Squark Production at the Tevatron

TL;DR

The next-to-leading order QCD corrections to the production of squark-antisquark pairs in {ital p{bar p}} collisions are determined and the renormalization scale dependence is reduced considerably.

Abstract

We have determined the QCD corrections to the production of squark-antisquark pairs in $p\bar p$ collisions at the Tevatron. If the next-to-leading order corrections are taken into account, the renormalization/factorization scale dependence of the theoretical prediction for the cross section is reduced considerably. The higher order corrections increase the production cross section at the Tevatron by about a factor two if we compare the next-to-leading order prediction at a scale near the squark mass with the lowest order prediction for which, in the experimental analyses, the scale was identified with the invariant energy of the parton subprocess. This results in a rise of the experimental lower bound on the squark mass from the Tevatron by about $20$ GeV.

Figures (3)

• Figure 1: Generic diagrams for squark-antisquark pair production: $(a_1)$, $(a_2)$ basic Born-level $q\bar{q}$ diagrams; $(b_1)$ and $(b_2)$ vertex corrections due to gluon and gluino exchange; $(c)$ gluon emission; $(d)$ gluon-quark process; $(e_1)$, $(e_2)$ gluon fusion.
• Figure 2: The scaling functions for squark-antisquark pair production in (a) $q\bar{q}$, (b) $q'\bar{q}$, (c) $qg$ and (d) $gg$ collisions. The notation follows eq.(\ref{['cross']}) with $\eta = \hat{s}/4m_{\tilde{q}}^2 -1$; V+S denotes the sum of the virtual and soft corrections, H the contribution of hard gluon emission. Mass parameters: $m_{\tilde{q}}= 250$ GeV and $m_{\tilde{g}} = 200$ GeV.
• Figure 3: Total cross section for the irreducible production of squark-antisquark pairs $p\bar{p} \to \tilde{q} \bar{\tilde{q}} X$ at the Tevatron energy $\sqrt{s} = 1.8$ TeV. (a) Dependence on the renormalization/factorization scale $Q$ for the leading order (LO) and the next-to-leading order (NLO) predictions, and sensitivity to different parton densities; mass parameters as in Fig.2; (b) Dependence of the cross section on the squark mass for $m_{\tilde{g}} = 200$ GeV; GRV parton densities for NLO, and EHLQ parton densities for LO used in the experimental analysis. massnew. Upper full line of the NLO prediction corresponds to the renormalization/factorization scale $Q/m_{\tilde{q}} = 1/3$, middle line $=1$ and lower line $=2$.