Non-Diagonal and Mixed Squark Production at Hadron Colliders

TL;DR

The paper addresses non-diagonal and mixed squark production at hadron colliders within the MSSM, highlighting the importance of electroweak channels alongside loop effects and including mixing for top and bottom squarks. It provides analytic squared helicity amplitudes for diagonal, non-diagonal, and mixed squark production up to $O(\alpha_s^4)$ and $O(\alpha^2)$, and presents numerical studies for Tevatron and LHC benchmark scenarios, including light squarks. The results show that electroweak contributions can dominate in certain channels and that associated light sbottom-stop production at the Tevatron offers a promising test of light-sbottom scenarios; the work also discusses polarized cross sections relevant to RHIC. The analytic expressions are suitable for implementation in Monte Carlo tools, enabling more precise predictions and potential measurements of SUSY parameters including the SUSY CKM matrix.

Abstract

We calculate squared helicity amplitudes for non-diagonal and mixed squark pair production at hadron colliders, taking into account not only loop-induced QCD diagrams, but also previously unconsidered electroweak channels, which turn out to be dominant. Mixing effects are included for both top and bottom squarks. Numerical results are presented for several SUSY benchmark scenarios at both the CERN LHC and the Fermilab Tevatron, including the possibilities of light stops or sbottoms. The latter should be easily observed at the Tevatron in associated production of stops and sbottoms for a large range of stop masses and almost independently of the stop mixing angle. Asymmetry measurements for light stops at the polarized BNL RHIC collider are also briefly discussed.

Figures (11)

• Figure 1: Tree-level QCD Feynman diagrams for diagonal squark production at hadron colliders. The upper right diagram is absent for top squarks due to the negligible top quark density in the proton.
• Figure 2: Dominant tree-level electroweak Feynman diagram for non-diagonal ($i\neq j$) squark production at hadron colliders.
• Figure 3: Feynman diagrams for non-diagonal ($i\neq j$) squark production at hadron colliders proceeding through $t$-channel gluino (left) and neutralino (right) exchange.
• Figure 4: Subdominant loop-level QCD Feynman diagrams for non-diagonal ($i\neq j$) squark production at hadron colliders.
• Figure 5: Dominant electroweak Feynman diagram for mixed ( e.g. top and bottom) squark production at hadron colliders.