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$m_{\tilde{t}_1}\lsim m_t$, decaying dominantly into a c-jet and the lightestneutralino, at the LHC. The principal idea is to exploit the Majorana nature ofthe gluino, leading to same-sign top quarks in events of gluino-pair productionfollowed by gluino decays into top and stop. The resulting signature is 2b-jets plus 2 same-sign leptons plus additional jets and missing energy. Weperform a Monte Carlo simulation for a benchmark scenario, which is inagreement with the recent WMAP bound on the relic density of dark matter, anddemonstrate that for $m_{\tilde{g}}\lsim 900$ 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 theshape of invariant-mass distributions. The derivation of the shape formulae isalso given.Comment: 20 pages, 6 figures, minor changes; version to appear in PR