Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy √s=7TeV with the ATLAS detector

Jets are identified and their properties studied in center-of-mass energy √ s = 7 TeV protonproton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the antik t algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.La lista completa de autores que integran el documento puede consultarse en el archivo.Instituto de Física La Plat

Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy √s=7TeV with the ATLAS detector

Jets are identified and their properties studied in center-of-mass energy √ s = 7 TeV protonproton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the antik t algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.La lista completa de autores que integran el documento puede consultarse en el archivo.Instituto de Física La Plat

The ATLAS Simulation Infrastructure

The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for largescale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.La lista completa de autores que integran el documento puede verse en el archivo asociado.Facultad de Ciencias Exacta

Luminosity determination in pp collisions at √s = 7 TeV using the ATLAS detector at the LHC

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0<μ<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.La lista completa de autores puede verse en el archivo asociado.Facultad de Ciencias Exacta

Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector

An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6fb-1 of integrated luminosity collected in 2011 at √8=7TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with p T>20GeV and |η|<2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(μμ) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(μμ) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e.g. doubly charged Higgs bosons (H ±±). Assuming pair production of H±± bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244)GeV and 251 (209)GeV for H±± bosons coupling to left-handed and right-handed fermions, respectively.La lista completa de autores que integran el documento puede consultarse en el archivo asociado.Instituto de Física La Plat

Luminosity determination in pp collisions at √s = 7 TeV using the ATLAS detector at the LHC

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0<μ<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.La lista completa de autores puede verse en el archivo asociado.Facultad de Ciencias Exacta

Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in √s = 7TeV pp collisions using 1 fb<SUP>-1</SUP> of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04 fb -1 of proton-proton collision data at √s = 7TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear R-parity violation.La lista completa de autores que integran el documento puede consultarse en el archivo asociado.Instituto de Física La Plat

Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector

An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6fb-1 of integrated luminosity collected in 2011 at √8=7TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with p T>20GeV and |η|<2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(μμ) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(μμ) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e.g. doubly charged Higgs bosons (H ±±). Assuming pair production of H±± bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244)GeV and 251 (209)GeV for H±± bosons coupling to left-handed and right-handed fermions, respectively.La lista completa de autores que integran el documento puede consultarse en el archivo asociado.Instituto de Física La Plat

The ATLAS Simulation Infrastructure

The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for largescale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.La lista completa de autores que integran el documento puede verse en el archivo asociado.Facultad de Ciencias Exacta

A study of the material in the ATLAS inner detector using secondary hadronic interactions

The ATLAS inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from ∼ 200μm to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum.La lista completa de autores que integran el documento puede consultarse en el archivo.Instituto de Física La Plat