FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order

Abstract: We introduce an improved version of the simulation code FEWZ (Fully Exclusive W and Z Production) for hadron collider production of lepton pairs through the Drell-Yan process at next-to-next-to-leading-order (NNLO) in the strong coupling constant. The program is fully differential in the phase space of leptons and additional hadronic radiation. The new version offers users significantly more options for customization. FEWZ now bins multiple, user-selectable histograms during a single run, and produces parton distribution function (PDF) errors automatically. It also features a signifcantly improved integration routine, and can take advantage of multiple processor cores locally or on the Condor distributed computing system. We illustrate the new features of FEWZ by presenting numerous phenomenological results for LHC physics. We compare NNLO QCD with initial ATLAS and CMS results, and discuss in detail the effects of detector acceptance on the measurement of angular quantities associated with Z-boson production. We address the issue of technical precision in the presence of severe phase-space cuts.

• The paper introduces FEWZ 2.0, a major upgrade that applies NNLO QCD calculations to enhance the precision of hadronic Z production simulations.
• It improves computational efficiency through parallelized integration over 230 sectors and supports extensive user customization for kinematic analyses.
• The code achieves sub-percent accuracy under severe cuts while automating PDF uncertainty evaluations, enabling precise LHC experimental comparisons.

Overview of FEWZ 2.0 for Hadronic Z Production

The discussed paper introduces significant advancements in the simulation code FEWZ 2.0, aimed at improving the study of hadronic Z production at the Large Hadron Collider (LHC) utilizing next-to-next-to-leading-order (NNLO) calculations in quantum chromodynamics (QCD). This version addresses many of the limitations observed in its predecessor and provides a comprehensive platform for both theoretical and experimental analyses of electroweak gauge boson production processes. In this essay, we will dissect the key improvements and implications of FEWZ 2.0, which are of particular relevance to researchers working on precision high-energy physics studies.

Key Features and Improvements

FEWZ 2.0 introduces several enhancements that significantly advance its applicability and accuracy:

1. Parallelization and Numerical Integration: The new code structure allows for the division of computational tasks into 230 separate sectors which can be executed in parallel. This capability dramatically enhances the efficiency of obtaining results, leveraging multi-core and distributed computing resources.
2. Enhanced User Customization: The code now supports a wider range of lepton and hadRONic observables, with users able to define multiple kinematic variables in a single runtime. This flexibility is crucial for tailoring studies to specific experimental conditions and hypotheses testing.
3. Automatic PDF Error Calculation: FEWZ 2.0 automates the calculation of parton distribution function (PDF) uncertainties across all current PDF sets, greatly streamlining the analysis workflow and improving accuracy in cross-section measurements.
4. Histogramming and Data Handling: The inclusion of automatic histogramming features enables researchers to generate various kinematic distributions without additional computational overhead, further supporting detailed phenomenological studies.
5. Integration Routine and Precision: The updated integration algorithms allow for sub-percent accuracy in phase-space regions with severe cuts, addressing previous limitations in technical precision.

Implications and Theoretical Considerations

The advancements in FEWZ 2.0 hold substantial theoretical and practical implications:

• Precision Physics at the LHC: By providing robust predictions for Drell-Yan processes beyond NLO with attention to systematic uncertainties, FEWZ 2.0 facilitates precision measurements crucial for constraining parton distribution functions and electroweak parameters within the Standard Model.
• Technical Precision and Experimental Comparisons: The ability to achieve technical precisions below 1% even with significant phase-space cuts enables more reliable comparisons with experimental data from LHC experiments such as ATLAS and CMS, reinforcing the analytical fidelity necessary for precision electroweak studies.
• Discussion on Higher-Order QCD Corrections: With results indicating minimal scale variation and dominant PDF uncertainty, FEWZ 2.0 highlights the need for further refinement in PDF extraction techniques and calls attention to potential areas for incorporating electroweak corrections in future iterations.
• Future Extensions: The modular nature of FEWZ 2.0 lays the groundwork for incorporating additional physics, such as NNLO electroweak effects or enhanced treatment of initial-state radiation, supporting the continued development of computational tools vital for advancing collider physics research.

Conclusion

FEWZ 2.0 constitutes a substantial software development in the field of high-energy phenOMENology, marking a critical step forward in the precision analysis of hadRONic Z production at hadRON colliders. By addressing previous limitations and incorporating a suite of enhancements tailored to the needs of the research community, it paves the way for more accurate testing of the Standard Model and exploration of potential new physics at LHC energies. With ongoing discussions about precision needs and the road to further improvements, FEWZ 2.0 promises to play an influential role in the theoretical and experimental landscape of particle physics.