Searches for 4th generation and vector-like quarks with the ATLAS detector

The Fourth Generation Quarks model and Vector Like Quarks model have been studied in ATLAS using proton-proton collisions at $\sqrt{s}$ = 7 TeV between 1.04 fb$^{-1}$ and 4.7 fb$­^{-1}$. Multiple signatures have been analysed (single lepton and dilepton channel for opposite-sign and same-sign leptons) to search for $b'$, $t'$ or exotic particles with charge $Q_{e}$ = -1/3, 2/3 and 5/3. The data were consistent with the expected background from Standard Model processes so limits have been extracted. For the $4^{th}$ generation quarks, the following results were obtained at 95\% CLs : m($Q$) > 350 GeV for up and down type quark $Q$, m($t'$) > 656 GeV for $t' \rightarrow W+b$ and m($b'$) > 670 GeV for $b' \rightarrow W+t$. The Vector Like Quarks Model has also been studied : a VLQ interpretation of t' has been done as well as a vector-like singlet $b'$ (with $b' \rightarrow Z+b$) mixing solely with the third SM generation which gives m($b'$) > 358 GeV. Limits on VLQs with charge 5/3 has been studied for different coupling values $\lambda(T_{5/3}tW)$ giving $m(T_{5/3})$ > 670 GeV for $\lambda \ll 1$, m($T_{5/3}$) > 680 GeV for $\lambda=1$ and m($T_{5/3}$) > 700 GeV for $\lambda=3$. The single production of VLQs coupling to light generations has been analysed for VLQs with different charges giving m($Q_{-1/3}$) > 1.08 TeV, m($Q_{2/3}$) = 1.12 TeV and m($Q_{5/3}$) = 1.42 TeV.