JRG Peter Fierlinger - Research

Measurement of the electric dipole moment of the neutron

We participate in an international collaboration to measure the EDM of the neutron using stored ultra-cold neutrons at PSI.

Measurement of the electric dipole moment of the 129-xenon

In Munich we are currently setting up a new experiment to measure the EDM of 129-Xe based on a new approach.

Development of a small LTC SQUID cryostat

We are currently developing a modular, small cold head to operate LTC SQUID sensors.

For thesis projects please contact us

Outline of our scientific program:

Our main research interests are searches for time-reversal symmetry (T) breaking effects at low energies. Assuming the conservation of CPT, violation of T also implies CP violation. Currently, such an effect has only been observed in the decay of The K and B meson and in accommodated for in the Standard Model of particle physics (SM) by a complex phase in the CKM matrix. However, this is by far too small to explain the observed Baryon asymmetry in the universe (BAU). As pointed out by Sakharov already in 1967, the explanation of this problem requires new sources of CP violation, baryon number non-conservation and processes out of thermal equilibrium. In addition, there is the unexplained question why the strong interaction does not violate CP, as it would naturally be expected by the CP violating product of the gluon operator and its dual within the QCD Lagrangian, weighted by the strongly restricted term theta. Well suited candidates to search for a further violation of such symmetries are electric dipole moments of fundamental systems. Our group focuses on the search for EDM in the neutron, which is a very prominent system due to its relatively simple composition and also in diamagnetic atoms. For this, we are currently setting up experiments at the Excellence-Cluster in Garching (Germany) and - within the ramework of an international collaboration - at the Paul Scherrer Institut (Switzerland). See also the Wikipedia entry for the neutron EDM . The neutron EDM experiment will be based on trapped ultra-cold neutrons (UCN) produced by a new source. As options for such a source we have the (i) UCN source at PSI, which is currently being constructed. It is based on a superthermal converter and will provide densities of 1000 UCN per cm3 in vacuum in the EDM experiment. Alternatively, (ii) we can use the UCN source currently being set up at the FRM-2 neutron source at the TU Munchen in Garching, Germany. As a measurement method we will use the commonly known method of separated oscillatory fields by Ramsey.

Ramseys method of separated oscillatory fields: starting with an ensemble of polarized ultra-cold neutrons, the polarization is flipped into a precession plane normal to the constant field B₀. During a long period of free precession, an additional electric field E is applied parallel or anti-parallel to B₀, causing a small phase in the angle after precession. As the spin is flipped back along B₀, the deviation is analyzed.

Stepwise improvements of magnetic field stability and measurement, as well as extensive investigations of systematic effects should provide in a first stage until around 2010 an improved limit on the EDM in the 10^-27 e.cm range. With the construction of a new apparatus based on the knowledge gained in ongoing tests, our approach should finally provide an improved sensitivity for an EDM of ~ 5.10^-28 e.cm until 2013. Our contributions to this collaboration are improvements of the magnetic field properties. This will be achieved by designing a active and passive stabilization and compensation of magnetic fields and gradients, mainly due to combining coils and Mu-metal magnetic shields. A main improvement in monitoring the fields will be achieved by combining various means of magnetometry and co-magnetometry inside and around the neutron storage cells. A schematic sketch is shown below:

	Figure: schematic view of the new n2EDM chamber. The neutrons are stored in a double-chamber arrangement to control on systematic effects. An array of Cs and SQUID magnetometers is placed around the chamber, two 3-He precession chambers are placed on top and bottom of the UCN chambers. Co-magnetometers are placed inside the chambers together with the neutrons.

At the Excellence-Cluster we are currently setting up an experiment to measure the EDM of 129-Xe, based on a novel measuring technique. The isotope 129Xe is diamagnetic and has one unpaired neutron in the nucleus. Due to the electron shell, the EDM is suppressed in first order by the Schiff moment, a re-arrangement of the shell to compensate for this effect and the expectation of the value from the SM is at a level of ~ 5.10-34 e.cm. The measurement will be based on a micro-fabricated structure with an array of liquid Xe droplets condensed onto it. The droplets are hyper-polarized and surrounded by HV electrodes. The precession of the spins of the polarized Xe can be monitored with superconducting pick-up coils and SQUID magnetometers. Our approach does not necessarily rely on Ramsey's Method of oscillatory fields, as in our case we use rotating electric fields, see figure:

	Figure: Left: precession of the polarization P with wL around B0 in the laboratory frame. Right: the electric field E rotates with a constant phase relative to P with wL. An EDM d causes a precession wE orthogonal to wL.

This approach opens new possibilities to investigate systematic effects in EDM experiments and should also be a well suited tool to investigate currently limiting systematic effects caused by magnetic field inhomogeneities, gradients and motional effects. With a statistical sensitivity of our experiment of < 10-29 e.cm we intend to control systematic effects on an unprecedented level and shift the current limits by more than three orders of magnitude. The experimental realization includes the development of a stable magnetic environment with Mu-metal shields and stable DC current sources, a SQUID cryostat and the micro-fabrication of a chip to condense liquid xenon. Our newly established lab at the FRM-2 site will house this setup in a thermally stabilized and magnetically controlled environment. We already acquired a multi-layer magnetic shield and built a highly stable current source, the cryogenic system is currently being set up. A laser-setup for hyper polarization is on the way.

	Concept of the EDM experiment: in the top view (a), three Xe droplets (filled circles) are surrounded by an array of electrodes. A rotating electric field is generated by pe- riodically adjusting voltages on the electrodes. The side view (b) shows a cut through the micro-structured glass plate with condensed Xe droplets. The glass plate is at the bottom of a tube connected to a gaseous Xe supply.

Within the framework of those two projects, we also investigate the feasibility of a novel co-magnetometer based on gaseous 129-Xe within the neutron EDM experiment to optimize HV behavior and to study systematic effects. Currently, we are also developing a minaturized cryostat to operate LTC-SQUID magnetometers. Several of these cryostat should be placed around the EDM chamber to provide vector information of the magnetic field and also read out the 3-He magnetometer cells placed on top and bottom of the UCN precession chambers. For more information please contact us