Measurement of W ±^{±} Z Production in Proton-Proton Collisions at √ s = 7 TeV with the ATLAS Detector

The ATLAS (A Toroidal Lhc ApparatuS) experiment at the Large Hadron Collider (LHC) explores the frontiers of particle physics. The experiment needs to control huge backgrounds to perform the entire physics programs. The muon trigger system of ATLAS filters events containing high transverse momentum ( p T ) muons and is one of the key components to conduct the challenging task. This study utilizes the full performance of the muon trigger system. The W ± Z process is one of interesting Standard Model processes because the process has not been tested at su ffi cient level at the past experiments. Furthermore anomalous Triple Gauge Couplings beyond the Standard Model could be observed in the production. The W ± Z → ℓνℓ ′ ℓ ′ channel can be identified with less backgrounds compared to the other processes because of the three high p T leptons coming from W and Z bosons. However, there are still significant back- grounds in the LHC environment. The event and object selections to reduce those backgrounds have been optimized. The isolation requirement for leptons is expected to largely reduce the backgrounds and the e ff ect of this requirement on the analysis has been investigated. Finally the W ± Z production cross section at √ s = 7 TeV is measured to be 19 . 0 + 1 . 4 − 1 . 3 (stat.) ± 0 . 9 (syst.) ± 0 . 4 (lumi.) pb with 4 . 6 fb − 1 data. This result is consistent with the Standard Model prediction within the uncertainties. The limit on anomalous Triple Gauge Coupling is also determined. Both results are consistent with the Standard Model prediction. The dominant uncertainty is statistics. Therefore further test with data with higher statistics is desirable. This study has confirmed that a precise measurement of anomalous TGC in the WZ process is a good probe to the search for physics beyond the Standard Mode

Search for Scalar Diphoton Resonances in the Mass Range 65−60065-600 GeV with the ATLAS Detector in pppp Collision Data at s\sqrt{s} = 8 TeVTeV

A search for scalar particles decaying via narrow resonances into two photons in the mass range 65–600 GeV is performed using $20.3\text{}\text{}{\mathrm{fb}}^{-1}$ of $\sqrt{s}=8\text{}\text{}\mathrm{TeV}$ $pp$ collision data collected with the ATLAS detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches