# Bulletin of the American Physical Society

# 2020 Fall Meeting of the APS Division of Nuclear Physics

## Volume 65, Number 12

## Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA

## Session KF: Mini-Symposium: Precision Beta Decay I |
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Chair: Daniel Salvat, IU |

Saturday, October 31, 2020 8:30AM - 9:06AM |
KF.00001: The lay of the land when mountains move: Beta decay today Invited Speaker: Leendert Hayen Hand in hand with several new experimental results many years in the making, substantial theory progress has changed the precision beta decay landscape in the last years. As experiments stand at the precipice of a new order of magnitude in precision, a further expanded collaboration with theory has resulted in a reevaluation of a number of inputs using state-of-the-art methods. Whereas several nuclear ab initio methods are maturing into the mass $A$=10-20 region, new radiative corrections have revived tension with top-row CKM unitarity. Meanwhile, advances in lattice QCD are opening new channels for model-independent Beyond Standard Model searches. We present a brief sketch of the current landscape in CKM unitarity tests, exotic current searches and the neutron lifetime and look ahead towards compelling cases for both theoretical and experimental study. [Preview Abstract] |

Saturday, October 31, 2020 9:06AM - 9:18AM |
KF.00002: Quantum Monte Carlo calculations of beta decay in $A \leq 12$ nuclei saori pastore In this talk, I will present recent Quantum Monte Carlo calculations of lepton-nucleus interactions, with emphasis on electroweak matrix elements entering beta decay and electron capture rates. The calculations are based on many-body interactions and associated many-body electroweak currents. [Preview Abstract] |

Saturday, October 31, 2020 9:18AM - 9:30AM |
KF.00003: Ab initio calculations of 10C $\to $ 10B super-allowed Fermi transition Michael Gennari, Petr Navratil Cabibbo-Kobayashi-Maskawa (CKM) matrix unitarity is one of the most sensitive probes for beyond standard model (BSM) physics. Extraction of the largest contributor to unitarity, the Vud matrix element, from super-allowed 0$+ \quad \to $ 0$+$ Fermi beta decay transitions requires theoretical calculation of the isospin symmetry breaking correction $\delta $C. We apply the No-Core Shell Model with Continuum (NCSMC) [1], a method for describing both bound and unbound states in light nuclei in a unified way, to investigate the 10C $\to $ 10B super-allowed Fermi transition. With chiral two- and three-nucleon interactions as the only input, we are able to calculate the isospin breaking correction $\delta $C in a more robust way than in other approaches. We also discuss several intermediate and related results, in particular, the nuclear structure of 10C, 10B, and 10Be, as well as our plans to calculate $\delta $C for 14O$\to $14N Fermi transition. [1] P. Navratil, S. Quaglioni, G. Hupin, C. Romero-Redondo, A. Calci, Physica Scripta 91, 053002 (2016). [Preview Abstract] |

Saturday, October 31, 2020 9:30AM - 9:42AM |
KF.00004: High precision half-life measurement of the isobaric analogue decay of $^{\mathrm{29}}$P P.D. Shidling, V. E. Iacob, J.C. Hardy, G. Chubarian, V. Kolhinen, D. McClain, M. Nasser, Asim Ozmetin, H.I. Park, B.T. Roeder, A. Saastamoinen, Benjamin Schroeder, Dan Melconian A set of five mirror nuclei are currently being used as an independent source to test the unitarity of the CKM matrix, including $^{\mathrm{29}}$P which is currently the least precise of the set. The precision of the \textit{ft }value is currently limited by the 0.14{\%} uncertainty in the half-life. In order to improve the world half-life value, a precision half-life measurement of $^{\mathrm{29}}$P has been performed using the MARS spectrometer and a fast-tape-transport system. The $^{\mathrm{29}}$P was produced via the p($^{\mathrm{30}}$Si,2n)$^{\mathrm{29}}$P reaction in inverse kinematics at a primary beam energy of 24 MeV/u. The MARS spectrometer transported the secondary beam and implanted the $^{\mathrm{29}}$P in an aluminized Mylar tape with purity greater than 99.9{\%}. The fast-tape-transport system, quickly transported the sample to a well shielded location, stopping it in the center of the gas-flow proportional counter. The recorded data was separated into several runs, each characterized by a different combination of experimental conditions. An overview of this 0.02 {\%} measurement will be presented. [Preview Abstract] |

Saturday, October 31, 2020 9:42AM - 9:54AM |
KF.00005: Improving the ft value of 37K via a precision measurement of the branching ratio Asim Ozmetin, Dan G. Melconian, Victor E. Iacob, Praveen Shidling, Veli Sakari Kolhinen, David J. McClain, Morgan Nasser, Benjamin Schroeder, Brian Roeder, Hyo-In Park, Melissa Anholm, Antti J. Saastamoinen The TRIUMF Neutral Atom Trap collaboration is searching for new physics via precision measurements of the isobaric analogue $\beta^+$ decay of $^{37}$K. The recent 0.3$\%$ measurement of the $\beta$ asymmetry parameter, $A_\beta$, was combined with the present $ft$ value to improve the value of $V_{ud}$ for this decay as well as to search for right-handed currents. Presently, uncertainties in $A_\beta$ remain the limiting factor in these standard model tests, however, the next $A_\beta$ measurement will reach $\leq0.1\%$ precision; at that point, uncertainties in the $ft$ value will no longer be negligible. This motivated us to improve the $ft$ value to ensure its precision does not limit our search for new physics. The current uncertainty in the $ft$ value is dominated by the branching ratio. This talk will describe how, using the fast-tape-transport system at the Cyclotron Institute and the world's most precisely calibrated HPGe, we measured the branching ratio to be 97.81(2)$\%$. This $5\times$ more precise result leads to, $ft=4585(4)$s, which is precise enough that $A_\beta$ would have to be measured to 0.07$\%$ before the $ft$ value limited searches for new physics. [Preview Abstract] |

Saturday, October 31, 2020 9:54AM - 10:06AM |
KF.00006: Analysis of the high-statistics UCN$\tau$ dataset Eric Fries There have been various measurements of the free neutron lifetime $(\tau_n)$ using either cold neutron beams, or ultracold neutrons (UCN) stored in a trap. There is a $\sim4\sigma$ discrepancy in measured lifetimes between the two methods. The UCN$\tau$ experiment at Los Alamos Neutron Science Center uses an asymmetric magneto-gravitational trap to store UCN and counts the UCN remaining in the trap after various holding times to measure $\tau_n.$ During 2017 and 2018, the UCN$\tau$ collaboration gathered roughly seven times as much data as in the 2016 run cycle. Three independent analyses of these data are in progress. We expect our analyses to result in a measurement of $\tau_n$ with statistical uncertainty below $0.3$ s and systematic uncertainty below $^{+0.2}_{-0.1}$ s. Here we present the methods used to extract $\tau_n$ and estimate the statistical uncertainty of the measurement, and outline the methods used to measure the dominant systematic effects. [Preview Abstract] |

Saturday, October 31, 2020 10:06AM - 10:18AM |
KF.00007: Update on the BL2 Experiment: An In-Beam Measurement of the Neutron Lifetime Jimmy Caylor 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. [Preview Abstract] |

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