Session FL: Mini-Symposium on Fundamental Symmetries: Theory and Experiment II

A Precision Measurement of the Parity Violation Present in the 0.734 eV p-wave Resonance in $^{139}$La Using the 'Double Lanthanum' Technique: Preliminary Results and Analysis

The Neutron OPtics Time Reversal EXperiment (NOPTREX) Collaboration aims to measure potential time-reversal (T) violating processes in neutron-nucleon forward scattering interactions in parity (P) violating nuclear resonances. Because the proposed theoretical T-violating cross-section is directly proportional to a P-violating cross-section, precision spectroscopy of these resonances is of critical importance. In particular, the 0.734 eV p-wave resonance in $^{139}$La exhibits a well known ~10\% P-violation effect, making it an outstanding candidate for the NOPTREX experiment. We aim to measure this effect in $^{139}$La to 1\% precision, improving upon previous (room temperature) measurements by using cryogenic targets (15K) to reduce Doppler broadening effects as well as running for a longer period of time to reduce statistical uncertainty. This experiment was conducted at Los Alamos National Laboratory in 2017-2019. This talk will briefly cover the experimental setup, the efforts to constrain systematic uncertainties, the data analysis process, and preliminary results.   

Polarized $^3$He Neutron Spin Filter for Parity-Odd Asymmetry Measurement on 0.88-eV p-Wave Resonance of $^{81}$Br

The Neutron OPtics Time Reversal Experiment (NOPTREX) collaboration plans to conduct a sensitive search for time reversal invariance violation in polarized neutron transmission through polarized nuclei by taking advantage of the very large amplification of symmetry-violating effects in p-wave resonances of certain heavy nuclei. As a step toward this experiment we are remeasuring parity violation in selected nuclei to greater precision at LANSCE. One such candidate is $^{81}$Br with a longitudinal asymmetry of $A = 0.024 \pm 0.004$ at the 0.88-eV resonance. We aim to measure this asymmetry to 5\% accuracy. This requires an intense source of polarized neutrons at eV energies. We plan to use a polarized $^3$He neutron spin filter based on the very large spin dependent neutron absorption cross-section of neutrons on $^3$He. In the $^3$He system under construction at Indiana University, $^3$He gas is polarized by spin-exchange optical pumping (SEOP). Key components include a $\mu$-metal shielded solenoid and $^3$He gas cell both generously provided by ORNL. This talk will describe the proposed $^{81}$Br experiment, motivation for choice of $^3$He SEOP for NOPTREX, and projected performance of the $^3$He spin filter.   

Spin Dependent Components of Slow Neutron-Nucleus Scattering in $^{131}$Xe and other Heavy Nuclei: Pseudomagnetic Precession Measurement and Calculation

In Neutron OPtics Time Reversal Experiment (NOPTREX) collaboration's searches for new time reversal sources, spin dependent components of slow neutron-nucleus scattering introduce a significant source of systematic error in forward scattering amplitude. We plan to measure for the first time the pseudomagnetic precession effect caused by spin dependent scattering in neutron transmission through polarized $^{131}$Xe and $^{129}$Xe. This experiment takes place at FRM II in Germany where we use a Neutron Spin Echo (NSE) device to measure pseudomagnetic precession and a Spin Exchange Optical Pumping (SEOP) system to polarize Xe isotopes. Furthermore, as the mechanism which gives rise to the pseudomagnetic precession has never been calculated before, we will theoretically evaluate the incoherent scattering length produced by the difference of $a_{+}-a_{-}$, which are the two neutron-nucleus scattering amplitudes corresponding to the two total angular momentum scattering channels $J=I\pm1/2$. Here we will present our calculation of the contribution from both potential scattering and resonance scattering, as well as our predictions of $a_{+}-a_{-}$ in Xe and other heavy nuclei, with the help of extensive n-A resonance data from National Nuclear Data Center (NNDC).   

Parity Violation in the 3.2 eV p-wave Neutron Resonance in $^{131}$Xe

Time reversal (TR) violation in polarized neutron transmission through polarized nuclei can be used to search for beyond the Standard Model physics. A few heavy nuclei including $^{139}$La, $^{81}$Br, and $^{131}$Xe can amplify both parity-odd and parity-odd/time-reversal odd effects due to their mixing of s-wave and p-wave resonances[1]. We focus on $^{131}$Xe, where a previous experiment observed a large P-odd asymmetry in the 3.2eV p-wave resonance of $^{131}$Xe[1,2]. We present the design for a cryogenic, solid Xe target to be used in a remeasurement of the P-odd asymmetry on the 3.2 eV resonance to higher precision. We will use a polarized 3He neutron spin filter to polarize the 3.2 eV neutrons. It has also been shown that $^{131}$Xe is polarizable using spin exchange optical pumping techniques[1,3], which will be important for future tests measuring TR asymmetry. [1] J.J. Szymanski, W. M. Snow, et al., Phys. Rev. C{\bf 53}, R2576 (1996). [2] A. Komives, J. D. Bowman, et al., {\it Resonance parameters and analyzing powers of neutron resonances in natural Xenon}, unpublished (1999). [3] Stupic KF, Cleveland ZI, Pavlovskaya GE, Meersmann T, {\it Hyperpolarized $^{131}$Xe NMR spectroscopy}, Nucl. Phys. {\bf A401}, Journal of Magnetic Resonance. {\bf 208}: 58–69 (2011).   

A Search for Possible Long Range Spin-Dependent Interactions of the Neutron from Exotic Vector Boson Exchange

An exotic axial vector interaction in the mm-$\mu$m range using spin-dependent neutron-atom interactions though exchange of spin-1 bosons has been predicted in some extensions of the Standard Model. An experiment in search of this interaction was performed on FP12 at LANSCE (LANL) by sending transversely polarized slow neutrons through a series of open parallel slots bounded by flat rectangular plates of copper and glass arranged so that the possible exotic interaction would tilt the plane of polarization along the neutron momentum [1]. The resulting rotation $\varphi'=[2.8\pm4.6(stat.)\pm4.0(sys.)]\times10^{-5}$ rad/m was consistent with zero [2]. For the potential $V_{5}=\frac{g^{2}_{A}}{4\pi m}\frac{e^{-m_{0}r}}{r}(\frac{1}{r}+\frac{1}{\lambda_{c}})\vec\sigma\cdot(\vec v \times \hat r)$ the upper bound on the coupling constant $g ^{2}_{A}$ was improved by about three orders of magnitude in the mm-$\mu$m range [3]. We discuss this result along with plans to further improve the sensitivity of our search by at least 2 orders of magnitude at the NIST NG-C beam using tungsten and glass plates as the target.\\ \\{[1]} C. Haddock et al., Nucl. Inst. Meth. A 885 (2018)\\{[2]} C. Haddock et al., Physics Letters B 783 (2018)\\{[3]} F. M. Piegsa and G. Pignol, Phys. Rev. Lett. 108 (2012)   

Status of an Apparatus to Measure the Parity-odd Neutron Spin Rotation in $^{4}$He

The weak interaction between nucleons is sensitive to quark-quark correlations in the nucleon and provides an opportunity to test the Standard Model in the low energy strongly interacting limit. Recent advances in theory [1] [2] coupled to the measurement of the weak pion exchange component of the NN weak interaction imply predictions for parity-odd neutron spin rotation in $^{4}$He of $d\phi/dz = 9 \pm 3 \times 10^{-7}$ rad/m. The previous measurement of $d\phi/dz = [+2.1 \pm 8.3(stat.) \pm 2.9(sys.)] \times 10^{-7}$ rad/m [3] lies just outside the theoretical value. A new non-magnetic pump and target system and other upgrades to the NSR apparatus can enable an experimental sensitivity approaching $< [\pm 1.0(stat.) \pm 1.0(sys.)] \times 10^{-7}$ rad/m [4] on the NG-C beam at NIST. This would constitute the first Standard Model test of strangeness-conserving nonleptonic weak interactions. The status of the NSR apparatus will be presented. \\ \\{[1]} S. Gardner, W. C. Haxton, and B. R. Holstein, Ann. Rev. Nucl. Part. Sci. \textbf{67}, 69, 024001, (2017).\\{[2]} R. Lazauskas and Y.-H Song, Phys. Rev. C {\bf 99}, 054002 (2019).\\{[3]} H. E. Swanson, {\it et al.}, Accepted to Phys. Rev. C., (2019).\\{[4]} W. M. Snow, {\it et al.}, Rev. Sci. Inst. \textbf{94}, 055101, (2015).   

Precision Half-life Measurement of $^{29}$P

In recent years, precision measurements have led to considerable advances in several areas of physics, including fundamental symmetry.Precise determination of $ft$ values for superallowed mixed transitions between mirror nuclides could provide an avenue to test the theoretical corrections used to extract the V$_{ud}$ matrix element from superallowed pure Fermi transitions. Calculation of the $ft$ value requires the half-life, branching ratio, and Q value. The $^{29}$P decay half-life is derived from a series of measurements of which all are over 35 years old. The life-time was determined by the $\beta$ counting of implanted $^{29}$P on a Ta foil that was removed from the beam for counting. The $^{29}$P beam was produced by a transfer reaction and separated by the TwinSol facility of the Nuclear Science Laboratory of the University of Notre Dame. The progress on the $^{29}$P analysis will be presented.   

Precise half-life measurement of the superallowed mixed-miror decaying $^{15}$O

The Standard Model encapsulates our current understanding of matter and interactions in the universe, however there are some known shortcomings which provide a strong incentive to probe explicit experimental evidence of new physics. One such test lies in investigating the unitarity of the CKM matrix. The current limit is provided by a determination of the $V_{ud}$ matrix element, which relies on measurements of half-lives, branching ratios, and Q-values for the ensemble of $0^+\rightarrow0^+$ decays in order to extract $\mathcal{F}$$t$ values. This calculation, however, also requires knowledge of theoretical corrections, so it is ambitious to confirm the result with another ensemble such as T=1/2 mixed-mirror decays. Aligning with these interests, the half-life of $^{15}$O was measured using the $\beta$-Counting Station at the Nuclear Science Laboratory of the University of Notre Dame. Prior to this measurement the uncertainty of the $\mathcal{F}$$t$ value was dominated by the lifetime. The measurement, along with its impact of the $\mathcal{F}$$t$ value will be presented.