2019 TUNL REU Projects

 

The student on this project will calculate the thresholds for charged--current electron neutrino and antineutrino interactions for many stable isotopes. The goal is to look for isotopes with the lowest thresholds that also might be reasonable candidates for low--threshold neutrino detectors. Criteria in identifying suitable candidates will include whether they are metals, have relatively high natural abundance, and are not frequently found in conjunction with radioactive substances. The student will then use the SNOwGLoBES software library to compute estimated cross sections and event rates for supernova fluxes in the candidate materials.

 

 

Sensitivity studies are the steering mechanism that guides Nuclear-Astrophysical experimental efforts. These studies seek to model a specific stellar environment with an emphasis on nuclear reaction networks. The models are run hundreds of times, varying the rate of a single reaction each time, to test its impact on various features of the environment. The Low-Mass X-ray Binary (XRB) is a neutron star in an accreting binary with a main-sequence star, that forms a disk of material in the plane of the orbital axis of the neutron star (NS). Due to the intense gravity of the NS, the material undergoes HCNO burning once it joins the surface. For a time this HCNO burning continues stably until a build up of material raises the temperature and density to a degenerate, thin-shell instability which causes a breakout into runaway nucleosynthesis. Here on Earth, we observe this runaway through a spike in the luminosity in the X-ray spectrum. In order to explain the various features of the X-ray burst, as well as the burst itself, we are interested in studying the effects of alterations to the nuclear network via the aforementioned methods.

 

In this project, the student will gain familiarity with Modules for Experimental Stellar Astrophysics (MESA - http://mesa.sourceforge.net/index.html) and design scripts via python, mathematica, or another agreed upon language, that will parse the results of stellar evolution models of the XRB into usable data and visualizations that will summarize the results of a sensitivity study in progress.

 

The polarization of Λ hyperons is revealed in the distribution of their decay products. This makes them sensitive tools for polarization dependent effects in the formation of hadrons from initial quarks. The study of Λ hyperons has therefore played an important role in our quest to understand the strong force. The CLAS12 experiment at Jefferson Labs Continuous Electron Beam Facility is at the frontier of our exploration of the role of the strong force in proton structure and hadron formation. It makes use of a polarized 12 GeV electron beam impinging on a polarized target. The goal of this project is to use simulated data to study the feasibility to reconstruct Λ hyperons from their decay products in processes where they are produced non-exclusively by the hadronization of the struck quark. Basic programming knowledge will be useful for this project.

 

 

Fission product yields (FPYs) are one of the most important observables of nuclear fission. This experiment will measure FPYs from the gamma-ray induced fission of uranium-238. Compared to the traditional approach of neutron-induced fission, gamma-ray induced fission has a fixed angular momentum transfer, making it ideal to benchmark theoretical models. A RApid Belt-driven Irradiated Target Transfer System (RABITTS) is being developed to quickly move targets between an in-beam irradiation position and a low background counting position. The gamma-rays will be provided by the High Intensity Gamma-ray Source (HIGS). A high-purity germanium (HPGe) detector will measure the activity of fission products as they decay. This system will allow us to measure the decay of multiple fission products with half-lives ranging from 0.5 seconds to 100 minutes. The student will be involved in the construction of the RABITTS system, a commissioning run with the HIGS beam, and data analysis to extract FPYs for ²³⁸U.

 

 

We plan to use a tritium gas target in experiments at the HIGS facility. Because tritium is a radioactive gas, safety systems will be implemented to reduce risk of gas loss. The safety protocol includes a scrubbing system in constant operation to clean the air inside the glovebox where the tritium is stored and tritium gas transfers are performed. Our plan is to use a CuZn based catalyst bed to convert tritium gas, T², to tritiated water, T²O or HTO. Once elemental tritium has been converted to water, a molecular sieve dryer bed will remove all water from the gas stream. The scrubber must be operable in atmosphere and must be leak tight. Further, the system will need to quickly and efficiently remove all hydrogen isotopes from the glovebox atmosphere. The REU student will be responsible for constructing and testing a scrubbing system that meets the technical specifications required for the tritium target safety system.

 

 

Full understanding of protons and neutrons, the basic building blocks of nuclear matter, has so far remained elusive. By performing Compton scattering with gamma photons off light nuclei, the electric and magnetic polarizabilities of nucleons—a measure of how “stiff” they are to electromagnetic fields—can be experimentally determined. These quantities can then be used to test our best theories of low-energy nuclear physics. The next goal of the Compton collaboration is to perform measurements with a liquid ³He target cooled to below 2 degrees Kelvin. This experiment will be performed using the free electron laser-based High Intensity Gamma-ray Source (HIGS) facility on Duke’s campus. The REU research effort will involve developing, installing, and testing cryogenic components and electronics during the the initial cooldowns of the ³He cryogenic target. Skills in automation using Labview-based programing and hands-on low temperature techniques will be advanced over the course of the work.

 

 

A non-zero neutron electric dipole moment would be a clear sign of physics beyond the standard model. There are several big projects around the world racing to be the first to discover it. At TUNL we are constructing a scaled down version of the experiment that will be conducted at the Spallation Neutron Source at Oak Ridge National Laboratory to develop some of the necessary advanced measurement techniques. For example, we are working with a dilution refrigerator at temperatures below 1K. This project would entail developing NMR measurement methods to detect the spins of ³He atoms dissolved in ⁴He liquid at milli-Kelvin temperatures.

 

The Young research group at TUNL is heavily involved in measurements of the properties of neutrons, especially those that pertain to a fundamental understanding of the weak interactions between nucleons. To facilitate the calibration and testing of equipment used in these searches, a small electron accelerator is being constructed at TUNL. The REU student on this project will be heavily involved in assembling, testing, and upgrading the pulsed linear electron accelerator from 100 keV to (after upgrade) 1 MeV. The project will combine hands-on activities in assembling and operating the accelerator for tests and modeling of electron trajectories in the system.

 

Searches for the decay of the Higgs and Z boson to charmonium c c and a photon ̄have so far exclusively been done for the J/ψ state decaying to a pair of leptons (6% branching ratio). We want to extend this to all charmonium states using all hadronic modes. Jets from charmonium typically contain fewer particles and are narrower. In this project, we aim to develop a charmonium tagger using a machine learning approach.

 

Useful skills: python, tensorflow, ROOT, C++

 

 

In the scenario that the Higgs boson is made of new constituent particles, it is likely that the top quark is also made up of similar particles. In this case, events with multiple top quarks could be produced in excess of predictions from current theories. We will design an analysis to look for events with 4 top quarks, using events with two leptons. This final state is likely to have small backgrounds.

 

Useful skills: programming

 

If dark matter is as complex as visible matter, there could be a strongly interacting dark sector in which the hidden “quarks” decay to the visible sector via multiple vertices that are displaced inside within the same jet. Pair-produced dark quarks could be identified as “emerging” jets.

 

Useful skills: ROOT, C++

 

 

Beyond-the-standard model processes that may explain dark matter or the mechanism of electroweak symmetry breaking might be missed at the Large Hadron Collider if they do not produce high-momentum signatures that can be reconstructed by online trigger systems. or large missing energy. One such example would be long-lived new particles that decay inside of the detectors. This project would explore the possibility of using pileup events – the extra pp collisions occuring with each event that are usually ignored in analysis.

 

Useful skills: ROOT, C++