Vector boson pair production at the LHC

Abstract: We present phenomenological results for vector boson pair production at the LHC, obtained using the parton-level next-to-leading order program MCFM. We include the implementation of a new process in the code, pp -> \gamma\gamma, and important updates to existing processes. We incorporate fragmentation contributions in order to allow for the experimental isolation of photons in \gamma\gamma, W\gamma, and Z\gamma production and also account for gluon-gluon initial state contributions for all relevant processes. We present results for a variety of phenomenological scenarios, at the current operating energy of \sqrt{s} = 7 TeV and for the ultimate machine goal, \sqrt{s} = 14 TeV. We investigate the impact of our predictions on several important distributions that enter into searches for new physics at the LHC.

• The paper presents NLO corrections for vector boson processes, showing significant 20%-60% increases in cross sections from LO to NLO.
• It refines the MCFM code by incorporating processes like pp → γγ with enhanced photon isolation and notable gluon contributions.
• The findings provide critical benchmarks for the Standard Model and improve experimental strategies for new physics searches.

Overview of Vector Boson Pair Production at the LHC

The academic paper under review provides a comprehensive analysis of vector boson pair production at the Large Hadron Collider (LHC), leveraging the Monte Carlo for FeMtobarn processes (MCFM) at next-to-leading order (NLO) to present phenomenological predictions. This research is significant for understanding both the Standard Model (SM) processes and the implications for new physics investigations.

The study introduces advancements in the MCFM code, including the implementation of the process $pp \rightarrow \gamma\gamma$ and improvements in existing simulations. These enhancements incorporate experimental isolation requirements for photons and consider initial states involving gluons, crucial for more precise predictions at the LHC energies of 7 TeV and 14 TeV.

Key Findings

The authors have calculated NLO corrections for vector boson processes and explored their impact on several distributions vital for new physics searches. The processes under study include $W^+W^-$, $WZ$, $ZZ$, $\gamma\gamma$, $W\gamma$, and $Z\gamma$ production. Notably, the inclusion of loop-level $gg \rightarrow VV$ processes adds to the calculation accuracy, considering the substantial gluon flux at the LHC.

Numerically, the paper reports a significant increase in cross sections when moving from leading order (LO) to NLO, usually by 20%-60%, dependent on the process and the energy under consideration. The incorporation of gluon-gluon contributions, while formally higher-order, can account for up to 10% or more of the NLO cross section, particularly for $WW$ and $ZZ$ processes, underlining their phenomenological importance.

Implications and Future Directions

This work has several practical and theoretical implications. On the practical side, the updated MCFM code with NLO predictions provides a critical tool for experimentalists analyzing data from the LHC, serving as a benchmark for SM predictions and aiding in background estimation in searches for new physics, like the Higgs boson or beyond-the-Standard-Model (BSM) particles. The theoretical analyses regarding the relative contributions of various subprocesses, including fragmentation contributions and $gg$ initial states, provide insights into the perturbative QCD framework and the importance of including higher-order corrections for accurate modeling.

The analysis of photon isolation effects and their impact on cross sections is instrumental for experimental setups, impacting detector strategies and data interpretation significantly. Furthermore, the study's findings on radiation effects in vector boson decays inform theoretical models involving anomalous couplings.

Looking ahead, the inclusion of higher-order corrections and fragmentation functions opens new research directions, particularly the potential for incorporating even higher precision calculations such as NNLO corrections for processes where gluon-gluon initiated contributions are non-negligible. This could substantially reduce theoretical uncertainties and provide more stringent tests of the SM and sensitivity to new phenomena. Additionally, extending these methods to accommodate more complex final states or alternative isolation criteria could further align theoretical predictions with experimental capabilities.

In conclusion, this paper makes a significant contribution to the field by enhancing theoretical models of vector boson pair production at the LHC, providing improved tools for both theoretical explorations and experimental measurements. Such advancements are pivotal as the LHC continues to probe fundamental particle interactions at unprecedented energies.