Physics & Astronomy Nuclear Science Seminar
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Title: From chiral effective field theory to perturbative QCD: A Bayesian model mixing approach to neutron star matter
Abstract: Constraining the equation of state (EOS) of strongly interacting, dense matter is the focus of significant experimental, observational, and theoretical effort. While chiral effective field theory (EFT) can describe the EOS between the typical densities of nuclei and those in the outer cores of neutron stars, perturbative QCD (pQCD) can be applied to properties of deconfined quark matter, both with quantified theoretical uncertainties.
However, describing the full range of densities in between with a single EOS that has well-quantified uncertainties is a challenging problem. Bayesian model mixing (BMM) can help bridge the gap between the two theories.
In this talk, I will present a BMM framework that can combine EOS constraints from different density regions in a principled way to construct a globally predictive, composite EOS model based on Gaussian processes (GPs). I will discuss applications of this BMM framework to the EOS and structure of neutron stars, as well as the statistical uncertainty quantification of the underlying microscopic EOS calculations.
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Title: Precision QED Corrections to the Neutron's Lifetime
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Title: The Los Alamos Neutron Electron Dipole Moment (LANL nEDM) Experiment
Abstract: Experimental searches for the neutron electric dipole moment (nEDM) provide sensitive probes into CP-violating physics. The Los Alamos Neutron Electric Dipole Moment Experiment (LANL nEDM) aims to measure the neutron EDM with a statistical uncertainty of 2x10^-27 e-cm in a year-equivalent of data collection using Ramsey’s method of separated oscillatory fields at the recently upgraded ultracold neutron (UCN) facility. A description of the apparatus and the current status will be reported with a particular focus on the magnetic field system.
Title: QCD and QED Radiation in Lepton-Hadron Scattering: A Joint Factorization Approach
Abstract: The factorization theorem plays an important role in the analysis of high energy quantum chromodynamic (QCD) processes, separating the nonperturbative hadronic interaction into the universal parton distribution functions (PDFs) and fragmentation functions (FFs) and the process-dependent interactions into short distance perturbative calculations, with any interference power suppressed. With a virtual photon exchange, lepton-hadron deep inelastic scattering (DIS) provides an electromagnetic hard probe for the partonic structure of colliding hadrons and has played an important role in the development of QCD factorization. However, the collision induced QED radiation can change the momentum of the exchanged but unobserved virtual photon, making the photon-hadron frame, where the factorization formalism for DIS and semi-inclusive DIS (SIDIS) was derived, ill defined. A new analogous factorization approach has been introduced to separate the leading power process-independent QED radiative contributions to the single photon exchange by introducing lepton distribution functions (LDFs) and lepton fragmentation functions (LFFs), while process-dependent effects are perturbatively calculated with large logarithms removed [J. High Energ. Phys. 2021, 157 (2021)]. These LDFs and LFFs are considered global, as they appear in many different interactions, such as $e^+ e^-$, DIS and SIDIS, so data from experiments can be used to fit and describe these functions across a wide range of lepton scattering. In this work, I will apply this new hybrid factorization approach to lepton-hadron DIS and SIDIS. For DIS, I derive the NLO short distance perturbative contribution to the cross section and demonstrate the effects the QED radiation has on the cross section using this approach using the CTEQ parameterization for the QCD functions. As part of the SIDIS analysis, I study the cross-section in two different kinematic regions: (1) the scattered lepton and observed hadron are not near back-to-back, and (2) they are close to back-to-back, where collinear QCD factorization works for (1) and TMD QCD factorization for (2) while collinear QED factorization works for both. As part of this work, I show the effects on the SIDIS cross section using fixed order calculations for the unpolarized structure function by first showing the effect of the radiative corrections on the main kinematic variables, especially how the internal transverse momentum is significantly correlated to the external angular dependence, and then the unpolarized structure function (or cross section) with matching between the descriptions for low and high transverse momentum. This work will impact the calculations for predictions for data from COMPASS and various Jefferson Lab experiments.
The axion is one of the best motivated dark matter candidates, simultaneously solving the Strong CP problem as well as providing the dark matter of the universe. However, in comparison to WIMPs the axion was historically neglected by experimental efforts. This has been changing in the last five years, which a bevy of new experiment proposals and results. I outline several recent updates for new detection ideas, including plasma haloscopes and axion detection with phonon-polaritons.