The jet fragmentation function and transverse profile for jets with 25 GeV < p T jet < 500 GeV and |η jet | < 1.2 produced in proton-proton collisions with a center-ofmass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb −1 . Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement. Introduction and overviewThis paper presents measurements of jet properties in proton-proton (pp) collisions at a center of mass energy of 7 TeV at the CERN LHC using the ATLAS detector. Jets are identified and their momenta measured using the calorimeters. Charged particles measured by the tracking system are then associated with these jets using a geometric definition. The structure of the jets is studied using these associated particles. Jets produced at large transverse momentum in protonproton collisions arise from the scattering of proton constituents leading to outgoing partons (quarks and gluons) with large transverse momenta. These manifest themselves as jets of hadrons via a "fragmentation process". While the scattering of the proton constituents is well described by perturbative QCD and leads, at lowest order, to final states of e-mail: atlas.publications@cern.ch gg, gq, and qq, the fragmentation process is more complex. First, fragmentation must connect the outgoing partons with the rest of the event as the jet consists of colourless hadrons while the initiating parton carries colour. Second, the process involves the production of hadrons and takes place at an energy scale where the QCD coupling constant is large and perturbation theory cannot be used. Fragmentation is therefore described using a QCD-motivated model with parameters that must be determined from experiment. The fragmentation function D h i (z, Q) is defined as the probability that a hadron of type h carries longitudinal momentum fraction z of the momentum p i of a parton of type iD(z, Q) depends on z and on the scale Q of the hard scattering process which produced the parton. While the value of D h i (z, Q) cannot be calculated in perturbative QCD, the variation with Q can be predicted provided Q is sufficiently large [1][2][3][4][5][6].In this paper a quantity related to D h i (z, Q) is measured. After jets have been reconstructed, the data are binned for fixed ranges of jet transverse momenta (p T jet ), each bin containing N jet jets; z is then determined for each charged particle associated with the jetwhere p jet is the momentum of the reconstructed jet and p ch the momentum of the charged particle. The following quantity is measu...

We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb À1 . Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N jet , for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity distributions of various combinations of leptons and final-state jets. The results, corrected for all detector effects and for all backgrounds such as diboson and top quark pair production, are compared with particle-level predictions from perturbative QCD. Leadingorder multiparton event generators, normalized to the next-to-next-to-leading-order total cross section for inclusive W-boson production, describe the data reasonably well for all measured inclusive jet multiplicities. Next-to-leading-order calculations from MCFM, studied here for N jet 2, and BLACKHAT-SHERPA, studied here for N jet 4, are found to be mostly in good agreement with the data.

The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and insitu calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 ± 0.9 µm and a relative momentum resolution σ p /p = (4.83 ± 0.16) ×

The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and insitu calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 ± 0.9 µm and a relative momentum resolution σ p /p = (4.83 ± 0.16) ×