha_s and the heavy-quark masses and keeps full account of the correlations among all non-perturbative parameters. At NNLO this returns the values of \alpha_s(M_Z) = 0.1132 +- 0.0011 and m_t(pole) = 171.2 +- 2.4 GeV for the top-quark pole mass.The fit results are used to compute benchmark cross sections for Higgs production at the LHC to NNLO accuracy. We compare our results to those obtained by other groups and show that differences can be linked to different theoretical descriptions of the underlying physical processes.

• The paper updates the ABM PDF model by tuning it with high-precision LHC data, which improves predictions within NNLO QCD.
• It employs a novel computational method that efficiently integrates charm DIS and Drell–Yan data, reducing calculation time while ensuring precision.
• The findings refine key parton distributions, notably the gluon, sea-quark, and d-quark contributions, offering actionable insights for collider experiments.

Detailed Analysis of the ABM PDF Optimization with LHC Data Integration

The paper "The ABM parton distributions tuned to LHC data" provides an exhaustive account of the ABM parton distribution functions (PDFs) and their adjustment to incorporate new data from the Large Hadron Collider (LHC). This research is situated at the core of Quantum Chromodynamics (QCD) investigations, aiming to refine our understanding of the proton's internal structure with emphasis on the deep-inelastic scattering (DIS) framework and the Drell-Yan process in both fixed-target and collider settings.

This analysis introduces several improvements over the previous iterations of the ABM PDFs, notably ABM11, incorporating precision data from LHC runs at 7 and 8 TeV. The research meticulously considers the theoretical underpinnings and perturbative corrections at the next-to-next-to-leading order (NNLO) QCD, finding $\alpha_s(M_Z) = 0.1132 \pm 0.0011$ for the strong coupling constant and a top-quark pole mass of $m_t({\rm pole}) = 171.2 \pm 2.4$ GeV, acknowledging the significant interplay between these variables and the PDFs.

Data Integration and Theoretical Precision

The paper details the integration of charm DIS production data and high-$Q^2$ neutral-current interactions, underscoring the constraints these impose on the low-$x$ gluon and sea-quark distributions. The complementary Drell-Yan data from LHC improves PDF determinations, particularly the $d$-quark distribution, crucial for advancing theoretical models not influenced by deuteron target corrections.

Moreover, the analysis employs benchmarks for cross-section predictions, focusing notably on Higgs production through gluon-gluon fusion at the LHC. Disparities between existing results and those from other groups arise primarily due to different theoretical treatments and assumptions in their model predictions.

Computational Methodology and Impact

A novel computational methodology is introduced for efficiently integrating NNLO corrections, using pre-calculated cross-section grids expedited by the ABM uncertainty parameters. This method drastically reduces computational time while maintaining precision, permitting iterative processes until convergence is achieved.

Significant findings underscore the stability of the ABM12 PDFs compared to ABM11. The PDFs are tightly aligned with international datasets yet reveal critical distinctions from outputs such as those from MSTW and CT10, inviting further examination on the impact of experimental uncertainties.

Future Implications and Reflections

The study suggests future trajectories, especially regarding improvements in electroweak and NNLO QCD corrections as new collider data becomes available. The insights here call for enhanced precision data at varying energies, potentially redefining proton models and theorizing polarization effects in parton interactions.

In conclusion, this research contributes significantly to the precision nucleon structure analysis by cross-validating collider data against established theoretical models, offering nuanced comprehension of non-perturbative effects within QCD. This analysis will serve as a reference for ongoing studies, speculating that future collider runs could further tighten these PDF constraints, sharpening our understanding of QCD dynamics.