- The paper introduces CT14 PDFs from a comprehensive NNLO QCD analysis that incorporates extensive LHC measurements.
- It employs flexible Bernstein polynomial parametrizations and contrasts Hessian and Lagrange techniques for robust error estimation.
- CT14 refines key distributions like strangeness and d/u ratios, enhancing theoretical predictions for Higgs production and collider phenomena.
Analysis of New Parton Distribution Functions from a Global QCD Analysis
The paper "New parton distribution functions from a global analysis of quantum chromodynamics" introduces novel parton distribution functions (PDFs) at next-to-next-to-leading order (NNLO) derived from an extensive global analysis by the CTEQ-TEA group. These PDF sets, labeled as CT14, incorporate data from LHC experiments and implement various technical and methodological advancements over previous CT PDF sets. The primary focus is on enhancing theoretical predictions for processes involving the Higgs boson production, among other significant observables at the Large Hadron Collider (LHC).
Key Features and Methodology
The principal advancement in CT14 PDFs lies in the inclusion of a broadened experimental dataset. This dataset is enriched by the latest measurements from the LHC, particularly those related to Higgs boson production, granted its significance in LHC Run-2 for exploring electroweak physics and potential new physics. The paper notably integrates the charged lepton rapidity asymmetry data from the DØ experiment and various LHC processes to provide robust constraints on the PDF parameters.
The paper introduces a more flexible parametrization for PDFs. Using Bernstein polynomials, the new parametrization delivers a refined fit accommodating varying quark flavor combinations and their interactions. This is instrumental in addressing subtle discrepancies observed with previous PDF models, such as flavor separation issues in the description of light quark PDFs.
Another cornerstone of the CT14 analysis is the comparison and cross-verification of results through alternative methodologies. The authors compare Hessian and Lagrange Multiplier techniques to estimate PDF uncertainties and validate their consistency. These approaches ensure that the refined error sets capture both symmetric and asymmetric error contributions to the PDFs, an aspect crucial for precise theoretical predictions, especially for processes like Higgs production via gluon-gluon fusion or top quark pair production.
Numerical Results and Implications
The CT14 PDFs exhibit marked differences compared to earlier versions, such as CT10, demonstrated by changes in the quark and gluon PDFs. Notably, the strangeness distribution is softer at low x, and the gluon distribution is adjusted at high x. Additionally, the d/u quark ratio shows a decrement supporting a more aligned approach with contemporary data.
The robustness of the CT14 PDFs is supported by their alignment with a suite of benchmark experimental data, noted with good agreement with LHC jet cross-section measurements. Such benchmarking is critical as it strengthens confidence in the CT14 PDFs across a variety of processes relevant at the LHC.
Theoretical and Practical Implications
The implications of the CT14 analysis are both foundational and practical. Theoretically, the refined PDFs facilitate more accurate perturbative QCD calculations, reducing theoretical uncertainties that have historically hindered precision tests of the Standard Model. Practically, they equip researchers with an indispensable tool for testing hypotheses in the search for new physics scenarios beyond the Standard Model at the LHC.
In closing, the paper makes a significant contribution to the field of high-energy physics by delivering comprehensive and refined PDFs, enhancing predictive accuracy for vital collider processes. Future work could further refine these tools to address remaining theoretical uncertainties and integrate new experimental datasets as they become available.
