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The HIBEAM/NNBAR experiment is a free-neutron search for n → sterile n and n → n ¯ oscillations planned to be installed at the European Spallation Source under construction in Lund, Sweden. A key component in the experiment is the detector to identify n – n ¯ annihilation events, which will produce on average four pions with a final state invariant mass of two nucleons, around 1.9 GeV. The beamline and experiment are shielded from magnetic fields which would suppress n → n ¯ transitions, thus no momentum measurement will be possible. Additionally, calorimetry for particles with kinetic energies below 600 MeV is challenging, as traditional sampling calorimeters used in HEP would suffer from poor shower statistics. A design study is underway to use a novel approach of a hadronic range measurement in multiple plastic scintillator layers, followed by EM calorimetery with lead glass. A prototype calorimeter system is being built, and will eventually be installed at an ESS test beam line for in situ neutron background studies.

The production rates of prompt and non-prompt J/psi and psi(2S) mesons in their dimuon decay modes are measured using 2.1 and 11.4 fb(-1) of data collected with the ATLAS experiment at the Large Hadron Collider, in proton-proton collisions at root s = 7 and 8 respectively. Production cross-sections for prompt as well as non-prompt sources, ratios of psi(2S) to J/psi production, and the fractions of non-prompt production for J/psi and psi(2S) are measured as a function of meson transverse momentum and rapidity. The measurements are compared to theoretical predictions.

The differential cross section for the process $Z/\\gamma^*\\rightarrow ll$ ($l=e,\\mu$) as a function of dilepton invariant mass is measured in pp collisions at $\\sqrt{s}=$7 TeV at the LHC using the ATLAS detector. The measurement is performed in the $e$ and $\\mu$ channels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb$^{-1}$ collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb$^{-1}$ of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.

The HIBEAM/NNBAR experiment is a free-neutron search for \\(n \\rightarrow\\) sterile \\(n\\) and \\(n \\rightarrow \\bar{n}\\) oscillations planned to be installed at the European Spallation Source under construction in Lund, Sweden. A key component in the experiment is the detector to identify \\(n-\\bar{n}\\) annihilation events, which will produce on average four pions with a final state invariant mass of two nucleons, around \\(1.9\\,\\)GeV. The beamline and experiment are shielded from magnetic fields which would suppress \\(n \\rightarrow \\bar{n}\\) transitions, thus no momentum measurement will be possible. Additionally, calorimetry for particles with kinetic energies below \\(600\\,\\)MeV is challenging, as traditional sampling calorimeters used in HEP would suffer from poor shower statistics. A design study is underway to use a novel approach of a hadronic range measurement in multiple plastic scintillator layers, followed by EM calorimetery with lead glass. A prototype calorimeter system is being built, and will eventually be installed at an ESS test beam line for \\textit{in situ} neutron background studies.

In this paper we briefly discuss the estimation of uncertainties in QCD backgrounds to searches for Supersymmetry under development by the ATLAS collaboration.