Data analysis

The focus of our research is to shed light on the question of what stabilizes the electroweak scale or more precisely the Higgs mass. A future more complete theory would allow to calculate the Higgs mass and in our current best understanding (known as standard model of particle physics) the Higgs mass would receive quantum loop corrections. The loops are in fact dominated by top quarks since these are the most heavy known elementary particles.

Figure 1: Loop corrections to the Higgs mass are dominated by top quark loops.

The loop corrections shift the Higgs mass effectively to the enormous Planck scale. However, the experimentally observed Higgs boson has a mass of about 125 GeV, much lower than the Planck mass either potentially indicating beyond the standard model effects to cancel these corrections or an incredible fine-tuning in that future theory.

We search for beyond the standard model effects by employing the top quark sector which is closely tied to the Higgs boson sector. An elegant way of avoiding the loop corrections in a future theory is by the exact cancellation of these loop corrections due to a partner of the top quark. Members of the group carry out direct searches for vector-like top quark partners up to highest achievable mass scales (see a Preliminary result here: CMS-B2G-16-002) and furthermore also search indirectly for any signs of deviations from the standard model via precision measurements in the top quark sector. An example being the analysis of top quark spin correlations via a differential cross section measurement.

Detector R&D

The LHC complex will undergo a series of upgrades (High Luminosity Phase of the LHC, HL-LHC) in order to increase the instantenous luminosity to unprecedented values at hadron colliders. The HL-LHC is expected to be ready for data taking in the 2020s with significant detector R&D already taking place now. The focus of the Jung group is on the instrumentation of the innermost region of the CMS tracking devices using silicon detectors. The Purdue Silicon Detector Lab is a state-of-the-art in-house facility for broad R&D aspects and assembly of silicon detectors for the HL-LHC.

Figure 2: Custom made sheets of individual layers of 60 micron thick carbon fiber plys, backbone of the support structures of silicon detectors.

Figure 2: Custom made sheets of individual layers of 60 micron thick carbon fiber plys employed as baseplates of the support structures of silicon detectors.

The precise track information is the basis for the identification of particle jets originating from b-quarks, which is one of the most efficient methods to enhance H→bb decays, top quark decays and a large amount of beyond the standard model signatures. A silicon detector provides the precise track reconstruction required to perform this identification. Non-active materials (support, cooling, electronics) in a silicon detector degrade the performance of the track reconstruction of charged particles going through the silicon detectors. Hence, the R&D focus is on light-weight materials and their use for support structures of silicon detectors. In particular carbon fiber is at the center of the ongoing R&D activities, since it is light-weight and mechanically very strong. The Jung group is collaborating with the Purdue Composite Manufacturing and Simulation Center to develop a carbon fiber based superstructure supporting the entire inner silicon pixel detector. The total length of the cylindric superstructure is about 5.4m, composed of 4 half-cylinders each with about 2.7m length.
Other examples being custom made carbon fiber sheets using an in-house facility, see Figure 2. These sheets are used to build mock-up silicon detector modules which are as close as possible to the real detector modules also using raw silicon. The mock-ups are employed to study and test the thermal performance under real conditions. The collected data is analyzed and compared to resuls of a finite element analysis of heat distribution. Figure 3 shows an example of a mock-up already equipped with temperature sensors.

Figure 2: Preparing for thermal measurements using realistic mock-ups of silicon detectors.

Figure 3: Preparing a silicon detector mock-up for thermal measurements using parts and pieces of real silicon detectors.

The Jung group is commissioning a cooling test stand employing liquid CO2 as coolant at the Purdue Silicon Detector Lab to facilitate local thermal tests of the mock-up modules build in house. Please take a look at the Open Positions/Contact page for Ph.D. and undergraduate research opportunities in the group. Undergraduate researchers are an integral and critical part of the research effort.

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