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.     

New insights into the neutron electric dipole moment

We analyze the CP-violating electric dipole form factor of the nucleon in the framework of covariant baryon chiral perturbation theory. We give a new upper bound on the vacuum angle, |θ₀|?2.5×¹⁰⁻¹⁰$|{\theta }_0|?2.5\times {10}^{-10}$. The quark mass dependence of the electric dipole moment is discussed and compared to lattice QCD data. We also perform the matching between its representations in the three- and two-flavor theories.     

On the question of determining molecular electric dipole moments from field-free frequency data

The effective masses in the Hamiltonian of a diatomic molecule with corrections for the breakdown of the Born-Oppenheimer approximation depend on the charge distribution in the molecule, and so the field-free energy levels are possible sources of information on the electric dipole moment of the molecule and other electromagnetic quantities. However, examination of explicit energy formulas and of a general indeterminacy in the effective Hamiltonian shows that this information is inseparable from effects due to the adiabatic correction to the potential. Electric dipole moments and other electromagnetic quantities obtained in this way are therefore not reliable.     

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.     

CP-violating dipole form factors of the top quark and tau lepton in scalar leptoquark models

We calculate the CP-violating electric and weak dipole form factors of the top quark and the tau lepton in models with scalar leptoquarks coupling only to the third generation of quarks and leptons. We obtain numerical values of the real and imaginary parts of these form factors at various energies for different values of leptoquark masses and couplings. The existing limits on the tau electric and weak dipole form factors allow us to put a limit on the masses and couplings of such leptoquarks and therefore on the top electric and weak dipole form factors. We also discuss constraints on the form factors coming from indirect limits on leptoquark masses and couplings deduced from LEP results on Z properties.     

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.     

Measurement of permanent electric dipole moments of charged hadrons in storage rings

Permanent Electric Dipole Moments (EDMs) of elementary particles violate two fundamental symmetries: time reversal invariance ( $\mathcal{T}$ ) and parity ( $\mathcal{P}$ ). Assuming the $\mathcal{CPT}$ theorem this implies $\mathcal{CP}$ violation. The $\mathcal{CP}$ violation of the Standard Model is orders of magnitude too small to be observed experimentally in EDMs in the foreseeable future. It is also way too small to explain the asymmetry in abundance of matter and anti-matter in our universe. Hence, other mechanisms of $\mathcal{CP}$ violation outside the realm of the Standard Model are searched for and could result in measurable EDMs. Up to now most of the EDM measurements were done with neutral particles. With new techniques it is now possible to perform dedicated EDM experiments with charged hadrons at storage rings where polarized particles are exposed to an electric field. If an EDM exists the spin vector will experience a torque resulting in change of the original spin direction which can be determined with the help of a polarimeter. Although the principle of the measurement is simple, the smallness of the expected effect makes this a challenging experiment requiring new developments in various experimental areas. Complementary efforts to measure EDMs of proton, deuteron and light nuclei are pursued at Brookhaven National Laboratory and at Forschungszentrum Jülich with an ultimate goal to reach a sensitivity of 10^???29 e·cm.     

Electric dipole moment of Dirac fermionic dark matter

The direct limit of electric dipole moment and direct searches for dark matter by electric dipole interaction are investigated with including the electromagnetic nuclear form factor, in case that the dark matter candidate is a Dirac particle. The electric dipole moment of dark matter constrained by direct searches must be lower than 7×¹⁰−22e cm for dark matter mass of 100 GeV to satisfy the current experimental exclusion limits at XENON10 and CDMS II. The CP violation of electric dipole moment and the dark matter discovery by electric dipole interaction in the future are considered.     

Electroweak baryogenesis

After a short general introduction to baryogenesis — the creation of a baryon asymmetry in our universe (BAU) — I will highlight some old and more recent models of electroweak baryogenesis: modifications of the Standard Model (SM), in particular supersymmetric ones as the MSSM, NMSSM, nMSSM, BMSSM, νμMSSM. I will also stress the role of electric dipole moments (EDMs) in limiting the CP violation needed for baryogenesis.     

Identifying multi‐excitons in quantum dots: the subtle connection between electric dipole moments and emission linewidths

The emission linewidths of excitonic complexes confined in quantum dots (QDs) mirror their interaction with a defect‐induced, fluctuating charge environment, a phenomenon known as spectral diffusion. Interestingly, extended excitonic complexes that comprise several interacting excitons exhibit significantly smaller emission linewidths if compared to the optical fingerprint of their building block, a sole exciton. Hence, it is not the absolute, but the relative electric dipole moment that governs the directly accessible emission linewidths. Exemplarily we investigate this matter based on differing exciton and biexciton emission linewidths of single GaN QDs with varying emission energies, i.e. QD dimensions. Our results establish the full width at half maximum (FWHM) or any other linewidths criterion for the identification of excitonic complexes, a technique that can directly be applied to polar but even non‐polar QD materials. Additionally, we find an emission energy dependent trend for the FWHM ratios of the biexciton and the exciton (XX_FWHM/X_FWHM) in perfect agreement with their relative dipole moment ratios as derived from our 8‐band‐ k · p based treatment of the Coulomb and exchange interaction within these multi‐particle complexes. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

The cyclotron gas stopper project at the NSCL

Permanent electric dipole moments (EDMs) violate parity and time-reversal symmetry. Within the Standard Model (SM), they require CP violation and are many orders of magnitude below present experimental sensitivity. Many extensions of the SM predict much larger EDMs, which are therefore an excellent probe for the existence of ‘new physics.’ So far only electrically neutral systems were used for sensitive searches of EDMs. Several techniques, based on storing fast particles in a magnetic storage ring, are being developed to probe charged particles for an EDM. With the introduction of these novel experimental methods, high sensitivity for charged systems, in particular light nuclei, is within reach. The author represents the Storage Ring EDM Collaboration.     

The effective chiral Lagrangian from dimension-six parity and time-reversal violation

We classify the parity- and time-reversal-violating operators involving quark and gluon fields that have effective dimension six: the quark electric dipole moment, the quark and gluon chromo-electric dipole moments, and four four-quark operators. We construct the effective chiral Lagrangian with hadronic and electromagnetic interactions that originate from them, which serves as the basis for calculations of low-energy observables. The form of the effective interactions depends on the chiral properties of these operators. We develop a power-counting scheme and calculate within this scheme, as an example, the parity- and time-reversal-violating pion–nucleon form factor. We also discuss the electric dipole moments of the nucleon and light nuclei.     

Electric dipole moments of acrylonitrile and of propionitrile measured in supersonic expansion

New determinations of the ground-state electric dipole moments of acrylonitrile and propionitrile have been made from Stark effect measurements at conditions of supersonic expansion. The measurements were made on selected Stark lobes of fully resolved hyperfine components of several lowest-J rotational transitions. The results are μ_a = 3.821(3) D, μ_b = 0.687(8) D, μ_tot = 3.882(3) D for acrylonitrile, and μ_a = 3.816(3) D, μ_b = 1.235(1) D, μ_tot = 4.011(3) D for propionitrile. The new value of μ_b for acrylonitrile is appreciably different from those reported previously and it has been substantiated by both ab initio calculations and relative intensity measurements. The new dipole moment implies a considerable revision in the calculated intensities of the strongest THz-region rotational transitions of acrylonitrile, to 59% of previous values.     

Determination of excited state electric dipole moment of the isomeric fluorophenylisocyanates from solvatochromic shift measurements

The excited state electric dipole moments of three isomeric fluorophenylisocyanates are determined using the method of solvatochromic shift measurements recently suggested from our laboratory.     

电偶极子的三种实用的基本模型

鉴于电极辐射的重要性，介绍了电偶极振子的三种实用的模型，并给出了有启发性的几道例题。     

Rotating dyonic dipole black rings: exact solutions and thermodynamics

New rotating dyonic dipole black ring solutions are derived in 5D Einstein-dilaton gravity with antisymmetric forms. The black rings are analyzed and their thermodynamics is discussed. New dyonic black string solutions are also presented.     

PbnSn(n=1-19)合金团簇电偶极矩和极化率的研究

利用基于密度泛函理论的有限电场方法对PbnSn(n=1-19)团簇的电偶极矩和极化率进行研究。PbnSn(n=1-19)合金团簇的高对称性抑制其电偶极矩的产生。在团簇原子总数N＜14时,团簇的电偶极矩与能隙表现出相反的变化趋势（同一尺寸下,高能隙与低电偶极矩相对应）,然而在14≤N≤19范围内,由于构型生长方式的转变,能隙与电偶极矩展现出相同的演化趋势。研究所得的极化率与实验值在部分尺寸相符合较好,但总体上与实验值还有一定的差别,这可能是实验中包含混合态或激发态的缘故。     

PbnSn(n=1-19)合金团簇电偶极矩和极化率的研究

利用基于密度泛函理论的有限电场方法对PbnSn(n=1-19)团簇的电偶极矩和极化率进行研究。PbnSn(n=1-19)合金团簇的高对称性抑制其电偶极矩的产生。在团簇原子总数N＜14时,团簇的电偶极矩与能隙表现出相反的变化趋势（同一尺寸下,高能隙与低电偶极矩相对应）,然而在14≤N≤19范围内,由于构型生长方式的转变,能隙与电偶极矩展现出相同的演化趋势。研究所得的极化率与实验值在部分尺寸相符合较好,但总体上与实验值还有一定的差别,这可能是实验中包含混合态或激发态的缘故。