Same-sign top quarks as signature of light stops at the CERN LHC

We present a new method to search for a light scalar top with $m_{{\tilde{t}}_1}\lesssim m_t$, decaying dominantly into a $c$-jet and the lightest neutralino, at the LHC. The principal idea is to exploit the Majorana nature of the gluino, leading to same-sign top quarks in events of gluino-pair production followed by gluino decays into top and stop. The resulting signature is 2 $b$-jets plus 2 same-sign leptons plus additional jets and missing energy. We perform a Monte Carlo simulation for a benchmark scenario, which is in agreement with the recent WMAP bound on the relic density of dark matter, and demonstrate that for $m_{\tilde{g}}\lesssim 900\mathrm{GeV}$ and $m_{\tilde{q}}>m_{\tilde{g}}$ the signal can be extracted from the background. Moreover, we discuss the determination of the stop and gluino masses from the shape of invariant-mass distributions. The derivation of the shape formulas is also given.