1,720,984 research outputs found
Measurements of multi-parton interactions at ATLAS
No full textMeasurements of multiple parton scattering in proton-proton collisions provide insight into the structure and long-range low-momentum scale interactions of the proton. In this talk we present two recent measurements using proton-proton collision data collected by the ATLAS experiment. The first measurement determines the double-parton scattering contribution to four-lepton events at √s=8 TeV. An artificial neural net is used to optimise the analysis and an upper limit on the double-parton scattering fraction is set at 0.042, which corresponds to an effective cross section of 1mb. In the second measurement, the underlying event activity is studied in events containing a Z-boson in √s=13 TeV data. Unfolded differential cross sections are presented for charged particle multiplicity and charged particle transverse momentum in regions of azimuth measured with respect to the Z-boson direction. The data are compared to a wide variety of predictions from Monte Carlo event generators
Upgrade of ATLAS Hadronic Tile Calorimeter for the High Luminosity LHC
No full textThe Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, with steel as absorber and plastic scintillators as active medium. The High-Luminosity phase of LHC, delivering five times the LHC nominal instantaneous luminosity, is expected to begin in 2029. TileCal will require new electronics to meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2026-2028. PMT signals from every TileCal cell will be digitized and sent directly to the back-end electronics, where the signals are reconstructed, stored, and sent to the first level of trigger at a rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. The modular front-end electronics feature radiation-tolerant commercial off-the-shelf components and redundant design to minimise single points of failure. The timing, control and communication interface with the off-detector electronics is implemented with modern Field Programmable Gate Arrays (FPGAs) and high speed fibre optic links running up to 9.6 Gb/s. The TileCal upgrade program has included extensive R&D and test beam studies. A Demonstrator module with reverse compatibility with the existing system was inserted in ATLAS in August 2019 for testing in actual detector conditions. The ongoing developments for on- and off-detector systems, together with expected performance characteristics and results of test-beam campaigns with the electronics prototypes will be discussed
Upgrade of ATLAS Hadronic Tile Calorimeter for the High Luminosity LHC
No full textThe Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, with steel as absorber and plastic scintillators as active medium. The High-Luminosity phase of LHC, delivering five times the LHC nominal instantaneous luminosity, is expected to begin in 2029. TileCal will require new electronics to meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2026-2028. PMT signals from every TileCal cell will be digitized and sent directly to the back-end electronics, where the signals are reconstructed, stored, and sent to the first level of trigger at a rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. The modular front-end electronics feature radiation-tolerant commercial off-the-shelf components and redundant design to minimise single points of failure. The timing, control and communication interface with the off-detector electronics is implemented with modern Field Programmable Gate Arrays (FPGAs) and high speed fibre optic links running up to 9.6 Gb/s. The TileCal upgrade program has included extensive R&D and test beam studies. A Demonstrator module with reverse compatibility with the existing system was inserted in ATLAS in August 2019 for testing in actual detector conditions. The ongoing developments for on- and off-detector systems, together with expected performance characteristics and results of test-beam campaigns with the electronics prototypes will be discussed
Recent QCD results from ATLAS
No full textThe ATLAS collaboration has performed studies of a wide range of QCD phenomena, from soft particle to hard photon and jet production. Recent soft-QCD measurements include studies of underlying event, vector meson production and quark confinement effects. Differential measurements of inclusive and multi-jet production provide stringent tests of high-order QCD predictions and provide input for determination of parton density functions. Measurements of isolated inclusive and di-photons cross sections for high p_T photons test various theoretical predictions and constrain parton density functions. In addition the total pp cross section at 7 TeV, together with the elastic and inelastic contributions, is measured and compared to various models. An overview of these results is given. Prospects at HL-LHC will also be discussed as an outlook
Calibration and Data Quality systems of the ATLAS Tile Calorimeter during the LHC Run-I operations
No full textThe Tile Calorimeter is the hadronic calorimeter covering the central region of the ATLAS detector at the LHC. It consists of thin steel plates and scintillating tiles. Wavelength shifting fibres coupled to the tiles collect the produced light and are read out by photomultiplier tubes. The calibration scheme of the Tile Calorimeter comprises Cs radioactive source, laser and charge injection systems. Each stage of the signal production of the calorimeter from scintillation light to digitization is monitored and equalized. Description of the different TileCal calibration systems as well as results on their performance in terms of calibration factors, linearity and stability will be given. The data quality procedures and data quality efficiency of the Tile Calorimeter during the LHC data-taking period are presented as well
Precision QCD Measurements from ATLAS
No full textPerturbative QCD calculations at next-to-next-to leading order are available for many processes since several years and can be rigorously tested with a large variety of final states. In this talk, we present the latest results from the ATLAS collaboration involving jets and dijets measured at center of mass energies of 13 TeV. All measured cross-sections are compared to state-of-the art theory predictions. Moreover, we present measurements of dijet correlations allowing to test the renormalization group equation and extracting the strong coupling constant. The talk concludes with the latest results of jet-substructure studies at 13 TeV, in particular the measurement of the jet soft-drop mass as a jet-substructure observable which can be predicted with perturbative calculations
Performance, Calibration and Optics Robustness of the ATLAS Tile Calorimeter
No full textThe Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, operating at the Large Hadron Collider (LHC) at CERN. TileCal is made of steel as absorber and plastic scintillators as active medium. The scintillators are read-out by wavelength shifting fibres coupled to photomultiplier tubes (PMTs). The analogue signals from the PMTs are amplified, shaped, digitized by sampling the signal every 25 ns and stored on detector until a trigger decision is received. The TileCal front-end electronics reads out the signals produced by about 10000 channels measuring energies ranging from about 30 MeV to about 2 TeV. During LHC runs, high-momentum isolated muons have been used to study and validate the electromagnetic scale, while hadronic response has been probed with isolated hadrons. The calorimeter time resolution has been studied with multi-jet events. Besides, the integrated cells signals from minimum bias events provide auxiliary information on the response stability from the whole detector during proton-proton collisions. The calibration systems are used to estimate the radiation damage suffered by the active media of the detector, the scintillators and the wavelengths shifting optical fibres that collect the light into the photodetectors readout. First results using early LHC Run-3 data will be shown. A summary of the performance results, including the calibration, stability, absolute energy scale, uniformity, time resolution and the plastic scintillators light output loss due to integrated dose will be presented
Performance, calibration and optics robustness of the ATLAS Tile Calorimeter
No full textThe Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, operating at the Large Hadron Collider (LHC) at CERN. TileCal is made of steel as absorber and plastic scintillators as active medium. The scintillators are read-out by wavelength shifting fibres coupled to photomultiplier tubes (PMTs). The analogue signals from the PMTs are amplified, shaped, digitised by sampling the signal every 25 ns and stored on detector until a trigger decision is received. The TileCal front-end electronics reads out the signals produced by about channels measuring energies ranging from about MeV to about TeV. During LHC runs, high-momentum isolated muons have been used to study and validate the electromagnetic scale, while hadronic response has been probed with isolated hadrons. The calorimeter time resolution has been studied with multi-jet events. Besides, the integrated cells signals from minimum bias events provide auxiliary information on the response stability from the whole detector during proton-proton collisions. The calibration systems are used to estimate the radiation damage suffered by the active media of the detector, the scintillators and the wavelengths shifting optical fibres that collect the light into the photodetectors readout. First results using early LHC Run-3 data will be shown. A summary of the performance results, including the calibration, stability, absolute energy scale, uniformity, time resolution and the plastic scintillators light output loss due to integrated dose will be presented
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