[en] A fully detailed simulation of the ATLAS experiment, in operation at the CERN Large Hadron Collider (LHC), has been implemented using the Geant4 toolkit. The simulation program, built within the ATLAS common framework (Athena) is being used for large-scale production of events on the LHC Computing Grid. Simulation software requires many components, from generators packages for simulation of particle collisions, to packages simulating the response of the various detectors and triggers. All of these components are steered by the ATLAS simulation infrastructure. The latest developments in this project addressed a better representation of the reality of the detector in all the possible details by providing increased functionality and robustness. The full simulation flow is constantly monitored and profiled. Performance improvements permit more effective use of the available resources without degradation in the quality and accuracy of the simulation. In this presentation, after a short introduction of the ATLAS detector itself, emphasis is put on validation efforts, performance tests, CPU and memory optimizations through the description of the entire process.

[en] The simulation program for the ATLAS experiment at CERN is currently in a full operational mode and integrated into the ATLAS common analysis framework, Athena. The OO approach, based on GEANT4, has been interfaced within Athena and to GEANT4 using the LCG dictionaries and Python scripting. The robustness of the application was proved during the test productions since 2004. The Python interface has added the flexibility, modularity and interactivity that the simulation tool requires in order to be able to provide a common implementation of different full ATLAS simulation setups, test beams and cosmic ray applications. Generation, simulation and digitization steps were exercised for performance and robustness tests. The comparison with real data has been possible in the context of the ATLAS Combined Test Beam (2004-2005) and cosmic ray studies (2006)

[en] It was drawn a possible scenario for the observation of massive long-lived charged particles at the LHC detector ATLAS. The required flexibility of the detector triggers and of the identification and reconstruction systems are discussed. As an example, it was focused on the measurement of the mass and lifetime of long-lived charged sleptons predicted in the framework of supersymmetric models with gauge-mediated supersymmetry (SUSY) breaking. In this case the next-to-lightest SUSY particle can be the light scalar partner of the tau lepton (τ₁), possibly decaying slowly into a gravitino. A wide region of the SUSY parameters space was explored. The accessible range and precision on the measurement of the SUSY breaking scale parameter of √ F achievable with a counting method are assessed

[en] Results are reported on a new measurement of the double diffractive reaction pp → (pπ⁺π^-) (pπ⁺π^-) at the ISR obtained with the Split Field Magnet detector. Experimental procedures and data analysis are discussed in detail. The cross section measured at the five standard ISR energies exhibits an increase of (55+-7%) in the s-range from 549 to 3892 GeV². (Auth.)

[en] The Italian National Centre of Hadrontherapy for Cancer Treatment (CNAO -Centro Nazionale di Adroterapia Oncologica) in Pavia, Italy, has started the treatment of selected cancers with the first patients in late 2011. In the coming months at CNAO plans are to activate a new dedicated treatment line for irradiation of uveal melanomas using the available active beam scan. The beam characteristics and the experimental setup should be tuned in order to reach the necessary precision required for such treatments. Collaboration between CNAO foundation, University of Pavia and INFN has started in 2011 to study the feasibility of these specialised treatments by implementing a MC simulation of the transport beam line and comparing the obtained simulation results with measurements at CNAO. The goal is to optimise an eye-dedicated transport beam line and to find the best conditions for ocular melanoma irradiations. This paper describes the Geant4 toolkit simulation of the CNAO setup as well as a modelised human eye with a tumour inside. The Geant4 application could be also used to test possible treatment planning systems. Simulation results illustrate the possibility to adapt the CNAO standard transport beam line by optimising the position of the isocentre and the addition of some passive elements to better shape the beam for this dedicated study.

[en] The charge-exchange reaction pp → (pπ⁺) (pπ^-) has been measured at √s = 23, 31, 45, 53, and 63 GeV at the ISR, using the Split Field Magnet detector. The data are characterized by a sharp forward peak of width 0.02 (GeV/c)², followed by a much gentler slope at higher mod(t); sizeable Δ⁺⁺, Δ⁰, and N⁰ production is observed in the (Nπ) mass spectra. Two different components are present in the data following power-law energy dependences of the type psup(-n)sub(lab) with n₁ = -1.63+-0.13 and n₂=-0.96+-0.07, respectively, indicating the onset of mechanisms in competition with pion exchange at ISR energies. (Auth.)

[en] Neutron-neutron interactions have been observed at the CERN ISR with deuteron colliding beams. The double-diffraction dissociation process nn→(pπ^-)(pπ^-) has been measured with the Split Field Magnet at √s=26 GeV detecting all final state particles, including the two spectator protons. Mass and t distributions are presented and compared with corresponding spectra observed in single neutron diffraction in the same energy range with supporting evidence for factorization. The cross-section of the process is 11.5+-2.8 μb and can be directly related to the corresponding value for double diffraction dissociation of protons in the same energy range. (Auth.)

[en] Results are presented of a systematic analysis of charge-exchange double dissociation in proton-proton collisions at the CERN Intersecting Storage Rings. The data, obtained with the Split-Field Magnet detector, cover the entire ISR energy range between √s = 23 GeV and √s = 63 GeV at five standard energies. Double resonance production is observed in the Δ⁺⁺Δ^- and Δ⁺⁺N⁰(1688) final states. The mass spectra of the pπ^- system show more pronounced resonant signals in the backward Jackson hemisphere. A detailed analysis of differential cross sections shows a forward peak typical of absorbed pion exchange decreasing as ssup(-1.81 +- 0.06), folowed by a much gentler exponential behaviour associated with a trajectory typical of rho-A₂ exchange. The high-energy transition to this regime is also indicated by a dramatic change in the s-dependence of total cross sections as compared with low-energy data. (Auth.)

[en] Results on exclusive double diffraction dissociation in (Nπ) and (Nππ) final states are reported for neutron-neutron interactions at √s=26.4 GeV and for proton-neutron interactions at √s=37.2 GeV. The data have been obtained at the CERN intersecting storage rings using split field magnet detector with proton-deuteron and deuteron-deuteron colliding beams. Factorization is shown to be verified to a very high degree in both mass- and t-differential cross-sections. The data confirm the previously observed rise in the proton-proton double diffractive cross-section as a function of c.m. energy. (Auth.)

[en] Final results from combined measurements of single and double diffraction of protons and neutrons into (Nπ) and (Nππ) final states are presented. The experiments were performed at the CERN Intersecting Storage Rings with Split Field Magnet detector using proton and deuteron colliding beams. The general properties of the dissociating vertex in single and double diffractive reactions are essentially identical. Mass spectra and decay angular distributions are compared with the predictions of a dual resonant Deck model. Decay angular correlations and a strong slope-mass correlation are observed also in double diffraction. Detailed tests of factorization indicate its validity over the full range of all kinematical variables and in their correlations. (orig./HSI)