Null radiation zone at the LHC

Abstract

The null radiation zone theorem states that, when special kinematical conditions are satisfied, all the helicity amplitudes of a parton-level subprocess where a vector current is emitted vanish due to destructive interference among different diagrams. We study the manifestation of the theorem in $pp$ collisions at the $\sqrt{s}=8$ TeV LHC. The theorem predicts that the cross section for $p p \rightarrow j j \gamma$ events is suppressed when the transverse momenta of the two jets are similar and when the rapidity difference between the photon and the cluster of the jets is nearly zero, because the $u u \rightarrow u u \gamma$ subprocess, which dominates in events with large $j j \gamma$ invaraint mass, has strong destructive interference in this region. We confirm this prediction by the calculation with MadGraph 5, and show that the suppression on the $p p \rightarrow j j \gamma$ cross section is observable at the LHC.