Search for electric dipole moments at storage rings

Twenty years ago, we published a paper entitled “Discovery of antiproton trapping by long-lived metastable states in liquid helium”. In retrospect, this was the discovery of antiprotonic helium atoms, the study of which is actively being done at CERN’s antiproton decelerator. A brief overview of this interesting exotic atom is given, together with some historical background.     

Nuclear electric dipole moments at ion storage rings

Upper limits on the electric dipole moments (EDM) of elementary particles and atoms are presented, and their physical implications are discussed. The implications following from the neutron and atomic experiments are of comparable interest. The nuclear EDMs can be studied at ion storage rings, with the expected sensitivity much better than . This would represent a serious progress in studies of the CP-violation problem. This revised version was published online in August 2006 with corrections to the Cover Date.     

New method of measuring electric dipole moments in storage rings

A new highly sensitive method of looking for electric dipole moments of charged particles in storage rings is described. The major systematic errors inherent in the method are addressed and ways to minimize them are suggested. It seems possible to measure the muon EDM to levels that test speculative theories beyond the standard model.     

Search for electric dipole moments of light ions in storage rings

The Standard Model (SM) of Particle Physics is not capable to account for the apparent matterantimatter asymmetry of our Universe. Physics beyond the SM is required and is searched for by (i) employing highest energies (e.g., at LHC), and (ii) striving for ultimate precision and sensitivity (e.g., in the search for electric dipole moments (EDMs)). Permanent EDMs of particles violate both time reversal (T) and parity (P) invariance, and are via the CPT-theorem also CP-violating. Finding an EDM would be a strong indication for physics beyond the SM, and pushing upper limits further provides crucial tests for any corresponding theoretical model, e.g., SUSY. Direct searches of proton and deuteron EDMs bear the potential to reach sensitivities beyond 10^?29 e cm. For an all-electric proton storage ring, this goal is pursued by the US-based srEDM collaboration [2], while the newly found Julich-based JEDI collaboration [1] is pursuing an approach using a combined electric-magnetic lattice which shall provide access to the EDMs of protons, deuterons, and ³He ions in the same machine. In addition, JEDI has recently proposed to perform a direct measurement of the proton and/or deuteron EDM at COSY using resonant techniques involving Wien filters.     

Electric dipole moments of charged particles

The existence of an electric dipole moment (edm) on a fundamental atomic particle would imply violation of both parity and time-reversal invariance. An edm on a neutral particle is detectable through its interaction with an applied electric field. The search for edms on charged particles such as the nucleus or the electron is made difficult by their acceleration in an electric field; conversely, a charged particle in equilibrium must be shielded from the field and the edm interaction will then vanish. A number of ingenious ways around this shielding theorem are discussed, as are the use of polar molecules to amplify the residual edm interactions. A range of atomic and molecular beam and optical pumping experiments are described and the results tabulated. The implications for particle theories beyond the standard model are briefly summarized.     

CP-violation and electric dipole moments

Searches for intrinsic electric dipole moments of nucleons, atoms and molecules are precision flavour-diagonal probes of new -odd physics. We review and summarise the effective field theory analysis of the observable EDMs in terms of a general set of CP-odd operators at 1 GeV, and the ensuing model-independent constraints on new physics. We also discuss the implications for supersymmetric models, in light of the mass limits emerging from the LHC.     

Additional stringy sources for electric dipole moments

We show that string models with low energy supersymmetry which accommodate the fermion mass hierarchy generally give nonuniversal soft trilinear couplings (A terms). In conjunction with the apparently large Cabibbo-Kobayashi-Maskawa (CKM) phase, this results in large fermion electric dipole moments (EDMs) even in the absence of CP violating phases in the supersymmetry breaking auxiliary fields and the micro term. Nonobservation of the EDMs therefore implies that strings select special flavor and/or supersymmetry breaking patterns.     

Measurement of the tensor electric polarizability of a deuteron in storage rings

When an electric field of resonant frequency acts on a deuteron beam in a storage ring, the tensor electric polarizability stimulates buildup of the vertical polarization of the beam (the Baryshevsky effect). This effect allows high-precision measurement of the tensor electric polarizability of the deuteron, which contains important information about spin-dependent nuclear forces. The general formulas describing the Baryshevsky effect are derived. It is shown that doubling of the resonant frequency leads to dramatic enhancement of the effect.     

Measurement of tau branching ratios to five charged hadrons

The branching ratios of the decay of the lepton to five charged hadrons have been measured with the OPAL detector at LEP using data collected between 1991 and 1995 at centre-of-mass energies close to the resonance. The branching ratios are measured to be where the first error is statistical and the second systematic. Received: 4 June 1998 / Published online: 11 March 1999     

Quadrupole moments of hadrons

We study an Abelian Higgs model in three, four and five dimensions using the mean field perturbation expansion with covariant gauge fixing. In four and five dimensions the mean field analysis shows three phases; a confined phase, a Coulomb phase with massless spin waves, and a Higgs phase in which the spin waves aquire a mass. The Higgs and confined phases are shown to be connected. In three dimensions we find a single phase.     

The relative electric dipole moments of singlets and triplets

A sensitivity analysis formalism is constructed for collinear reactive systems with multiple electronic potential energy surfaces. The work extends the sphere of application of sensitivity theory into the reactive domain. Expressions are obtained for the first order elementary sensitivity coefficients (i.e. partial derivatives) of both the reactive and non-reactive component elements of the scattering matrix with respect to an arbitrary system parameter. In the case of the non-reactive elements, the sensitivity coefficients involve essentially the piecewise integration of a function matrix containing the available solution of the scattering problem. The reactive sensitivity coefficients draw on both forward and backward propagated solutions. The paper concludes with a discussion of the scope and applicability of reactive sensitivity analysis.     

Bino-driven electroweak baryogenesis with highly suppressed electric dipole moments

It is conventional wisdom that successful electroweak baryogenesis in the Minimal Supersymmetric extension of the Standard Model (MSSM) is in tension with the non-observation of electric dipole moments (EDMs), since the level of CP-violation responsible for electroweak baryogenesis is believed to generate unavoidably large EDMs. We show that CP-violation in the bino–Higgsino sector of the MSSM can account for successful electroweak baryogenesis without inducing large EDMs. This observation weakens the correlation between electroweak baryogenesis and EDMs, and makes the bino-driven electroweak baryogenesis scenario the least constrained by EDM limits. Taking this observation together with the requirement of a strongly first-order electroweak phase transition, we argue that a bino-driven scenario with a light stop is the most phenomenologically viable MSSM electroweak baryogenesis scenario.     

Relation between electric quadrupole and magnetic dipole nuclear moments

The values of electric quadrupole moments are described by gyromagnetic ratios of bound and free nucleons. A comparison with the experimental data shows an agreement within 15% for non-magic strongly deformed nuclei and within 50% for other ones. The expressions obtained are sensitive to a change in the order of subshell filling which takes place for proton and neutron subshells near Fermi surface.     

Higgs-boson two-loop contributions to electric dipole moments in the MSSM

The complete set of Higgs-boson two-loop contributions to electric dipole moments of the electron and neutron is calculated in the minimal supersymmetric standard model. The electric dipole moments are induced by CP-violating trilinear couplings of the `CP-odd' and charged Higgs bosons to the scalar top and bottom quarks. Numerical estimates of the individual two-loop contributions to electric dipole moments are given.