Rapidity Correlations in $Wγ$ Production at Hadron Colliders

TL;DR

This paper identifies photon–lepton rapidity correlations as a robust observable to probe the Standard Model radiation zero in Wγ production at hadron colliders. By analyzing the Δη(γ,ℓ) distribution and the double differential d^2σ/dη(γ)dη(ℓ) at the Tevatron, it shows a characteristic dip near Δη ≈ −0.3 that signals the radiation zero without requiring neutrino momentum reconstruction. It then assesses the impact of higher-order QCD corrections, jet activity, and anomalous WWγ couplings, finding that NLO effects can fill the dip, but jet veto strategies can preserve it to some extent. For LHC and higher energies, large QCD corrections largely wash out the signal, though careful event selection and normalization techniques can still provide partial sensitivity to the underlying SM structure and to anomalous couplings.

Abstract

We study the correlation of photon and charged lepton pseudorapidities, $η(γ)$ and $η(\ell)$, $\ell=e,\,μ$, in $p\,\pbar \rightarrow W^\pmγ+X\rightarrow \ell^\pm p\llap/_Tγ+X$. In the Standard Model, the $Δη(γ,\ell)= η(γ) - η(\ell)$ differential cross section is found to exhibit a pronounced dip at $Δη(γ,\ell) \approx \mp 0.3$ ($=0$)in $p\bar p$ ($pp$) collisions, which originates from the radiation zero present in $q\bar q'\rightarrow Wγ$. The sensitivity of the $Δη(γ,\ell)$ distribution to higher order QCD corrections, non-standard $WWγ$ couplings, the $W+$~jet ``fake'' background and the cuts imposed is explored. At hadron supercolliders, next-to-leading order QCD corrections are found to considerably obscure the radiation zero. The advantages of the $Δη(γ,\ell)$ distribution over other quantities which are sensitive to the radiation zero are discussed. We conclude that photon lepton rapidity correlations at the Tevatron offer a {\it unique} opportunity to search for the Standard Model radiation zero in hadronic $Wγ$ production.