Current Electric Dipole Moments Research Articles

Precision Storage Rings for Electric Dipole Moment Searches: A Tool En Route to Physics Beyond-the-Standard-Model

Electric Dipole Moments (EDM) of particles (leptons, nucleons, and light nuclei) are currently deemed one of the best indicators for new physics, i.e., phenomena which lie outside the Standard Model (SM) of elementary particle physics—so-called physics “Beyond-the-Standard-Model” (BSM). Since EDMs of the SM are vanishingly small, a finite permanent EDM would indicate charge-parity (CP) symmetry violation in addition to the well-known sources of the SM, and could explain the baryon asymmetry of the Universe, while an oscillating EDM would hint at a possible Dark Matter (DM) field comprising axions or axion-like particles (ALPs). A new approach exploiting polarized charged particles (proton, deuteron, 3He) in precision storage rings offers the prospect to push current experimental EDM upper limits significantly further, including the possibility of an EDM discovery. In this paper, we describe the scientific background and the steps towards the realization of a precision storage ring, which will make such measurements possible.

Left-right symmetry and electric dipole moments. A global analysis

We perform a global fit using results of searches for electric dipole moments (EDM) of diamagnetic systems within the context of the minimal left-right symmetric model. In this way, we disentangle the new “left-right” electroweak and θ¯ contributions that cannot be separated using a single EDM system. Although the fit is done for a specific model, the approach can be applied to any particle physics model. Finally, we revisit the constraint on the D coefficient in β-decay and find that current EDM bounds do not preclude observation of this T-violating effect in a possible next generation β-decay experiment.

Exploring Supersymmetric CP Violation after LHC Run\xa02 with Electric Dipole Moments and B Observables

We consider the prospects for measuring distinctive signatures of the CP-violating phases in the minimal supersymmetric extension of the Standard Model (MSSM) in light of the limits on sparticle masses from searches at the LHC. We use the CPsuperH code to evaluate model predictions and scan the parameter space using a geometric approach that maximizes CP-violating observables subject to the current upper limits on electric dipole moments (EDMs). We focus on the possible CP-violating asymmetry A_{mathrm{CP}} in b rightarrow s gamma decay and on a possible CP-violating contribution to the B_s - {overline{B}}_s mass difference Delta M^{NP}_{B_s}, as well as future measurements of the EDMs of the proton, neutron and electron. We find that the current LHC and EDM limits are consistent with values of A_{mathrm{CP}}, Delta M^{NP}_{B_s} and the proton EDM that are measurable with the Belle-II detector, LHCb and a proposed measurement of the proton EDM using a storage ring, respectively. Measurement of a non-zero proton EDM would constrain A_{mathrm{CP}} significantly, but it and a CP-violating contribution to Delta M^{NP}_{B_s} could still be measurable, along with neutron and electron EDMs. A more accurate measurement of A_{mathrm{CP}} with the current central value would favour stop and chargino masses within reach of future LHC runs as well as a potentially measurable value of Delta M^{NP}_{B_s}.

C P violation from \u03c4 , t and b dimension-6 Yukawa couplings \u2014 interplay of baryogenesis, EDM and Higgs physics

We explore the implications of the Standard Model effective field theory (SMEFT) with dimension-six terms involving the Higgs boson and third-generation fermion fields on the rate of Higgs boson production and decay into fermions, on the electric dipole moments (EDMs) of the electron, and on the baryon asymmetry of the Universe. We study the consequences of allowing these additional terms for each flavor separately and for combinations of two flavors. We find that a complex τ Yukawa coupling can account for the observed baryon asymmetry {Y}_B^{mathrm{obs}} within current LHC and EDM bounds. A complex b (t) Yukawa coupling can account for 4% (2%) of {Y}_B^{mathrm{obs}} , whereas a combination of the two can reach 12%. Combining τ with either t or b enlarges the viable parameter space owing to cancellations in the EDM and in either Higgs production times decay or the total Higgs width, respectively. Interestingly, in such a scenario there exists a region in parameter space where the SMEFT contributions to the electron EDM cancel and collider signal strengths are precisely SM-like, while producing sufficient baryon asymmetry. Measuring C P violation in Higgs decays to τ leptons is the smoking gun for this scenario.

T violation in radiative β decay and electric dipole moments

In radiative β decay, T violation can be studied through a spin-independent T-odd correlation. We consider contributions to this correlation by beyond the standard model (BSM) sources of T-violation, arising above the electroweak scale. At the same time such sources, parametrized by dimension-6 operators, can induce electric dipole moments (EDMs). As a consequence, the manifestations of the T-odd BSM physics in radiative β decay and EDMs are not independent. Here we exploit this connection to show that current EDM bounds already strongly constrain the spin-independent T-odd correlation in radiative β decay.

Electric dipole moment signatures of PeV-scale superpartners

A possible supersymmetric interpretation of the new Higgs-like 126 GeV resonance involves a high sfermion mass scale, from tens of TeV to a PeV or above. This scale provides sufficiently large loop corrections to the Higgs mass and can naturally resolve the constraints from flavor-violating observables, even with a generic flavor structure in the sfermion sector. We point out that such high scales could still generate CP-violating electric dipole moments (EDMs) at interesting levels due to the enhancement of left-right (LR) sfermion mixing. We illustrate this by saturating the light fermion mass corrections from the sfermion threshold, leaving the gaugino masses unconstrained. In this framework, we find that the current EDM bounds probe energy scales of 0.1 PeV or higher; this is competitive with the reach of $\epsilon_K$ and more sensitive than other hadronic and leptonic flavor observables. We also consider the sensitivity to higher dimensional supersymmetric operators in this scenario, including those that lead to proton decay.

Supersymmetric electroweak baryogenesis via resonant sfermion sources

We calculate the baryon asymmetry produced at the electroweak phase transition by quasi-degenerate third generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment (EDM) of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large $\tan\beta$, where third-generation down-type (s)fermions become relevant. We show that in the case of stop and sbottom sources, the viable parameter space is ruled out by constraints from the non-observation of the Mercury EDM. We introduce a new class of CP violating sources, quasi-degenerate staus, that escapes current EDM constraints while providing large enough net chiral currents to achieve successful "slepton-mediated" electroweak baryogenesis.

Electric Dipole Moments of Light Nuclei and the Implications for CP Violation

A definitive measurement of an electric dipole moment (EDM) would likely imply new physics beyond the standard model. Although the standard model strong interaction term could theoretically produce an EDM of any size, that it is constrained by the current neutron EDM limit to be some 10 orders of magnitude smaller than 1 suggests that the electroweak sector and CP violation will be the source of a measurable EDM. The weak interaction standard model EDM is itself orders of magnitude smaller than contemporary experiments can measure. Direct measurement of the neutron EDM lies in the next decade; measurement of the proton EDM could well come first. A BNL proposal for an electrostatic storage ring measurement lies in the offing. Unless the EDM proves to be an isoscalar, one will need other measurements to separate the isoscalar, isovector, and isotensor components. Measurement of a nuclear EDM will be required: 2H, 3H, or 3He being the simplest nuclear systems. A storage ring measurement of the triton EDM could be accomplished in a manner analogous to that proposed for the proton. However, the deuteron EDM measurement offers certain advantages, even though the experiment would be more complex, involving electric and magnetic fields, than that required for the proton and triton. The COSY facility in the Forschungszentrum Juelich is almost an ideal facility to house such an experiment; one could also measure in the same ring the EDM for the proton and He. The deuteron is the one nucleus for which exact model calculations can easily be performed. We briefly explore the model dependence of deuteron EDM calculations. Using a separable potential formulation of the Hamiltonian, we examine the sensitivity of the deuteron EDM to variations in the nucleon–nucleon interaction, including contemporary potential models, and we explore the dependence upon intermediate state multiple scattering in the 3P1 channel. We investigate the tensor force contribution to the model results and examine the effects of short-range repulsion that characterize realistic, contemporary potential models of the deuteron. Because one-pion exchange dominates the EDM calculation, separable potential model calculations appear to provide an adequate description of the deuteron EDM until such time as a measurement of better than 10 % is achieved.

Search for a permanent electric-dipole moment using atomic indium

We propose indium (In) as a possible candidate for observing the permanent electric dipole moment (EDM) arising from the violations of parity (P) and time-reversal (T) symmetries. This atom has been laser cooled and therefore the measurement of its EDM has the potential of improving on the current best EDM limit for a paramagnetic atom which comes from thallium. We report the results of our calculations of the EDM enhancement factor due to the electron EDM and the ratio of the atomic EDM to the electron-nucleus scalar-pseudoscalar (S-PS) interaction coupling constant in In in the framework of the relativistic coupled cluster theory. It might be possible to get new limits for the electron EDM and the S-PS CP violating coupling constant by combining the results of our calculations with the measured value of the EDM of In when it is available. These limits could have important implications for the standard model (SM) of particle physics.

A comprehensive analysis of electric dipole moment constraints on CP-violating phases in the MSSM

We analyze the constraints placed on individual, flavor diagonal CP-violating phases in the minimal supersymmetric extension of the Standard Model (MSSM) by current experimental bounds on the electric dipole moments (EDMs) of the neutron, Thallium, and Mercury atoms. We identify the four CP-violating phases that are individually highly constrained by current EDM bounds, and we explore how these phases and correlations among them are constrained by current EDM limits. We also analyze the prospective implications of the next generation of EDM experiments. We point out that all other CP-violating phases in the MSSM are not nearly as tightly constrained by limits on the size of EDMs. We emphasize that a rich set of phenomenological consequences is potentially associated with these generically large EDM-allowed phases, ranging from B physics, electroweak baryogenesis, and signals of CP-violation at the CERN Large Hadron Collider and at future linear colliders. Our numerical study takes into account the complete set of contributions from one- and two-loop EDMs of the electron and quarks, one- and two-loop Chromo-EDMs of quarks, the Weinberg 3-gluon operator, and dominant 4-fermion CP-odd operator contributions, including contributions which are both included and not included yet in the CPsuperH2.0 package. We also introduce an open-source numerical package, 2LEDM, which provides the complete set of two-loop electroweak diagrams contributing to the electric dipole moments of leptons and quarks.

Electric dipole moments of fundamental particles

Electric dipole moments (EDM) are at the fore-front of search for physics beyond the standard model. Thenext generation searches promise to improve by several orders of magnitude the current EDM sensitivity levels.

Grand unification scaleCPviolating phases and the electric dipole moment

The question of CP violating phases in supersymmetry and electric dipole moments (EDMs) is considered within the framework of supergravity grand unification (GUT) models with a light (\ensuremath{\lesssim}1 TeV) mass spectrum. In the minimal model, the nearness of the t-quark Landau pole automatically suppresses the t-quark cubic soft breaking phase at the electroweak scale. However, current EDM data require the quadratic soft breaking phase to be small at the electroweak scale unless $\mathrm{tan}\ensuremath{\beta}$ is small $(\mathrm{tan}\ensuremath{\beta}\ensuremath{\lesssim}3),$ and the EDM data combined with the requirement of electroweak symmetry breaking require this phase to be both large and highly fine-tuned at the GUT scale unless $\mathrm{tan}\ensuremath{\beta}$ is small. Nonminimal models are also examined and generally show the same behavior.