Norwegian High Energy Particle Physics research with the ATLAS detector at the Large Hadron Collider.

The Large Hadron Collider LHC at the CERN laboratory in Geneva continues to probe deeper than ever before into matter, reproducing conditions in the first picoseconds in the life of the Universe by colliding beams of protons or lead nuclei. The first major LHC discovery, the Higgs boson, happened in 2012. The 2013 Nobel prize was awarded to Englert and Higgs with explicit mention of the ATLAS and CMS collaborations. The Higgs boson is observed to decay to gauge bosons and tau leptons pair. Properties such as mass (125 GeV), spin (0) and parity (+) have been established. This project period coincides with the end of the long shutdown 1 (LS1), from March 2013 to March 2015, and with the successful start of Run 2 at an unprecedented energy of 13 TeV. LS1 was devoted to detector consolidation, installation of the Insertable pixel B-layer (IBL), and to software and computing improvements and redesign. During this period we have been active within physics analysis and combined performance groups. Our publications cover searches for new physics and measurements of Standard Model processes. By the end of 2015 ATLAS has produced 470 publications in refereed journals; we have made direct contributions to about 15% of these, have acted as editorial board members or internal referees for some of them, and presented Run1 and Run 2 results at international conferences and workshops. We reconstructed and studied b-quark particles and searched for rare decays of B-mesons. These decays are sensitive to new physics at a higher energy scale and complement the direct searches at the LHC energy scale. We made important contributions to the search for the Higgs boson decaying to photon pairs, tau-lepton pairs and ZZ pairs, as well as to the combination of ATLAS and ATLAS+CMS Higgs results. We lead and performed searches at 7, 8 and 13 TeV for signs of new physics in final states with electrons, muons and taus and extended the previous limits on possible scenarios: - supersymmetric particles, such as the electroweak gauginos, including setting the limits on sleptons, first on a hadron collider. - supersymmetric Dark Matter production, re-analysing all ATLAS results. - new charged and neutral gauge bosons, which would mediate new interactions and thus facilitate unification of fundamental forces - extra space dimensions through the graviton, the hypothetical mediator of gravity, or microscopic black holes. In the 13 TeV searches for new interactions we have extended the Run 1 limits to higher particle masses. We contributed to the interpretation of the searches for new, heavy particles decaying into W and Z boson pairs and searched for the hypothetical charged Higgs boson. The experimental contributions are complemented by theoretical calculations and predictions, carried out in extensive collaboration with experimentalists in Norway and abroad. Areas of particular interest have been supersymmetry, properties of multi-Higgs models, and dark matter. ATLAS service work and qualification tasks proceed in connection with the expertise in computing, software and detector developments and operations. Our key contribution is to develop and deploy Grid middleware and software and to set up the WLCG distributed computing infrastructure necessary to exploit the large amount of data produced by LHC. The NorduGrid Advanced Resource Connector (ARC) is deployed by many large-scale distributed computing infrastructures, including the Nordic NeIC, the European Grid Infrastructure (EGI) and the WLCG. ARC has been used by the LHC experiments for more than 10 years and is a highly successful and adaptable distributed computing platform. This makes it ideally suited for use with HPC systems, which traditionally are in highly secure environments with no inbound connectivity, and with volunteer computing. We have made significant contributions to offline software, including the performance of the event reconstruction. We designed and implemented the derivation Framework used in Run 2 to produce the new data analysis format. In order to hold its promises the LHC will run at higher collision rates. ATLAS detector upgrades are necessary to increase the sensitivity to new physics. We contributed to the IBL, a new innermost pixel layer for the tracker installed in 2014 and operated in 2015 at 13 TeV. We developed pixel detectors together with SINTEF with the longer-term plan to contribute to the new all-silicon tracker. We continued leading the development of educational material and methods based on LHC data. The invariant mass technique allows high-school students to measure short-lived particles, search for and work with Higgs boson candidate events, and search for new physics, using real ATLAS data. The ATLAS measurement we developed is by far the most popular among all LHC measurements. Four PhD (2 defending by March 2016) and four master students finished in 2015.

The goal of High Energy Particle Physics is to discover and understand the basic constituents of matter and the interactions among them. The ATLAS experiment is designed to explore particle collisions in the Large Hadron Collider (LHC), which reproduce conditions in the first tens of picoseconds in the life of the universe. We are in a unique position to discover the Higgs boson and search for exotic new physics phenomena such as supersymmetric particles, and heavy resonance production that may shed l ight on electroweak symmetry-breaking, the origin of particle masses, the origins and composition of luminous and possibly dark matter, new symmetries, new interactions, extra space dimensions and the quantum nature of gravity. The Norwegian HEPP communi ty has made substantial contributions to all stages of the ATLAS experiment, from the early planning through the recent publication of first results, with major contributions to the Silicon part of the Inner tracking Detector (ID, Grid computing and distr ibuted analysis. During the first period of this proposal (2012-2015) we aim to: o analyse and publish physics results based on the 10-15 fb-1 of 8 TeV data to be collected by the end of 2012: - concentrate on searches of Higgs bosons decaying to pairs of photons or taus - perform model-independent searches for supersymmetric and other exotic particles in the multi-lepton final state. o prepare for higher luminosity and 14 TeV total energy from 2015 - construct, test and commission the insertable pi xel B-layer and deploy a full 3D active-edge pixel sensors in the forward tracker for phase 1 upgrade - adapt the computing infrastructure - improve the analysis and statistical tools and techniques - perform phenomenological studies to increase the sensi tivity of ATLAS to physics beyond the Standard Model and to understand any discoveries. In the second period (2016-2019) we will collect and analyze a few 100 fb-1 of data and contribute strongly to the ID R&D.