Properties of b-hadrons with ATLAS

Properties of b-hadrons with ATLAS. Talk for EPSHEP 2013, Stockholm July 18-24

Performance of the ATLAS Trigger with Proton Collisions at the LHC

The ATLAS trigger has been used very successfully to collect collision data during 2009 and 2010 LHC running at centre of mass energies of 900 GeV, 2.36 TeV, and 7 TeV. The trigger system reduces the event rate, from the design bunch‐crossing rate of 40 MHz, to an average recording rate of 200Hz. The ATLAS trigger is composed of three levels. The first (Level 1) uses custom electronics to reject most background collisions, in less than 2.5μs, using information from the calorimeter and muon detectors. The upper two trigger levels, known collectively as the High Level Trigger (HLT), are software‐based triggers. As well as triggers using global event features, such as missing transverse energy, there are selections based on identifying candidate muons, electrons, photons, tau mesons or jets. We give an overview of the performance of these trigger selections based on extensive online running during LHC collisions and describe the progress towards fully commissioning these triggers. Distributions of key selection variables based on calorimeter and tracking information are shown calculated at the different trigger levels and are compared with offline reconstruction. We include examples of online triggering of Standard Model physics such as candidate W‐boson decays. Comparisons between data and simulations are shown for some important selection variables, already illustrating a very good level of understanding of the detector a nd trigger performance. We describe how the trigger has evolved with increasing LHC luminosity and give a brief overview of plans for forthcoming LHC running

Properties of bb-hadrons with ATLAS: Bs0B^0_s rare decays and Λb\Lambda_b decay properties.

Measurements of the properties of $b$-hadrons are presented based on 5.25~$fb^{-1}$ of $pp$\ncollision data recorded by the ATLAS experiment during 2011 LHC operation. \nWe present an updated limit on the the $B_s\rightarrow\mu^+\mu^-$ branching ratio, a determination of the the $\Lambda^0_b$ mass and lifetime and a new measurement of the parity violation asymmetry parameter $\alpha_b$ and helicity amplitudes of the decay of the $\Lambda^0_b\rightarrow{J/\psi}(\mu^+\mu^-)\Lambda^0(p^+\pi^-)$

An evaluation of the potential of GPUs to accelerate tracking algorithms for the ATLAS trigger

The potential of GPUs has been evaluated as a possible way to accelerate trigger algorithms for the ATLAS experiment located at the Large Hadron Collider (LHC). During LHC Run-1 ATLAS employed a three-level trigger system to progressively reduce the LHC collision rate of 20 MHz to a storage rate of about 600 Hz for offline processing. Reconstruction of charged particles trajectories through the Inner Detector (ID) was performed at the second (L2) and third (EF) trigger levels. The ID contains pixel, silicon strip (SCT) and straw-tube technologies. Prior to tracking, data-preparation algorithms processed the ID raw data producing measurements of the track position at each detector layer. The data-preparation and tracking consumed almost three-quarters of the total L2 CPU resources during 2012 data-taking. Detailed performance studies of a CUDA™ implementation of the L2 pixel and SCT data-preparation and tracking algorithms running on a Nvidia® Tesla C2050 GPU have shown a speed-up by a factor of 12 for the tracking code and by up to a factor of 26 for the data preparation code compared to the equivalent C++ code running on a CPU. A client-server technology has been used to interface the CUDA™ code to the CPU-based software, allowing a sharing of the GPU resource between several CPU tasks. A re-implementation of the pixel data-preparation code in openCL has also been performed, offering the advantage of portability between various GPU and multi-core CPU architectures

Precipitation pathways for five new ice core sites in Ellsworth Land, West Antarctica

Ice cores provide a wealth of information about past climate and atmospheric circulation however a good understanding of the precipitation patterns, potential source regions and transport pathways is essential in their interpretation. Here we investigate the precipitation pathways for a transect of five new ice cores drilled in the southern Antarctic Peninsula and Ellsworth Land. We utilize in situ observations from automatic weather stations to confirm that the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data adequately captures annual and sub-annual variability, with evidence of a slight cold bias in the 2 m temperatures. Back trajectory analysis, from the British Atmospheric Data Centre trajectory service, reveals that warm and snowy years are associated with air masses that originate (5 days before reaching the site) from the Amundsen-Bellingshausen Sea, while cold and dry years are associated with air masses from the Antarctic continent. There is a clear seasonal migration in the trajectories at each site, reflecting the east to west migration of the Amundsen Sea Low, known to have a strong influence on climate in this region

Overview of the High-Level Trigger Electron and Photon Selection for the ATLAS Experiment at the LHC

The ATLAS experiment is one of two general purpose experiments to start running at the Large Hadron Collider in 2007. The short bunch crossing period of 25ns and the large background of soft-scattering events overlapped in each bunch crossing pose serious challenges that the ATLAS trigger must overcome in order to efficiently select interesting events. The ATLAS trigger consists of a hardware-based First-Level Trigger and of a software-based High-Level Trigger, which can be further divided into the Second-Level Trigger and the Event Filter. This paper presents the current state of development of methods to be used in the High-Level Trigger to select events containing electrons or photons with high transverse momentum. The performance of these methods is presented, resulting from both simulation studies, timing measurements, and test beam studies

Electroweak parameters of the z0 resonance and the standard model

Contains fulltext : 124399.pdf (publisher's version ) (Open Access

Overview of the high-level trigger electron and photon selection for the ATLAS experiment at the LHC

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in pp collisions at 14 TeV center-of-mass energy, whilst rejecting the enormous number of background events. The High-Level Trigger (HLT = second level trigger and Event Filter), which is a software based trigger will need to reduce the level-1 output rate of ≈ 75 kHz to ≈ 200 Hz written out to mass storage. In this talk an overview of the current physics and system performance of the HLT selection for electrons and photons is given. The performance has been evaluated using Monte Carlo simulations and has been partly demonstrated in the ATLAS testbeam in 2004. The efficiency for the signal channels, the rate expected for the selection, the global data preparation and execution times will be highlighted. Furthermore, some physics examples will be discussed to demonstrate that the triggers are well adapted for the physics programme envisaged at the LHC. © 2005 IEEE