WW scattering at the LHC

TL;DR

This paper evaluates WW scattering at the LHC in a no-new-particles scenario using the electroweak chiral Lagrangian. It implements two unitarisation schemes (Padé and N/D) to predict possible scalar or vector resonances in WW scattering and embeds the EWChL in Pythia to simulate signal and backgrounds for the semi-leptonic final state. A novel hadronic-W tagging method based on jet substructure is introduced, along with a set of selection cuts (top veto, tag jets, minijet veto) to suppress backgrounds. The study suggests that resonances up to about 1.5 TeV could be observable with 100 fb^-1, with differential cross-sections and angular distributions enabling some spin discrimination, albeit with substantial systematic uncertainties from the underlying event.

Abstract

A detailed study is presented of elastic WW scattering in the scenario that there are no new particles discovered prior to the commissioning of the LHC. We work within the framework of the electroweak chiral lagrangian and two different unitarisation protocols are investigated. Signals and backgrounds are simulated to the final-state-particle level. A new technique for identifying the hadronically decaying W is developed, which is more generally applicable to massive particles which decay to jets where the separation of the jets is small. The effect of different assumptions about the underlying event is also studied. We conclude that the channel WW -> jj+l+nu may contain scalar and/or vector resonances which could be measurable after 100 fb^(-1) of LHC data.

Figures (16)

• Figure 1: Map of the parameter space as determined by the Padé protocol LHCsensitivity. The small triangle in the centre is the region of no resonances and the region below the dotted line is forbidden. Also shown are the points corresponding to the various scenarios considered in the text.
• Figure 2: Contours of constant scalar resonance mass in steps of 100 GeV. The horizontal lines are obtained using the Padé protocol and the curved lines are obtained using the N/D method which depends upon the parameter $M$.
• Figure 3: Contours of constant vector resonance mass in steps of 100 GeV. The horizontal lines are obtained using the Padé protocol and the curved lines are obtained using the N/D method which depends upon the parameter $M$.
• Figure 4: Contours of constant isotensor resonance mass in steps of 100 GeV. The curved lines are obtained using the N/D method which depends upon the parameter $M$. The horizontal lines and dotted curves populate the unphysical region of parameter space, see the discussion in the text.
• Figure 5: Parton level cross-section for Scenario A. We compare the Padé result (solid line) with the N/D results for $M=10^{3}$ GeV(dashed line), $M=10^{4}$ GeV (dashed-dotted line) and $M=10^{5}$ GeV (dotted line).