Neutron Electric Dipole Moment Research Articles

Linear programming analysis of the R-parity violation within EDM-constraints

The constraint on the $R$-parity violating supersymmetric interactions is discussed in the light of current experimental data of the electric dipole moment of neutron, $^{129}$Xe , $^{205}$Tl, and $^{199}$Hg atoms, and YbF and ThO molecules. To investigate the constraints without relying upon the assumption of the dominance of a particular combination of couplings over all the rest, an extensive use is made of the linear programming method in the scan of the parameter space. We give maximally possible values for the EDMs of the proton, deuteron, $^3$He nucleus, $^{211}$Rn, $^{225}$Ra, $^{210}$Fr, and the $R$-correlation of the neutron beta decay within the constraints from the current experimental data of the EDMs of neutron, $^{129}$Xe, $^{205}$Tl, and $^{199}$Hg atoms, and YbF and ThO molecules using the linear programming method. It is found that the $R$-correlation of the neutron beta decay and hadronic EDMs are very useful observables to constrain definite regions of the parameter space of the $R$-parity violating supersymmetry.

StrongPinvariance, neutron electric dipole moment, and minimal left-right parity at LHC

In the minimal left-right model the choice of left-right symmetry is twofold: either generalized parity $\mathcal{P}$ or charge conjugation $\mathcal{C}$. In the minimal model with spontaneously broken strict $\mathcal{P}$, a large tree-level contribution to strong $CP$ violation can be computed in terms of the spontaneous phase $\ensuremath{\alpha}$. Searches for the neutron electric dipole moments then constrain the size of $\ensuremath{\alpha}$. Following the latest update on indirect $CP$ violation in the kaon sector, a bound on ${W}_{R}$ mass at 20 TeV is set. Possible ways out of this bound require a further hypothesis, either a relaxation mechanism or explicit breaking of $\mathcal{P}$. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is recomputed and provides an estimate of the weak contribution. Combining this constraint with other $CP$-violating observables in the kaon sector allows for ${M}_{{W}_{R}}\ensuremath{\gtrsim}3\text{ }\text{ }\mathrm{TeV}$. On the other hand, $\mathcal{C}$ symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.

Sensitivity requirements for accessing interior magnetic field vector components in neutron electric dipole moment experiments via exterior boundary-value measurements

We study the sensitivity requirements for determining the vector components of the magnetic field in the interior regions of electric dipole moment experiments via exterior boundary-value measurements. The basic concept for our method is as follows. If a closed three-dimensional boundary surface surrounding the fiducial volume of an experiment can be defined such that its interior encloses no currents or sources of magnetization, each of the interior vector field components and the magnetic scalar potential will satisfy a Laplace equation. Therefore, if either the vector field components or the normal derivative of the scalar potential can be measured on the surface of this boundary, thus defining a Dirichlet or Neumann boundary-value problem, respectively, the interior vector field components or the scalar potential (and, thus, the field components via the gradient of the potential) can be uniquely determined via solution of the Laplace equation. We discuss the applicability of this technique to the determination of the interior magnetic field components during the operating phase of neutron electric dipole moment experiments when it is not, in general, feasible to perform direct in situ measurements of the interior field components. We then study the specifications that a vector field probe must satisfy in order to determine the interior vector field components to a certain precision.

Baryogenesis from strong CP violation and the QCD axion.

We show that strong CP violation from the QCD axion can be responsible for the matter antimatter asymmetry of the Universe in the context of cold electroweak baryogenesis if the electroweak phase transition is delayed below the GeV scale. This can occur naturally if the Higgs couples to a O(100) GeV dilaton, as expected in some models where the Higgs is a pseudo-Nambu-Goldstone boson of a new strongly interacting sector at the TeV scale. The existence of such a second scalar resonance with a mass and properties similar to the Higgs boson will soon be tested at the LHC. In this context, the QCD axion would not only solve the strong CP problem, but also the matter antimatter asymmetry and dark matter.

SUSY FLAVOR v2.5: A computational tool for FCNC and CP-violating processes in the MSSM

SUSY FLAVOR v2.5: A computational tool for FCNC and CP-violating processes in the MSSM

Dynamic stabilization of the magnetic field surrounding the neutron electric dipole moment spectrometer at the Paul Scherrer Institute

The Surrounding Field Compensation (SFC) system described in this work is installed around the four-layer Mu-metal magnetic shield of the neutron electric dipole moment spectrometer located at the Paul Scherrer Institute. The SFC system reduces the DC component of the external magnetic field by a factor of about 20. Within a control volume of approximately 2.5 m × 2.5 m × 3 m, disturbances of the magnetic field are attenuated by factors of 5–50 at a bandwidth from 10−3 Hz up to 0.5 Hz, which corresponds to integration times longer than several hundreds of seconds and represent the important timescale for the neutron electric dipole moment measurement. These shielding factors apply to random environmental noise from arbitrary sources. This is achieved via a proportional-integral feedback stabilization system that includes a regularized pseudoinverse matrix of proportionality factors which correlates magnetic field changes at all sensor positions to current changes in the SFC coils.

Constraining axion dark matter with Big Bang Nucleosynthesis

We show that Big Bang Nucleosynthesis (BBN) significantly constrains axion-like dark matter. The axion acts like an oscillating QCD θ angle that redshifts in the early Universe, increasing the neutron–proton mass difference at neutron freeze-out. An axion-like particle that couples too strongly to QCD results in the underproduction of He4 during BBN and is thus excluded. The BBN bound overlaps with much of the parameter space that would be covered by proposed searches for a time-varying neutron EDM. The QCD axion does not couple strongly enough to affect BBN.

Fermion EDMs with minimal flavor violation

We study the electric dipole moments (EDMs) of fermions in the standard model supplemented with right-handed neutrinos and its extension including neutrino seesaw mechanism under the framework of minimal flavor violation (MFV). In the quark sector, we find that the current experimental bound on the neutron EDM does not yield a significant restriction on the scale of MFV. In addition, we consider how MFV may affect the contribution of the strong theta-term to the neutron EDM. For the leptons, the existing EDM data also do not lead to strict limits if neutrinos are Dirac particles. On the other hand, if neutrinos are Majorana in nature, we find that the constraints become substantially stronger. Moreover, the results of the latest search for the electron EDM by the ACME Collaboration are sensitive to the MFV scale of order a few hundred GeV or higher. We also look at constraints from $CP$-violating electron-nucleon interactions that have been probed in atomic and molecular EDM searches.

Development of a simulation for measuring neutron electric dipole moment

The neutron electric dipole moment (nEDM) is sensitive to new physics beyond the standard model and could prove to be a new source of CP violation. Several experiments are being planned worldwide for its high-precision measurement. The nEDM is measured as the ultracold neutron (UCN) spin precession in a storage bottle under homogeneous electric and magnetic fields. In nEDM measurement, the systematic uncertainties are due to the motion of the UCNs, the geometry of the measurement system, and inhomogeneous electric and magnetic fields. Therefore, it is essential to quantitatively understand these effects in order to reduce them. Geant4UCN is an ideal simulation framework because it can compute the UCN trajectory, evaluate the time evolution of the spin precession due to arbitrary electric and magnetic fields, and define the storage geometry flexibly. We checked how accurately Geant4UCN can calculate the spin precession. We found that because of rounding errors, it cannot simulate it accurately enough for nEDM experiments, assuming homogeneous electric and magnetic fields with strengths of 10 kV/cm and 1 μT, respectively, and 100 s of storage. In this paper, we report on its discrepancies and describe a solution.

Finite-volume corrections to the CP-odd nucleon matrix elements of the electromagnetic current from the QCD vacuum angle

Nucleon electric dipole moments originating from strong CP-violation are being calculated by several groups using lattice QCD. We revisit the finite volume corrections to the CP-odd nucleon matrix elements of the electromagnetic current, which can be related to the electric dipole moments in the continuum, in the framework of chiral perturbation theory up to next-to-leading order taking into account the breaking of Lorentz symmetry. A chiral extrapolation of the recent lattice results of both the neutron and proton electric dipole moments is performed, which results in dn=(−2.7±1.2)×10−16eθ0 cm and dp=(2.1±1.2)×10−16eθ0 cm.

Nucleon electric dipole moments and the isovector parity- and time-reversal-odd pion–nucleon coupling

The isovector time-reversal- and parity-violating pion–nucleon coupling g¯π(1) is uniquely sensitive to dimension-six interactions between right-handed light quarks and the Standard Model Higgs doublet that naturally arises in left-right symmetric models. Recent work has used the g¯π(1)-induced one-loop contribution to the neutron electric dipole moment dn, together with the present experimental dn bound, to constrain the CP-violating parameters of the left-right symmetric model. We show that this and related analyses are based on an earlier meson theory dn computation that is not consistent with the power-counting appropriate for an effective field theory. We repeat the one-loop calculation using heavy baryon chiral perturbation theory and find that the resulting dn sensitivity to g¯π(1) is suppressed, implying more relaxed constraints on the parameter space of the left-right symmetric model. Assuming no cancellations between this loop contribution and other contributions, such as the leading order EDM low-energy constant, the present limit on dn implies |g¯π(1)|≲1.1×10−10.

A SQUID magnetometry system for a cryogenic neutron electric dipole moment experiment

1Current address: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USAPrecision magnetometry is an essential component of any neutron electric dipole moment experiment in order to correct shifts in the neutron precession frequency due to changes in the magnetic field. We have developed a magnetometry system using 12 SQUID sensors, designed to operate in 0.5K superfluid helium. The pick-up loops located near the neutron cell are connected to the SQUID sensors by ~2m twisted wire pairs. The SQUID readout cables are run via an intermediate stage at 4.2K. The system has been installed and tested in the cryoEDM apparatus at the ILL, Grenoble, and used to characterise the magnetic environment. Further tests in a suitable low noise environment confirm it meets our requirements.

Dipole operator constraints on composite Higgs models.

Flavour- and CP-violating electromagnetic or chromomagnetic dipole operators in the quark sector are generated in a large class of new physics models and are strongly constrained by measurements of the neutron electric dipole moment and observables sensitive to flavour-changing neutral currents, such as the B{,rightarrow ,} X_sgamma branching ratio and epsilon '/epsilon . After a model-independent discussion of the relevant constraints, we analyze these effects in models with partial compositeness, where the quarks get their masses by mixing with vector-like composite fermions. These scenarios can be seen as the low-energy limit of composite Higgs or warped extra dimensional models. We study different choices for the electroweak representations of the composite fermions motivated by electroweak precision tests as well as different flavour structures, including flavour anarchy and U(3)^3 or U(2)^3 flavour symmetries in the strong sector. In models with “wrong-chirality” Yukawa couplings, we find a strong bound from the neutron electric dipole moment, irrespective of the flavour structure. In the case of flavour anarchy, we also find strong bounds from flavour-violating dipoles, while these constraints are mild in the flavour-symmetric models.

CP -violating phenomenology of flavor conserving two Higgs doublet models

We analyze the constraints on $CP$-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral $CP$-even states and the EDMs probing the effect of mixing between the $CP$-even and $CP$-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron and diamagnetic atom EDM searches could yield competitive or even more severe constraints. We analyze the quantitative impact of hadronic and nuclear theory uncertainties on the interpretation of the latter systems and conclude that these uncertainties cloud the impact of projected improvements in the corresponding experimental sensitivities.

Characterisation of superconducting capillaries for magnetic shielding of twisted-wire pairs in a neutron electric dipole moment experiment

The cryoEDM neutron electric dipole moment experiment requires a SQUID magnetometry system with pick-up loops inside a magnetically shielded volume connected to SQUID sensors by long (up to 2m) twisted-wire pairs (TWPs). These wires run outside the main shield, and therefore must run through superconducting capillaries to screen unwanted magnetic pick-up. We show that the average measured transverse magnetic pick-up of a set of lengths of TWPs is equivalent to a loop area of 5.0×10−6m2/m, or 14 twists per metre. From this we set the requirement that the magnetic shielding factor of the superconducting capillaries used in the cryoEDM system must be greater than 8.0×104. The shielding factor—the ratio of the signal picked-up by an unshielded TWP to that induced in a shielded TWP—was measured for a selection of superconducting capillaries made from solder wire. We conclude the transverse shielding factor of a uniform capillary is greater than 107. The measured pick-up was equal to, or less than that due to direct coupling to the SQUID sensor (measured without any TWP attached). We show that discontinuities in the capillaries substantially impair the magnetic shielding, yet if suitably repaired, this can be restored to the shielding factor of an unbroken capillary. We have constructed shielding assemblies for cryoEDM made from lengths of single core and triple core solder capillaries, joined by a shielded Pb cylinder, incorporating a heater to heat the wires above the superconducting transition as required.

Neutron optics of noncentrosymmetric crystals: New possibility of searches for the neutron electric dipole moment and CP-violating forces

New neutron-optics effects, which were predicted and discovered quite recently in noncen- trosymmetric crystals and which can be used to study the fundamental properties of the neutron, are discussed. In particular, strong electric fields of strength up to 10 8 or 10 9 V/cm may act in such crystals on the neutron, and this provides new possibilities for measuring the neutron electric dipole moment (EDM) by the crystal-diffraction method. It also becomes possible to perform searches for pseudomagnetic forces acting on neutrons and violating CP invariance. For the range of such forces that satisfies the condition λA < 10 −5 cm, the best constraints on the product of the scalar and pseudoscalar coupling constants have already been obtained for the interaction induced by the exchange of a light pseudoscalar (axion-like) particle. The present-day status and prospects of neutron-optics crystal-diffraction experiments aimed at searches for the neutron EDM and pseudomagnetic forces are considered.

Colored scalars and the neutron electric dipole moment

We investigate new contributions to the neutron electric dipole moment induced by colored scalars. As an example, we evaluate contributions coming from the color octet, weak doublet scalar, accommodated within a modified Minimal Flavor Violating framework. These flavor non-diagonal couplings of the color octet scalar might account for the $A_{CP} (D^0 \to K^- K^+) - A_{CP} (D^0 \to \pi^+ \pi^-)$ asymmetry on the tree level. Using these charm asymmetry constrained couplings, we calculate two-loop contributions to the neutron electric dipole moment and find that they are of the same order as the experimental bound. We comment also on contributions of higher dimensional operators to the neutron electric dipole moment within this framework.

Searches forCP-violating dimension-6 electroweak gauge boson operators

We reconsider the prospects for observing a dimension-6, CP-violating operator involving $W^+W^-Z$ at the LHC. Firstly, we correct a number of earlier calculations of the loop contribution to the neutron electric dipole moment of a companion operator, involving $W^+W^-\gamma$, showing that measurements imply a very strong bound on the companion operator. Secondly, we quantify the link between the two operators, showing that strongly-coupled new physics could only be observable in proposed searches if it appeared at a scale below $\sim 170$ GeV. This is most unlikely, given the null results of other searches at the LHC and elsewhere.

Surface-conductivity enhancement of PMMA by keV-energy metal-ion implantation

An experiment has been proposed to measure the neutron electric dipole moment (nEDM) with high precision at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source. One of the requirements of this experiment is the development of PMMA (Lucite) material with a sufficiently conductive surface to permit its use as a high-voltage electrode while immersed in liquid He. At the ORNL Multicharged Ion Research Facility, an R&D activity is under way to achieve suitable surface conductivity in poly-methyl methacrylate (PMMA) using metal ion implantation. The metal implantation is performed using an electron-cyclotron-resonance (ECR) ion source and a recently developed beam line deceleration module that is capable of providing high flux beams for implantation at energies as low as a few tens of eV. The latter is essential for reaching implantation fluences exceeding 1×1016cm−2, where typical percolation thresholds in polymers have been reported. In this contribution, we report results on initial implantation of Lucite by Ti and W beams with keV energies to average fluences in the range 0.5–6.2×1016cm−2. Initial measurements of surface-resistivity changes are reported as function of implantation fluence, energy, and sample temperature. We also report X-ray photoelectron spectroscopy (XPS) surface and depth profiling measurements of the ion implanted samples, to identify possible correlations between the near surface and depth resolved implanted W concentrations and the measured surface resistivities.

New measurements of the neutron electric dipole moment

We report a new measurement of the neutron electric dipole moment with the PNPI EDM spectrometer using the ultracold neutron source PF2 at the research reactor of the ILL. Its first results can be interpreted as a limit on the neutron electric dipole moment of |d n | < 5.5 × 10−26 e cm (90% confidence level).