Session J02: Nuclear & Particle Physics

Chiral-Odd GPDs in the Bag Model

We study chiral-odd GPDs in the framework of the MIT bag model. We display our results for these GPDs along with those for the nucleon tensor form factors, compare our results to other theoretical results in literature, and discuss the phenomenological implications.   

Classical Models of the Neutron and Proton: Insights on the Energy-Momentum Tensor and the D-term

The description of the structure of the nucleon requires a relativistic quantum field theoretical framework. However, studies in classical relativistic field theories can offer clearer insights into fundamental properties without the intricate quantum corrections. This is particularly valuable when examining aspects tied to the long-range nature of electromagnetic interactions. Using the classical proton model developed by Bialynicki-Birula has especially revealed the profound influence of the long-range Coulomb force on the D-term form factor, which has been previously overlooked in models and lattice studies of quantum chromodynamics (QCD). This investigation involves transforming Bialynicki-Birula's classical "dust particle" field model into an adequate​ classical model​ of the neutron. We compute the neutron​ D-term and draw a comparison with the proton's D-term, which was noted to exhibit a divergence due to the influence of the classical Coulomb field. Notably, our findings confirm​ that the regularization approach​ proposed​ for the proton D-term is reasonable because it gives numerically very similar results to the neutron D-term.   

Measurement of quadrupole deformations from E2 transitions in order to identify candidate isotopes for atomic EDM measurement

Measuring a non-zero electric dipole moment (EDM) helps us seek new sources of CP violations and explore new physics beyond the Standard Model. We aim to characterize nuclear deformation since atomic EDM and magnetic quadrupole moment (MQM) are enhanced in octupole and quadrupole-deformed nuclei, respectively. We use data from the National Nuclear Data Center to gather information on the nuclear level scheme by surveying the energy levels relevant for electric quadrupole (E2) transitions from the ground state while ensuring the ground state parity doublet is not degenerate. To identify quadrupole deformation in the mass ranges from A=150 to 250, we produce a Weisskopf plot where the transition lifetime is a function of transition energy. We identify likely deformed nuclei by comparing existing experimental data to Weisskopf estimates. While the Weisskopf plot gives us qualitative information regarding nuclear deformation, we support these by explicitly calculating the quadrupole deformation using transition lifetimes. We have computationally calculated Eλ and Mλ transition matrix elements to supplement our calculation of quadrupole deformation from E2 transition strengths via the measurement of transition lifetimes. We present preliminary results on the experimental determination of quadrupole deformation of certain nuclei.   

Towards a Spectral Shape Measurement of the Decay of 137Xe to the (5/2+) 137Cs State

EXO-200 was the first kilomole-scale neutrinoless double beta decay (0νββ) experiment. It operated a single-phase liquid xenon time projection chamber (TPC) with ~150 kg of xenon enriched to 80% in the isotope 136 and made the first observation of the 2νββ decay of ¹³⁶Xe to the ground state of ¹³⁶Ba. In late 2018, an AmBe neutron source was deployed as part of an end-of-run detector calibration which produced ¹³⁷Xe inside the detector by neutron capture on ¹³⁶Xe. ¹³⁷Xe beta decays via two modes: to the ground state and the first excited state of ¹³⁷Cs. Combined, the measurement of the spectral shape of the decays can inform on the effective value of the axial coupling constant, g_A, in these nuclei. EXO-200 measured the β⁻ decay of ¹³⁷Xe to the ground state of ¹³⁷Cs in 2020.  This talk will go over the methodology behind the ongoing measurement of the beta decay of ¹³⁷Xe to the 5/2+ excited state of ¹³⁷Cs, which is accompanied by the emission of a 455 keV γ ray. Progress on calibrating both the ionization charge and scintillation light signals to measure this topologically distributed signal will be presented.   

Photon and Jet Energy Reconstruction from Low to High Momenta for Future Muon Collider Studies

In addition to the Future Circular Collider, groups are working on proving the feasibility of a muon collider. This collider will have the benefit of having a smaller circumference (10km vs. 100km) and will let all the energy imparted into the particle be used in the collision. Muons decaying in the beam tube produce a radiation background, flooding the detector with particles such as photons. These particles leave tracks and energy deposits that obscure important particles resulting from μμ collision events. This study provides a baseline benchmark for future studies that add beam-included background into their simulation. The accuracy of the reconstructed energy from the incoming particle(s) can be increased by applying a correction factor based on the reconstructed polar angle and reconstructed energy. This correction factor function is broken into multiple sinusoidal functions along the polar angle axis and along the reconstructed energy axis there is an exponential decay term. Applying this correction factor to the reconstructed photons shifts the mean of a deltaE/E from 0.04317 → 0.00004732, showing an increase in energy accuracy and precision. Similarly, applying these correction factors to the reconstructed jets sees a mean shift in the deltaE/E plot from -0.378 → 0.0124 and shifts the invariant mass of the original jet producing Z' boson from 6271 GeV/c^2 → 8152 GeV/c^2, much closer to the true invariant mass of 8675 GeV/c^2.   

Collisional Damping of Wakes in Doped Semiconductors

We examine the role of collisional damping in plasmonic wakefield accelerators. Three regimes are identified for wakefields driven in a doped semi-conductor by a charged particle beam: At low intensities of the driver pulse, the mobility of the free carrier electrons is limited by collisions. The mean free path of an electron is short compared to the quiver amplitude of a free electron, and the resulting wake is very small. A threshold intensity is found above which the conduction electrons in the semiconductor are driven to such high speeds that their Coulomb collision cross-section drops sharply, and the resulting wake can resemble that in a hollow collisionless plasma of density equal to that of the conduction electrons in the semi-conductor tube. At yet higher intensities, the entire tube can be ionized during the pulse rise, and electrons in the latter portion of the wake fill in the hollow region of the tube. This is the "crunch-in" or non-linear hollow plasma wakefield regime that can potentially produce TeV/m peak acceleration gradients. Lattice effects and laser drivers are briefly discussed.