S. Arfaoui

Measurement of the cross section for the production of a W boson in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector

A measurement is presented of the cross section for the produ cti n of aW boson with one or two jets, of which at least one must be a b-jet, in pp collisions at √ s = 7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb −1of data collected with the ATLAS detector at the LHC. The W+b-jet cross section is defined for jets reconstructed with the anti -kt clustering algorithm with transverse momentum above 25 GeV and rapidity within±2.1. Theb-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay chan nel of theW boson and is found to be 10.2 ± 1.9 (stat) ± 2.6 (syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent wit h, the measured value.

A prototype hybrid pixel detector ASIC for the CLIC experiment

A prototype hybrid pixel detector ASIC specifically designed to the requirements of the vertex detector for CLIC is described and first electrical measurements are presented. The chip has been designed using a commercial 65 nm CMOS technology and comprises a matrix of 64 × 64 square pixels with 25 μm pitch. The main features include simultaneous 4-bit measurement of Time-over-Threshold (ToT) and Time-of-Arrival (ToA) with 10 ns accuracy, on-chip data compression and power pulsing capability.

Data quality from the Detector Control System at the ATLAS experiment

At the ATLAS experiment, the Detector Control System (DCS) is used to oversee detector conditions and supervise the running of equipment. It is essential that information from the DCS about the status of individual sub-detectors be extracted and taken into account when determining the quality of data taken and its suitability for different analyses. DCS information is written to the ATLAS conditions database and then summarised to provide a status flag for each sub-detector and displayed on the web. We discuss how this DCS information should be used, and the technicalities of making this summary.

The ATLAS Detector Control System

The ATLAS experiment is one of the multi-purpose experiments at the Large Hadron Collider (LHC) at CERN, constructed to study elementary particle interactions in collisions of high-energy proton beams. Twelve different sub detectors as well as the common experimental infrastructure are controlled and monitored by the Detector Control System (DCS) using a highly distributed system of 140 server machines running the industrial SCADA product PVSS. Higher level control system layers allow for automatic control procedures, efficient error recognition and handling, manage the communication with external systems such as the LHC controls, and provide a synchronization mechanism with the ATLAS data acquisition system. Different databases are used to store the online parameters of the experiment, replicate a subset used for physics reconstruction, and store the configuration parameters of the systems. This contribution describes the computing architecture and software tools to handle this complex and highly interconnected control system.

Performance of the ATLAS liquid argon calorimeter

The Liquid Argon calorimeter (LAr) is a key detector component in the ATLAS experiment at the LHC. It provides precision measurements of electrons, photons, jets and missing transverse energy produced in the LHC proton-proton collisions. The calorimeter system consists of an electromagnetic barrel calorimeter and two electromagnetic endcaps (EMECs), hadronic (HEC) and forward (FCal) calorimeters. The lead-liquid argon sampling technique with an accordion geometry was chosen for the barrel electromagnetic calorimeter (EMB) and adapted to the electromagnetic endcaps. A presampler (PS) is installed in the cryostat in front of the EM calorimeter to provide a measurement of the energy lost upstream. The hadronic endcap calorimeter (HEC) uses a copper-liquid argon sampling technique with plate geometry. Finally, the forward calorimeter is composed of three modules featuring cylindrical electrodes with thin liquid argon gaps. The barrel and the two endcaps are housed into three cryostats kept at about 88 K. We present results assessing the liquid argon calorimeter performance obtained using random triggers, calibration data and LHC proton-proton collisions. Properties of the read-out channels such as pedestal, noise and gain have been measured and show the high stability of the LAr electronics over several months of data taking. First physics results concerning key calorimeter measurements like identification of photons, electrons, and missing tranverse energy are also shown.