Session G15: Mini-symposium: Precision Measurements for Standard Model and Beyond Standard Model Physics

Search for an electroweak tensor contribution using trapped 8Li with the Beta-decay Paul Trap Mk IV

The Beta-decay Paul Trap (BPT) measures the beta-neutrino angular correlation coefficient a_βν in the Gamow-Teller decays of ⁸Li and ⁸B (decaying to ⁸Be^∗→2α) to search for a tensor component of the weak interaction, a beyond-Standard Model possibility. The new BPT Mk IV trap reduces β-scattering by a factor of 4, a key source of systematic uncetainty, and has recently been commissioned with ⁸Li with 2.7 million triple coincidence events. In addition, a complete detector characterization has been performed with an α beam to reduce systematic uncertainties associated with the silicon strip detector response. This new high-statistics ⁸Li data set, coupled with the experimental advancements, will allow for improved sensitivity to a tensor contribution. In the near future, the BPT should be able to reach an uncertainty of ?|C_T /C_A|² ≤ 10⁻³, though the theoretical understanding of the nuclear structure still requires improvement.   

Precision Beta-Decay Studies of 8B: Reconstructing the Neutrino Energy Spectrum and Setting Tensor Current Limits

⁸B beta decay is the dominant source of the high-energy neutrinos generated in the Sun and observed on Earth. Furthermore, the large Q value of the decay and the fact that the daughter ⁸Be breaks up into two alpha particles makes it particularly sensitive to Beyond the Standard Model Physics. Preliminary results from a high-statistics experiment performed using the Beta-decay Paul Trap (BPT) surrounded by four double-sided silicon strip detectors at Argonne National Laboratory will be presented. Precise measurements of the alpha and beta particle energies were performed to set limits on the exotic tensor current contribution to the weak interaction. Additionally, the kinematics of the decay products were leveraged to reconstruct the undistorted ⁸B neutrino energy spectrum, an important input for the analysis of solar neutrino astrophysics experiments.   

SALER@FRIB: Searching for BSM Physics via Nuclear Decay in Superconducting Sensors

The Superconducting Array for Low Energy Radiation (SALER) is a new project at FRIB that will measure sub-keV decay radiation using Superconducting Tunnel Junction (STJ) quantum sensors operated “on-line” for the first time.  The experimental concept is based on the success of the BeEST experiment to measure eV-scale nuclear recoils following the electron capture decay of ⁷Be for BSM neutrino physics.  The initial physics goals for SALER are to search for exotic scalar and tensor currents in the weak interaction and performing high-precision beta decay measurements related to the top-row CKM unitarity test.  Initial testing of the refrigeration equipment and sensors has been performed at STAR Cryoelectronics including measuring the I(V) response of the STJs.  In this talk I will report on the progress of the first tests of this equipment, as well as the near-term plans for the SALER commissioning at FRIB.    

3D Reconstruction of Ion-Beam Implantation Profile in Superconducting Tunnel Junctions using Atom Probe Tomography

Recent use of superconducting tunnel junctions (STJs) to perform precision, low-energy nuclear decay experiments from implanted radioactive ions have shown tremendous promise in our search for BSM physics.  In particular, the Beryllium Electron capture in Superconducting Tunnel junction (BeEST) experiment searches for BSM neutrino-mass physics in the electron capture decay of ⁷Be.  The search is currently limited by unexpected peak broadening, which may be due to interaction of the implanted ⁷Be within the STJ detector materials.  In this talk, I will present the working progress for transmission electron microscopy (TEM) imaging and atom probe tomographic (APT) 3D reconstruction of ⁷Be and ⁷Li implanted into Ta-based and Al-based STJs.  Such reconstructions will be compared to density functional theory modeling of the electronic structure of lithium atoms in different atomic environments of polycrystalline Ta and Al.  This comparison and associated data will clarify in-medium effects to better understand the observed peak broadening towards higher sensitivity searches for new physics using STJs.   

Enhancing β-decay experimental searches for exotic weak interactions with accurate nuclear calculations

An increasing body of evidence suggests that the Standard Model (SM) of particle physics is incomplete. Recent experiments showing deviations from the SM in high-precision measurements highlight the importance of the nuclear precision frontier in beyond the SM searches.

The talk will focus on the search for exotic weak interactions using β-decays precision measurements. It will describe the theory's challenge of nuclear calculations and present a general framework for assessing β-decay precision experiments. It will demonstrate how this formalism opens the door to new measurements, such as those of forbidden β-decays, as well as to highly accurate and controlled calculations of β-decay observables relevant to ongoing experiments. Using this formalism in conjunction with ab-initio nuclear calculations for 6He and 23NE decays and comparing them with newly available measurements, I will present some recent boundaries for tensor exotic weak interactions.   

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Several inconsistencies between Standard Model (SM) predictions and experimental data, motivate PIONEER, the next-generation rare pion decay experiment. By probing the difference between decay of pion into electron and muon with a precision of 1 part in 10⁴ and the rare process of pion beta decay, with 3 to 10-fold improvement in sensitivity, the experiment aims to test the lepton flavor universality and CKM unitarity respectively, which is very important in light of the recently emerged tensions. The aimed precision requires excellent reconstruction of decay particles which the collaboration aims to achieve with a detector consisting of a segmented Low Gain Avalanche Detector (LGAD) based Active Target (ATAR), a Liquid Xenon Calorimeter of 25 radiation lengths and a gaseous detector based tracker. A GEANT based optimization study of a μ-RWell tracker surrounding the ATAR to achieve the required precision has been highlighted here.   

Progress Towards An Improved Lifetime Experiment at Los Alamos Neutron Science Center

UCNτ+ is an upgrade to the UCNτ experiment at the Los Alamos Neutron Science Center. UCNτ has provided the most precise value for the neutron lifetime, a critical input for a nuclear structure-independent measurement of the CKM matrix element V_ud. The goal of UCNτ+ is to produce at least a factor of two improvement in the sensitivity of the UCNτ experiment, strongly motivated by the current status of the "Cabbibo-anomaly" in the couplings to up quarks. The UCNτ+ upgrade targets are increasing the loaded number of UCN in the magneto-gravitational trap and improving the high rate performance of the UCNτ extit{in situ} detector. We summarize modeling of the adiabatic loading system and the hardware progress for this experiment, providing an update on the mechanical design of UCNτ+, the testing program for the prototype system, and UCNτ+ commissioning. In addition, we discuss the performance of the UCNτ+ detector which was implemented during this previous run cycle.   

Spin Correlations in Lepton+Jets events with Lorentz-boosted top quarks in pp collisions at √s = 13 TeV

The current LHC data set contains a record number of top quark-antiquark (ttbar) events. This has enabled precision studies of results regarding ttbar production and decay mechanisms predicted by the Standard Model. A well established fact about these ttbar pairs is that they decay weakly before interacting strongly with other quarks and forming hadrons. The decay products of the ttbar pair therefore inherit the spin information that was present in the system at the moment of decay, thus enabling us to observe any spin correlations that were present in the ttbar system via the spins of their decay products. The Standard Model predicts sinusoidal modulations to the azimuthal sum and difference distributions of two decay products. This modulation is a result of interference between different helicity channels. This phenomenon has been studied in the past by CDF at Fermilab and by ATLAS at the LHC but never with the precision afforded by the current LHC data set. We measure these modulations as a function of the boost of the top quark and antiquark using the entire Run 2 CMS dataset of 138fb^-1.