ATLAS - AG Lacker
ATLAS is a multipurpose detector for elementary particles at the Large Hadron Collider (LHC) at CERN. Using highest-energy proton beams searches for New Physics beyond the standard model of elementary particle physics are performed. The ATLAS-collaboration consists of more than 2000 physicists from more than 35 different countries all over the world. The ATLAS-group located at Humboldt-University is especially involved in the following selection of topics: Search for heavy charged particles, search for a potentially existing fourth generation of quarks, measurements in the field of top-quark physics and implementing of the higher trigger level of the ATLAS detector.
A possible additional fourth generation of quarks and leptons has some theoretically attractive features and is not excluded by current experimental data. If these particles exist they can be discovered at the LHC. The data analysis concentrates on searches of fourth generation quarks and leptons.
Pixel Detector Upgrade
Simulation studies and alternative powering schemes: An envisaged luminosity upgrade of the LHC (SLHC) requires in various areas also upgrades of subdetectors. To make a design decision for the upgrade pixel detector simulation studies of the tracking performance for different pixel detector layouts are investigated. Alternative powering schemes (e.g. DC-DC coupling) have to be studied for the upgrade pixel detector.
Strip Tracker Upgrade
To increase the potential of the discovery of new physics and to allow for taking precision measurements of the “known” physics, it is planned to upgrade the LHC (which will be called HL-LHC – high luminosity LHC) by increasing its maximum luminosity up to 1035 cm-2s-1 and the beam energy up to 7 TeV aiming ultimately to collect data of ~3000 fb-1. After such a powerful upgrade of LHC, detectors to register products of proton-proton collisions in HL-LHC have necessarily to be upgraded as well. One of the areas of ATLAS considerable upgrade is a replacement of the SCT and TRT detectors by a new silicon strip detector, which will be suited to the harsh HL-LHC condition in terms of particle rates and radiation doses as well as to cope with the substantial increase in pile-up events as the higher luminosity.
Measurement of the Underlying Event
The Underlying Event (UE) is an irreducible background to all proton-collisions at the LHC due to the composite nature of proton. Typically the scales of UE processes are not high enough for perturbative methods to be successful. Hence, data-analyses are depdendent on phenomenological models to describe this effect. In order for these models to be succesful, its parameters need to be adjusted to data of dedicated UE measurements. We conduct such an analysis using events where Z-bosons are produced in the hard interaction, thus leading to a scenario where the hard sub-process is not colour-connected to all other activities, e.g. multiple parton scatterings. Further, the decay products of the Z-boson can easily be removed from an event. We measure the topological shape of the remaining event activity using specialised observables, called event-shapes.