First results and status of the ATLAS detector at the LHC

The road with early ATLAS data towards top physics is discussed. This includes a detailed understanding of the detector performance for key components of top quark decays like jets, tracking and lepton identification as well as measurements on minimum bias and underlying event physics. The status of these studies based on the first tens of nb −1 is presented

A new method to determine the electroweak couplings of individual light flavours at LEP

A method is presented for determining the yields and properties of individual light quark flavours in $Z^0$ decays that is essentially free of detailed assumptions about hadronisation. The method uses an equation system with the number of events which are single and double tagged by high energy hadrons as inputs. In addition, SU(2) isospin symmetry and the flavour independence of QCD are used to derive general relations between hadron production from the various primary light quarks. Assuming the branching fractions $R_q$ of the $Z^0$ into down and strange quarks to be the same, five million hadronic $Z^0$ decays may allow a precisions of $\delta{(R_d=R_s)}/(R_d=R_s)\sim{0.05}$ and $\delta A_{FB}(d=s) \sim \delta A_{FB}(u) \sim{0.015}$ for the corresponding asymmetries. The method can be extended to include somewhat more model dependent symmetries of hadron production, which then allows the electroweak observables for each of the individual light quarks to be determined

Test Beam Results of Geometry Optimized Hybrid Pixel Detectors

The Multi-Chip-Module-Deposited (MCM-D) technique has been used to build hybrid pixel detector assemblies. This paper summarises the results of an analysis of data obtained in a test beam campaign at CERN. Here, single chip hybrids made of ATLAS pixel prototype read-out electronics and special sensor tiles were used. They were prepared by the Fraunhofer Institut fuer Zuverlaessigkeit und Mikrointegration, IZM, Berlin, Germany. The sensors feature an optimized sensor geometry called equal sized bricked. This design enhances the spatial resolution for double hits in the long direction of the sensor cells.Comment: Contribution to Proceedings of Pixel2005 Workshop, Bonn Germany 200

ATLAS Pixel Detector Timing Optimisation with the Back of Crate Card of the Optical Pixel Read out System

As with all detector systems at the Large Hadron Collider (LHC), the assignment of data to the correct bunch crossing, where bunch crossings will be separated in time by 25 ns, is one of the challenges for the ATLAS pixel detector. This document explains how the detector system will accomplish this by describing the general strategy, its implementation, the optimisation of the parameters, and the results obtained during a combined testbeam of all ATLAS subdetectors

The Control System for a new Pixel Detector at the sLHC

For the upgrade of the LHC, the sLHC (super Large Hadron Collider), a new ATLAS Pixel Detector is planned, which will require a completely new control system. To reduce the material budget new power distribution schemes are under investigation, where the active power conversion is located inside the detector volume. Such a new power supply system will need new control strategies. Parts of the control must be located closer to the loads. The minimization of mass, the demand for less cables and the re-use of the outer existing services are the main restrictions to the design of the control system. The requirements of the DCS (Detector Control System) and a first concept will be presented. We will focus on a control chip which necessarily has to be implemented in the new system. A setup of discrete components has been built up to investigate and verify the chip’s requirements. We report on the status of the work

Detector Control System of the ATLAS Insertable B-Layer

soumis à publicationTo improve tracking robustness and precision of the ATLAS inner tracker an additional fourth pixel layer is foreseen, called Insertable B-Layer (IBL). It will be installed between the innermost present Pixel layer and a new smaller beam pipe and is presently under construction. As, once installed into the experiment, no access is available, a highly reliable control system is required. It has to supply the detector with all entities required for operation and protect it at all times. Design constraints are the high power density inside the detector volume, the sensitivity of the sensors against heatups, and the protection of the front end electronics against transients. We present the architecture of the control system with an emphasis on the CO2 cooling system, the power supply system and protection strategies. As we aim for a common operation of pixel and IBL detector, the integration of the IBL control system into the Pixel one will be discussed as well

Jet Quenching in the Opposite Direction of a Tagged Photon in High-Energy Heavy-Ion Collisions

We point out that events associated with large $E_T$ direct photons in high-energy heavy-ion collisions can be used to study jet energy loss in dense matter. In such events, the $p_T$ spectrum of charged hadrons from jet fragmentation in the opposite direction of the tagged photon is estimated to be well above the background which can be reliably subtracted at moderately large $p_T$. We demonstrate that comparison between the extracted fragmentation function in $AA$ and $pp$ collisions can be used to determine the jet energy loss and the interaction mean-free-path in the dense matter produced in high-energy heavy-ion collisions.Comment: 4 pages in RevTex twocolumn with embedded psfigure

An Investigation of Hadronization Mechanism at Z0Z^{0} Factory

We briefly review the hadronization pictures adopted in the LUND String Fragmentation Model(LSFM), Webber Cluster Fragmentation Model(WCFM) and Quark Combination Model(QCM), respectively. Predictions of hadron multiplicity, baryon to meson ratios and baryon-antibaryon flavor correlations, especially related to heavy hadrons at $Z^0$ factory obtained by LSFM and QCM are reported.Comment: 18 pages, 6 figures. accepted by Sci China Phys Mech Astro