W physics at the LHC with FEWZ 2.1

Abstract: We present an updated version of the FEWZ (Fully Exclusive W and Z production) code for the calculation of W and gamma*/Z production at next-to-next-to-leading order in the strong coupling. Several new features and observables are introduced, and an order-of-magnitude speed improvement over the performance of FEWZ 2.0 is demonstrated. New phenomenological results for W production and comparisons with LHC data are presented, and used to illustrate the range of physics studies possible with the features of FEWZ 2.1. We demonstrate with an example the importance of directly comparing fiducial-region measurements with theoretical predictions, rather than first extrapolating them to the full phase space.

• The paper introduces FEWZ 2.1, significantly speeding up NNLO calculations and broadening observable metrics for W boson analysis.
• It adds new observables such as beam thrust and transverse mass, enabling precise probing of W boson dynamics.
• Integration with multiple PDF sets and LHAPDF allows robust comparisons with LHC data to refine theoretical predictions.

Insights into "W Physics at the LHC with FEWZ 2.1"

The paper "W Physics at the LHC with FEWZ 2.1," authored by Ryan Gavin, Ye Li, Frank Petriello, and Seth Quackenbush, presents an advanced computational framework, FEWZ version 2.1, aimed at enhancing the analysis and understanding of W boson production at the Large Hadron Collider (LHC). This updated version addresses previous limitations and introduces novel features that make next-to-next-to-leading order (NNLO) precision calculations more accessible and efficient for high-energy physics analyses.

Summary of FEWZ 2.1 Enhancements and Utility

1. Performance Improvement: FEWZ 2.1 highlights a significant optimization in computational speed—by an order-of-magnitude—compared to its predecessor, FEWZ 2.0. This improvement stems from efficiencies in sector decomposition and cache utilization, among other algorithmic enhancements, enabling rapid NNLO calculations on contemporary computing systems.
2. Broadened Observables: This version introduces new observables for W boson studies, specifically beam thrust and transverse mass, which are crucial for investigating the intricate dynamics of W and Z boson production. Beam thrust, as implemented, facilitates comparisons with resummation techniques and the transverse mass provides critical insights into the W boson properties independent of the unobserved neutrino longitudinal momentum.
3. User-Centric Features: The program includes user-friendly features such as customizable histogram bin sizes and cumulative histogram outputs, aiding physicists in performing more refined analyses without the need for repetitive multiple runs.
4. LHAPDF Integration: Incorporation of the LHAPDF format enables users to explore various PDF sets, including HERA, MSTW, and NNPDF, thereby accommodating a wide range of experimental scenarios and theoretical investigations.
5. Comparison with LHC Data: Utilizing multiple PDF sets, the paper provides phenomenological results on W production, specifically the charge asymmetry and cross-section ratios at the LHC, corroborated with existing ATLAS data. Such analyses affirm the compatibility of FEWZ 2.1's NNLO calculations with experimental measurements, underscoring its predictive prowess.

Practical Implications and Future Directions

FEWZ 2.1 constitutes a crucial tool for precision predictions at the LHC, reducing uncertainties in W and Z boson production calculations and enabling more direct comparisons with experimental data by avoiding the extrapolation to full phase space. The ability to accurately compute fiducial cross sections allows for enhanced discrimination between different PDFs and theoretical models, sharpening the interpretation of LHC observations.

From a theoretical perspective, this tool strengthens the foundation for exploring beyond Standard Model physics through improved background characterizations and constraining PDF uncertainties. Practically, the speed advancements and modularity enhance its applicability in large-scale computational clusters, offering efficiencies invaluable in real-time data analysis and future LHC runs.

Conclusion

The developments presented within FEWZ 2.1 signify a pragmatic evolution in computational particle physics, serving as a reflection of the continual advancements necessary to meet the rigorous demands of modern hadron collider experiments. As the LHC continues to produce a wealth of data, FEWZ 2.1 stands as a potent asset for physicists aiming to unlock deeper insights into electroweak sector dynamics and validate the consistency and predictions of the Standard Model. Future work might focus on incorporating these computational gains into more complex processes or adapting these methodologies to emerging collider frameworks.