Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session QE: Undergraduate Research IV |
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Chair: Anthony Kuchera, Davidson College Room: Park & Scollay |
Thursday, October 14, 2021 11:30AM - 11:42AM |
QE.00001: Probability threshold truncation in a symplectic basis for ab initio nuclear structure calculations Colin V Coane, Anna E McCoy, Jakub Herko, Mark A Caprio, Patrick J Fasano, Zhou Zhou, Tomas Dytrych The size of bases used in ab initio nuclear structure calculations explodes with the number of nucleons and allowed excitation quanta. Thus, finite computational resources limit the convergence of calculated observables. The symplectic no-core configuration interaction (SpNCCI) framework reorganizes the basis into Sp(3,R) irreducible representations (irreps), allowing us to truncate this basis by symplectic symmetry. Here, we apply a truncation scheme where the basis is truncated based on probability contributions of Sp(3,R) irreps to a reference wavefunction obtained in an initial small-scale calculation. This lets us retain only irreps which dominantly contribute to the wavefunction and incorporate high-lying basis states within these irreps previously unattainable given fixed resource constraints, in attempt to better converge long-range observables such as charge radii and quadrupole moments. We explore the effect of this truncation on convergence of calculated observables and the size of the SpNCCI basis. |
Thursday, October 14, 2021 11:42AM - 11:54AM |
QE.00002: Approximating Kaon Structure Data with Machine Learning Sarah C Fields Quantum Chromodynamics (QCD), is the study of quark gluon interactions, and the strong nuclear force. There are currently many experiments and studies being conducted to try to further the understanding of QCD and the structure of subatomic particles. One of the particles of interest in a kaon (K). A kaon is a particle that consists of an anti-stange and up quark pair. Kaons are of particular interest because they are unstable, resulting in a very quick decay. The quick decay makes kaons very difficult to study experimentally. Fortunately, vital information regarding particle structure can be gained through studying Lattice QCD correlator functions. These functions can be quite computationally expensive to solve for, and for this reason machine learning techniques were tested to estimate additional correlator data. Machine Learning is a computational method that utilizes a data set to make a model that can predict further data. Specifically in this work, machine learning methods were examined and refined in order to predict later distance and greater momentum kaon correlator data with earlier data points. |
Thursday, October 14, 2021 11:54AM - 12:06PM |
QE.00003: Physics analysis of peripheral and ultraperipheral high-energy nuclear collisions with the ATLAS detector. Corben D Browne At the Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC), relativistic heavy ion collisions such as lead on lead (Pb+Pb) are used to create droplets of quark-gluon plasma (QGP). The defining signals of QGP diminish as the overlapping area of the colliding nuclei decreases. However, small systems like proton on proton (p+p) and proton on lead (p+Pb) exhibit hydrodynamic behavior, suggesting that QGP may still be created in smaller systems including in peripheral heavy ion collisions. Ultra-peripheral collisions (UPC's) may form a background to the peripheral A+A collisions of interest and thus peripheral event data should be corrected for their contributions. In this study we have investigated methods of detecting and removing the contributions of UPC's. We will show how we have used the Monte Carlo simulation programs, EPOS, HIJING, and DPMJET to estimate the contributions of different processes. The simulation outputs are compared against real peripheral 5.02 TeV Pb+Pb data recorded by the ATLAS detector at the Large Hadron Collider. |
Thursday, October 14, 2021 12:06PM - 12:18PM |
QE.00004: Event Selection in Extremely Peripheral Pb+Pb Collisions with ATLAS Megan Byres In order to investigate the quark gluon plasma through jet quenching, one wants to understand the continuum from Pb+Pb to pp collisions. Thus, it is useful to investigate peripheral Pb+Pb collisions, where jet quenching effects are expected to smoothly turn off. Ultra-peripheral collisions (UPCs) are a background for these collisions, and the pT spectra of charged hadrons in these events are significantly different from hadronic Pb+Pb collisions for reasons unrelated to jet quenching. They therefore should be removed in order to get an unbiased measurement of the effect of jet quenching. Recent measurements have shown that the sum of the pseudorapidity gaps between the particles in the event can be used to efficiently separate the UPCs from the hadronic Pb+Pb collisions. Using these pseudorapidity gap variables in low-multiplicity 5.02 TeV Pb+Pb data from the ATLAS experiment at the Large Hadron Collider, as well as those in simulated events from HIJING and DPMJET, we estimate the fraction of peripheral and ultra-peripheral Pb+Pb collisions in ATLAS Pb+Pb data and investigate the effectiveness of using gap variables to separate them. |
Thursday, October 14, 2021 12:18PM - 12:30PM |
QE.00005: Searching for Strangeness Enhancement in Ultra-Peripheral Pb+Pb Collisions with ATLAS Morgan B Knuesel Strangeness enhancement is considered a signature of the formation of a quark-gluon plasma and has thus been studied in various collisions involving different particle species. This study investigates the feasibility of measuring strange hadrons in photonuclear ultra-peripheral collisions using 5.02 TeV Pb+Pb collision data collected by the ATLAS experiment at CERN's Large Hadron Collider. γ+Pb collisions have recently been found to exhibit collective phenomena similar to that of a QGP. Hence, it is natural to search for strangeness enhancement as well. By fitting distributions of the energy lost by low-momentum reconstructed charged particle tracks as they traverse ATLAS's Pixel Detector (dE/dx), the yields of identified pions, kaons, and protons can be extracted. We explore the identified charged-particle yields as a function of charged-particle multiplicity, along with the ratio of identified kaons to pions, and compare with Monte Carlo simulations of γ+Pb collisions. Additionally, we seek to compare the charged-particle multiplicity dependence of the kaon-to-pion ratio in γ+Pb collisions to that in peripheral Pb+Pb collisions, where strangeness enhancement is expected. |
Thursday, October 14, 2021 12:30PM - 12:42PM |
QE.00006: Correlation between fragment lifetime, alignment, and composition in heavy ion collision simulations Emily Engelthaler, Bryan M Harvey, Sherry J Yennello When two nuclei collide at intermediate collision energies there is a tendency for a neck to form between the projectile and the target, and for this neck to be neutron-rich compared to the whole system. Following the neck rupture, the resulting excited projectile-like fragment (PLF*) and the target-like fragment are typically deformed and are likely to undergo dynamical decay. Because of the neutron-rich neck, the PLF* typically begins with a more neutron-rich side and a less neutron-rich side. The PLF* may further break into two more fragments (one more neutron-rich and one less neutron-rich). Of interest is the relationship between how long the PLF* lasts before breaking, the angular alignment of the two fragments it breaks into, and how much the neutron and proton density evens out across the PLF* while it exists. The time scales at which this process happens are on the order of zeptoseconds. While the timescale at which PLF* lasts cannot be measured directly in an experiment, the whole process can be simulated with molecular dynamics model calculations. Data from an Antisymmetrized Molecular Dynamics (AMD) simulation of a zinc-70 on zinc-70 collision with energy of 35MeV/nucleon was analyzed to determine the relationship between the lifetime of the PLF*, the angular alignment of the two largest fragments resulting from the PLF*, and the proton/neutron richness of the two fragments. |
Thursday, October 14, 2021 12:42PM - 12:54PM |
QE.00007: Extracting fission barriers in the Pb region from simultaneous fits Bergen H Kendziorski, Adam K Anthony, William G Lynch An experiment in summer 2020 at the National Superconducting Cyclotron Laboratory measured the fission properties of nuclei in the neutron-deficient Pb region. A goal of this work was to extract fission barriers from the measured fission cross-sections. The two dominant decay modes for an excited nucleus in this region are fission and neutron emission. As the internal energy of the nucleus before decay (excitation energy) approaches the fission barrier from above, the cross-section drops off exponentially. The fission barrier of a nucleus can be extracted from fission cross-sections using a statistical decay model parameterized by the fission barrier, and the level densities of the compound nucleus both at the scission point and post neutron emission. As the experimental data does not go to low excitation energies and the model becomes more sensitive to the fission barrier at low energies, information from multiple nuclei was required to constrain the problem. We hypothesized that the level density parameters could be modeled as a function of the mass number for a region of the chart of nuclides. By simultaneously fitting a set of existing cross-section data in the Pb region, we verified this assumption and extracted a model for the level density parameters. |
Thursday, October 14, 2021 12:54PM - 1:06PM |
QE.00008: Microscopic Descriptions of 12C+α for the Oxygen-16 States in the Stellar Alpha-Capture Rate Evaluation William P Good, Matthew B Burrows, Kristina D Launey We report the first calculations of low-lying excited 0+ states in 16O and their rotational bands within a no-core shell-model framework. Such descriptions pose a challenge as a result of the cluster and collective nature of these states, but become feasible in the no-core symplectic shell model (NCSpM). The model utilizes the almost perfect symmetry of nuclear dynamics, the symplectic symmetry that preserves equilibrium shapes. It uses an inter-nucleon interaction deduced in the symplectic effective field theory, with only four parameters. The NCSpM yields the low-lying positive-parity energy spectrum of 16O, electric quadrupole transition strengths, and the ground-state rms radius, in a reasonable agreement with experiment. We use the NCSpM wave functions of the first two excited 0+ states, their rotational bands, and the low-lying 1- and 3- states in 16O to project onto 12C+α cluster wave functions. Using the cluster wave functions, we calculate alpha partial widths and asymptotic normalization coefficients. Our results are in good agreement with available experimental data and point to the importance of collectivity to reproduce the data. These results are crucial to further improving the evaluation of the 12C(α, γ)16O reaction rate at astrophysical temperatures. This rate is also of cosmological importance and may further inform studies of the masses of black holes produced by pulse pair instability supernovae. |
Thursday, October 14, 2021 1:06PM - 1:18PM |
QE.00009: Comparisons of single identified hadron spectra in heavy ion collisions to models using Rivet Ralph Davenport
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