Top-pair production at the LHC through NNLO QCD and NLO EW (1705.04105v2)

Abstract: In this work we present for the first time predictions for top-quark pair differential distributions at the LHC at NNLO QCD accuracy and including EW corrections. For the latter we include not only contributions of ${\cal O}(\alpha_s^2 \alpha)$, but also those of order ${\cal O}(\alpha_s \alpha^2)$ and ${\cal O}( \alpha^3)$. Besides providing phenomenological predictions for all main differential distributions with stable top quarks, we also study the following issues. 1) The effect of the photon PDF on top-pair spectra: we find it to be strongly dependent on the PDF set used -- especially for the top $p_T$ distribution. 2) The difference between the additive and multiplicative approaches for combining QCD and EW corrections: with our scale choice, we find relatively small differences between the central predictions, but reduced scale dependence within the multiplicative approach. 3) The potential effect from the radiation of heavy bosons on inclusive top-pair spectra: we find it to be, typically, negligible.

• The paper presents refined predictions for top-quark pair production by calculating differential distributions with NNLO QCD and NLO EW corrections.
• It demonstrates that the multiplicative approach for combining QCD and EW corrections effectively reduces scale uncertainties compared to the additive method.
• It investigates photon PDF effects and heavy boson radiation, emphasizing the need for precise modeling to improve the fidelity of theoretical predictions.

Analysis of Top-Pair Production at the LHC: NNLO QCD and NLO EW Contributions

The paper delineates an advanced theoretical analysis of top-quark pair production at the Large Hadron Collider (LHC). It specifically addresses predictions of differential distributions at Next-to-Next-to-Leading Order (NNLO) in Quantum Chromodynamics (QCD), supplemented with Next-to-Leading Order (NLO) electroweak (EW) corrections. This work is instrumental in refining theoretical models against high-precision LHC data.

Technical Summary

Top-pair production constitutes a critical testbed for QCD calculations and is pivotal for indirect searches for new physics phenomena in high-energy collisions. The paper embarks on elucidating several facets of these predictions, including:

1. Photon PDFs: The role of the photon parton distribution function (PDF) in influencing top-pair spectra is studied. The impact varies significantly depending on the PDF set utilized, notably affecting distributions such as the top transverse momentum.
2. Combination Approaches: The analysis contrasts two methods for combining QCD and EW corrections—additive and multiplicative. It demonstrates their respective implications, finding the multiplicative approach beneficial for scale dependence reduction due to its assumption of factorization of dominant QCD and EW effects.
3. Heavy Boson Radiation: The potential impact of heavy boson emissions (e.g., W, Z, and Higgs) on inclusive top-pair spectra is explored, although found to be negligible within the studied context.

Findings and Numerical Highlights

• The paper presents a comprehensive assessment of differential distributions, focusing on the invariant mass $m\left(t\bar{t}\right)$ and transverse momentum $p_T$. EW corrections show a significant influence on high $p_T$ regions, wherein negative Sudakov logarithms are notably impactful.
• Notably, while the influence on rapidity distributions is minimal, the $p_T$ distribution depicts a pronounced negative contribution from EW corrections reaching approximately -25% at around 3 TeV.
• Photon PDF uncertainties, most pronounced in the NNPDF3.0QED set, showcase significant variances in scenarios involving photon-initiated processes, emphasizing the relevance of precise photon density understanding from the LUXQED set as a reference.

Implications and Future Research

The incorporation of precise electroweak corrections alongside NNLO QCD calculations is a step forward in minimizing discrepancies between theoretical predictions and experimental observations. The implications extend to improving the determination of PDFs, informing high-energy physics analyses where precise modeling of background processes is crucial. The insights gained from the stochastic combination of QCD and EW corrections can be applied to refine predictions, thereby reducing uncertainties in future LHC analyses.

Theoretical and Practical Contribution

The paper's results are crucial in enhancing the fidelity of Monte Carlo event generators used at the LHC, which are integral in simulating particle collisions. With accurate predictions, LHC experiments can more effectively sieve possible new physics signals from the background arising from well-understood processes like top-pair production. Rescaling methods, proposed in the paper for modification via K-factor adjustments, provide a pathway to efficiently incorporate complex corrections into existing data analyses.

Conclusion

This paper makes substantial progress in interpreting top-pair production at LHC energies. It establishes a robust bridge between high-order theoretical predictions and experimental data, playing a pivotal role in ongoing efforts to predict and potentially discover new physics phenomena. The multiplicative approach for merging QCD and EW effects stands as a recommendation for future analyses, advocating for its theoretical advantages in handling high-energy processes. Researchers venturing into similar domains may further explore dynamic approaches to incorporate these precision corrections in broader hadronic processes anticipated at future collider experiments.