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Abstract:

The results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using 36.1 fb^-1 of integrated luminosity from proton–proton collisions at √s = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark t˜ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay t˜ → b χ˜±1 into a b-quark and the lightest chargino with χ˜±1 → Wχ˜01, the decay t˜ → t χ˜01 into an on-shell top quark and the lightest neutralino, the three-body decay t˜ → bW χ˜01 and the four-body decay t˜ → b`𝓁vχ˜01 . No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the t˜ and χ˜01 masses. The results exclude at 95% confidence level χ˜01 masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.

Abstract:

We describe the commissioning of a system which has been built to investigate optimal operation of CCDs for the LSST telescope. The test system is designed for low vibration, high stability operation and is capable of illuminating a detector in flat-field, projected spot, projected pattern and Fe-55 configurations. We compare and describe some considerations when choosing a gain calibration method for CCDs which exhibit the brighter-fatter effect. An optimisation study on a prototype device of gain and full well with varying back substrate bias and gate clock levels is presented.