Improved squark and gluino mass limits from searches for supersymmetry at hadron colliders

Squarks and gluinos have been searched for at hadron colliders in events with multiple jets and missing transverse energy. No excess has been observed to date, and from a comparison of experimental cross section limits and theoretical cross section predictions one can deduce lower bounds on the squark and gluino masses. We present an improved analysis of squark and gluino mass bounds which is based on state-of-the-art cross section calculations including the summation of large threshold corrections. For illustration, we consider experimental data obtained by the CDF collaboration at the Fermilab Tevatron and discuss the impact of the improved cross section predictions on the squark and gluino mass limits.

Figure 1

The scale dependence of the LO, NLO, and $\mathrm{NLO}+\mathrm{NLL}$ cross sections for the four different squark and gluino production processes at the Tevatron. The squark and gluino masses have been set to $m_{\tilde{q}}=m_{\tilde{g}}=m=500\mathrm{GeV}$. The CTEQ6.6 [41] PDF has been adopted.

Figure 2

The NLL $K$-factor $K_{\mathrm{NLL}}={\sigma }_{\mathrm{NLO}+\mathrm{NLL}}/{\sigma }_{\mathrm{NLO}}$ for squark and gluino-pair-production processes at the Tevatron as a function of the average sparticle mass $m$. The CTEQ6.6 [41] PDF has been adopted.

Figure 3

SUSY signal selection efficiencies for different inclusive jet multiplicities, as determined using PYTHIA Monte Carlo samples normalized according to NLO cross sections with CTEQ6.1M [40] and CTEQ6.6 [41] PDFs, or using $\mathrm{NLO}+\mathrm{NLL}$ cross sections with CTEQ6.6 PDFs. Different squark and gluino mass configurations are considered and the efficiencies are presented as a function of squark and gluino masses.

Figure 4

NLO cross section prediction using CTEQ6.1M [40] and CTEQ6.6 [41] PDFs, and $\mathrm{NLO}+\mathrm{NLL}$ cross sections with CTEQ6.6 PDFs. Different squark and gluino mass configurations are considered and the predictions are presented as a function of squark and gluino masses. The error bars indicate the PDF and renormalization and factorization scales added in quadrature. Note that for display purposes the NLO and $\mathrm{NLO}+\mathrm{NLL}$ CTEQ6.6 cross sections are shown at mass coordinates shifted by 4 GeV and 8 GeV, respectively, with respect to the NLO CTEQ6.1 cross section.

Figure 5

Expected and observed 95% C.L. upper limit on the SUSY production cross section in the case of degenerate squarks and gluinos. The new limits (using $\mathrm{NLO}+\mathrm{NLL}$ and CTEQ6.6 PDFs theoretical predictions) are compared to previous CDF published results [6].

Figure 6

Observed 95% C.L. exclusion region in the squark/gluino mass plane. The new results (dashed line) are compared to CDF published results [6] (solid line).