# Research Projects

##

Research in Symmetries at the University of Kentucky

Project | Mentor | |
---|---|---|

1. |
Data Acquisition and Analysis of Neutron Experiments * |
Christopher Crawford |

2. |
Lost Muon Mechanism in the Fermilab g-2 Experiment * |
Renee Fatemi |

3. |
Single Crystal Growth of Quantum Magnetic Materials |
William Gannon |

4. |
LC Circuits for Dark Matter Direct Detection * |
Susan Gardner |

5. |
Digital Signal Processing (DSP) of Fermilab g-2 Data * |
Tim Gorringe |

6. |
Geometrically Frustrated Magnetism * |
Ribhu Kaul |

7. |
Laser Frequency Stabilization System |
Wolfgang Korsch |

8. |
Simulations and Data Analysis for the NEDM@SNS Experiment * |
Brad Plaster |

9. |
Topological Heterostructures with Broken T-reversal Symmetry |
Ambrose Seo |

10. |
RR Lyrae Variable Stars |
Ron Wilhelm |

* this project can be performed remotely if on-site research is restricted this summer.

**Pick any three!**

1. **Data Acquisition and Analysis of Neutron Experiments** Mentor: **Christopher Crawford **

Skills learned: Data analysis, finite impulse response (FIR) filters, least squares fitting

Modern nuclear spectroscopy, such as in the Nab neutron decay correlation experiment, is performed by digitizing unprocessed electronic signals of particle detectors directly into waveform data. These data are analyzed to determine the pulse height (energy) and arrival time of particles and identify different particles. Two commonly used methods of analysis are the recursive trapezoid filter, which flattens out an exponentially decaying pulse to quickly determine its energy, and off-line least squares fitting of the waveforms to determine the most accurate parameters. This project is to develop and test a new algorithm which combines the best features of both algorithms and can run in real time as the data are being collected. The tasks associated with this project are: a) implement the recursive trapezoid filter in Excel and Matlab; b) implement a sliding least-squares (SLS) fitter using convolutions in Matlab; c) develop the trapezoid filter as a sliding least-squares fit to determine the associated chi-square; d) analyze spectroscopic data from test beta-sources in the Nab spectrometer using all three methods to compare the energy resolution. Variants of this project involve programming the recursive SLS filter in different hardware systems (NVIDIA CUDA for GPUs, LabVIEW FPGA, RedPitaya), optimally weighting LSQ fits by according to the power spectrum, and analyzing spectroscopy data to optimize filter parameters.

2. ** Lost Muon Mechanism in the Fermilab g-2 Experiment ** Mentor: **Renee Fatemi**

Skills learned: MC simulation (GEANT4), data analysis (ROOT) involving large datasets.

The Fermilab g-2 experiment aims to measure the anomalous magnetic moment of the muon to a precision of 140 parts-per-billion. This requires the measurement of the spin precession frequency of muons as they circulate in the g-2 storage ring. The muon moment is extracted from fits to the time spectrum of the decay positrons. Muons that leave the storage area before decaying may introduce a systematic bias to the determination of the moment. Therefore, it is critical to understand the mechanisms (collimators, field non-uniformities) that lead to lost muons, and the signature of these lost muons in the ring detectors. The tasks associated with this project are 1) Implement a lost-muon gun that will shoot muons uniformly across the five ring collimators. 2) Study the energy deposited in each of the collimators as a function of muon energy. 3) Study the time it takes for each muon to exit the storage region as a function of muon energy and strike position of the muon. 4) Study the effect of non-uniformities in dipole field on the time dependence and rate of lost muons. 5) Characterize the differences (if any) of lost muon signals from calorimeter interactions versus field non-uniformities. The REU student will use the Fermilab computing system and job submission tools, the GEANT4 implementation of g-2 experiment and ROOT analysis package.

3. **Single Crystal Growth of Quantum Magnetic Materials** Mentor: **William Gannon **

Skills learned: Crystal growth from molten flux, x-ray diffraction, electron microscopy

A promising set of compounds that potentially host Quantum Spin Liquid (QSL) phases in metals is Yb2Si2Al1-xMgx, where magnetic Yb ions sit on the geometrically frustrated Shastry-Sutherland lattice . In Yb2Si2Al, the Yb ions have a valence of 2.7, indicating strong hybridization of the Yb f-electrons; no magnetic order is observed for temperature T > 1.8K. When doped with Mg on the Al site, the Yb valence is dramatically altered leading to magnetic order at T <5 K for 50% magnesium . Yb2Si2Al1-xMgx is an excellent candidate for systematic study of QSL phase transitions in metals, but thus far only polycrystalline samples have been made for x>0, making detailed study difficult. This project involves (a) initiating the growth of single crystals of Yb2Si2Al1-xMgx from molten flux , (b) evaluating the results using x-ray diffraction and scanning electron microscopy, and (c) using the results of (a) and (b) to refine the growth conditions and grow more crystals. Once suitable crystals are made, the student will characterize them by measuring specific heat and basic magnetic properties. The ultimate goal will be to use these crystals in a neutron scattering experiment at a national laboratory. The student will participate in beam time scheduled during the REU, or will go to Oak Ridge National Laboratory to visit with colleagues and see how these types of experiments work.

Skills Learned: Analytical and numerical methods, dark matter physics, particle physics

Astrometric measurements that probe the cosmos at different stages of its history speak to the preponderance of "dark matter" that is both very long lived and weakly interacting. Some properties of dark matter (DM) are established, but its intrinsic nature is unknown and experiment plays a key role in our ability to rule out or establish possible DM candidates. In this project we consider DM candidates that are so light in mass that they are field-like, bearing similarity to the electromagnetic field. The candidates can also interact with light. Thus, in the presence of this type of DM the familiar equations of electrodynamics are modified, and the presence of this sort of DM can be probed through a high Q-factor, resonant LC circuit. Thus far "axion" and "dark photon" DM candidates have been considered from this perspective. The problem proposed is to solve the modified Maxwell equations for the DM signal within a conducting shield, of different possible geometries. Ultimately, it is the generated magnetic field that can be detected, through a resonant enhancement in the LC circuit.

5. ** Digital Signal Processing (DSP) of Fermilab g-2 data** Mentor: **Tim Gorringe**

Skills learned: Data analysis, programming in Python, Matlab and ROOT.

The muons anomalous magnetic moment is determined by measurement of its corresponding anomalous precession frequency. Within the g-2 collaboration the UK group is responsible for the collection and the analysis of the so-called Qmethod dataset for themeasurement. The Qmethod data consists of continuously digitized traces from the twenty-four g-2 electromagnetic calorimeters. The baseline analysis for extracting the moment utilizes a rolling-average DSP technique to identify the signals of positrons from muon decays. This REU project will use the existing Qmethod dataset to study alternative processing techniques to identify positron signals. The project will expose REU students to topics including discrete-time sampling, information theory, time/frequency domains, noise/filtering, DSP algorithms, compression algorithms, and machine learning that are important in such areas as image, video, and speech processing.

6. **Geometrically Frustrated Magnetism** Mentor: **Ribhu Kaul **

Skills learned: Monte Carlo Simulation, data analysis

Many materials realize magnets on frustrated lattices in which simple antiferromagnetic interactions between the spins cannot all be satisfied even at the classical level. The interplay of energy mini- mization and entropic fluctuations then leads to surprising behaviors when the magnetic structure of these materials are measured in laboratories . In this project REU students will construct a model for such materials and then study the physical properties of the models through Monte Carlo simulations. We shall work specifically on models of spin ice in rare-earth pyrochlores.

7. **Laser Frequency Stabilization System ** Mentor: **Wolfgang Korsch **

Skills learned: Operation of lasers, atomic spectroscopy, frequency stabilization

Basically all modern experiments in atomic physics rely on the usage of frequency-stabilized lasers. A long-term frequency stability of much better than 1 MHz is often essential for such applications. For example, nuclear spin-polarized helium-3 targets are presently used in a variety of fundamental physics experiments, such as the search for a magnetically induced Faraday effect, nucleon spin- structure studies at Jefferson Lab, or precision magnetometry in searches for permanent EDMs, to name a few. All these experiments could vastly benefit from the usage of frequency-stabilized lasers. However, most diode laser systems exhibit a typical long-term stability of a few 100 MHz to a few GHz. The REU student will construct and implement a laser frequency stabilization system either based on dichroic atomic vapor laser locking or absorption spectroscopy locking methods on Rb and K transitions. In case of successful demonstration of the frequency stabilization, the system will be used for Faraday rotation measurements on spin-polarized helium-3 targets which are polarized via spin-exchange optical pumping. A detailed characterization of density and polarization distribution profiles of these vapors inside such target cells is of great interest to the above-mentioned experiments.

8. **Simulations and Data Analysis for the nEDM@SNS Experiment** Mentor: **Brad Plaster **

Skills Learned: Finite element analysis, computer control, data analysis

A new experiment under development for the Spallation Neutron Source at Oak Ridge National Laboratory will search for a non-zero electric dipole moment of the neutron (nEDM). A value for the nEDM will be extracted from a comparison of the neutron’s Larmor precession frequency in parallel and anti-parallel electric and magnetic fields. Time variations in the magnetic field will be monitored via measurements of the Larmor precession frequency of Helium-3 co-magnetometer atoms, whose precessing magnetization will be detected in SQUID pick-up loops. The goal of this REU project will be to develop a simulation of the signal and noise expected in the SQUID pick-up loops, and then develop data analysis strategies to correct for magnetic field time variations in the extraction of the nEDM.

9. **Topological heterostructures with broken T-reversal symmetry** Mentor: **Ambrose Seo**

Skills learned: Vacuum technology, Crystal growth, Spectroscopic analysis

In simple theoretical models, the state of matter is governed by its atoms and how they are bonded to one another in crystal structures. However, properties of materials can change at phase transitions as external conditions are varied, even though the atoms and structures remain the same. These phenomena lead to novel concepts such as the order parameter and spontaneous symmetry breaking. We are now witnessing another paradigm shift: The state of matter is also governed by topological invariants. This means that the state of matter depends on how quantum wavefunctions are tied in a knot. This REU project will study the nontrivial topological phenomena that emerge in low dimensional systems such as thin-film heterostructures consisting of iridates and ruthenates due to the interplay between strong electron correlations and the relativistic spin-orbit interaction.

10. **RR Lyrae Variable Stars** Mentor: **Ron Wilhelm **

Skills learned: Data analysis, spectrum and imaging simulation

RR Lyrae variable stars (RRL) are ancient, evolved, low-metallicity, helium-core burning stars that pulsate fundamentally in the radial mode. New technology and temporal surveys have revealed complex interactions, such as the effects of resonant frequencies and non-radial pulsation modes. It is becoming increasingly likely that classical, stable pulsating RRLs do not exist. One recognized RRL pulsation complexity is Stochastic Period-Fluctuating variables (SPF). The SPFs have rapid period changes that are not correlated to either external (orbital changes due to binarity) or internal effects (periodic Blazhko effect). Our project involves high-precision, photometry observations of SPF, coupled with analysis of ground base monitoring programs, such as the Kilo degree Little Telescope (KELT), and space-based observations such as the Transiting Exoplanet Survey Satellite (TESS). This project includes the following tasks: a) collection of observational data over the course of the REU project, using our on-campus, MacAdam Student Observatory, or remote observations using the Moore Observatory. b) Data reduction and analysis using the software package AstroImageJ to produce high-precision light curves for the individual SPF. c) Analysis of light curve data using the software Period04 to produce a Fourier spectrum, identify frequency peaks and produce frequency, amplitude and phase information for all significant Fourier structure. All data and results will become part of our ongoing monitoring program of SPFs.