Electroweak Precision Tests in High-Energy Diboson Processes

TL;DR

Franceschini et al. develop a precision EW test program at the LHC by isolating energy-growing BSM effects in high-energy diboson and associated Higgs processes. They define four high-energy primaries that capture leading $E^2$-enhanced interference with the SM, map these to EFT operators and low-energy observables, and identify fully leptonic $WZ$ as the most sensitive channel. Their analysis shows HL-LHC and future hadron colliders can reach per-mille level constraints on key EW parameters, with notable synergy and complementarity relative to LEP and direct resonance searches. The work emphasizes the necessity of high experimental and theoretical accuracy and outlines concrete selection optimizations and avenues for extending the program to additional channels and observables.

Abstract

A promising avenue to perform precision tests of the SM at the LHC is to measure differential cross-sections at high invariant mass, exploiting in this way the growth with the energy of the corrections induced by heavy new physics. We classify the leading growing-with-energy effects in longitudinal diboson and in associated Higgs production processes, showing that they can be encapsulated in four real "high-energy primary" parameters. We assess the reach on these parameters at the LHC and at future hadronic colliders, focusing in particular on the fully leptonic $WZ$ channel that appears particularly promising. The reach is found to be superior to existing constraints by one order of magnitude, providing a test of the SM electroweak sector at the per-mille level, in competition with LEP bounds. Unlike LHC Run-1 bounds, which only apply to new physics effects that are much larger than the SM in the high-energy tail of the distributions, the probe we study applies to a wider class of new physics scenarios where such large departures are not expected.

Figures (8)

• Figure 1: Bounds from LEP LEP:2003aa, run-$1$ LHC (which includes $20\,$fb$^{-1}$ at $8\,$TeV and $3\,$fb$^{-1}$ at $13\,$TeV) Falkowski:2016cxu, and the expected $95\%$ CL reach from fully leptonic $WZ$, on the high-energy primary parameter $a^{(3)}_q$ as a function of the new physics scale $M$. See section \ref{['sec:nloanalysis']} for a detailed description of the figure.
• Figure 2: Representative diagrams for $q'{\bar{q}}\rightarrow\Phi\Phi'$ production.
• Figure 3: Contributions to longitudinal diboson processes from different BSM scenarios: Strongly-coupled quarks and Higgs (a), strongly-coupled Higgs and transverse vectors (b), and "Weak" type models (c,d).
• Figure 4: Differential $\cos \theta^{*}$ cross-section for $pp \rightarrow W^+ Z$, where the solid (dashed) lines correspond to the final state with two longitudinally polarized gauge bosons (all the other polarizations). Left: LO results at invariant mass $m_{\textsc{wz}} = 1\ \rm{TeV}$. Right: tree-level results matched with an extra jet with invariant mass $m_{\textsc{wz}} \geq 1\ \rm{TeV}$.
• Figure 5: Rescaled accuracy as a function of the cut on the scattering angle $|\cos \theta^{*}|$ (left panel) and of the transverse momentum of the $WZ$ system $p_{T,VV}$ (right panel). The solid, dashed, dot-dashed and dotted lines correspond to the three $p_{T,V}$ bins described in the main text. The black lines are obtained by imposing the additional cuts $p_{T,VV} \leq p_{T,V}/2$ in the left plot and $|\cos \theta^*| < 0.5$ in the right plot. The orange lines are obtained with no additional cut.