Exploring minijets beyond the leading power

Abstract

The crucial parameter of the current Monte Carlo models of high energy hadron-hadron interaction is the transverse momentum cutoff $p_{T0}$ for parton-parton interactions which slowly grows with energy and regularizes the cross section. This modification of the collinear factorization formula goes beyond the leading power and thus a natural question arises if such cutoff can be extracted from a formalism which takes into account power corrections. In this work, we consider the High Energy Factorization (HEF) valid at small $x$ and a new model, based on a similar principle to HEF, which in addition has a limit respecting the Dokshitzer-Dyakonov-Troyan formula for the dijet momentum disbalance spectrum. Minijet cross section and its suppression is then analyzed in two ways. First, we study minijets directly in the low-$p_T$ region, and demonstrate that higher twist corrections do generate suppression of the inclusive jet production cross section though these effects are not leading to the increase of the cutoff with incident energy. Second, we consider hard inclusive dijet production where Multi Parton Interactions (MPIs) with minijets produce power corrections. We introduce an observable constructed from differential cross section in the ratio $\tau$ of dijet disbalance to the average dijet $p_T$ and demonstrate that the $\tau>1$ region is sensitive to the cutoff $p_{T0}$ in the MPI minijet models. The energy dependence of the cutoff is reflected in the energy dependence of the bimodality coefficient $b$ of the $\tau$ distribution. We compare $b$ calculated from $\mathsf{pythia}$, where one can conveniently control MPIs by the program parameters, and HEF for a few unintegrated gluon distributions (UGDs). We find that the energy dependence of $b$ is very sensitive to the particular choice of UGD and in some models it resembles predictions of the Monte Carlo models.