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Theoretical Particle and Astroparticle Physics

The standard model of elementary particle physics has turned out to be very successful. It describes the behaviour of all known elementary particles: each 6 quarks (from which protons and neutrons are built) and leptons (among them electrons and massless neutrinos), in addition 4 gauge bosons (among them photons and gluons), and the experimentally not yet detected Higgs boson, as well as the corresponding antiparticles. The proof of neutrino masses provided the first solid evidence for “new physics” beyond the standard model. The theoretical work on this at MPIK ranges from basic models for neutrino masses and mixings via phenomenological studies to the development of the simulation software GLoBES for present and future oscillation experiments. Theoretical insufficiencies of the standard model are also suggesting extended theories that replace the hypothetical Higgs boson by alternative mechanisms.

An exemplary topic of theoretical particle and astroparticle physics is the asymmetry of matter and antimatter in the universe (the universe consists of matter and not of antimatter). This in fact cannot be explained by the standard model of particle physics. Sseveral mechanisms are being discussed for it, e.g., leptogenesis. The as yet mostly unknown nature of dark matter and dark energy (of which about 95% of the universe is composed) and their cosmological implications (e.g. directly after the big bang) is a further subject. Overall, results from neutrino physics, astroparticle physics, and experiments at accelerators are combined and used to search for direct and indirect hints on a "new physics" beyond the standard model of particle physics. The overall aim is a more deep understanding of the fundamental laws of nature.

Division Lindner

Theoretical Elementary-Particle Physics beyond the Standard Model (pdf)

Theoretical Astropartilce Physics and Cosmology (pdf)

Heavy Flavour Physics

The new Large Hadron Collider (LHC) of CERN in Geneva will help to answer the question for the origin of mass and the limits of the standard model of particle physics. The large-scale experiments ATLAS and CMS primarily search for the Higgs boson or new supersymmetric particles. The rare decays of heavy quarks are investigated with the LHCb experiment in order to gain information about the cause for the asymmetry of matter and antimatter in the universe. A group at MPIK has been involved in developing this detector and now focuses on the analysis of the experimental data.

Division Hofmann LHCb

The LHCb Experiment: B-Physics, Antimatter and Dark Matter (pdf)

Experimental Neutrino Physics

Presently, scientists at the MPIK are involved in four international large-scale experiments investigating different aspects of neutrino physics. The laboratory work at the institute concentrates on high-purity materials and the detection of weakest (interfering) signals, as well as on photomultipliers for registration of the scintillation light through which neutrinos are detected. As neutrinos penetrate matter almost unopposed and interact with it very rarely, large and sensitive detectors are required in order to detect them.

The Borexino experiment in the Gran Sasso underground laboratory in Italy for the measurement of low-energy neutrinos started taking data in May 2007 after a long period of construction work. After only two months of measurements, the Borexino collaboration for the first time succeeded to unambiguously identify in real time neutrinos which are released in the electron capture of ⁷Be in the core of the Sun and thereby to verify independently neutrino oscillations.

From 2009, the neutrino-oscillation experiment Double Chooz, currently under construction, will use antineutrinos from a nuclear power plant in France to investigate in detail the periodic changeover between the three neutrino types electron, muon, and tauon neutrino ("neutrino oscillations"). In the Gran Sasso underground laboratory, the GERDA experiment for the search of the neutrinoless double-beta decay in germanium crystals is under construction. If neutrinoless double beta decay is found, it would mean that neutrinos are so-called Majorana particles, i.e., they are their own antiparticles. The neutrino observatory IceCube is already operational while under construction at the South Pole using 1 km³ ice at depths between 1450 and 2450 m in its final state, into which strings of photomultiplier tubes are inserted to detect neutrinos from high-energy cosmic sources.

Division Lindner Division Hofmann IceCube Borexino GERDA Double Chooz

Double Chooz: Search for the Third Mixing Angle of the Neutrinos (pdf)

Borexino: Spectroscopy of Solar Neutrinos (pdf)

GERDA: Are Neutrinos and Antineutrinos Identical? (pdf)

IceCube: High-Energy Astronomy with Neutrinos (pdf)

High-Energy Gamma Astronomy

The research in high-energy gamma astronomy at MPIK is focused on the observation of very-high-energy gamma radiation from the universe using the H.E.S.S. telescope system in Namibia. The very-high-energy gamma rays, a trillion times more energetic than ordinary starlight, are produced when charged particles are extremely accelerated, e.g. in a supernova explosion or in the vicinity of a black hole, and then interact with radiation fields or the surrounding medium. In contrast to the charged particles, gamma rays travel on straight lines through space, allowing us to image the sky in gamma light and to identify the sources. When entering the earth's atmosphere, the gamma quanta collide with molecules forming cascades of electrically charged secondary particles, so-called particle showers. These emit weak bluish and extremely short flashlight (Cherenkov light) which can be observed on the ground in dark moonless nights with large reflector telescopes and fast photodetectors. To trace the exact direction the particle showers come from, they are observed stereoscopically by several telescopes simultaneously. The H.E.S.S. telescopes have already detected numerous, partly novel types of gamma sources and took the first spatially and temporally resolved pictures of these objects. Most of these objects are located along the galactic equator in the central part of the Milky Way. Some, nowever, are distant active galaxies observed for the first time by the H.E.S.S. telescopes.

Division Hofmann H.E.S.S.

H.E.S.S.: Cosmic Accelerators in the Light of Gamma Rays (pdf)

Theoretical Astrophysics and Infrared Astrophysics

The work on theoretical astrophysics is closely correlated to the experimental investigations with H.E.S.S.. At the heart of this work is the quest to identify and to quantitatively understand the so-called nonthermal processes, through which large fractions of the overall energy in the interstellar and intergalactic medium come to be carried by a small minority of relativistic particles. This energetic particle- and gamma radiation is produced under extreme conditions impossible to reproduce in accelerator facilities on earth. Known sources of cosmic radiation are exploding stars, rotating neutron stars and black holes, as well as interstellar and intergalactic shock waves.

The research at MPIK addresses the acceleration and radiative processes in extreme astrophysical environments, the propagation of the nonthermal radiation in space, and its interaction with matter and magnetic or radiation fields. Another topic is the effect of the considerable energy densities of cosmic radiation on the evolution of structures in the universe, in particular shock waves.

Observation of the interstellar and intergalactic dust in the far infrared light by satellite instruments aboard ISO (Infrared Space Observatory, ESA) and its successor Spitzer Space Observatory (NASA) are being evaluated using theoretical models, e.g. of the dust distribution in galaxies. This is done with respect to the formation and development of gas-rich galaxies and the star-formation rates in dependence on the dust distribution.

Division Hofmann High-Energy Astrophysics (Theory) Theoretical Astrophysics Infrared Astrophysics

Cosmic Dust

With instruments on board spacecraft, in-situ measurements of the interplanetary and interstellar dust present in the Solar system are performed. The dust detectors, which were developed at MPIK, are tested and calibrated with the dust accelerator. The sensors determine the velocity, size, and chemical composition of micrometeoroids impacting at velocities between 5000 and 1 million km/h. The sensitivity of the detectors is higher by a factor of 1000 compared to optical instruments due to the analysis of single dust grains. The most important current mission is Cassini/Huygens (NASA/ESA) in the Saturnian system where spectacular discoveries succeeded. For example, there is the detection of ice volcanism on the moon Enceladus, which ejects ice particles with enclosed silicates, organic compounds or salts and thus feeds the big outer dust ring of Saturn. A dust detector aboard the spacecraft Ulysses orbiting around the Sun on an ellipse almost perpendicular to the planetary plane, investigated until mid 2008 the interstellar dust entering the Solar system.

Dust Group

Cosmic Dust (pdf)