ATLAS is a multi-purpose detector for the LHC and will detect proton-proton collisions with center of mass energy of 14 TeV. Part of the central inner detector, the Semi-Conductor Tracker (SCT) barrels, were assembled and tested at Oxford University and later integrated at CERN with the TRT (Transition Radiation Tracker) barrel. The barrel SCT is composed of 4 layers of silicon strip modules with two sensor layers with 80 micro m channel width. The design of the modules and the barrels has been optimized for low radiation length while maintaining mechanical stability, bringing services to the detector, and ensuring a cold and dry environment. The high granularity, high detector efficiency and low noise occupancy (< 5*10^-4) of the SCT will enable ATLAS to have an efficient pattern recognition capability. Due to the binary nature of the SCT read-out, a stable read-out system and the calibration system is of critical importance. SctRodDaq is the online software framework for the calibration and also the physics running of the SCT and has been developed and tested during construction and commissioning of the detector with cosmics. It reliably measures the SCT performance parameters for each of the 6.3*10^6 channels in the SCT, identifies defects and problematic modules and writes them to an offline database for access from Athena, the ATLAS offline software framework. This dataflow chain has been exercised during the cosmics run at CERN, where a 5*10^5 cosmics sample for the combined SCT and TRT detectors was collected with a scintillator based trigger. It is now being commissioned in the ATLAS pit.

Angular distributions of jet pairs (dijets) produced in proton-proton collisions at a centre-of- mass energy √s = 7 TeV have been studied with the ATLAS detector at the Large Hadron Collider using the full 2011 data set with an integrated luminosity of 4.8 fb−1, and reaching dijet masses up to 4.5 TeV. All angular distributions are consistent with QCD predictions. Analysis of the dijet angular distribution, using a novel technique simultaneously employing the dijet mass, is employed. This analysis is sensitive to both resonant new physics and phenomena with a slow-onset in mass. Using this technique, new exclusion limits have been set at 95% credibility level for several hypotheses of physics beyond the standard model including: quantum gravity scales, with 6 extra dimensions, below 4.11 TeV, quark contact interactions below a compositeness scale of 7.6 TeV, and excited quarks with a mass below 2.75 TeV. In a large and complex scientific experiment, such as ATLAS, the collection, management and usability of coherent data and metadata is a challenging operation. The availability of these data to physicists within the experiment is essential to all analysis efforts. A new web-based interface called “RunBrowser”, which makes ATLAS and LHC operations data available to the ATLAS Collaboration, is introduced.

Une étude théorique et expérimentale sur la simple et double ionisation de petites molécules par impact électronique a été effectuée dans le présent travail. Des expériences de simple ionisation des trois orbitales de valence de l'ammoniac pour une énergie incidente de l'ordre de 600 eV ont été réalisées à Orsay (ISMO). Ces expériences, notées (e,2e), consistent à détecter les électrons diffusé et éjecté en coïncidence. Nous avons comparé les expériences correspondantes à des théories perturbatrices telles que la première approximation de Born : 1CW (One Coulomb Wave) et 1DW (One Distorted Wave). Ainsi que le modèle BBK (pour l'acronyme Brauner, Briggs and Klar). Nos résultats ont montré un accord raisonnable entre l'expérience et la théorie en ce qui concerne la distribution du lobe binaire. Par contre, le lobe de recul est largement sous-estimé. L'application du modèle BBK incluant la prise en compte des déphasages à courte portée est une intéressante perspective pour la description de l'ionisation simple de la molécule d'ammoniac. De même, nous avons étudié les processus d'ionisation du méthane par impact d'électrons. Pour la simple ionisation du méthane, nous avons fourni des approches théoriques pour décrire la distribution angulaire des sections efficaces doublement et triplement différentielle. Nos résultats ont été comparés aux expériences réalisées à Afyon en Turquie. Pour la double ionisation du méthane, nous avons réalisé des expériences (e,3-1e) (dans laquelle l'électron diffusé et un des éjectés sont détectés en coïncidence) pour la couche externe 1t2 à Orsay (ISMO). La théorie que nous avons appliquée est du premier ordre et ne peut pas décrire complétement les deux lobes. Par conséquent, le développement d'un modèle dans le cadre de la deuxième approximation de Born s'avère nécessaire. / A theoretical and experimental study on simple and double ionization of small molecules by electron impact is reported in the present work. Experiments of simple ionization of the three valence orbitals of ammonia with an incident energy of about 600 eV were performed in Orsay (ISMO). These experiments, named (e,2e), consist in the detection of the scattered and ejected electrons in coincidence. We compared the correspondent experiments to perturbative theories such as first Born approximation: 1CW (One Coulomb Wave) and 1DW (One Distorted Wave). In addition to the BBK model (for the acronym Brauner, Briggs and Klar). Our results show a reasonable agreement between the experiment and the theory concerning the distribution of the binary lobe. On the contrary, the recoil lobe was largely under-estimated. The application of the BBK model by taking into account the short range phases will be an interesting perspective for the description of simple ionization of ammonia molecule. In addition, we studied the ionization process of methane by electron impact. For the simple ionization of methane, we developed theoretical approaches in order to describe the angular distribution of double and triple differential cross sections. Our results were compared to experimental data performed in Afyon in Turkey. For the double ionization of methane, we performed experiments for the external shell 1t2 in Orsay (ISMO) by using the (e,3-1e), during which the scattered and one of the two ejected electrons are detected in coincidence. The theory which we applied is of first order and it could not describe completely the two lobes. Consequently, the development of a second order model sounds necessary.