ATLAS Searches in Run I

Title: Searches for di-Higgs production in 4b final states and new phenomena with boosted Higgs using the ATLAS detector at LHC Run I Abstract : Measurement of Higgs boson pair production has a fundamental importance in understanding the nature of the Higgs boson and electroweak symmetry breaking. TeVscale resonances decaying to a pair of Higgs boson are also predicted in various extensions of the Standard Models, e.g, Kaluza-Klein excitation of the gravitons in the bulk Randall- Sundrum extra dimensions, heavy scalar particles in two-Higgs-doublet models. This talk highlights ATLAS Run I searches for di-Higgs production in 4b final states with resolved topology using small-radius jets and boosted topology using large-radius jets with associated b-tagged track-jets. Other Run I searches employing techniques to identify boosted Higgs bosons are also presented in this talk. Title: Searches for vector-like quarks and resonances decaying into top-quarks with the ATLAS detector at LHC Run I Abstract : In theories beyond the Standard Model (SM) incorporating mechanism to cancel Higgs boson mass divergence, the presence of fermionic top/bottom quark partners, usually referred to as vector-like quarks (VLQs), is often predicted. The high-mass VLQs, preferentially coupling to the third generation quarks in the SM, would result in topologies with boosted top quarks, W, Z and Higgs bosons. Direct production of heavy resonances decaying into a pair of top quarks or top and bottom quarks, predicted, e.g, by extended gauge theories or bulk extra dimension scenarios, have been also searched for at LHC Run I, including techniques to detect hadronically decaying top-quarks. This talk summarizes ATLAS Run I searches for VLQs and top-quark related resonances, placing some emphasis on the techniques used in boosted regime. Title: Searches for R‐Parity Violating Supersymmetry With Jet Substructure Using the ATLAS Detector at LHC Run 1 Abstract: Searches for supersymmetry usually assume the presence of R‐parity, an additional symmetry which guarantees the stability of the lightest supersymmetric particle (LSP) and leads to dramatic missing‐energy signatures. In R‐parity violating (RPV) models, however, the LSP can decay to Standard Model (SM) particles, thereby greatly changing the final state. We present the results of two searches for hadronic RPV, where the LSP decays to quarks. In the first, gluino cascade decays lead to very high multiplicity events, where the techniques of accidental substructure can play a critical role in signal identification. In the second, directly produced stops decay to pairs of quarks: these boosted particles are reconstructed as single jets and substructure selections are used to identify the signal. Both analyses see no excess over the SM prediction, and set new limits on their corresponding models. The role of jet substructure is critical in both analyses, and helps significantly expand searches for completely hadronic final states at the Large Hadron Collider.