Session B14: Fundamental Symmetries

On Demand

A combination of pionless effective field theory and large-$N_c$ expansion has demonstrated great potential for analyzing few-body hadronic parity violation (PV) at low energies. Here we focus on three-derivative nucleon-nucleon interactions that contribute to $P$-$D$ transitions as well as corrections to $S$-$P$ transitions. We show that the large-$N_c$ expansion can systematically separate low-energy constants (LECs) into those that occur at leading order in $N_c$ and those that occur at next-to-leading order in $N_c$. Relationships among the PV LECs emerge at leading order in $N_c$. Details of their subtraction-point dependent behaviors based on the current understanding of parity-conserving LECs are also presented. Finally, we discuss how our analysis may impact the prioritization of future PV experiments and lattice QCD calculations in this sector.   

On Demand

The Fermilab E-989 Muon g-2 Experiment aims to measure the anomalous magnetic moment of the muon ($a_\mu$) as a precision test of the Standard Model of particle physics. We perform this measurement by observing the spin precession frequency of a stored muon beam along with the magnetic field in the muon storage ring. The ring features a set of electrostatic quadrupoles which are necessary to maintain vertical storage of the beam. These quadrupoles also introduce a significant correction to $a_\mu$ known as the “E-field correction,” which depends on the momentum distribution of the muon beam. Here we present a method for recovering the momentum distribution via Fourier analysis of the muon beam’s cyclotron motion (or “fast rotation”). We motivate the procedure analytically, demonstrate its application empirically, and discuss sources of systematic uncertainty as it applies to Run-1.   

On Demand

Linear polyatomic molecules are highly sensitive probes of nuclear spin-dependent parity violation (NSDPV). Measurements in these systems will enable experimental determination of poorly known electroweak coupling parameters. To date, measurements have focused on heavy nuclei where the NSDPV effect is enhanced by relativistic and collective nuclear effects. However, cold trapped polyatomic molecules should allow for the NSDPV effect to be measured to 10{\%} uncertainty~in nuclei as light as Be. We focus on four light species: Be and Mg cyanide and isocyanide. Importantly, molecular and nuclear calculations are highly accurate for these light systems, allowing experiment to directly test Standard Model predictions.   

On Demand

Neutron beta decay is the simplest example of semi-leptonic decay. The neutron lifetime provides an important test of unitarity and consistency of the Standard Model. The neutron lifetime is also the largest uncertainty in Big Bang Nucleosynthesis calculations of light element abundance. A precise measurement of the neutron lifetime and $\lambda$, the ratio of axial vector and vector coupling constants of the weak interaction, allow for a determination of the CKM matrix element V$_{ud}$ that is free from nuclear structure effects. A new measurement of the neutron lifetime using the in-beam method is ongoing at the NIST Center for Neutron Research. This method requires the absolute counting of decay protons in a neutron beam of precisely known flux. Improvements in the neutron and proton detection systems as well as the use of a new analysis technique should allow for a thorough investigation of major systemic effects. The experimental status, systematic tests, analysis techniques and early data will be presented.   

Status of the Nab Detector System

The Nab experiment will extract the electron-neutrino correlation coefficient and Fierz Interference term for neutron beta decay from precise measurements of electron energy and proton momentum. To meet stated uncertainty goals, Nab requires $10^{-4}$ level precision on electron energy and, as proton momentum will be extracted from proton time of flight, average systematic timing bias understood to within 0.3 ns. Nab uses large area silicon detectors at the ends of a unique spectrometer. An update on the detector system, including completed and planned testing, will be presented.   

GPU Based Nearline Analysis System for the Nab Experiment

The Nab neutron decay correlation experiment will utilize a pair of 127-pixel silicon detectors to measure the electron-neutrino correlation coefficient from the 2D energy distribution of protons and electrons. For each decay event, analog signals from ~30 pixels are digitized at a rate of 250 MHz resulting in an approximately 50 MB/s data rate. First-order timing and energy results are extracted by the data acquisition firmware using traditional filtering techniques, but in order to reach the precision goals of the experiment, a new technique is required. A GPU-based weighted least squares fitting routine has been developed that fits template waveforms, while subtracting baseline noise features, at an excess of 100 MB/s per GPU. This system will be used as part of the data acquisition process as well as during offline analysis on GPU clusters.