Abstract
The tree-level partonic angular distribution of Standard Model Wγ production possesses a feature known as the Radiation Amplitude Zero (RAZ) where destructive interference causes the cross section to vanish. At the proton level the exact cancellation disappears, however, one can find a dip in the central region of the angular distributions, here called the Radiation Valley (RV). In this paper, we show how the sensitivity for W(ℓv)γ resonances can be significantly improved if one focuses on events in the RV region. Using this technique, we find that the LHC could probe a larger range of resonance masses, equivalent to increasing the luminosity by a factor of 2–3 over conventional searches. The exact increase depends on the spin of the Wγ resonance and exactly how it couples to electroweak gauge bosons.
Highlights
We begin with a review of the current search for W γ resonances performed by the LHC in the leptonic channel [30] and we show how the results can be improved using our technique
We showed that the Radiation Valley (RV) — the remnant of the Radiation Amplitude Zero (RAZ) at a hadron collider — can play an important role in the discovery of exotic resonances that decay to W ( ν)γ
While the RAZ is encoded in several different kinematic variables, we found that the best proxy for it is the difference in rapidity between the lepton and the photon in the case of resonance searches
Summary
The largest contaminants are photon final state radiation (FSR), next-to-leading order corrections (NLO), and the reconstruction of the partonic center of mass frame Even including these washout effects, a clear dip in the angular distribution remains [28, 29], as we will discuss below. We present the shape of the angular distributions for the background and a benchmark signal from a scalar resonance. We discuss how the RAZ manifests at parton and proton levels For the latter we introduce a series of kinematic cuts that can be implemented to mitigate the washout effects due to NLO corrections and FSR. The tree-level partonic angular distribution of SM W γ production shows an exact zero at cos θ∗ = ∓1/3 for W ± production This zero in the cross section is the RAZ feature, shown in figure 2.
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