Session Q9: New Particle Searches I

Search for pair production of a new $b'$ quark that decays to a $Z$ boson and a bottom quark with the ATLAS detector at the LHC

We report a search for a new down-type quark, denoted $b'$, that is pair produced in $pp$ collisions at $\sqrt{s} = 7$ TeV with at least one $b'$ decaying to a $Z$ boson and a bottom quark. This search complements recent searches for a $b'$ in the $W$ boson plus top quark mode, and is particularly relevant for vector-like quark models. The data comprise 2.0 fb${}^{-1}$ of integrated luminosity collected by the ATLAS detector at the LHC in 2011. From events containing both a Z boson reconstructed from electrons, and a b-tagged jet, we enrich any potential signal by selecting a subsample with large $b'$ candidate $p_T$. We present limits on the mass of the $b'$.   

A Search for Supersymmetry with three or more leptons using $4.7 fb^{-1}$ of $\sqrt{s} = 7$ TeV CMS data

A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to $4.7 fb^{-1}$ of integrated luminosity in $pp$ collisions at $\sqrt{s} = 7$ TeV collected by the CMS experiment at the LHC. Fifty-two exclusive multileptonic channels have been investigated. Standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimize the reliance on simulation. The observations are consistent with expectations from standard model processes. These results are used to exclude previously unexplored regions of the supersymmetric parameter space.   

Search for $W^\prime$ boson production in the top quark decay channel

We present a search for the production of a heavy gauge boson PWpr. We study different models of PWpr boson production using the decay channel $PWpr\to tb$, which includes an arbitrary combination of left-~and right-handed couplings. The analysis is based on events with the final state signature $\mu\nu$+jets and $e \nu$+jets.   

Search for W' production in the single top channel with the ATLAS detector

We present the search for W' $\rightarrow$ tb using the LHC pp collision data collected with the ATLAS detector at a center-of- mass energy of 7 TeV. The largest backgrounds are the $t\bar{t}$ , W+jets, and multijets processes. To reduce their contribution we require an energetic final state including two jets, at least one must be tagged as a b-jet, one lepton, and missing energy. This measurement gives the latest limits on the W' $\rightarrow$ tb cross section times branching ratio as a function of the W' mass.   

Search for Lepton Flavor Violation in the $e\mu$ Continuum with the ATLAS detector

We present a search for the $t$-channel exchange of a lepton flavor violating scalar top quark in the $e\mu$ continuum using 2.08 fb$^{-1}$ of data collected by the ATLAS detector in $\sqrt{s}=7$ TeV $pp$ collisions at the LHC from March to June 2011. Data are found to be consistent with the standard model background. The 95\% CL upper limits on the production cross section of the scalar top quark are set. The observed cross section limit extends from 150 fb for $M_{\tilde{t}}=95$ GeV to 80 fb for $M_{\tilde{t}}=225$ GeV. In addition, limits on the sum of R-parity violating coupling constants are calculated as a function of scalar top mass.   

Search for SUSY in events with a single lepton, jets, and missing transverse momentum using a neural net approach

Supersymmetry is searched for in proton-proton collisions at $\sqrt{s}$ = 7 TeV using events with a single isolated lepton, energetic jets, and large missing transverse momentum. The analyzed data, which were recorded in the CMS detector at the LHC, correspond to a total integrated luminosity of 4.7 fb$^{-1}$. The search uses a multivariate analysis technique based on neural networks to suppress Standard Model backgrounds, and estimates residual backgrounds using a fully data-driven method. The analysis is performed in both the muon and electron channels, and the combined result is interpreted in the framework of the CMSSM parameter space.   

Search for technicolor in the Z + gamma channel in 7 TeV ATLAS data

A search for $\omega$$_{tc}$ decaying to Z + $\gamma$ using data from the ATLAS experiment is presented. Several $\omega$$_{tc}$ masses from 225-350 $GeV$ are investigated, and an upper limit on the production cross section is calculated for each mass.   

Search for a Heavy Exotic partner of the top quark with charge 5/3

Presented is a study of searches for two exotic particles - a heavy top quark partner with a fractional charge of 5/3, $T_{5/3}$, and its partner, the heavy $B$ quark with charge -1/3. These particles decay to a top quark and a $W$ boson, leading to very busy events with multi-leptons and multi-jets. Processes where same-sign dileptons are produced are considered. The backgrounds are predominantly from $t\overline t$, QCD multi-jets, $Z$+jets, $t\overline t WW$, $t\overline t W$ and multiple-$W$+jets production. A study using the data collected by the CMS detector at the LHC during 2011 has been performed.   

Signal optimization for a $W' \rightarrow t\bar{b}$ search in proton-proton collisions at 7~TeV with the ATLAS detector

Many theories beyond the Standard Model, e.g. extra-dimension model, technicolor theory and little higgs theory, predict the existence of $W'$ boson. Here, we present the search of $W'$ production in single top channel using the LHC pp collision data collected with the ATLAS detector at a center-of-mass energy of 7~TeV. The top quark decays via $t \rightarrow Wb$ with only the semileptonic decay channel being considered, thus $W' \rightarrow t\bar{b} \rightarrow l \nu b\bar{b}$. In this case, the $W'$ signal appears in the detector as two jets from b-quarks, a lepton and missing transverse energy from a neutrino. In order to distinguish this process from the background contribution that mainly consists of multijets, W+jets and top quark pair events, with smaller contributions from Z+jets, single top and diboson events, additional variables are applied to optimize the $W'$ signal. A fitting method using the invariant mass distribution of the final state particles has been used to set limits on the $W' \rightarrow t\bar{b}$ cross section times branching ratio as a function of the $W'$ mass.