Rapidity Correlations in $W\gamma$ Production at the Tevatron

Abstract

We study the correlation of photon and charged lepton pseudorapidities, $\eta(\gamma)$ and $\eta(\ell)$, $\ell=e,\,\mu$, in $p\bar p\rightarrow W^\pm\gamma+X\rightarrow \ell^\pm p\llap/_T\gamma+X$ at the Tevatron. In the Standard Model, the $\Delta\eta(\gamma,\ell)= \eta(\gamma) - \eta(\ell)$ differential cross section is found to exhibit a pronounced dip at $\Delta\eta(\gamma,\ell) \approx \mp 0.4$, which originates from the radiation zero present in $q\bar q'\rightarrow W\gamma$. The sensitivity of the $\Delta\eta(\gamma,\ell)$ distribution to higher order QCD corrections, non-standard $WW\gamma$ couplings, and the cuts imposed is explored. The $\Delta\eta(\gamma,\ell)$ distribution is compared with other quantities which are sensitive to the radiation zero.