Ruprecht Karls Universität Heidelberg
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Stellenangebote - Master Arbeiten

Master Arbeiten

Improving charged-particle tracking in ALICE with the Transition Radiation Detector Klaus Reygers,
The Large Hadron collider (LHC) provides collisions between lead ions at extreme-high energies, which allows for the creation of conditions similar to those just after the big bang in the laboratory environment. ALICE has been specifically designed to study the formation of a new phase of matter, the Quark-Gluon Plasma (QGP), which is expected at these high energy densities. Its particle identification (PID) capabilities down to momenta of 100 MeV/c makes it unique at the LHC to investigate the properties of QGP. Particle Identification is carried on following a precise tracking of the particles emerging from a Pb−Pb collision in the central barrel of ALICE, which is composed of several sub- detectors: Inner Tracking System (ITS), Time Projection Chamber (TPC), Transition Radiation Detector (TRD) and Time of Flight (TOF) detector. At the start of the first LHC run in 2009 the TRD participated with seven out of eighteen super-modules. Therefore it has not been used in the tracking. Installation of the remaining super-modules was completed in 2013-2014 and the TRD is now ready to be used for the tracking. According to the simulation results, the TRD is expected to improve significantly the overall momentum resolution and the tracking capabilities of the ALICE central barrel by providing additional space points. The aim of this project is to include TRD into the official track reconstruction framework and study its impact on the overall tracking, and thus the PID, performance of the ALICE detector.

Investigating models of pathlength-dependent jet energy loss in the quark-gluon plasmaJohanna Stachel,
In high-energy collisions of heavy nuclei, such as those that take place at the Large Hadron Collider (LHC), the temperature and density are so high that normal matter melts into its constituent particles and forms a state known as the quark-gluon plasma (QGP). Studying the properties of the QGP is the main focus of the heavy-ion program at the LHC and of the dedicated heavy-ion experiment, ALICE (A Large Ion Collider Experiment). A typical experimental technique for studying the internal structure of an unknown substance is to send in a probe, such as a laser or electron beam, and then to observe how that probe has been modified when it exits the medium. While the QGP produced in heavy-ion collisions is too small and too short-lived to be studied using these traditional methods, it can instead be probed by high- momentum quarks and gluons that are produced early in the collision. These quarks and gluons then traverse the QGP before fragmenting into collimated “jets” of hadrons, acting as internally-generated probes which can give insight into the interactions of a colored object moving through a strongly-interacting medium. Of particular interest is the mechanism by which jets lose energy to the QGP, and how that energy loss depends on the length of the jet’s path through the medium. Jets and their modifications due to in-medium interactions can be observed in measurements of two-particle correlations, multi-particle correlations, and fully-reconstructed jets. The goal of this project is to understand how jet mod- ification, and particularly its pathlength dependence, are manifested in various correlation observables. To accomplish this, the student will investigate these observables in several Monte Carlo models of jet-medium interactions, such as JEWEL and YaJEM-DE. This analysis will determine which observables are most sensitive to pathlength-dependent effects, thus clarifying the interpreta- tion of data from ALICE and other heavy-ion experiments, and also providing direction for future measurements in the field.

Development and implementation of a moving-baseline correction for the ALICE Common Readout UnitJohanna Stachel,
Our group is developing the online data pre-processing for the Time Projection Chamber of the ALICE experiment at CERN. The pre-processing, involving a charge cluster finder, is done on-the-fly during the readout of the newly developed GEM based readout chambers in the so-called Common Readout Unit. One feature of the design of these chambers is the so called common-mode effect, where a strong signal in one of the readout pads will induce the same signal with inverted polarity distributed over all other pads. This results effectively in a moving baseline which has to be corrected for during the pre-processing. We are looking for a motivated student with good programming skills to implement this baseline correction on an FPGA to improve the data quality of the main detector of the ALICE experiment.


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