Top squark mass: current limits revisited and new limits from Tevatron Run-I

Abstract

Analyzing the $\ell +n$-$jets+\text{met}$ (where $n\ge 2$), data from Run-I of the Tevatron using the Bayesian technique, we obtain model independent limits on the product $\text{br}(\text{lstop}\text{ra}b{e}^{+}{\nu }_e\text{lspone})\times \text{br}({\text{lstop}}^{\ast }\text{ra}\bar{b}q\overline{q^{\prime }}\text{lspone})$ for different values of the lighter top squark($\text{lstop}$) mass and the lightest supersymmetric particle($\text{lspone}$) mass. The SUSY signals have been simulated by interfacing the 4-body decay of $\text{lstop}$ at the parton level with the event generator PYTHIA. These limits have been translated into exclusion plots in the $\text{mlstop}$-$\text{mlspone}$ plane, which also turn out to be fairly model independent for fixed values of the BR of the competing loop decay mode $\text{lstop}\text{ra}c\text{lspone}$. Assuming the loop decay BR to be negligible and using the leading order cross section for $\text{lstoplstop}$ pair production, we obtain conservatively $\text{mlstop}\ge$77.0 (74.5) GeV for $\text{mlspone}$=5(15) GeV, while for $\text{br}(\text{lstop}\text{ra}c\text{lspone})$=20%, the corresponding limits are $\text{mlstop}\ge$68.0 (65.0) GeV. Using the larger next to leading order cross-section stronger limits are obtained. For example, if $\text{br}(\text{lstop}\text{ra}c\text{lspone})$=20%, $\text{mlstop}\ge$73.0 (72.7) GeV for $\text{mlspone}$=5(15) GeV. Our limits nicely complement the ALEPH bounds which get weaker for low $\text{mlspone}$.

Comments: 11 pages, 5 figures, few comments added