Research Topics

The research performed in the IMPRS on precision tests of fundamental symmetries covers broad aspects in Particle Physics, Nuclear Physics, Atomic Physics and Astroparticle Physics, for instance:

Electroweak Symmetry Breaking and New Physics

Structure of IMPRS-PTFS Future Neutrino Experiments and their Physics Potential

Fundamental Physics with Penning Traps

Test of CPT-symmetry and Special Relativity

Low Background Experiments for Astroparticle Physics

Flavor in the LHC Era

Precision Cosmology

Phenomenological Consequences of Grand Unification

Development of Detector Technologies and Analysis Techniques


Electroweak Symmetry Breaking and New Physics

(Lindner, Plehn, Rodejohann)
The electro-weak symmetry breaking sector of the Standard Model (SM) is so far experimentally untested and it is only motivated by minimality. The scalar (Higgs) doublet of the SM is modified in extensions in various ways, offering unique insights into new physics. It is the main goal of the CERN Large Hadron Collider (LHC) to identify the mechanism behind electro-weak symmetry breaking, which involves a very broad theoretical and experimental research program. The many unexplained features of the SM imply that it is just the low energy limit of a broader and more general theory. From the many approaches to this theory (e.g. supersymmetry, extra dimensions etc.), there are several common features, such as novel particles at future colliders or Lepton Flavour Violation (LFV). Many of the ultraviolet completions of the SM include also a dark matter candidate. The LHC has therefore also an excellent potential to test the existence of weakly interacting dark matter and other new physics. Phenomenological studies require a solid understanding of signals and backgrounds at the LHC at a quantitative level, including QCD effects. Moreover the structure of the underlying models and how generic their predictions are must be understood. And last but not least the extraction of new physics parameters has to be statistically sound. Both UH and MPIK are involved in the experimental program at the LHC as well as in theoretical studies of predictions of theories beyond the SM. After final commissioning of the detectors with first collision data the groups will focus on analysis of LHC data with the aim to find signatures of new physics. This requires a good understanding of the detector performance and QCD as the dominant background. Thus, extensive Monte Carlo studies on the ATLAS jet- and trigger-performance are necessary. The KIP has a long-standing expertise in high-energy physics, in particular concerning triggering, calorimetry and precision electro-weak and QCD studies, providing thus a very good basis for the training of students to analyze LHC data. (back to top)

Future Neutrino Experiments and their Physics Potential

(Blaum, Lindner, Rodejohann)
Upcoming next generation neutrino experiments will with their precision measurements put the many models and mechanisms for neutrino mass generation and lepton flavour physics to the test. In addition, the minimal picture of three active neutrinos whose mixing with each other is described by a unitary matrix can be checked. Phenomenological studies for the prospects of future facilities to probe the neutrino parameters are therefore persued. This includes superbeam experiments, neutrino factories, beta-beams, but also non-standard novel ideas such as the use of Mößbauer neutrinos. A remarkable breakthrough in the relative kinematic precision of ion traps (values of 1 in 10^11 are within reach) happened in recent years. This implies for a beta decaying nucleon with a mass of order GeV that a sensitivity to (sterile) neutrino masses of order 10 keV can be achieved if energy and momentum of the electron and final nucleus can be measured with sufficient accuracy. This is important, since this is exactly the range in which neutrinos are dark matter candidates. The possibility to perform experiments along these lines will be pursued and models in which these particles are predicted will be constructed. A further promising direction for neutrino physics with ion traps are endpoint measurements for neutrino mass experiments with beta and double beta decay experiments, which would reduce their uncertainty. On the theory side the physics potential and the implications of upcoming experimental searches for observables related to neutrino mass, indirect searches, neutrino-less double beta decay and cosmology are studied. Models with flavour symmetries and mechanisms being able to explain the incoming data will be analyzed. (back to top)

Fundamental Physics with Penning Traps

(Blaum)
With the nowadays achievable accuracy in Penning trap experiments on short-lived exotic nuclides as well as stable atoms, precision fundamental tests can be performed. Among them are tests of fundamental properties of the Standard Model of particle physics, in particular with regard to the weak interaction, the CPT symmetry conservation, and the unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. In addition, Penning trap based experiments can provide important information for neutrino physics, for instance by precisely determining the end-point energy for neutrino mass measurements. (back to top)

Test of CPT-symmetry and Special Relativity

(Blaum, Hinton, Kellerbauer)
High-precision measurements of the mass and magnetic moment of the proton and the antiproton aim at testing the fundamental symmetry between matter and antimatter. This is the CPT-symmetry, where C stands for charge conjugation, P for parity inversion and T for time reversal. CPT symmetry is a property of Lorentz-invariant local quantum-field theories like the Standard Model. Theories beyond the Standard Model involve often novel concepts beyond local fields and there is thus a common expectation that CPT symmetry is violated at some level. However, there are no specific predictions in which systems and at what level CPT violation should be observed. The challenge for the experimental side is therefore to make optimal use of a few antimatter systems which can be handled for precision experiments and to test the symmetry between matter and antimatter at every increasing levels of precision. Lorentz invariance is the principle underlying all currently accepted theories describing the fundamental interactions of Nature -- the quantum field theories of the strong and electro-weak forces and general relativity. This is a strong motivation to test the theory of special relativity (SR) experimentally with ever-higher precision, as any deviation from its predictions would have profound consequences for our understanding of Nature. Recently, there has been much renewed interest, triggered by technological advances but also by theories attempting to unify the Standard Model of particle physics and gravity, such as string theory and loop-gravity, which predict the breakdown of Lorentz invariance. In storage rings, Einstein's theory of special relativity can be tested with unprecedented accuracy by state-selective excitation of relativistic (v/c~0.4) stored ions by counter-propagating laser beams permitting Doppler-free measurements. Another interesting topic is gravitational interaction of ultracold neutrons, which impose limits on fifth forces on the level 10^(30) alpha_s; gravitational tests with similar limits are done using a cold beam of 3He in a spin-echo setup for the measurement of atomic Casimir forces. A complementary test of fundamental symmetries can be performed by H.E.S.S., CTA or MAGIC, via gamma-ray travel time differences from objects at cosmological distances, thus checking Lorentz invariance. (back to top)

Experiments for Astroparticle Physics

(Hinton, Hofmann, Lindner, Marrodan)
The next goal in neutrino oscillation physics is to enter the precision, or three flavour era. The Double Chooz experiment, where MPIK is significantly involved, aims at pinning down the value of the final unknown lepton mixing angle, which would put flavour and/or GUT models to the test and open the possibility to discover genuine three flavour phenomena like leptonic CP violation and the neutrino mass ordering. Besides that other applications (e.g. proliferation control or search for new neutrino physics) will be performed. Expertise in low background physics is crucial here, but also in other low energy neutrino and dark matter experiments. Low background expertise is also important for the GERDA project, which looks for neutrino-less double beta decay and is therefore sensitive to lepton number violation, the neutrino mass scale and BSM physics. The Borexino experiment, which is measuring neutrino oscillations and the spectrum of solar neutrinos, depends also substantially on low background expertise. Furthermore, low background expertise is also required for new sensitivity levels in the search for Dark Matter particles. Studies to perform Dark Matter experiments with liquid noble gases as well as phenomenological studies on Dark Matter will also be performed. Indirect detection of Dark Matter via annihilation signatures will also be searched for. (back to top)

Flavor in the LHC Era

(Hansmann-Menzemer, Schmelling, Uwer)
Flavour physics has shown that there are approximate symmetries which forbid for example flavor-changing neutral currents. The upcoming LHCb experiment at the LHC will perform precision measurements of CP-violation and rare decays of B-mesons, i.e. heavy mesons containing a b-quark. These kind of mesurements, especially in the Bs-sector, are sensitive to effects from heavy virtual particles and thus allow to search for New Physics in a way which is complementary to the direct searches by the general purpose detectors ATLAS and CMS. The results may also shed some light on the origin of the matter-antimatter asymmetry of the Universe and the origin of the mass hierarchy of the known elementary particles. LHCb will also measure decay amplitudes described by penguin diagrams, i.e. processes which have a high sensitivity for physics from beyond the Standard Model. The obtained flavour information is very valuable, especially when combined with flavour information on leptons from neutrino experiments. The measurements at LHCb can also be compared with precision measurements of free neutron decay to test left-right symmetry or to test the unitarity of the quark-mixing CKM-matrix. (back to top)

Precision Cosmology

(Hebecker, Wetterich)
One of the most important questions of physics concerns the nature of dark energy, which may well involve a new ~quintessence~ field and dilatation symmetry. Interesting suggestions exist that higher dimensional dilatation symmetry forbids an effective four-dimensional cosmological constant. Time varying scalar fields may also lead to a time variation of fundamental couplings and an apparent violation of the weak equivalence principle, which will be investigated. The present density of dark energy almost equals the density of dark matter, although the two components have very different properties. This is the coincidence, or "why now", problem of many dark energy scenarios. The coincidence problem motivated the idea that dark energy and dark matter actually "know" each other through a direct interaction. In one such model dark energy couples to massive neutrinos, inducing a very specific growth of the neutrino mass. Several aspects will be studied, from the fundamental origin of dark energy to more concrete models explaining why dark energy becomes the dominant energy component only in the present cosmological epoch and to tests of models by comparison with observations. The predictions of the models will be compared to present data and new forecasts for future large-scale surveys will be produced. New observables, like the redshift drift, will also be investigated. (back to top)

Phenomenological Consequences of Grand Unification

(Hebecker)
The enlarged gauge symmetry of Grand Unification is one of the new fundamental symmetries of Nature with the strongest experimental support. It comes from (supersymmetric) precision gauge coupling unification, the matter content and charge quantization in the Standard Model, and the proximity of the right-handed neutrino mass scale to the scale of Grand Unification. It is important to derive further and more precise implications of this general framework. We use the improving understanding of supersymmetry breaking and of the embedding of unified models in string compactifications, as well as new field-theoretical ideas to make predictions relevant, e.g., to LHC as well as proton decay, neutrino and dark matter experiments. Specific subtopics of particular current interest are: (1) Overcoming the little hierarchy problem of the minimal supersymmetric Standard Model without sacrificing the success of high-scale Grand Unification. The possibility of Grand Unification in a strongly-coupled regime is beneficial for solutions employing extra scalar multiplets. (2) Understanding the implications of higher-dimensional or string theory realizations of Grand Unification for superpartner masses, neutrino mixing and proton decay. The new field of F-theory compactifications with fluxes is particularly promising. We have built up technical expertise in this field over the last years which we plan to apply to derive phenomenological predictions. (back to top)

Development of Detector Technologies and Analysis Techniques

(Brandt, Schöning, Schultz-Coulon)
New detector technologies are needed for the next generation of high-energy physics experiments. Better performance, faster trigger and readout capabilities and more radiation hard devices are the main requirements needed and are thus the focus of related detector R&D and research. The trigger upgrade of the ATLAS detector needed for very high luminosity running and research work for a high-performance hadron calorimeter for the International Linear Collider (ILC) are examples. The improvement of the ATLAS data selection capabilities based on data gathered during the first year of LHC running will form a major goal of the work. This work will be done in close cooperation with international project partners. A recurring problem in the analysis of experimental data is the separation of a signal from an often dominant background. In the past years multivariate analysis techniques have become increasingly important to address this issue, taking advantage of available computing power to find an optimal classification scheme directly in a high dimensional phase space. Compared to classical cut-based analysis, multivariate analysis techniques offer a significantly improved performance. Training in this field is aims at a solid understanding of multivariate techniques, with the goal to employ and control these methods at the same level as the classical methods. (back to top)
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