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At least 1,531 records · Page 85
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DOE OSTI2018

Disconnected Hadronic Vacuum Polarization Contribution to the Muon g-2 with HISQ

We describe a computation of the contribution to the anomalous magnetic moment of the muon from the disconnected part of the hadronic vacuum polarization. We use the highly-improved staggered quark (HISQ) formulation for the current density with gauge configurations generated with four flavors of HISQ sea quarks. The computation is performed by stochastic estimation of the current density using the truncated solver method combined with deflation of low-modes. The parameters are tuned to minimize the computational cost for a given target uncertainty in the current-current correlation function. The calculation presented here is carried out on a single gauge-field ensemble of size $32^3\times48$ with an approximate lattice spacing of $\sim0.15$ fm and with physical sea-quark masses. We describe the methodology and the analysis procedure

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

The Muon $g-2$ experiment at Fermilab and the First Physics Run

Measurement of the muon anomalous magnetic moment (muon g-2) is a sensitive tool for testing the Standard Model (SM) and searching for new physics. It is an important and complementary tool to probe the high energy frontier. In this talk, I will provide an overview on the Fermilab Muon g-2 experiment, which aims to perform the measurement the muon g-2 with a precision goal of 140 parts per billion, a fourfold improvement over the previous BNL measurement. The first physics run finished in 2018 collecting a data sample with similar size of the BNL measurement. The current experimental status and prospects of the experiment will also be discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Small experiment, Big Data: the data production of the Muon $g-2$ Experiment

The Muon $g-2$ Experiment at Fermilab aims to measure the muon anomalous magnetic moment with the unprecedented precision of 140 parts per billion (ppb). In April 2021 the collaboration published the first measurement, based on the first year of data taking. The result confirmed the previous experiment at Brookhaven National Laboratory (BNL), and increased the long-standing tension with the Standard Model prediction to 4.2 $\sigma$. The experiment is now running the sixth year of data acquisition of positive muon data, having accumulated a total of $\sim$19 times the statistics of the BNL experiment. A collaboration-wide effort is now in place to help produce the multi-petabyte-sized data sets, a challenge typically faced by much bigger experiments. Having a quick production turnaround time is of critical importance in order to achieve a timely analysis and publication schedule. In this paper I will describe the production workflow, the former and current challenges, the resources, tools, and the future prospects of the Muon $g-2$ Experiment.

Girotti, Paolo↗
DOE OSTI2024

Muon g-2 experiment and future muon experiments

The Muon g-2 experiment at Fermilab aims to measure the muon anomalous magnetic moment, $a_{\mu}$, with a final precision of 140 part per billions (ppb). The first results from the Run-1 dataset were released on April 7, 2021, showing a very good agreement with the previous experimental result at Brookhaven National Laboratory (BNL) [1]. In light of the new theoretical calculation of the hadron vacuum polarization contribution of $a_{\mu}$ by the BMW group using the Lattice QCD, a strong tension arose within the theoretical side. Here we discuss this high precision measurement and the current work towards a new result, Run-2/3 analysis, on the muon anomaly that aims to reach a statistical uncertainty of 200 ppb and a systematic uncertainty of 70 ppb. Furthermore, a brief overview of other muon experiments will be given.

Bottalico, Elia↗
DOE OSTI2025

Status and prospects of Muon g-2 experiment

This article reviews the muon g-2 experiment, a cornerstone in precision tests of the Standard Model of particle physics. The experiment measures the anomalous magnetic moment of the muon with unprecedented accuracy, seeking potential discrepancies between theoretical predictions and experimental results that might indicate physics beyond the Standard Model. We trace the evolution of this measurement from its beginnings at CERN in the 1960s to the current state-of-the-art experiment at Fermilab, highlighting the remarkable engineering achievements required to achieve parts-per-billion precision. Recent results from Runs 1-3 have achieved a systematic uncertainty of 70 ppb, exceeding design goals, while ongoing theoretical calculations continue to refine predictions. Despite these advances, the analysis remains statistics-limited, with continued data collection and novel experimental approaches at MUonE and J-PARC promising further insights into this fundamental physical quantity.

Karuza, Marin [INFN, Trieste; Rijeka U.] (ORCID:00↗
DOE OSTI2022

Measurement of the Muon Magnetic Anomaly $\boldsymbol{a}_{\boldsymbol{\mu}}$ in the Muon $\boldsymbol{g-2}$ Experiment at Fermilab

The Fermilab Muon g-2 experiment measures the muon anomalous magnetic moment with high precision. Together with recent improvements on the theory front, the first results of the experiment confirm the long-standing discrepancy between the experimental measurements and the Standard Model predictions. The observed value of $a_{\mu}({\textrm{FNAL}})=116\,592\,040(54)\times 10^{-11}(\text{0.46 ppm})$, combined with the previous experimental measurement, results in a discrepancy of $(251\pm 59)\times 10^{-11}$ with the theoretical prediction, corresponding to $4.2\sigma$. This note presents the first results, the current status and the future prospects of the Muon $g-2$ experiment at Fermilab.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Many-Body Effects in FeN4 Center Embedded in Graphene

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce generalized gradient approximation (GGA)+U results when ignoring inter-orbital Coulomb repulsion U ′ and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN 4 centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, U ′ changes the relative position of the peaks in the density of states, particularly on the iron d z 2 orbital, which is expected to affect the binding of ligands greatly.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-Temperature Thermodynamics of Uranium from Ab Initio Modeling

We present high-temperature thermodynamic properties for uranium in its γ phase (γ-U) from first-principles, relativistic, and anharmonic theory. The results are compared to CALPHAD modeling. The ab initio electronic structure is obtained from density-functional theory (DFT) that includes spin–orbit coupling and an added self-consistent orbital-polarization (OP) mechanism for more accurate treatment of magnetism. The first-principles method is coupled to a lattice dynamics scheme that is used to model anharmonic lattice vibrations, namely, Self-Consistent Ab Initio Lattice Dynamics (SCAILD). The methodology can be summarized in the acronym DFT + OP + SCAILD. Upon thermal expansion, γ-U develops non-negligible magnetic moments that are included for the first time in thermodynamic theory. The all-electron DFT approach is shown to model γ-U better than the commonly used pseudopotential method. In addition to CALPHAD, DFT + OP + SCAILD thermodynamic properties are compared with other ab initio and semiempirical modeling and experiments. Our first-principles approach produces Gibbs free energy that is essentially identical to CALPHAD. The DFT + OP + SCAILD heat capacity is close to CALPHAD and most experimental data and is predicted to have a significant thermal dependence due to the electronic contribution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Pb-Apatite Framework as a Generator of Novel Flat-Band CuO-Based Physics

Based upon density functional theory (DFT) calculations, we present the basic electronic structure of CuPb 9 (PO 4 ) 6 O (Cu-doped lead apatite, aka LK-99), in two scenarios: (1) where the structure is constrained to the P3 symmetry and (2) where no symmetry is imposed. At the DFT level, the former is predicted to be metallic while the latter is found to be a charge-transfer insulator. In both cases the filling of these states is nominally d 9 , consistent with the standard Cu 2+ valence state, and Cu with a local magnetic moment of order 0.7 μ B . In the metallic case we find these states to be unusually flat (∼0.2 eV dispersion), giving a very high density of electronic states (DOS) at the Fermi level that we argue can be a host for novel electronic physics. The flatness of the bands is the likely origin of symmetry-lowering gapping possibilities that would remove the spectral weight from E F . Motivated by some initial experimental observations of metallic or semiconducting behavior, we propose that disorder (likely structural) is responsible for closing the gap. Here, we consider a variety of possibilities that could possibly close the charge-transfer gap but limit consideration to kinds of disorder that preserve electron count. Of the possible kinds we considered (spin disorder, O populating vacancy sites, and Cu on less energetically favorable Pb sites), the local Cu moment, and consequently the charge-transfer gap, remains robust. We conclude that disorder responsible for metallic behavior entails some kind of doping where the electron count changes. Further, we claim that the emergence of the flat bands should be due to weak wave function overlap between the orbitals on Cu and O sites, owing to the directional character of the constituent orbitals. Therefore, finding an appropriate host structure for minimizing hybridization between Cu and O while allowing them to still weakly interact should be a promising route for generating flat bands at E F which can lead to interesting electronic phenomena, regardless of whether LK-99 is a superconductor.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanoscale Superconducting States in the Fe-Based Filamentary Superconductor of Pr-Doped CaFe 2 As 2

The low-temperature scanning tunneling microscope and spectroscopy (STM/STS) are used to visualize superconducting states in the cleaved single crystal of 9% praseodymium-doped CaFe 2 As 2 (Pr-Ca122) with Tc ≈ 30 K. The spectroscopy shows strong spatial variations in the density of states (DOS), and the superconducting map constructed from spectroscopy discloses a localized superconducting phase, as small as a single unit cell. The comparison of the spectra taken at 4.2 K and 22 K (below vs. close to the bulk superconducting transition temperature) from the exact same area confirms the superconducting behavior. Nanoscale superconducting states have been found near Pr dopants, which can be identified using dI/dV conductance maps at +300 mV. There is no correlation of the local superconductivity to the surface reconstruction domain and surface defects, which reflects its intrinsic bulk behavior. We, therefore, suggest that the local strain of Pr dopants is competing with defects induced local magnetic moments; this competition is responsible for the local superconducting states observed in this Fe-based filamentary superconductor.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Single Crystal Diffuse Neutron Scattering

Diffuse neutron scattering has become a valuable tool for investigating local structure in materials ranging from organic molecular crystals containing only light atoms to piezo-ceramics that frequently contain heavy elements. Although neutron sources will never be able to compete with X-rays in terms of the available flux the special properties of neutrons, viz. the ability to explore inelastic scattering events, the fact that scattering lengths do not vary systematically with atomic number and their ability to scatter from magnetic moments, provides strong motivation for developing neutron diffuse scattering methods. Here, we compare three different instruments that have been used by us to collect neutron diffuse scattering data. Two of these are on a spallation source and one on a reactor source.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Lorentz and CPT Tests Using Penning Traps

The theoretical prospects for quantum electrodynamics with Lorentz-violating operators of mass dimensions up to six are revisited in this work. The dominant effects due to Lorentz and CPT violation are studied in measurements of magnetic moments of particles confined in Penning traps. Using recently reported experimental results, new coefficients for Lorentz violation are constrained and existing bounds of various coefficients are improved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Scintillating Bubble Chambers for Rare Event Searches

The Scintillating Bubble Chamber (SBC) collaboration is developing liquid-noble bubble chambers for the detection of sub-keV nuclear recoils. These detectors benefit from the electron recoil rejection inherent in moderately-superheated bubble chambers with the addition of energy reconstruction provided from the scintillation signal. The ability to measure low-energy nuclear recoils allows the search for GeV-scale dark matter and the measurement of coherent elastic neutrino-nucleus scattering on argon from MeV-scale reactor antineutrinos. The first physics-scale detector, SBC-LAr10, is in the commissioning phase at Fermilab, where extensive engineering and calibration studies will be performed. In parallel, a functionally identical low-background version, SBC-SNOLAB, is being built for a dark matter search underground at SNOLAB. SBC-SNOLAB, with a 10 kg-yr exposure, will have sensitivity to a dark matter–nucleon cross section of 2×10 –42 cm 2 at 1 GeV/c 2 dark matter mass, and future detectors could reach the boundary of the argon neutrino fog with a tonne-yr exposure. In addition, the deployment of an SBC detector at a nuclear reactor could enable neutrino physics investigations including measurements of the weak mixing angle and searches for sterile neutrinos, the neutrino magnetic moment, and the light Z’ gauge boson.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Stochastic Ion Acceleration by the Ion-cyclotron Instability in a Growing Magnetic Field

Using 1D and 2D particle-in-cell simulations of a plasma with a growing magnetic field ${\boldsymbol{B}}$, we show herein that ions can be stochastically accelerated by the ion-cyclotron (IC) instability. As ${\boldsymbol{B}}$ grows, an ion pressure anisotropy ${p}_{\perp ,i}\gt {p}_{| | ,i}$ arises due to the adiabatic invariance of the ion magnetic moment (${p}_{| | ,i}$ and $p_{⊥,i}$ are the ion pressures parallel and perpendicular to ${\boldsymbol{B}}$). When initially $β_ i$ = 0.5 (${\beta }_{i}\equiv 8\pi {p}_{i}/| {\boldsymbol{B}}{| }^{2}$, where $p_i$ is the ion isotropic pressure), the pressure anisotropy is limited mainly by inelastic pitch-angle scattering provided by the IC instability, which in turn produces a nonthermal tail in the ion energy spectrum. After ${\boldsymbol{B}}$ is amplified by a factor of ~2.7, this tail can be approximated as a power law of index ~3.4 plus two nonthermal bumps and accounts for 2%–3% of the ions and ~18% of their kinetic energy. On the contrary, when initially $β_i$ = 2, the ion scattering is dominated by the mirror instability, and the acceleration is suppressed. This implies that efficient ion acceleration requires that initially, $β_{i} \lesssim$ 1. Although we focus on cases where ${\boldsymbol{B}}$ is amplified by plasma shear, we check that the acceleration occurs similarly if ${\boldsymbol{B}}$ grows due to plasma compression. Our results are valid in a subrelativistic regime where the ion thermal energy is ~10% of the ion rest-mass energy. This acceleration process can thus be relevant in the inner region of low-luminosity accretion flows around black holes.

79 ASTRONOMY AND ASTROPHYSICS↗