W+W-, WZ and ZZ production in the POWHEG BOX

Abstract: We present an implementation of the vector boson pair production processes ZZ, W+W- and W Z within the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. The implementation is built within the POWHEG BOX package. The Z/\gamma^* interference, as well as singly resonant contributions, are properly included. We also considered interference terms arising from identical leptons in the final state. As a result, all contributions leading to the desired four-lepton system have been included in the calculation, with the sole exception of the interference between ZZ and W+W- in the production of a pair of same-flavour, oppositely charged fermions and a pair of neutrinos, which we show to be fully negligible. Anomalous trilinear couplings can be also set in the program, and we give some examples of their effect at the LHC. We have made the relevant code available at the POWHEG BOX web site.

• The paper presents a novel NLO+SMC implementation for simulating W+W-, WZ, and ZZ production, enabling precise modeling of four-lepton final states.
• It incorporates complex interference effects and leverages multiple PDF sets to ensure minimal scale variation in key cross-sectional predictions.
• The work offers a robust simulation tool for LHC analyses, enhancing the exploration of anomalous trilinear couplings and improving background estimates.

Overview of $W^+W^-$, $WZ$, and $ZZ$ Production in High-Energy Collisions

The paper under review presents a detailed implementation of vector boson pair production processes—specifically, $W^+W^-$, $WZ$, and $ZZ$—within the framework that integrates next-to-leading order (NLO) calculations with shower Monte Carlo (SMC) simulations. This development is significant for the precise prediction and simulation of these processes at high-energy colliders like the LHC.

The authors have meticulously included several complex components in their calculations: the interference of $Z/\gamma^*$ as well as singly resonant contributions, and even interference terms from identical leptons in the final state, which are often crucial for accurate representation of experimental conditions. However, they note the negligible interference between $ZZ$ and $W^+W^-$ in the production of same-flavour, oppositely charged fermions when coupled with neutrinos, opting not to include this in their model.

Numerical Results and Technical Implementation

The implementation's strength lies in its comprehensive inclusion of all relevant NLO diagrams leading to a four-lepton system. Notably, the authors released the corresponding code, providing a tool for the experimental collaborations to adequately simulate their backgrounds away from the resonant region. They cite numerical results supporting the robustness of their simulations, employing various parton distribution function (PDF) sets like MSTW2008, CT10, and NNPDF2.1, highlighting slight variations in cross-sectional predictions based on these PDFs.

Despite the absence of gluon fusion initiated NNLO contributions, which remains significant, the results demonstrate minimal scale variation, asserting the reliability of NLO calculations. The authors further explore detailed examinations of distinctive observables. For instance, appreciable differences emerge when comparing NLO and LHE (Les Houches Event) results, particularly in exclusive channels probing the hardest jets in the processes, suggesting improvements in precision measurement capabilities at LHC.

Theoretical and Practical Implications

The inclusion of Next-to-Leading Order corrections dramatically enhances the reliability of theoretical predictions for collider processes—which is critical for probing the robustness of the Standard Model and exploring phenomena indicating potential new physics, such as anomalous trilinear couplings (ATGCs). They probe the sensitivity of their model towards ATGCs by examining their impact on the production processes at LHC energy scales, incorporating form factors to maintain the unitarity of scattering amplitudes at high energies.

This specific aspect holds significant promise for future research directions as it equips experimental physicists with a more nuanced tool to sift out potential new physics signals, especially in the increasingly precise studies planned at LHC.

Speculative Evolution in AI Applications

Considering its thorough handling of complex calculations and data-intensive operations, this research exemplifies the trajectory for increasing automation in theoretical physics simulations, hinting at future developments in AI that might further streamline such complex calculations, enhance accuracy, and interpret vast datasets from high-energy physics experiments.

As advancements in computational capabilities continue, the integration of AI in simplifying and refining NLO processes may lead to broader applications and more efficient explorations of particle behaviors, paving the way for novel insights into the fundamental forces of nature. The implementation of these complex systems marks a pivotal point in automated simulations and could serve as a blueprint for future computational models addressing similar high-stakes physics scenarios.