Session M02: Undergraduate Research II

Calorimeter Construction: Precision Measurements of η and η' Decays Using the Jefferson Lab Eta Factory

We introduce a new experiment conducted in experimental Hall D at the Thomas Jefferson National Accelerator Facility, dubbed the Jefferson Lab Eta Factory (JEF). This forthcoming project will perform precision measurements of various η and η' decays focusing on rare neutral modes. The JEF experiment requires upgrading the inner part of the forward lead glass calorimeter of the GlueX detector with high-granularity and improved resolution lead tungstate scintillating crystals. The new calorimeter consists of 1,596 modules undergoing fabrication. During the summer of 2023, we worked on fabricating the calorimeter modules and performed quality assurance tests using a light-emitting diode. We will give an overview of the design of the calorimeter modules, the fabrication of the modules, and the testing procedure for functionality and their results.   

Investigating the Neutrino Mass Ordering Problem via Ternary Plots

In this analysis of the Neutrino Mass Ordering problem, we use ternary plots to visualize the flavor composition of various supernova neutrino emission models from the SNEWPY software package. Through our analysis of several models, we have explored potential discriminants between the Normal and Inverted mass orderings in the ternary representations of the models' fluxes. We analyze the statistical significance of mass ordering discriminants through simulated detector responses.   

A Neutron Elevator to Increase Neutron Loading Efficiency and Improve the Neutron Lifetime Precision in the UCNτ+ Experiment

Measurement of the neutron lifetime τ_n to a precision of 0.1 s is key to calculate the CKM matrix element V_ud, the probability of up-to-down quark transition in charge-current weak decays, accurately enough to test the unitarity of the CKM matrix and investigate physics beyond the Standard Model. The UCNτ experiment at Los Alamos National Laboratory (LANL) traps ultra-cold neutrons (UCNs) in a bowl-shaped Halbach array using gravity. Sheets of cleaner materials then remove neutrons with energy >38 meV via both up-scattering and capture. The resulting population of neutrons in the trap, measured via coincidence events between two PMTs over some time period, is then fitted to an exponential decay curve to determine τ_n. UCNτ has measured a value of τ_n = 877.75 +- 0.28_stat + 0.22/- 0.16_syst s, the most precise τ_n measured so far.

The UCNτ+ upgrade increases loading efficiency via an elevator to lower UCNs into the trap: higher-energy neutrons will transfer energy to the elevator by colliding with its front wall, resulting in a lower-energy population of UCNs. This minimizes error by reducing the number of higher-energy neutrons that escape the trap and maximizing the number of UCNs cold enough to remain after cleaning. It is critical that the elevator moves smoothly: any vibrations will transfer energy from the elevator back to the neutrons, heating them up. This poster will describe the UCNτ+ procedure and present accelerometer data on the elevator’s vibrations that demonstrates the repeatability of the motion.   

Interpolating the 't Hooft model between Instant Form dynamics and Light-Front dynamics in the Coulomb gauge

The 1+1D model of quantum chromodynamics (QCD) in the infinite number of colors, or ‘t Hooft model, is interpolated between the instant form dynamics (IFD) and the light-front dynamics (LFD) using an interpolation parameter δ in the interpolating Coulomb gauge which links the Coulomb gauge (A⁰ = 0) in IFD and the light-front gauge (A+ = 0). While calculations such as these were performed [1] in the interpolating axial gauge which links the spatial or axial gauge (A1 = 0) in IFD and the light-front gauge (A+ = 0), there are a number of benefits to the Coulomb gauge that cannot be ignored. All degrees of freedom are physical, making this an ideal choice for finding the bound-state equations and for renormalizability. Using this parameter δ, we find the mass gap equation using both hamiltonian formalism and feynman diagram analysis, noting that it reproduces both the results for IFD and LFD in the Coulomb gauge and the light-front gauge, respectively. We then derive the quark-antiquark bound-state equation in the interpolating dynamics using the dressed fermion propagator and compare with results obtained in the interpolating axial gauge [1]. The meson mass spectra of such mesons that follow Regge trajectories are independent of δ, which are observed in both IFD and LFD calculations using the interpolating axial gauge condition. We also obtain the bound-state wave functions in the interpolating dynamics. These wavefunctions are particularly useful in the calculation of quasi-parton distribution functions (quasi-PDFs), in which we can produce an alternative approach to the quasi-PDFs not only with the frame dependence but also with the δ dependence. The Coulomb gauge in IFD is particularly interesting in this way, because the A0 component is renormalization group invariant [2]. Thus, the interpolation may lead to an alternative quasi-PDF that can be implemented in the lattice QCD without suffering from the large momentum boost.

1. Ma, Bailing, and Chueng-Ryong Ji. “Interpolating ’t Hooft Model between Instant and Front Forms.”

Physical Review D, vol. 104, no. 3, 2021,

https://doi.org/10.1103/physrevd.104.036004.

2. Zwanziger, D. (1998). Coulomb-Gauge in QCD: Renormalization and confinement.

Progress of Theoretical Physics Supplement, 131, 233-242.

https://doi.org/10.1143/ptps.131.233   

An Unconventional Deformation of the Spin-1/2 Fermi Gas

Interacting bosonic and fermionic systems can be expressed in terms of their noninteracting versions (in an external field) by using a Hubbard-Stratonovich transformation. When treating interactions in that fashion, the quantum statistics enters through the form of the noninteracting partition functions $mathcal{Z}_0$. The logarithm of $mathcal{Z}_0$ for bosons and fermions are distinguished mathematically, by the former being given by an infinite series, while the latter is a truncated sum due to the Pauli principle. By truncating the bosonic series in different ways, one obtains an extension of quantum statistics in an unconventional direction that interpolates between fermions and bosons, where only up to K particles may occupy a single-particle state, with K varying between 1 and infinity.

In this work, we explore such a deformation in a particular case, which amounts to twisting the chemical potential of the Fermi gas in the complex plane.  In particular, in the conformally invariant case of the unitary limit of spin-1/2 fermions, we obtain a class of equally conformally invariant theories of particles obeying alternate statistics. We provide a first description of the thermodynamics of such a system and compare it with known results for conventional spin-1/2 fermions.   

Using Rivet to perform model comparisons in Relativistic Heavy Ion Physics

When nuclei collide near the speed of light, a hot and dense form of matter called the Quark Gluon Plasma (QGP) is formed. Properties of the QGP can be determined through systematic comparison between data and models. The Rivet (Robust Independent Validation of Experiment and Theory) toolkit simplifies the process of comparison between different Monte Carlo event generators and the experimental data. Rivet only requires one code to be written in order to be used for multiple models whereas other approaches usually require code which is only used once. Several Rivet analyses are implemented and used to compare Monte Carlo models such as PYTHIA Angantyr and JETSCAPE (Jet Energy-loss Tomography with a Statistically and Computationally Advanced Program Envelope) with data from the PHENIX experiment.   

The Search for the X17 boson: Analyzing e+e- pair production processes with the prototype AT-TPC using Geant4

In 2016, a group of scientists discovered a possible candidate for a dark fifth-force carrier of the Universe during an experiment in ATOMKI in Debrecen, Hungary. This hypothetical boson would come from an internal pair creation of the decay of 8Be. In particular, scientists had measured the angular correlations of e⁺e^- pairs and observed that at large angles, a neutral particle with a mass of 16.70±0.35(stat)±0.5(syst) MeV/c² and J^π=1⁺ was created, hence the name, X17.

The prototype Active-Target Time-Projection Chamber (pAT-TPC) was used to conduct an experiment at the tandem facility of Notre Dame to search for the X17 resonance via the ⁷Li(p,g)⁸Be reaction. The angular distribution of the produced e⁺e^- pair from the g conversion will be reconstructed to identify the possible existence of this boson. Preliminary analysis of the data indicates a relatively high identification of triple tracks of two electrons and one positron. A realistic Geant4 Monte Carlo simulation was developed to describe the experimental setup, understand the background, and provide information on the efficiency and resolution of the system. In this presentation, I will discuss and present results from this study. This research is part of PING - Physicists Inspiring the Next Generation: Exploring the Nuclear Matter 2023.   

Mixed Sterile Neutrino Dark Matter Models and the Early Universe Quark-Gluon Plasma

Astrophysics points to the possibility of a 7.1 keV sterile neutrino dark matter particle, inferred from an unidentified 3.55 keV X-ray line in the stacked spectra of galaxies and clusters. Sterile neutrino dark matter provides an interesting way to probe nuclear physics in the early universe, as sterile neutrino dark matter is formed prior to the QCD transition, when the universe is a high-entropy quark gluon plasma (QGP). Consequently, the production of sterile neutrino dark matter is greatly influenced by both the characteristics of the QGP and neutrino interactions within it. In this talk, we consider mixed sterile neutrino dark matter models that combine cold dark matter and sterile neutrino dark matter. Our investigation focuses on how the interplay between properties of the QGP and neutrinos are imprinted on these mixed sterile neutrino dark matter models, along with their consequential astrophysical implications.   

Studies of the Proton target and current fragmentations in the Deep Inelastic Regime

Studies of the properties and the azimuthal distribution of hadrons produced in the Target Fragmentation Region serve as a test of our complete understanding of the different mechanisms in the SIDIS production of hadrons and provide additional information on the QCD dynamics that are not accessible with single hadron production in the Current Fragmentation Region. We present studies of beam SSA for semi-inclusive protons (ep → e′p'+X), produced in the TFR, that can be related to higher twist Fracture Functions describing the F_LU structure function. Such measurements were performed with the CLAS12 detector in Hall B at Jefferson lab using a longitudinally polarized 10.6~GeV electron beam on an unpolarized hydrogen target. Preliminary results of this study captured the transition between the TFR and CFR regions showing a clear sign change of the SSA for protons produced in the backward region in CM, dominated by TFR protons providing a criteria for experimental separation of CFR and TFR regions. These findings are opening a new avenue for studies of nucleon structure.   

Neutrino Detectors and Neural Networks for Nuclear Nonproliferation

The CHANDLER detector is planned to measure the neutrino spectrum of nuclear reactors for nonproliferation monitering. The use of neural networks to classify events in this detector by particle type and evaluate the strength of variables as classifiers is explored. Two types of perceptron network are trained on a computer-simulated monte carlo dataset that identifies the event as a neutron or a neutrino, then gives a list of data values for the event. The first network– which optimized a single hyperplane cut– achieved a significance of 100, and the second network– a more sophisticated model with four ReLu processing neurons– achieved a significance of 146, outperforming the decision tree used previously for the CHANDLER detector. Subsequently, separate iterations of these networks were trained on 1-gamma and 2-gamma events to allow them to isolate features individual to these classes of events. This procedure found that 1-gamma events were classified very poorly by both networks, so a new variable that measures the escape probability of the second gamma was introduced, achieving a small improvement at selecting for 1-gamma IBDs. An alternative method of separating 1-gamma IBDs from 2-gamma IBDs was also found through the analysis of 2-d histograms, which improved the classification rate further. Finally, a new reward function that optimized for significance directly was introduced to train the neural network, greatly reducing the amount of manual tuning and re-learning needed to train an effective network. The combination of all of these achieved a significance of 170, outperforming all prior classification methods.   

Simulation of a KLong-Muon Detector (KLM) for the U.S. Electron Ion Collider

The Electron Ion Collider (EIC) aims to investigate the dynamics of quarks and gluons within nucleons and nuclei. The EIC design allows for two detectors, with the ePIC detector currently being the project detector and an opportunity for development of a second detector. Muon detection is of interest for some nuclear reactions, such as J/psi production. Here, we report on simulation studies of a KLM detector specifically designed to detect muons at the EIC. Acceptance and pion-muon separation power are quantities of interest. We utilized the Fun4All simulation of the COmpact DetectoR for EIC (CORE) detector, which was designed as a second EIC detector [1]. We implemented the EIC KLM design, derived from the BELLE II KLM design, consisting of scintillator and steel layers in the simulation and generated samples of muons and pions with controlled momentum and pseudorapidity at the interaction point. In this presentation, we will show the minimum momentum a muon needs to reach the KLM detector, which is located outside the magnet, as a function of field strength and pseudorapidity, as well as a comparison of the signals produced by muons and pions in the KLM. This work supports the proof-of-principle of the EIC KLM design and the results will be used in future design optimizations. 

[1] CORE Proto-Collaboration, “CORE – a compact detector for the EIC,” https://doi.org/10.5281/zenodo.6536630 (2021).    

Understanding Stellar Nucleosynthesis by Measuring Nuclear Level Densities via Proton Evaporation

Nuclear level densities are of great importance to astrophysical phenomena, which require an understanding of nuclear reaction rates. Existing theoretical Hauser-Feshbach models vary by factors of three or more when used to calculate reaction rates. Thus, additional measurements of nuclear level densities are necessary to improve existing models. The common method of using particle evaporation from compound nuclear reactions is known for its ability to study the nuclear level density. Proton evaporation is then a natural approach to further current understanding. EMPIRE was used to model proton-evaporation reactions, and preliminary results in the study of Al(12C,p) data from the Edwards Accelerator Laboratory will be presented. These results consist of outputs from two separate programs: the first is a sorting code, written in Fortran, that translates and organizes the files from the digital data acquisition hardware in the lab into a single output file for each run of the accelerator; the second is an analysis code, written in C++ and using the ROOT framework, which reads the sorted output file and calculates differential cross section as a function of angle and energy.