Pion Energy Reconstruction by the Local Hadronic Calibration Method with ATLAS Combined Test Beam 2004 data

The pion energy reconstruction by the local hadronic calibration method on the basis of the 2004 combined test beam data in the energy range 10 -- 350 GeV and $\eta = 0.25$ is performed. In this method energies deposited in each cell are weighted. The weights are determined by the Monte Carlo simulation using Calibration Hits software. We have modified this method by applying cuts in weights. The obtained fractional energy resolution with the conventional method of determination of the energy deposit in the dead material between LAr and Tile calorimeters is $\sigma/E = (67\pm2)\%/\sqrt{E} \oplus (3.9\pm0.2)\% \oplus (95\pm22)\%/E$. This is about 1.5 times better than the results for the hadronic calibration method obtained by the Oxford-Stockholm group and slightly better than the H1 method results for CTB04 obtained by Pisa group. The energy linearity is within $\pm$1\%. We have determined the general normalization constant of 0.91 for which the mean value linearity for the weight cut of 1.05 is about 1. At using this normalization constant the energy resolution has not worsen. We have corrected the cesium miscalibration of the $Tile_1$ and $Tile_2$ longitudinal samplings. The mean value of energy linearity has been increased by about 1\% and becomes equal to 1.002$\pm$0.002. The energy resolution did not change. We have performed weighting without knowing of the beam energies. For this the special procedure has been developed. In this case the energy resolution shows 9\% degradation. Linearities are within $\pm$1\%. We have applied the Neural Networks to the determination of the energy deposit between LAr and Tile calorimeters. The essential improvement of energy resolution is obtained. In this case we have reached the projected energy resolution for hadrons in the ATLAS detector $\sigma/E = 50\%/\sqrt{E} \oplus 3\%$

Artificial Neural Networks for reconstruction of energy losses in dead materials between barrel LAr and Tile calorimeters: exploration and results

In the course of computational experiments with Monte-Carlo events for ATLAS Combined Test Beam 2004 setup Artificial Neural Networks (ANN) technique was applied for reconstruction of energy losses in dead materials between barrel LAr and Tile calorimeters (Edm). The constructed ANN procedures exploit as their input vectors the information content of different sets of variables (parameters) which describe particular features of the hadronic shower of an event in ATLAS calorimeters. It was shown that application of ANN procedures allows one to reach 40% reduction of the Edm reconstruction error compared to the conventional procedure used in ATLAS collaboration. Impact of various features of a shower on the precision of $Edm$ reconstruction is presented in detail. It was found that longitudinal shower profile information brings greater improvement in $Edm$ reconstruction accuracy than cell energies information in LAr3 and Tile1 samplings

Study of the Transition Effect with the ATLAS Tile Calorimeter

With the aim to establish the electromagnetic energy scale of the ATLAS Tile calorimeter and understanding the performance of the calorimeter to electrons 12% of modules have been exposed in electron beams with various energies. On a basis of the obtained electromagnetic calibration constants we have determined the e/mip values in dependence of the absorber thickness using different beam incident angles. We have observed the transition effect (e/mip < 1) and, for the first time, its behaviour as a function of the absorber thickness --- the e/mip ratio decreases logarithmically when the absorber thickness increases this is well described by the GEANT4 version 6.2 Monte Carlo simulation. These results are important for precision electromagnetic energy scale determination for the ATLAS Tile calorimeter

Electromagnetic Cell Level Calibration for ATLAS Tile Calorimeter Modules

We have determined the electromagnetic calibration constants of 11% TileCal modules exposed to electron beams with incident angles of 20 and 90 degrees. The gain of all the calorimeter cells have been pre-equalized using the radioactive Cs-source that will be also used in situ. The average values for these modules are equal to: for the flat filter method 1.154+/-0.002 pC/GeV and 1.192+/-0.002 pC/GeV for 20 and 90 degrees, for the fit method 1.040+/-0.002 pC/GeV and 1.068+/-0.003 pC/GeV, respectively. These average values for all cells of calibrated modules agree with the weighted average calibration constants for separate modules within the errors. Using the individual calibration constants for every module the RMS spread value of constants will be 1.9+/-0.1 %. In the case of the global constant this value will be 2.6+/-0.1 %. Finally, we present the global constants which should be used for the electromagnetic calibration of the ATLAS Tile hadronic calorimeter data in the ATHENA framework. These constants are equal to 1.15 pC/GeV in the case of the flat filter method and 1.04 pC/GeV for the fit one

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson

Measurement of the top quark pair cross section with ATLAS in pp collisions at √s=7 TeV using final states with an electron or a muon and a hadronically decaying τ lepton

A measurement of the cross section of top quark pair production in proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 7 TeV is reported. The data sample used corresponds to an integrated luminosity of 2.05 fb -1. Events with an isolated electron or muon and a τ lepton decaying hadronically are used. In addition, a large missing transverse momentum and two or more energetic jets are required. At least one of the jets must be identified as originating from a b quark. The measured cross section, σtt-=186±13(stat.)±20(syst.)±7(lumi.) pb, is in good agreement with the Standard Model prediction

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN