Session B19: Undergrad Research II

Assessing Mean Transverse Momentum of Ultracentral Collisions as a Tool for Extracting the Speed of Sound in Quark-Gluon Plasma

In high energy nuclear collisions, a new state of hot and dense matter, called quark-gluon plasma (QGP), is predicted to be formed. Experimentally constraining the equation of state (EoS) of QGP remains a key challenge. In steps towards quantifying the EoS, recent measurements by the Compact Muon Solenoid (CMS) experiment at the CERN’s Large Hadron Collider have spurred precise estimations of the speed of sound in QGP. These estimates assume that, in ultracentral collisions, the rate of change of the average transverse momentum (<p_T>) over the number of charged particles (N_ch), corresponds to the speed of sound. However, to what extent the speed of sound is quantitatively connected to this experimental observable has not been tested in a systematic way.

In this work, we apply a state-of-the-art relativistic hydrodynamic model, MUSIC, to conduct a comprehensive study of this assumption. By manipulating the input EoS which governs the speed of sound (e.g., varying from Lattice QCD calculations to hadronic gas and ideal gas models), we will present results on how the slope of <p_T> vs N_ch responds to EoS variations in the MUSIC model and compare with CMS data. Our findings will demonstrate the robustness and limitations of extracting the speed of sound via <p_T> in ultracentral collisions.   

The FoCaL Detector of ALICE at the LHC

CERN (European Center for Nuclear Research) is a global laboratory that studies proton and heavy ion collisions at the Large Hadron Collider (LHC). ALICE (A Large Ion Collider Experiment) is one of four large experiments at the LHC. ALICE is dedicated to studying the transition of matter to Quark-Gluon Plasma in heavy ion collisions. The experiment is currently taking data in Run 3, and preparing for upgrades after the third long shutdown (LS3) in 2025-26. To this end, ALICE is undertaking an initiative to extend its physics capabilities. Among these improvements is the Forward Calorimeter (FoCal). The Forward Calorimeter is a highly granular electromagnetic calorimeter combined with a conventional sampling hadronic calorimeter. The primary objectives of the FoCal are to obtain high-precision measurements of direct photons and jets, as well as coincident gamma-jet and jet-jet measurements. This presentation will describe the FoCal detector, its capabilities, and the results from particular performance simulations.   

Interpolating the 't Hooft model between instant and front forms 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 the spatial or axial gauge (A¹ = 0) in IFD and the light-front gauge (A⁺ = 0), there are several benefits to the Coulomb gauge that cannot be ignored. For example, we involve neither Gribov copies nor ghost fields in the Coulomb gauge. Using this parameter δ, we will solve for the mass gap equation using both Hamiltonian formalism and Feynman diagram analysis, expecting the independence of gauge choice when compared to axial gauge calculations. We then will derive the quark-antiquark bound-state equation in the interpolating dynamics using the dressed fermion propagator and compare with the results obtained in the interpolating axial gauge [1]. We expect meson mass spectra of such mesons that follow Regge trajectories to be independent of δ and gauge choice. We are planning to obtain the bound-state wave functions and compare the results between the interpolating Coulomb gauge and the interpolating axial gauge. Since QCD respects the gauge symmetry, these results should all be independent of the gauge choice. Thus, we expect identical results to [1] for the physical quantities. Using interpolation techniques, we can produce an alternative approach to quasi-PDFs not only with the frame dependence but also with the δ dependence. These interpolating quasi-PDFs can be implemented in the lattice QCD without suffering from the large momentum boost.

Identification and analysis of two-pixel correlated events in BeEST Phase-III Data

The Beryllium Electron Capture in Superconducting Tunnel Junctions (BeEST) experiment measures Lithium-7 atomic recoils from the electron capture decay of Beryllium-7 as a precision search for neutrino-coupled BSM physics. Following the single-pixel demonstration in Phase-II, Phase-III uses a 6x6 grid of superconducting tunnel junction (STJ) detectors, allowing us to analyze spatial correlations and simultaneity between devices. Due to the sensitivity of the detector, there are external events that must be identified and filtered out for the creation of the final Phase-III limit. In this talk, we present a systematic analysis of two-pixel correlated events for their location, time, energy and pulse shape to identify anomalous events and hypothesize their origins. By examining the shape and occurrence of these events, we can understand and reduce systematic uncertainty in our data and contribute to the design of the Phase-IV detector array.   

Classifying Pulse Shapes from Superconducting Tunnel Junctions for the BeEST Experiment

The Beryllium Electron capture in Superconducting Tunnel junctions (BeEST) experiment aims to detect physics beyond the Standard Model by measuring atomic recoils from the electron capture decay of Beryllium-7 (Be-7). The experiment utilizes superconducting tunnel junction (STJ) sensors to measure the daughter recoil kinetic energy spectrum to search for neutrino-coupled BSM physics. In this talk, we present systematic studies that aim to distinguish between events occurring in the top and bottom electrodes of the STJs to search for the presence of a line-splitting artifact that could mimic a heavy neutrino signal. This is accomplished by analyzing the rise and fall times of the electrical pulses generated by the nuclear decays. Two primary techniques, 10-90% Rise Time Analysis and Charge Integration, are employed to investigate the pulse characteristics. While the former exhibits challenges in noise and pile-up events, the latter reveals a clear separation in the data, indicating differences in the STJ electrodes. The study proposes further investigation into the segregation observed and explores alternative methods for event separation.   

Determining the Longitudinal Double-spin Asymmetry (ALL) for η Production from STAR 2013 Endcap Calorimeter Data

The Solenoidal Tracker at RHIC (STAR), located at Brookhaven National Laboratory, uses longitudinally polarized proton-proton collisions to study the gluon spin contribution to the known proton spin. One method is to measure the longitudinal double-spin asymmetry (A_LL) in the production of η mesons from the longitudinally polarized proton-proton collisions at √s = 510 GeV. The η mesons that are produced from the collision quickly decay (in about 5.0×10^-19 s) into two photons that are detected using the Endcap Electromagnetic Calorimeter (EEMC, 1.09 < η < 2.00). The EEMC determines the energies and positions of the incoming photons. With the data from the EEMC, we can calculate the invariant mass of the photon pairs and produce a two-photon invariant mass spectrum. This spectrum is fitted with a Gaussian function to represent the η mesons plus a third-order polynomial function to describe the background photon pairs. The total number of η mesons is then obtained by integrating the fitted Gaussian function. The asymmetry is calculated using the number of η mesons resulting from the collisions of protons with different spin alignments. The status of the analysis of the 2013 dataset to measure the η meson A_LL will be presented.   

Determining Gluon Contribution to Proton Spin with STAR 2015 Endcap Electromagnetic Calorimeter Data

Longitudinally polarized protons are collided in the Solenoidal Tracker at RHIC (STAR) located at Brookhaven National Laboratory to study the gluon spin contribution to the spin of the proton. Refining our knowledge of the gluon spin contribution to the proton's spin will help us solve the proton spin puzzle and is one significant goal of the STAR collaboration. This study analyzes the data from 2015 longitudinally polarized proton-proton collisions (√s = 200 GeV) and the resulting neutral pions (π⁰) that are created. The π⁰s decay almost instantaneously (~10^-16 s) into two photons that can be detected with STAR's Endcap Electromagnetic Calorimeter (EEMC, 1.09 < η < 2.00). By analyzing the π⁰s that are produced we can calculate the spin-dependent asymmetry, A_LL, of the π⁰ which is related to the gluon contribution to the spin of a proton. We have analyzed the 2015 data to form photon and π⁰ candidates. To ensure quality data for the eventual A_LL analysis, we monitor distributions such as the reconstructed π⁰ mass and the number of EEMC towers hit per event. We will present the status of the 2015 EEMC π⁰ reconstruction and quality assurance effort.