Associated production of weak bosons and jets by multiple parton interactions

Abstract

The sources of $W + n$-jet events in hadron collisions are higher-order QCD processes, but also multiple-parton interactions. A subprocess producing a $W + k$-jet final state, followed by one producing $l$ jets in the same nucleon-nucleon interaction, will result in a $W + n$-jet event if $k + l = n$. In the simplest case a $W + 2$-jet event can be produced by a quark-antiquark annihilation into $W$ and a 2-jet event occurring in the same proton-antiproton interaction. We compute that this happens at the 10% level of the higher-order QCD processes for the type of cuts made by the Tevatron experiments. For jet $p_T$ values of order $5{\sim}10$ GeV, multiple-parton interactions dominate higher-order QCD-processes. The emergence of this new source of $W + n$-jet events towards lower $p_T $ simulates the running of $\alpha_s$; it is imperative to remove these processes from the event sample in order to extract information on the strong coupling constant. Also, BFKL studies of low-$p_T$ jet cross sections are held hostage to a detailed understanding of the multiple-parton interactions. We perform the calculations required to achieve these goals. A detailed experimental analysis of the data may, for the first time, determine the effective areas occupied by quarks and gluons in the nucleon. These are not necessarily identical. We also compute the multiple-parton contribution to $Z + n$-jet events.