Fundamental Interactions and Symmetries

TRIµP is a user facility at the AGOR cyclotron . Beams of radioactive nucleids can be  produced in inverse kinematics heavy ion reactions. Selected isotopes are stored  in atom and ion traps. The main objective is to investigate fundamental interactions in nature, in particular to search for new physics which is not yet provided in the standard model of particle physics. Applications of radioactive beams are included in the program, for which we encourage further proposals.

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In particle physics the standard model provides a theoretical framework which allows to describe all confirmed experimental observations to date very well. However, it does not provide physical explanations for a variety of experimental facts such as the origin of parity violation in weak interactions, the masses of fundamental fermions or the nature of CP violation or the dominance of matter and antimatter in the universe. In order to solve such questions a variety of speculative models have been invented. This includes supersymmertry, left-right symmetry, technicolor and many others.

There exist two principally different approaches in order to test predictions of such theories: Firstly, new particles and interactions can be directly searched for in high energy physics (collider) experiments. Secondly, there are precision experiments at lower energies, in which quantities are determined that can be calculated to sufficient accuracy using standard theory. In this case small deviations are searched for. This approach is complementary to high energy experiments and can probe physics at mass scales well above the energies reachable with any of today available and near future accelerators. Indications for deviations of standard theory from precise measurements have recently been suggested for the muon magnetic anomaly.

At KVI the research programme TRIµP started in the summer of 2001. The activities have been approved by the Stichting voor Fundamenteel Onderzoek der Materie (FOM) with projected progamme duration until 2013. They are jointly financed by FOM and the Rijksuniversiteit Groningen (RUG). A user facility has been set up which provides instrumentation for investigating fundamental interactions in physics with radioactive atoms and ions. A spectrum of radioactive isotopes has already been produced in inverse kinematics reactions using heavy ion beams from the AGOR cyclotron. The reaction products are separated from the primary beam in a magnetic double separartor device. The isotopes of interest are stopped in a hot tungsten foil stack. From these singly charged ions are extracted, the beam of which is radially confined by a radiofrequency quadrupole system. After neutralisation the atoms are cooled to below mK temperatures and stored in atom traps (magneto-optical trap) which are formed essentially by six laser beams, which pairwise counterpropagate in all three directions of space. Alternatively the ions can be stored in a radiofrequency (Paul) trap where a properly designed radiofrequency quadrupole field makes it possible to store them. 

Trapped atom and ion research covers a wide range of physics topics in atomic, nuclear and particle physics (see Figure 2). The KVI research group concentrates on nuclear β-decays and searches for a permanent electric dipole moment (edm) of atoms and of nuclei. The standard theory describes β-decay using vector and axial-vector operators (V-A) theory. Through precision measurements of the β-particle and neutrino angular correlation other type interactions could be found. For example, right-handed currents could give rise to such deviations from standard theory predictions. Systems of interest are ¹⁹Ne, ²¹Na and ²²Na, where ¹⁹Ne has the highest physics potential, but requires metastable atom trapping. The Na isotopes are well suited from the experimental point of view, particularly also in view of the trapping experience at KVI. Because the low neutrino reaction cross sections prohibit their direct observation in such experiments, the recoil nucleus is detected instead. The advantage of atom traps arises from the shallow meV trapping potential which is small compared to the typically a few 10 eV recoil energy. Violations of the time reversal (T) symmetry can be searched by investigating the decay of polarized nuclei.

 

A permanent electric dipole moment (edm) of a fundamental particle would violate both parity (P) and time reversal (T) invariance. The combined charge conjugation (C) and T symmetry would be violated, if the validity of the CPT theorem were assumed. The standard model predicts edms through higher order loops, which involve known CP violating processes, at a level of more than 4 orders of magnitude below the present experimental bounds. Therefore any observed edm would be a clear signal of physics beyond the standard model. This research derives strong motivation from the fact that the known sources of CP violation are by far insufficient to explain the evident dominance of matter over antimatter in the universe. The KVI approach will use Radium isotopes where atomic and nuclear enhancements of a fundamental particle edm have been predicted over the so far best atomic system, the mercury atom.

The exchange of a Z⁰ boson in atoms gives rise to parity violating effects. These can be studied , e.g., in single stored Ra⁺ ions. Heavy atoms have the advantage of large parity violating effects, because they are proportional to the third power of the nuclear charge. The effect can be used to extract the so called weak mixing angle θ_W, which has an potential to unreveal new physics.

Within TRIµP research in many other fields can be envisaged. The various parts of TRIµP offer possibilities for nuclear physics, nuclear astrophysics, plasma physics and atomic physics. Particularly areas, which are directed towards applications, may benefit. It should be possible to deposit cold polarised b-radioactive atoms on condensed matter surfaces. The method of b-NMR, which is well established in bulk matter research, could be employed to investigate surface magnetism, diffusion and catalysis processes. The atomic physics group at KVI has started the ALCATRAZ project within the framework of a FOM projectruimte, which has close relations to TRIµP. Here a system for rare isotope detection is being set up which uses light forces in two stages to separate ⁴¹Ca from a Ca atomic beam and to boost the fluorescence yield from the isotope by storing it in an atom trap. Possible direct applications for dating and in medical research (using shorter-lived Ca isotopes as tracers) are evident.

The TRIµP group is part of European projects (NIPNET, GASCATCHER, SPIRRAL II Preparatory Phase) which were founded to jointly address technical aspects related to ion and atom trapping. The team encourages external user groups already at this stage to formulate their special requirements for experiments where they can be most conveniently accommodated.

The TRIµP FOM programme was evaluated very positively by an international panel in December 2008 and by the FOM COMOP commission in February 2009.

 

> Press release FOM about TRIµP

> FOM Express

> University Journal (UK)