Session D17: Precision Measurements of Magnetic Moments and Electric Dipole Moments

Geane Track Reconstruction for Fermilab Muon g-2

The Fermilab Muon g-2 experiment has the goal of measuring the anomalous magnetic moment of the muon to 140 ppb. This measurement is made by analyzing the modulation of decay positrons from positive muons detected with calorimeters. Two straw tracking detectors are used to measure the beam profile, identify pileup and muons lost from the beam storage region, and to cross-calibrate the calorimeters. The implementation of a Geant4-based error propagation and chi-squared minimization fitting algorithm for track reconstruction will be presented, along with simulation and commissioning data results.   

High Precision Magnetic Field Measurement for the Muon g-2 Experiment

The Muon g-2 Experiment (E989) at Fermilab will measure the anomalous magnetic moment of muon $a_{\mu}$ with a precision of 140~part-per-billion (ppb), aiming at resolving the 3.5 standard deviation between the previous measurement of $a_{\mu}$ at Brookhaven (E821) and the Standard Model calculation of $a_{\mu}$. In E989, the muon spin precession frequency $\omega_{a}$ is measured in a storage ring magnet, and the magnetic field has to be measured with comparable precision as that for $\omega_{a}$. A magnetic field measurement system was developed to measure the magnetic field experienced by the muons with a precision of 70~ppb. Nuclear magnetic resonance (NMR) probes were designed to measure the magnetic field. The field scanning system in E821 that carries the NMR probes to measure the field in the muon-storage region was refurbished and upgraded with modern motion control and electronic readout systems. 378 new NMR probes and readout electronics were installed to monitor the field drift in between field scans. A special NMR probe which has a simpler and well-measured geometry and low magnetic perturbation was designed to calibrate the probes in the field scanning system. All systems were successfully commissioned, and ready for data taking starting in February 2018.   

Precision Magnetic Field Calibration for the Muon $g-2$ Experiment at Fermilab

The Muon g-2 Experiment at Fermilab (E989) has been designed to determine the muon anomalous magnetic moment to a precision of 140 parts per billion (ppb), a four-fold improvement over the Brookhaven E821 measurement. Key to this precision goal is the determination of the magnetic field of the experiment's muon storage ring to 70 ppb. The magnetic field will be measured by nuclear magnetic resonance (NMR) probes, mounted on a trolley and pulled through the muon storage region when muons are not stored. These trolley probes will be calibrated in terms of the free-proton Larmor precession frequency by a specially-constructed NMR calibration probe. In E821, the uncertainty in the field measurement was 170 ppb, of which 90 ppb was due to the calibration procedure of the trolley and 50 ppb was due to the calibration probe. In E989, these uncertainties will be reduced to 30 ppb and 35 ppb, respectively. These reduced uncertainties directly improve the experiment's sensitivity to new physics. To meet these stringent requirements, a new probe has been built. Details of the probe, NMR electronics, and calibration procedure will be presented; additionally, the main field systematic uncertainties will be discussed.   

Improving Magnetic Field Uniformity in the Muon g-2 Storage Ring

The muon g-2 experiment at Fermilab (E989) aims to measure the anomalous magnetic moment of the muon $a_\mathrm{\mu}$ to a precision of 140 ppb. This new measurement will shed light on the 3.5 sigma deviation between Standard Model calculations and the previous measurement (E821) at Brookhaven National Laboratory, and will test Standard Model extensions. The muon g-2 experiment measures the difference between the cyclotron and spin precession frequencies of muons in a highly uniform magnetic field, where the magnetic field over a muon's trajectory must be known to 70 ppb. The last passive step in achieving the required field homogeneity was the adjustment and installation of over 10,000 iron shims in and around the muon storage region. Higher order multipole moments of the magnetic field distribution across the storage region are controlled using 100 concentric coils located above and below the vacuum chambers. The current distribution in these so called surface coils is adjusted to reduce magnetic field variations across the storage region to less than 2 parts per million. An overview of the surface coil system, their calibration, and the current optimization procedure used to arrive at the final magnetic field in the magnetic storage region will be presented.   

Development of a Novel Helium-3 Probe for the Cross-Check of the Magnetic Field Measurement Calibration for Muon g-2

The muon g-2 experiment at Fermilab (E989) investigates the >3.3-$\sigma$ discrepancy between the standard model prediction and the current experimental measurement of the muon magnetic moment anomaly, a$_{\mu}$ = (g-2)/2. This effort requires a precise measurement of the 1.45 T magnetic field of the muon storage ring to 70 ppb. The final measurement will employ multiple absolute calibration probes: water probes and a $^{3}$He probe. The $^{3}$He probe offers a cross-check of the water probes with different systematic corrections, adding a level of confidence to the measurement. A low-field $^{3}$He probe was developed at the Univ. of Michigan by employing a method called MEOP for the hyper-polarization of $^{3}$He gas, followed by NMR to determine the frequency proportional to the magnetic field in which the probe is placed. A modified probe design for operation under high fields is currently in production at Argonne National Lab. Future development involves the study of the systematic uncertainties to attain the error budget of <30 ppb for the calibration. Next, the calibration from the probes will be transferred to g-2 through several steps of a calibration chain ending in the final step of calibrating the NMR probes which measure the field in the muon storage ring at Fermila   

Beam dynamics in the Muon (g-2) experiment

Major systematic uncertainties in the Muon $(g-2)$ experiment are related to beam dynamics in the muon storage ring. In this talk, we give an overview of the beam dynamics in the storage ring, describe major beam-dynamics-related systematic uncertainties, and present preliminary results of our measurements of characteristics of the muon beam.   

Search for the permanent electric dipole moment of $^{129}$Xe

CP-violation in Beyond-the-Standard-Model physics, necessary to explain the baryon asymmetry, gives rise to permanent electric dipole moments (EDMs). EDM measurements of the neutron, electron, paramagnetic and diamagnetic atoms constrain CP-violating parameters. The current limit for the $^{129}$Xe EDM is $6\times10^{-27}~e\cdot\mathrm{cm}$ (95$\%$ CL). The HeXeEDM experiment uses a stable magnetic field in a magnetically shielded room, spin-precession detection with SQUID magnetometer arrays and a $^3$He co-magnetometer to measure the $^{129}$Xe EDM with the potential to improve the sensitivity by two orders of magnitude. Results from a June 2017 test run and plans for production data will be presented.   

Computing the Chromo-Electric Contribution to the Nucleon EDM using the Feynman-Hellmann Method and Lattice QCD

The universe is observed to be in a matter anti-matter asymmetric state, with an observed baryon dominance on the order of one part per billion. A necessary condition for the generation of this asymmetry is the violation of the combined symmetries of charge conjugation (C) and parity (P). CP violation within the standard model of particle physics is orders of magnitude too small to account for this asymmetry, leading to the search for beyond standard model sources. Beyond standard model sources of CP violation invariably give rise to new interactions between standard model particles that can, in principle, be detected. Lattice QCD is uniquely suited for investigating these contributions in the strong sector, as it allows a non-perturbative solution of the low-energy, strong coupling, region of QCD with fully controllable systematics. In this talk I will present progress towards a Lattice QCD measurement of the leading beyond standard model contribution to the Neutron Electric Dipole moment using a method which has been shown to provide increased control over systematics as compared to previous measurement methods.   

Improving the Optical Trapping Efficiency in the $^{225}$Ra Electric Dipole Moment Experiment via Monte Carlo Simulation

In an effort to study and improve the optical trapping efficiency of the $^{225}$Ra Electric Dipole Moment experiment, a fully parallelized Monte Carlo simulation of the laser cooling and trapping apparatus was created at Argonne National Laboratory and now maintained and upgraded at Michigan State University. The simulation allows us to study optimizations and upgrades without having to use limited quantities of $^{225}$Ra (15 day half-life) in the experiment's apparatus. It predicts a trapping efficiency that differs from the observed value in the experiment by approximately a factor of thirty. The effects of varying oven geometry, background gas interactions, laboratory magnetic fields, MOT laser beam configurations and laser frequency noise were studied and ruled out as causes of the discrepancy between measured and predicted values of the overall trapping efficiency. Presently, the simulation is being used to help optimize a planned blue slower laser upgrade in the experiment's apparatus, which will increase the overall trapping efficiency by up to two orders of magnitude.