First measurements of the W → ℓν and Z/γ * → ℓℓ (ℓ = e, μ) production cross sections in proton-proton collisions at \( \sqrt {s} = 7\;{\text{TeV}} \) are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ℓν and 179 Z/γ * → ℓℓ candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb. The measured total W and Z/γ ∗-boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are \( \sigma_W^{\text{tot}} \). BR(W → ℓν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and \( \sigma_{{{Z} \left/ {\gamma } \right.}}^{\text{tot}} \) BR(Z/γ ∗ → ℓℓ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09(lumi) nb (within the invariant mass window 66 < m ℓℓ < 116GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W + and W − production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.

The Barrel and Endcaps of the ATLAS SemiConductor Tracker have been installed in the ATLAS cavern since summer 2007. All the electrical and optical services were connected and rapid tests performed to verify their continuity. Problems with the cooling circuits, meant that the time for detailed tests in 2007 was limited. These problems have now been resolved allowing the SCT to be operated and participate in combined ATLAS Cosmic ray data taking runs. The results of these runs have been used to determine the hit efficiency of the modules as well as providing invaluable constraints for the detector alignment.

The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation.

A. Abdesselam, k T. Barber, a A.J. Barr, k* P. Bell, c† J. Bernabeu, q J.M. Butterworth, p J.R. Carter, a A.A. Carter, m E. Charles, r A. Clark, e A.-P. Colijn, i M.J. Costa, q J.M. Dalmau, m B. Demirköz, k‡ P.J. Dervan, g M. Donega, e M. D’Onifrio, e C. Escobar, q D. Fasching, r D.P.S. Ferguson, r P. Ferrari, c D. Ferrere, e J. Fuster, q B. Gallop, bl C. García, S. Gonzalez, r S. Gonzalez-Sevilla, q M.J. Goodrick, a A. Gorisek, c§ A. Greenall, g A.A. Grillo, n N.P. Hessey, i J.C. Hill, a J.N. Jackson, g R.C. Jared, r P.D.C. Johannson, o P. de Jong, i J. Joseph, r C. Lacasta, q J.B. Lane, p C.G. Lester, a M. Limper, i S.W. Lindsay, g R.L. McKay, f C.A. Magrath, i M. Mangin-Brinet, e S. Martí I García, q B. Mellado, r W.T. Meyer, f B. Mikulec, e M. Miñano, q V.A. Mitsou, q G. Moorhead, h M. Morrissey, l E. Paganis, o M.J. Palmer, a M.A. Parker, a H. Pernegger, c A. Phillips, a P.W. Phillips, l M. Postranecky, p A. RobichaudVéronneau, e D. Robinson, a S. Roe, H. Sandaker, j F. Sciacca, p A. Sfyrla, e E. Stanecka, cd S. Stapnes, j A. Stradling, r M. Tyndel, l A. Tricoli, k** T. Vickey, r J.H. Vossebeld, g M.R.M. Warren, p A.R. Weidberg, k P.S. Wells c and S.L. Wu r

The ATLAS SemiConductor Tracker (SCT) was built in three se ctions: a barrel and two end-caps. This paper describes the design, constructio n and final integration of the barrel section. The barrel is constructed around four nested cylin ders that provide a stable and accurate support structure for the 2112 silicon modules and their ass ociated services. The emphasis of this paper is directed at the aspects of engineering design that t urned a concept into a fully-functioning detector, as well as the integration and testing of large sub -sections of the final SCT barrel detector. The paper follows the chronology of the construction. The ma in steps of the assembly are described with the results of intermediate tests. The barrel s ervice components were developed and fabricated in parallel so that a flow of detector modules, cooling loops, opto-harnesses and Frequency-Scanning-Interferometry (FSI) alignment stru ctures could be assembled onto the four cylinders. Once finished, each cylinder was conveyed to the n ext site for the mounting of modules to form a complete single barrel. Extensive electrical and t hermal function tests were carried out on the completed single barrels. In the next stage, the four sin gle barrels and thermal enclosures were combined into the complete SCT barrel detector so that it cou ld be integrated with the Transition Radiation Tracker (TRT) barrel to form the central part of th e ATLAS inner detector. Finally, the completed SCT barrel was tested together with the TRT barrel in noise tests and using cosmic rays.

Since the summer of 2005, the vacuum ultra-violet Free-ele ctron LASer in Hamburg (FLASH) has operated as a user facility at the Deutsches Elek tronen-Synchrotron (DESY), delivering ultra-short laser pulses of tens of femtosecond durat ion with a high peak brilliance of up to 1028photons/(smm2 mrad2 0.1%bandwidth). Due to the statistics of the Self-Amplified Spontaneous Emission (SASE) process, each photon pulse differs fr om the previous one in the number of modes per pulse, the wavelength (0 .5% fluctuations) and the intensity, making experiments more complicated. Thus, for certain experiments the detail ed knowledge of the beam properties on a shot-to-shot basis is mandatory. In this paper we descri be an online method to gain spectral information about the individual Free-Electron Laser (FEL) pulses that is based on rare-gas photoionization and photoelectron spectroscopy.

The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented – these will be of interest to other builders of large-scale tracking detectors. The SCT end-caps will be fully connected at the start of 2008. Further commissioning will continue, to be ready for proton-proton collision data in 2008.

Optical links are used for the readout of the 4088 silicon microstrip modules that make up the SemiConductor Tracker of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The optical link requirements are reviewed, with particular emphasis on the very demanding environment at the LHC. The on-detector components have to operate in high radiation levels for 10 years, with no maintenance, and there are very strict requirements on power consumption, material and space. A novel concept for the packaging of the on-detector optoelectronics has been developed to meet these requirements. The system architecture, including its redundancy features, is explained and the critical on-detector components are described. The results of the extensive Quality Assurance performed during all steps of the assembly are discussed.

This paper describes the AC-coupled, single-sided, p-in-n silicon microstrip sensors used in the Semiconductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The sensor requirements, specifications and designs are discussed, together with the qualification and quality assurance procedures adopted for their production. The measured sensor performance is presented, both initially and after irradiation to the fluence anticipated after 10 years of LHC operation. The sensors are now successfully assembled within the detecting modules of the SCT, and the SCT tracker is completed and integrated within the ATLAS Inner Detector. Hamamatsu Photonics Ltd. supplied 92.2% of the 15,392 installed sensors, with the remainder supplied by CiS.